15036143 Bockheim, J. G. (University of Wisconsin, Department of Soil Science, Madison, WI). Global distribution of Cryosols with mountain permafrost; an overview: Permafrost and Periglacial Processes, 26(1), p. 1-12, illus. incl. 3 tables, sketch map, 20 ref., March 2015.
About 30 per cent of the mountain soils with permafrost have an active layer depth (ALD) of less than 1 or 2 m and, therefore, can be classified as Cryosols. Mountain Cryosols have a total area of approximately 1.26 million km2 and account for approximately 12 per cent of the Cryosols worldwide. An ALD of less than 2 m appears to occur only where the mean annual air temperature is <-6°C. There is a negative correlation (R=0.86; p <0.001) between latitude (°N) and elevation (m) at which the ALD occurs at less than 2 m. Mountain Cryosols are most abundant in the western Cordillera of the USA and Canada (360 000 km2), the Qinghai-Tibet Plateau of China (280 000 km2), Greenland (185 000 km2), the Yablonoi-Sayan-Stanovoi Mountains of Russia (153 000 km2) and the Ural Mountains of Russia (90 000 km2). Despite that the Qinghai-Tibet Plateau contains 70 per cent of the world's mountain permafrost, only about 20 per cent of the soils are Cryosols, because they are limited to areas above 5100 m asl. Cryosols occur in the central Andes above 4900 m asl and in the southern Andes above 1000 m asl. Potential impacts of recent climate warming on mountain permafrost and Cryosols are discussed. Abstract Copyright (2010), John Wiley & Sons, Ltd.
15036146 Zhou, Xiaohai (Swiss Federal Institute of Technology, Institute of Environmental Engineering, Zurich, Switzerland); Buchli, Thomas; Kinzelbach, Wolfgang; Stauffer, Fritz and Springman, Sarah M. Analysis of thermal behaviour in the active layer of degrading mountain permafrost: Permafrost and Periglacial Processes, 26(1), p. 39-56, illus., 37 ref., March 2015.
Mountain permafrost is highly susceptible to the effects of climate warming, because its thermal regime is close to 0°C. This can be evidenced by the acceleration of average annual creep rates of several rock glaciers in the Swiss Alps, whereby some exhibit even more extreme signs of degradation. Measurements obtained from a borehole drilled from a relatively flat area on a rock glacier, below the Furggwanghorn peak, Turtmanntal (Switzerland), showed positive mean annual values of ground temperatures in the active layer over two hydrological years, from 1 October 2010 to 30 September 2012. The thermal conditions in this borehole were much warmer than those measured at the same time in other boreholes in the same rock glacier. A test pit excavated in the active layer close to this borehole, and instrumented with thermistors, indicated similar thermal conditions. It was hypothesised that the thick snow cover that accumulated on the flat area during winter and an existing supra-permafrost talik were responsible for the warm thermal regime, given the relevant meteorological inputs over this period. The degradation of the rock glacier in this flat area was probably driven by a high summer heat flux into the rock glacier, which could not be reversed in winter due to a thick insulating snow layer that accumulated from October onwards. A coupled one-dimensional numerical model, based on SNOWPACK and HYDRUS, was developed to interpret the thermal behaviour in the active layer. The resulting numerical analysis was validated, showing that the simulated ground temperatures agreed well with measured values at various depths. The heat loss from the ground was found to be very small during the winter, due to insulation by autumnal snowfalls, whereas the heat flux to the ground had been relatively high in recent summers. The mean positive heat flux to the supra-permafrost talik was calculated to be 1.75 Wm-2 over the 2 year period, which is sufficient to cause considerable ice melt. Furthermore, water flow in the supra-permafrost talik appeared to limit temperature variations in the active layer to 0.12°C in summer. Abstract Copyright (2010), John Wiley & Sons, Ltd.
15039413 Grewer, David M. (University of Toronto, Department of Physical and Environmental Sciences, Toronto, ON, Canada); Lafrenière, Melissa J.; Lamoureux, Scott F. and Simpson, Myrna J. Potential shifts in Canadian High Arctic sedimentary organic matter composition with permafrost active layer detachments: Organic Geochemistry, 79, p. 1-13, illus. incl. 2 tables, sketch map, 114 ref., February 2015.
Increased temperature and precipitation in Arctic regions have led to deeper thawing and structural instability in permafrost soil. The resulting localized disturbances, referred to as active layer detachments (ALDs), may transport organic matter (OM) to more biogeochemically active zones. To examine this further, solid state cross polarization magic angle spinning 13C nuclear magnetic resonance (CPMAS NMR) and biomarker analysis were used to evaluate potential shifts in riverine sediment OM composition due to nearby ALDs within the Cape Bounty Arctic Watershed Observatory, Nunavut, Canada. In sedimentary OM near ALDs, NMR analysis revealed signals indicative of unaltered plant-derived material, likely derived from permafrost. Long chain acyclic aliphatic lipids, steroids, cutin, suberin and lignin occurred in the sediments, consistent with a dominance of plant-derived compounds, some of which may have originated from permafrost-derived OM released by ALDs. OM degradation proxies for sediments near ALDs revealed less alteration in acyclic aliphatic lipids, while constituents such as steroids, cutin, suberin and lignin were found at a relatively advanced stage of degradation. Phospholipid fatty acid analysis indicated that microbial activity was higher near ALDs than downstream but microbial substrate limitation was prevalent within disturbed regions. Our study suggests that, as these systems recover from disturbance, ALDs likely provide permafrost-derived OM to sedimentary environments. This source of OM, which is enriched in labile OM, may alter biogeochemical patterns and enhance microbial respiration within these ecosystems. Abstract Copyright (2015) Elsevier, B.V.
15039410 Wu Qingbai (Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Hou Yandong; Yun Hanbo and Liu Yongzhi. Changes in active layer thickness and near-surface permafrost between 2002 and 2012 in alpine ecosystems, Qinghai-Xizang (Tibet) Plateau, China: Global and Planetary Change, 124, p. 149-155, illus. incl. 3 tables, sketch map, 36 ref., January 2015.
Between 2002 and 2012, daily soil temperature measurements were made at 10 sites within five alpine ecosystems in the Beiluhe area of the central Qinghai-Tibet Plateau. Changes in freeze-thaw occurrence, active-layer thickness and near-surface permafrost temperature in barren, desert grassland, alpine steppe and alpine meadow ecosystems indicate that alpine ecosystems are sensitive to climate variability. During this time, the average onset of spring thawing at 50-cm depth advanced by at least 16 days in all but the barren alpine settings, and the duration of thaw increased by at least 14 days for all but the desert grassland and barren ecosystems. All sites showed an increase in active-layer thickness (ALT) and near-surface permafrost temperature: the average increase of ALT was ~ 4.26 cm/a and the average increase in permafrost temperatures at 6 m and 10 m depths were, respectively, ~ 0.13 °C and ~ 0.14 °C. No apparent trend in mean annual air temperature was detected at the Beiluhe weather station. However, an increasing trend in precipitation was measured. This suggests that the primary control on the ALT increase was an increase in summer rainfall and the primary control on increasing permafrost temperature was probably the combined effects of increasing rainfall and the asymmetrical seasonal changes in subsurface soil temperatures. Abstract Copyright (2015) Elsevier, B.V.
15035824 Li Jing (Chinese Academy of Sciences, Laboratory of Frozen Soil Engineering, Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Sheng Yu; Chen Ji; Wu Jichun and Wang Shengting. Variations in permafrost temperature and stability of alpine meadows in the source area of the Datong River, northeastern Qinghai-Tibet Plateau, China: Permafrost and Periglacial Processes, 25(4), p. 307-319, illus. incl. 2 tables, sketch maps, 30 ref., December 2014.
Zonal alpine meadow is widespread in the source area of the Datong River, northeastern Qinghai-Tibet Plateau, China, and can be divided into typical meadow and swamp meadow, according to variations in the soil moisture content. A total of 56 measurements of the mean annual ground temperature (MAGT) revealed a significant difference in the MAGT of the two vegetation types. The measured MAGT varied from -2.8 to 0.46°C in the swamp meadow, and from -0.6 to 2.5°C in the typical meadow. Measurements of 0°C were found at approximately 3710 m asl and 3660 m asl in the typical meadow and swamp meadow, respectively. Using the measured MAGT and calculated topo-climatic parameters as dependent and independent variables, two statistical models of MAGT were constructed for each vegetation type. The calculated results were classified into different zones and types to determine the permafrost stability in different vegetated areas. Semi-stable permafrost (-3.0°C < MAGT ≤&eq; -1.5°C) and transitory permafrost (-1.5°C < MAGT ≤&eq; -0.5°C) were the two predominant permafrost types in the swamp meadow, whereas unstable permafrost (-0.5°C < MAGT ≤&eq; +0.5°C) and seasonally frozen ground (MAGT > 0.5°C) were the two main types in the typical meadow. The differences in permafrost temperatures and stability between the two vegetation types can be explained by the local environmental characteristics, including vegetation cover and soil water content. Abstract Copyright (2010), John Wiley & Sons, Ltd.
15035817 Lupascu, M. (University of Bristol, Bristol Glaciology Centre, Bristol, United Kingdom); Wadham, J. L.; Hornibrook, E. R. C. and Pancost, R. D. Methanogen biomarkers in the discontinuous permafrost zone of Stordalen, Sweden: Permafrost and Periglacial Processes, 25(4), p. 221-232, illus. incl. sketch map, 22 ref., December 2014.
Permafrost peatlands are both an important source of atmospheric CH4 and a substantial sink for atmospheric CO2. Climate change can affect this balance, with higher temperatures resulting in the conversion of permafrost soils to wetlands and associated accelerated mineralisation and increased CH4 emission. To better understand the impact of such processes on methanogen populations, we investigated the anaerobic decay of soil carbon in a low Arctic, discontinuous permafrost peatland. Cores were collected monthly from sedge and Sphagnum mires in north Sweden during the summer of 2006. We determined CH4 concentrations and production potentials, together with variations in the size of the methanogenic community as indicated by concentrations of archaeal lipid biomarkers (phosphorylated archaeol, archaeol and hydroxyarchaeol). Concentrations of methanogen biomarkers generally were higher at the sedge site, increased with depth for all sites and months, and were usually below the detection limits in shallow (<10 cm) Sphagnum peat. The distribution of biomarkers reflects the strong influence of water table depth on anaerobic conditions and methanogen populations, while differences in biomarker concentrations can be explained by differences in vegetation cover and pH. However, methanogen populations inferred from biomarker data show a decoupling from in-situ CH4 production over the season and from CH4 production potential, suggesting that other factors such as the availability of labile organic substrates can influence methanogen abundance. Archaeal lipid biomarkers appear to offer a potential new means to investigate permafrost biogeochemical processes but the interpretation of signals remains complex. Abstract Copyright (2010), John Wiley & Sons, Ltd.
15035820 Semenova, Olga (Gidrotehproekt, Saint Petersburg, Russian Federation); Vinogradov, Yury; Vinogradova, Tatyana and Lebedeva, Luidmila. Simulation of soil profile heat dynamics and their integration into hydrologic modelling in a permafrost zone: Permafrost and Periglacial Processes, 25(4), p. 257-269, illus. incl. 4 tables, sketch map, 45 ref., December 2014.
To improve hydrologic modelling in permafrost zones, we present a new hydrological modelling approach to simulate ground thaw/freeze processes and the consequent contribution to the hydrologic response. We apply several techniques to simplify the differential equations of heat transfer in soil profiles, from which we derive an analytical solution that accounts for phase changes in soil and includes specific approaches for heat transfer and phase-dependent soil and snow conductivity. Use of soil horizon physical properties as the model parameters allows robust assessment relative to landscape characteristics. Following integration of these methods within the Hydrograph hydrological model, verification was conducted against a time series of soil temperature observed at the Kolyma Water Balance Station in the continuous permafrost zone of northeast Russia. Abstract Copyright (2010), John Wiley & Sons, Ltd.
15036999 Yang Sizhong (Chinese Academy of Sciences, State Key Laboratory of Frozen Soils Engineering, Lanzhou, China); Wen Xi; Zhao Liang; Shi Yulan and Jin Huijun. Crude oil treatment leads to shift of bacterial communities in soils from the deep active layer and upper permafrost along the China-Russia Crude Oil Pipeline route: PloS One, 2014(E96552), illus., 69 ref., May 2, 2014.
The buried China-Russia Crude Oil Pipeline (CRCOP) across the permafrost-associated cold ecosystem in northeastern China carries a risk of contamination to the deep active layers and upper permafrost in case of accidental rupture of the embedded pipeline or migration of oil spills. As many soil microbes are capable of degrading petroleum, knowledge about the intrinsic degraders and the microbial dynamics in the deep subsurface could extend our understanding of the application of in-situ bioremediation. In this study, an experiment was conducted to investigate the bacterial communities in response to simulated contamination to deep soil samples by using 454 pyrosequencing amplicons. The result showed that bacterial diversity was reduced after 8-weeks contamination. A shift in bacterial community composition was apparent in crude oil-amended soils with Proteobacteria (esp. a-subdivision) being the dominant phylum, together with Actinobacteria and Firmicutes. The contamination led to enrichment of indigenous bacterial taxa like Novosphingobium, Sphingobium, Caulobacter, Phenylobacterium, Alicylobacillus and Arthrobacter, which are generally capable of degrading polycyclic aromatic hydrocarbons (PAHs). The community shift highlighted the resilience of PAH degraders and their potential for in-situ degradation of crude oil under favorable conditions in the deep soils.
15031356 Rellini, Ivano (University of Genova, Dipartimento di Scienze della Terra, Genoa, Italy); Trombino, Luca; Rossi, Pietro Mario and Firpo, Marco. Frost activity and ice segregation in a palaeosol in the Ligurian Alps (Beigua Massif, Italy); evidence of past permafrost?: Geografia Fisica e Dinamica Quaternaria (Testo Stampato), 37(1), p. 29-42 (Italian sum.), illus. incl. 2 plates, 1 table, sketch maps, 54 ref., 2014.
This research is a part of a broader paleopedological investigation aimed at characterising and verifying the extent of the permafrost zone during the Last Glacial Maximum (LGM) in the Ligurian Alps. The paper presents the results of a micromorphological study of a palaeosol located at an elevation of 650 m a.s.l., near a blockstream deposit on Beigua Massif in northwestern Italy. We examined a profile exposing sandy sediments characterised by macroscopic structures that are clearly cryogenic in origin. These features were interpreted with their micromorphological characteristics, and we found that during the LGM, this unglaciated area of the Ligurian Alps was characterised by a periglacial environment with discontinuous permafrost even at low elevations.
15040434 Pokrovsky, O. S. (Université de Toulouse, Géoscience Environnement Toulouse, Toulouse, France); Shirokova, L. S.; Kirpotin, S. N.; Kulizhsky, S. P. and Vorobiev, S. N. Impact of Western Siberia heat wave 2012 on greenhouse gases and trace metal concentration in thaw lakes of discontinuous permafrost zone: Biogeosciences, 10(8), p. 5349-5365, illus. incl. 1 table, 93 ref., 2013.
During the anomalously hot summer in 2012, surface air temperatures in Western Siberia were 5 to 15 °C higher than those observed during the previous period of > 30 yr. This unusual climate phenomenon provided an opportunity to examine the effects of short-term natural heating of water in thermokarst ponds and lakes in discontinuous permafrost zones and compare these observations to previous field results obtained when the temperature was normal during the summer of 2010 in the same region. In 2012, thermokarst bodies of water shrank significantly, water levels dropped approximately 50 cm in large lakes and small (< 10-100 m2) ponds, and shallow soil depressions disappeared. Based on samples from ~ 40 bodies of water collected previously and in 2012, first-order features of changes in chemical composition in response to increased water temperatures (from 14.1 ± 2.2 to 23.8 ± 2.3 °C in 2010 and 2012, respectively) were established. In these thermokarst bodies of water that covered a full range of surface areas, the average conductivity and pH were almost unchanged, whereas dissolved organic carbon (DOC), Cl- and SO42- concentrations were higher by a factor of ~ 2 during summer 2012 compared to periods with normal temperatures. Similarly, most divalent metals and insoluble trivalent and tetravalent elements were more concentrated by a factor of 1.7-2.4 in the summer of 2012 than normal periods. The average concentrations of dissolved CO2 and CH4 during the hot summer of 2012 increased by factors of 1.4 and 4.9, respectively. For most of the trace elements bound to colloids, the degree of colloidal binding decreased by a factor of 1.44 ± 0.33 (for an average of 40 elements) during the hot summer of 2012 compared to normal periods. Increases in CO2 and CH4 concentrations with the decreasing size of the body of water were well-pronounced during the hot summer of 2012. The concentrations of CO2 and CH4 rose by factors of 5 and 150, respectively, in small (≤&eq; 102 m2) compared to large (>&eq; 104 m2) thermokarst (thaw) lakes. Taken together, these trends suggest that, for a conservative scenario of lake size distribution, lake water warming at high latitudes will produce (1) a significant increase in methane emission capacity from thaw lake surfaces; (2) decreased molecular sizes of trace element complexes and potential bioavailability of metal micronutrients in water columns; and (3) relatively conservative responses by CO2, DOC and trace element concentrations.
15044700 Krainer, Karl (University of Innsbruck, Institute of Geology and Paleontology, Innsbruck, Austria); Bressan, David; Dietre, Benjamin; Haas, Jean Nicolas; Hajdas, Irka; Lang, Kathrin; Mair, Volkmar; Nickus, Ulrike; Reidl, Daniel; Thies, Hansjörg and Tonidandel, David. A 10,300-year-old permafrost core from the active rock glacier Lazaun, southern Otztal Alps (South Tyrol, northern Italy): Quaternary Research, 83(2), p. 324-335, illus. incl. 2 tables, sketch map, 79 ref., March 2015.
Two cores were drilled on rock glacier Lazaun in the southern Otztal Alps (N Italy). The average ice content of core Lazaun I is 43 vol.% and of core Lazaun II is 22 vol.%. Radiocarbon dating of plant macrofossil remains of core Lazaun I yielded ages ranging from 8960 cal yr BP at a depth of ca. 23.5 m to 2240 cal yr BP at a depth of 2.8 m, indicating that the ice near the base is approximately 10,300 yr old. The rock glacier was intact since that time and the ice persisted even during warm periods of the Holocene. An ice-free debris layer between 16.8 and 14.7 m separates the rock glacier into two frozen bodies. Inclinometer measurements indicate that both frozen bodies are active and that deformation occurs within a shear horizon at a depth of 20-25 m at the base of the lower frozen body and to a minor extent at a depth of approximately 14 m at the base of the upper frozen body. The ice-free debris layer in the middle of the Lazaun rock glacier indicates a more than five centennial long drought period, which dates to about 4300-3740 cal yr BP. Abstract Copyright (2015) Elsevier, B.V.
15043002 Arzhanov, M. M. (Russian Academy of Sciences, Obukhov Institute of Atmospheric Physics, Moscow, Russian Federation) and Mokhov, I. I. Model assessments of organic carbon amounts released from long-term permafrost under scenarios of global warming in the 21st century: Doklady Earth Sciences, 455(1), p. 346-349, illus., 15 ref., March 2014.
15036145 Grimm, Robert E. (Southwest Research Institute, Planetary Science Directorate, Boulder, CO) and Stillman, David E. Field test of detection and characterisation of subsurface ice using broadband spectral-induced polarisation: Permafrost and Periglacial Processes, 26(1), p. 28-38, illus., 34 ref., March 2015. Includes appendix.
Low-frequency (LF, <<1 kHz) electrical resistivity is useful in discriminating frozen from unfrozen ground in periglacial environments, but it cannot distinguish whether frozen materials are dry or ice-rich, nor can it provide reliable estimates of ice content. However, polarisabilities due to unfrozen, interfacial water and protonic defects in ice both have strong dielectric relaxations (frequency dependence), resulting in a large decrease in resistivity at high frequencies (HF, >>1 kHz). From laboratory measurements of samples collected at the US Army Permafrost Tunnel (Fox, Alaska), we find temperature-dependent relationships between ice volume fraction and the resistivity frequency effect (RFE, defined as the LF-normalised difference in LF and HF resistivities). We report the first field detection of H2O polarisability in permafrost, using a broadband spectral-induced polarisation system at the permafrost tunnel. By comparing laboratory and field spectra, we found a best-fitting ice temperature of -3±0.5°C. Laboratory RFE at the selected temperature was then used to map the RFE in the tunnel wall to 45-95 per cent ice by volume. Both of these results agreed quantitatively with the bulk properties of the tunnel, and the ice content image correlated qualitatively with major permafrost features. The RFE approach may be expedient using simpler instrumentation, but the close agreement of laboratory and field spectra indicates that the ice and interfacial water signatures can be individually quantified by broadband fitting of both amplitude and phase. This will provide more accurate constitutive relations, but more importantly will yield better remote temperature measurement of the subsurface using known dependencies of the dielectric relaxation frequencies. Abstract Copyright (2010), John Wiley & Sons, Ltd.
15036148 Scapozza, Cristian (University of Applied Sciences and Arts of Southern Switzerland, Canobbio, Switzerland); Baron, Ludovic and Lambiel, Christophe. Borehole logging in alpine periglacial talus slopes (Valais, Swiss Alps): Permafrost and Periglacial Processes, 26(1), p. 67-83, illus. incl. sketch map, 35 ref., March 2015.
Geophysical measurements were carried out in six boreholes at three periglacial talus slopes in the Swiss Alps in order to determine the talus structure and the geological and permafrost stratigraphy. These are important elements of interpretation of the palaeoclimatic significance of Alpine talus slopes. This study combined three nuclear well logging methods. Natural radioactivity of rocks and ice-rich permafrost were determined by using natural gamma-ray logs through the lack of radioactivity of massive ice. Quantification of the ice content in frozen layers and the air content in unfrozen layers by variations in bulk density was provided by the application of gamma-gamma logs. Neutron-thermal neutron logs were used to calculate the water content, linked with the porosity of the formation. Combination of the three logs allowed three-phase models (rock, ice and air/water) of the subsurface to be obtained. Results show that the air content decreases with depth because of the increasing in-situ stresses that cause compression of the rock debris and the existence of a fine matrix filling the voids. Calculation of the ice content variations shows that talus slopes are frequently partially saturated with ice or, at most, slightly supersaturated with ice. All three logs provide complementary information on the progressive infilling of the voids with depth and the occurrence of ice-rich layers. A similar trend in ice content and the apparent porosity was highlighted by the joint application of gamma-gamma and neutron-neutron logs, which provide a mirror image of these two parameters. Abstract Copyright (2010), John Wiley & Sons, Ltd.
15035819 Brooker, Alexander (University of Ottawa, Department of Geography, Ottawa, ON, Canada); Fraser, Robert H.; Olthof, Ian; Kokelj, Steve V. and Lacelle, Denis. Mapping the activity and evolution of retrogressive thaw slumps by Tasselled Cap trend analysis of a Landsat satellite image stack: Permafrost and Periglacial Processes, 25(4), p. 243-256, illus. incl. 2 tables, sketch map, 34 ref., December 2014.
Retrogressive thaw slumps are a dominant agent of geomorphic change in ice-rich permafrost landscapes and may remain active for decades. Previous studies of slump activity have used aerial photographs and/or high-resolution satellite images acquired at (multi)-decadal time intervals. This study investigates if the calculation of the three Tasselled Cap transformations (brightness, greenness and wetness) from a dense stack of Landsat Thematic Mapper and Enhanced Thematic Mapper+ images can be used to identify slump activity and map slump evolution at near-annual resolution. Results obtained from analysis of slumps in the Richardson Mountains-Peel Plateau region of the Northwest Territories, Canada, suggest that Tasselled Cap linear trend images effectively identify both active and stable thaw slumps. In addition, the analysis of single-date Tasselled Cap values at the pixel level can be used to map the initiation, growth and stabilisation of slumps at near-annual timescales. The Tasselled Cap trend analysis method therefore offers the possibility to: (1) map the distribution of thaw slumps by activity level (active, stable or relict); (2) derive headwall retreat rates at near-annual resolution; and (3) determine patterns of stabilisation and re-vegetation over the period of available Landsat images. The rich temporal information provided by Landsat analysis complements conventional, higher spatial resolution (but lower temporal resolution) methods that map slumps from pairs of aerial photographs and high-resolution satellite imagery. Abstract Copyright (2010), John Wiley & Sons, Ltd.
15035823 Dashtseren, Avirmed (Hokkaido University, Graduate School of Environmental Science, Sapporo, Japan); Ishikawa, Mamoru; Iijima, Yoshihiro and Jambaljav, Yamkin. Temperature regimes of the active layer and seasonally frozen ground under a forest-steppe mosaic, Mongolia: Permafrost and Periglacial Processes, 25(4), p. 295-306, illus. incl. 2 tables, sketch maps, 30 ref., December 2014.
Permafrost underlying forested north-facing slopes and seasonally frozen ground underlying mountain steppes on south-facing slopes co-exist within a small mountain basin that represents the most general landscape type in northern central Mongolia. A 5-year time series of hydro-meteorological parameters on these slopes is presented in order to identify the factors controlling ground temperature regimes. A thick organic layer (0.2-0.4 m) beneath the forest on a north-facing slope impedes the effects of summer air temperature on the ground, and the forest canopy strongly blocks downward shortwave radiation during summer. Active layer thickness was determined by summer warmth. The mountain steppe on a dry south-facing slope receives a large amount of downward shortwave radiation compared to an adjacent forested slope, and therefore the surface temperature exceeds air temperature during summer, leading to a warm soil profile. In winter, snow cover was the main factor controlling interannual variations in the thickness of seasonally frozen ground. The onset of soil thawing in the forested area was later than in the mountain steppe, even though soil freezing began simultaneously in both areas. Overall, the forest cover keeps the ground cool and allows permafrost to persist in this region. Abstract Copyright (2010), John Wiley & Sons, Ltd.
15035822 Jean, Mélanie (Université Laval, NSERC Northern Research Chair, Département de Biologie and Centre d'Études Nordiques, Quebec City, QC, Canada) and Payette, Serge. Effect of vegetation cover on the ground thermal regime of wooded and non-wooded palsas: Permafrost and Periglacial Processes, 25(4), p. 281-294, illus. incl. sketch maps, 30 ref., December 2014.
Although warming air temperatures are contributing to permafrost degradation across the circumpolar zone, understanding of permafrost and environmental feedbacks to climate change is limited. Palsas can be used as indicators of permafrost stability given their sensitivity to changes in temperature and precipitation. However, field observations on the effects of vegetation cover are needed to compare permafrost dynamics of wooded and non-wooded palsas. This study examined the influence of vegetation on the soil thermal regime of wooded palsas covered by black spruce trees and non-wooded palsas covered by shrubs in discontinuous permafrost of the Boniface River area of northern Quebec, Canada. It investigated the effects of organic layer thickness, vegetation and snow depth on soil temperature at 50 cm and 100 cm depths for over 2 years. The coldest summer soil temperatures were associated with thick organic layers. In summer, soil temperatures were colder under spruce stands than under shrub canopies and forest openings, whereas the thick snow cover in spruce stands and forest openings maintained warmer winter soil temperatures than under shrub canopies. Well-defined zero-curtain periods during fall and spring could be an early indicator of current changes in the soil thermal regime of palsas. At the northern edge of discontinuous permafrost, non-wooded palsas have the most favourable conditions for permafrost stability, because heterogeneous vegetation cover on wooded palsas promotes snow trapping and lateral heat transfer. Vegetation types should be considered in estimating future rates of permafrost degradation. Abstract Copyright (2010), John Wiley & Sons, Ltd.
15035821 Lebedeva, Liudmila (Nansen International Environmental and Remote Sensing Centre, Saint Petersburg, Russian Federation); Semenova, Olga and Vinogradova, Tatyana. Simulation of active layer dynamics, Upper Kolyma, Russia, using the hydrograph hydrological model: Permafrost and Periglacial Processes, 25(4), p. 270-280, illus. incl. sketch maps, 22 ref., December 2014.
Freeze/thaw simulations were performed for seven permafrost sites at the Kolyma Water Balance Station (KWBS), northeast Russia, using the hydrological model Hydrograph equipped with a heat transfer analytical solution that accounts for soil profile phase changes. The study sites include slopes and plateaus with thaw depths of 0.5 to 1.8 m. Landscape conditions are characterised as rocky talus, mountain tundra with dwarf tree brush, moss-lichen cover and sparse-growth forest or larch forest. Soil horizons are distinguished as moss-lichen cover, peat layer, clay with a high stone content and weathered clayey shale. Schematisation of soil-vegetation profiles and model parameters were developed for each landscape. Parameterised model output was verified using time series of observed active layer thickness for the period of 1950 to 1990. The simulated values agree well with the observed values at the study sites. The results suggest that the soil profile schematisation and model parameters, along with the proposed algorithm of heat transfer, effectively simulate active layer dynamics under various landscape conditions at the KWBS and are suitable for hydrological modelling in the permafrost zone. The modelling efforts and results are highly relevant because the natural conditions at the KWBS are representative of large areas of northeastern Russia. Abstract Copyright (2010), John Wiley & Sons, Ltd.
15038875 Mingjing Jiang (Tongji University, Department of Geotechnical Engineering, Shanghai, China); Zhu Fangyuan; Fang Liu and Utili, Stefano. A bond contact model for methane hydrate-bearing sediments with interparticle cementation: International Journal for Numerical and Analytical Methods in Geomechanics, 38(17), p. 1823-1854, illus. incl. 4 tables, 74 ref., December 10, 2014.
While methane hydrates (MHs) can be present in various forms in deep seabeds or permafrost regions, this paper deals with MH-bearing sediments (MHBS) where the MH has formed bonds between sand grains. A bond model based on experimentally validated contact laws for cemented granules is introduced to describe the mechanical behavior of the MH bonds. The model parameters were derived from measured values of temperature, water pressure and MH density. Bond width and thickness adopted for each bond of the MHBS were selected based on the degree of MH saturation. The model was implemented into a 2D distinct element method code. A series of numerical biaxial standard compression tests were carried out for various degrees of MH saturation. A comparison with available experimental data shows that the model can effectively capture the essential features of the mechanical behavior of MHBS for a wide range of levels of hydrate saturation under drained and undrained conditions. In addition, the analyses presented here shed light on the following: (1) the relationship between level of cementation and debonding mechanisms taking place at the microscopic level and the observed macro-mechanical behavior of MHBS and (2) the relationship between spatial distribution of bond breakages and contact force chains with the observed strength, dilatancy and deformability of the samples. Abstract Copyright (2010), John Wiley & Sons, Ltd.
15035826 Rangecroft, Sally (University of Exeter, Environment and Sustainability Institute, Exeter, United Kingdom); Harrison, Stephan; Anderson, Karen; Magrath, John; Castel, Ana Paola and Pacheco, Paula. A first rock glacier inventory for the Bolivian Andes: Permafrost and Periglacial Processes, 25(4), p. 333-343, illus. incl. 3 tables, 34 ref., December 2014.
Rock glaciers in the arid Bolivian Andes are potentially important water sources, but little is known about their spatial distribution and characteristics. We provide the first rock glacier inventory for the region (15-22°S), based on mapping using remote sensing data in Google Earth, supported by field validation. Of the 94 rock glaciers identified, 57 per cent were classified as active (containing ice) and the remaining as relict (not containing ice). The majority (87%) have a southerly aspect (SE, S and SW), and the rock glacier length and area averages were 500 m and 0.12 km2, respectively. We approximate the lower limit of permafrost to be at 4700 m in the Bolivian Andes, with the mean minimum altitude of rock glacier fronts estimated to be 4980 m for active rock glaciers, and about 100 m lower for relict rock glaciers. The inventory provides an important first step towards assessing the spatial distribution of regional permafrost as well as information to allow permafrost-based water resources in the Bolivian Andes to be understood against a backdrop of severe glacier recession. Abstract Copyright (2010), John Wiley & Sons, Ltd.
15035818 Thomazini, André (Federal University of Espírito Santo, Department of Plant Production, Alegre, Brazil); Teixeira, Daniel de Bortoli; Turbay, Caio Vinicius Gabrig; La Scala, Newton, Jr.; Schaefer, Carlos Ernesto G. R. and Mendonca, Eduardo de Sa. Spatial variability of CO2 emissions from newly exposed paraglacial soils at a glacier retreat zone on King George Island, maritime Antarctica: Permafrost and Periglacial Processes, 25(4), p. 233-242, illus. incl. sketch map, 37 ref., December 2014.
Thawed soils in Antarctica represent organic carbon (C) reservoirs with great potential to increase the net losses of CO2 to the atmosphere under climate change scenarios. This study spatially zones CO2 emissions from soil and vegetation along a transect in front of the retreating margin of Ecology Glacier in Admiralty Bay, King George Island, South Shetlands, near the Polish Antarctic station Henryk Arctowski. Two experiments were carried out to determine soil respiration: (1) a transect of 150 measuring points spaced 1 m apart, statistically analysed with split moving windows, identified three regions with different patterns of CO2 emissions; (2) a survey with three grids containing 60 sampling points, with a minimum distance between points of 0.30 m, totalling 2.7´1.5 m, in each of the identified locations. The survey showed that CO2 emission rates decreased (from 2.38 to 0.00 mmol m-2 s-1) and soil temperature at 5 cm depth increased (from 1.9 to 7°C) near the glacier. The site farthest from the glacier provided an emission 3.5 times higher than the closest site. The spatial variability of CO2 emissions decreased with distance from the glacier. Soil development and vegetation are identified as key drivers of CO2 emissions. Soil formation and vegetation growth increased with longer exposure since deglaciation, leading to enhanced homogeneity of CO2 emissions, independent of permafrost occurrence and stability. Abstract Copyright (2010), John Wiley & Sons, Ltd.
15043559 Kurylyk, Barret L. (University of New Brunswick, Department of Civil Engineering, Fredericton, NB, Canada); MacQuarrie, Kerry T. B. and McKenzie, Jeffrey M. Climate change impacts on ground water and soil temperatures in cold and temperate regions; implications, mathematical theory, and emerging simulation tools: Earth-Science Reviews, 138, p. 313-334, illus. incl. 1 table, 215 ref., November 2014.
Climate change is expected to increase regional and global air temperatures and significantly alter precipitation regimes. These projected changes in meteorological conditions will likely influence subsurface thermal regimes. Increases in groundwater and soil temperatures could impact groundwater quality, harm groundwater-sourced ecosystems, and contribute to the geotechnical failure of critical infrastructure. Furthermore, permafrost thaw induced by rising subsurface temperatures will likely alter surface and subsurface hydrology in high altitude and/or latitude regions and exacerbate the rate of anthropogenic climate change by releasing stored carbon into the atmosphere. This contribution discusses the theory and development of subsurface heat transport equations for cold and temperate regions. Analytical solutions to transient forms of the conduction equation and the conduction-advection equation with and without freezing are detailed. In addition, recently developed groundwater flow and heat transport models that can accommodate freezing and thawing processes are briefly summarized. These models can be applied to simulate climate change-induced permafrost degradation and dormant aquifer activation in cold regions. Several previous reviews have focused on the impact of climate change on subsurface hydraulic regimes and groundwater resources, but this is the first synthesis of studies considering the influence of future climate change on subsurface thermal regimes in cold and temperate regions. The current gaps in this body of knowledge are highlighted, and recommendations are made for improving future studies by linking atmospheric global climate models to subsurface heat transport models that consider heat advection via groundwater flow. Abstract Copyright (2014) Elsevier, B.V.
15030729 Gubler, S. (University of Zurich, Department of Geography, Zurich, Switzerland); Endrizzi, S.; Gruber, S. and Purves, R. S. Sensitivities and uncertainties of modeled ground temperatures in mountain environments: Geoscientific Model Development (GMD), 6(4), p. 1319-1336, illus. incl. 4 tables, 88 ref., 2013.
Model evaluation is often performed at few locations due to the lack of spatially distributed data. Since the quantification of model sensitivities and uncertainties can be performed independently from ground truth measurements, these analyses are suitable to test the influence of environmental variability on model evaluation. In this study, the sensitivities and uncertainties of a physically based mountain permafrost model are quantified within an artificial topography. The setting consists of different elevations and exposures combined with six ground types characterized by porosity and hydraulic properties. The analyses are performed for a combination of all factors, that allows for quantification of the variability of model sensitivities and uncertainties within a whole modeling domain. We found that model sensitivities and uncertainties vary strongly depending on different input factors such as topography or different soil types. The analysis shows that model evaluation performed at single locations may not be representative for the whole modeling domain. For example, the sensitivity of modeled mean annual ground temperature to ground albedo ranges between 0.5 and 4 °C depending on elevation, aspect and the ground type. South-exposed inclined locations are more sensitive to changes in ground albedo than north-exposed slopes since they receive more solar radiation. The sensitivity to ground albedo increases with decreasing elevation due to shorter duration of the snow cover. The sensitivity in the hydraulic properties changes considerably for different ground types: rock or clay, for instance, are not sensitive to uncertainties in the hydraulic properties, while for gravel or peat, accurate estimates of the hydraulic properties significantly improve modeled ground temperatures. The discretization of ground, snow and time have an impact on modeled mean annual ground temperature (MAGT) that cannot be neglected (more than 1 °C for several discretization parameters). We show that the temporal resolution should be at least 1 h to ensure errors less than 0.2 °C in modeled MAGT, and the uppermost ground layer should at most be 20 mm thick. Within the topographic setting, the total parametric output uncertainties expressed as the length of the 95% uncertainty interval of the Monte Carlo simulations range from 0.5 to 1.5 °C for clay and silt, and ranges from 0.5 to around 2.4 °C for peat, sand, gravel and rock. These uncertainties are comparable to the variability of ground surface temperatures measured within 10 m ´ 10 m grids in Switzerland. The increased uncertainties for sand, peat and gravel are largely due to their sensitivity to the hydraulic conductivity.
15041659 Arnold, Chelsea L. (University of California, Merced, Life and Environmental Sciences, Merced, CA) and Ghezzehei, Teamrat A. A method for characterizing desiccation-induced consolidation and permeability loss of organic soils: Water Resources Research, 51(1), p. 775-786, illus., 52 ref., January 2015.
A new method was developed to measure soil consolidation by capillary suction in organic soils. This method differs from previous methods of measuring soil consolidation in that no external load is utilized and only the forces generated via capillary suction consolidate the soil matrix. This limits the degree of consolidation that can occur, but gives a more realistic ecological perspective on the response of organic soils to desiccation in the field. This new method combines the principles behind a traditional triaxial cell (for measurements of volume change), a pressure plate apparatus, (to facilitate drainage by capillary suction), and the permeameter, (to measure saturated hydraulic conductivity) and allows for simultaneous desaturation of the soil while monitoring desiccation-induced volume change in the soil. This method also enables detection of historic limit of dryness. The historic limit of dryness is a novel concept that is unique to soils that have never experienced drying since their formation. It is fundamentally equivalent to the precompression stress of externally loaded soils. This method is particularly important for forecasting structural and hydrologic changes that may occur in soils that were formed in very wet regimes (e.g., wet meadows at the foot of persistent snowpacks and permafrost peats) as they respond to a changing climate. Abstract Copyright (2014), . American Geophysical Union. All Rights Reserved.
15039385 Terhorst, Birgit (University of Würzburg, Institute of Geography and Geology, Wurzburg, Germany); Sedov, Sergey; Sprafke, Tobias; Peticzka, Robert; Meyer-Heintze, Simon; Kühn, Peter and Solleiro Rebolledo, Elizabeth. Austrian MIS 3/2 loess-palaeosol records; key sites along a west-east transect: Palaeogeography, Palaeoclimatology, Palaeoecology, 418, p. 43-56, illus. incl. sketch map, 80 ref., January 15, 2015.
Based on a W-E transect through the northern loess regions of Austria, paleoenvironmental studies were carried out in three loess-paleosol sequences (Gunderding, Krems-Wachtberg and Stillfried B locus typicus) to complement available results in the context of a multi-methodological approach. On the base of previously published datings, our study concentrates on the MIS 3/2 transition. The results of detailed micromorphological investigations prove that paleopedogenesis, frost processes, and sedimentation rates differ in their spatial occurrence in the loess belt of Austria. All three sequences are in line with the general trend of a reduced intensity of pedogenic and cryogenic features from western to (south-)eastern Europe, which can be explained by lower Atlantic moisture influence towards the east. Interstadial cambic horizons are well developed in the MIS 3 sequence of western Austria, whereas the eastern loess profiles only show weak pedogenesis. In all studied sequences frost processes were active during the upper MIS 3 and MIS 2. The studied MIS 2 records are characterized by tundra soils with reductaquic horizons, which is a clear sign for prolonged phases of permafrost. On the spatial scale, the sedimentation rate increases in the eastern loess regions and particularly the Krems-Wachtberg sequence in the center of the transect experienced an exceptionally high sedimentation rate and can thus be seen as one of the most important high resolution records for the MIS 3/2 transition in European loess regions. Abstract Copyright (2015) Elsevier, B.V.
15035825 Bolch, Tobias (University of Zurich, Department of Geography, Zurich, Switzerland) and Gorbunov, Aldar P. Characteristics and origin of rock glaciers in northern Tien Shan (Kazakhstan/Kyrgyzstan): Permafrost and Periglacial Processes, 25(4), p. 320-332, illus. incl. 4 tables, sketch map, 36 ref., December 2014.
Northern Tien Shan is characterised by a distinct periglacial belt that contains many rock glaciers with an area of 1 km2 or more. To investigate the reason for their large size and variable occurrence, we analysed a representative subsample of the rock glaciers with respect to topographic and climatic variables. A simple permafrost model indicates that the rock glaciers originate in the zone where permafrost occurrence is very likely and some large rock glaciers flow down to elevations where permafrost is unlikely to exist outside the rock glaciers themselves. Correlation and multiple regression analyses revealed that the occurrence and characteristics of the rock glaciers can only be partly explained by the characteristics of the contributing area (e.g. its area or the headwall height). The correlation is greater with talus-type rock glaciers than with moraine-type rock glaciers. The climate can explain the general occurrence of rock glaciers but not their specific characteristics. It is hypothesised that the main reason for the specific distribution and characteristics of these large rock glaciers relates to the interaction with polythermal glaciers, topographic characteristics, intensive weathering and rock avalanches triggered by seismic activity. Abstract Copyright (2010), John Wiley & Sons, Ltd.
15043570 Rawlence, Nicolas J. (University of Waikato, School of Science, Hamilton, New Zealand); Lowe, David J.; Wood, Jamie R.; Young, Jennifer M.; Churchman, G. Jock; Huang, Yu-Tuan and Cooper, Alan F. Using palaeoenvironmental DNA to reconstruct past environments; progress and prospects: JQS. Journal of Quaternary Science, 29(7), p. 610-626, illus. incl. 2 tables, 197 ref., October 2014.
Palaeoenvironmental DNA (PalEnDNA) is defined as ancient DNA (aDNA) originating from disseminated genetic material within palaeoenvironmental samples. Sources of PalEnDNA include marine and lake sediments, peat, loess, till, ice, permafrost, palaeosols, coprolites, preserved gut contents, dental calculus, tephras, and soils as well as deposits in caves/rockshelters and at archaeological sites. PalEnDNA analysis provides a relatively new tool for Quaternary and archaeological sciences and its applications have included palaeoenvironmental and palaeodietary reconstructions, testing hypotheses regarding megafaunal extinctions, human-environment interactions, taxonomic studies, and studies of DNA damage. Because PalEnDNA samples comprise markedly different materials, and represent wide-ranging depositional and taphonomic contexts, various issues must be addressed to achieve robust, reproducible findings. Such issues include climatic and temporal limitations, the biological origin and state (free versus bound) of PalEnDNA, stratigraphic reliability, sterile sampling, ability to distinguish modern from aDNA signals, DNA damage and PCR amplification, DNA extraction methods, and taxonomic resolution. In this review, we provide a non-specialist introduction to the use of PalEnDNA for Quaternary and archaeological researchers, assess attributes and limitations of this palaeoenvironmental tool, and discuss future prospects of using PalEnDNA to reconstruct past environments. Abstract Copyright (2010), John Wiley & Sons, Ltd.
15041188 Wadhawan, S. K. (Geological Survey of India, Calcutta, India); Raju, M.; Ghosh, Saibal; Bodas, M. S.; Ghoshal, Timir Baran and Jaiswal, Pankaj. Geoscience considerations in formulation of National Landslide Disaster Management Plan: in Landslides, Indian Journal of Geosciences, 67(3-4), p. 203-216, illus. incl. 1 table, 37 ref., December 2013.
Nearly 15% of Indian landmass (about 0.49 million km2) in mountainous terrains (including permafrost and ice-covered areas) are prone to landslide hazards. Like other natural hazards such as earthquake, flood, landslide-related disasters also cause havoc and often register considerable, fatality and complex nature of damage pattern in mountainous terrains in India. Therefore, to minimize its losses, an effective Landslide Disaster Management Plan (LDMP) is needed. According to the National Disaster Management Act (2005), LDMP should give maximum stress on preparedness and mitigation rather than incurring more expenditure and making ad-hoc arrangements for relief and rehabilitation measures. Thus, the onus of effectively managing landslide-related hazards becomes a challenging task because preventing or minimizing losses owing to an inevitable and consequential geomorphic phenomenon like landslides needs proper geoscientific appraisal and studies which should be the integral part of any detailed disaster management plan. To successfully implement the LDMP, the roles of the-State Governments and all the stakeholders including Geological Survey of India (GSI) being the nodal agency are crucial which needs to be defined in a well-coordinated manner. This paper documents in the form of a Standard Operating Procedure (SOP), the roles and responsibilities of the relevant and best geoscientific practices for effectively mitigating and managing this particular hazard which could be the fundamental basis for framing the LDMP for landslide-prone areas in India.
15036147 Frehner, Marcel (ETH Zurich, Geological Institute, Zurich, Switzerland); Ling, Anna Hui Mee and Gärtner-Roer, Isabelle. Furrow-and-ridge morphology on rockglaciers explained by gravity-driven buckle folding; a case study from the Murtèl rock glacier (Switzerland): Permafrost and Periglacial Processes, 26(1), p. 57-66, illus., 40 ref., March 2015.
Rockglaciers often feature a prominent furrow-and-ridge topography. Previous studies suggest that this morphology develops due to longitudinal compressive flow during rockglacier creep; however, no satisfactory mechanical/physical model has been provided explaining both the observed characteristic wavelength and the growth rate necessary to amplify the structure to its final size. Our study identifies viscous buckle folding as the dominant process forming the furrow-and-ridge morphology on rockglaciers. Buckle folding is the mechanical response of layered viscous media to layer-parallel compression. The Murtel rockglacier (Switzerland) exhibits a spectacular furrow-and-ridge morphology and is chosen as a case study. Its well-determined internal structure can be approximated by two layers: the upper 3-5 m thick active layer consisting mainly of rock boulders and fragments above a thick, almost pure, ice layer, both assumed to exhibit viscous rheology. We analysed a high-resolution digital elevation model of the Murtel rockglacier using analytical buckle-folding expressions, which provide quantitative relationships between the observed wavelength, the layer thickness and the effective viscosity ratio between the folded layer and the underlying ice. Based on this geometrical and rheological information, we developed a finite-element model to simulate dynamical gravity-driven two-dimensional rockglacier flow. A buckling instability of the upper layer develops and amplifies self-consistently, reproducing several key features of the Murtel rockglacier (wavelength, amplitude and distribution of the furrow-and-ridge morphology), as well as the quasi-parabolic deformation profile observed in boreholes. Comparing our model with published surface flow velocities constrains the time necessary to produce the furrow-and-ridge morphology to about 1000-1500 years. Abstract Copyright (2010), John Wiley & Sons, Ltd.
15038110 Yamagishi, Chizuru (University of Tsukuba, Department of Life and Environmental Sciences, Tsukuba, Japan) and Matsuoka, Norikazu. Laboratory frost sorting by needle ice; a pilot experiment on the effects of stone size and extent of surface stone cover: Earth Surface Processes and Landforms, 40(4), p. 502-511, illus. incl. 2 tables, 29 ref., March 30, 2015.
Sorted patterned ground is ubiquitous where gravelly fine soil experiences freeze-thaw cycles, but experimental studies have rarely been successful in reproducing such patterns. This article reports an attempt to reproduce miniature sorted patterns by repeating needle-ice formation, which simulates frost sorting in regions dominated by diurnal freeze-thaw cycles. Six full-scale laboratory models were tested. They consisted of near-saturated volcanic fine soil topped by small stones of uniform size; the models explored a range of stone size (~6, ~12, ~17 and ~22 mm) and surface abundance (20, 40 and 60% cover). The stones were placed in a grid on the surface. These models were subjected to 20-30 temperature excursions between 10 °C and -5 °C in 12 hours. The evolution of surface patterns were visually traced by photogrammetry. A data logging system continuously monitored vertical soil displacements, soil temperatures and moistures at different depths. All experimental runs displayed needle-ice formation (2-3 cm in height) and resulting displacement of stones. The soil domains tended to heave faster and higher than the stones, leading to outward movement of the former and concentration of the stones. In plan view, smaller stones showed relatively fast and long-lasting movements, while larger stones stabilized after the first five cycles. The 20% stone cover produced stone islands, whereas the 40% cover resulted in sorted labyrinths (a circle-island complex) that may represent incipient sorted circles. The average diameter or spacing of these forms are 12-13 cm, being comparable to those in the field. The experiments imply that needle-ice activity promotes rapid formation of sorted patterns, although the formation of well-defined sorted circles may require hundreds of diurnal frost heave cycles. Copyright 2014 John Wiley & Sons, Ltd.
15044392 Zhou, Xiaohai (Swiss Federal Institute of Technology, Institute of Environmental Engineering, Zurich, Switzerland); Zhou Jian; Kinzelbach, Wolfgang and Stauffer, Fritz. Simultaneous measurement of unfrozen water content and ice content in frozen soil using gamma ray attenuation and TDR: Water Resources Research, 50(12), p. 9630-9655, illus. incl. 3 tables, 45 ref., December 2014.
The freezing temperature of water in soil is not constant but varies over a range determined by soil texture. Consequently, the amounts of unfrozen water and ice change with temperature in frozen soil, which in turn affects hydraulic, thermal, and mechanical properties of frozen soil. In this paper, an Am-241 gamma ray source and time-domain reflectometry (TDR) were combined to measure unfrozen water content and ice content in frozen soil simultaneously. The gamma ray attenuation was used to determine total water content. The TDR was used to determine the dielectric constant of the frozen soil. Based on a four-phase mixing model, the amount of unfrozen water content in the frozen soil could be determined. The ice content was inferred by the difference between total water content and unfrozen water content. The gamma ray attenuation and the TDR were both calibrated by a gravimetric method. Water contents measured by gamma ray attenuation and TDR in an unfrozen silt column under infiltration were compared and showed that the two methods have the same accuracy and response to changes of water content. Unidirectional column freezing experiments were performed to apply the combined method of gamma ray attenuation and TDR for measuring unfrozen water content and ice content. The measurement error of the gamma ray attenuation and TDR was around 0.02 and 0.01 m3/m3, respectively. The overestimation of unfrozen water in frozen soil by TDR alone was quantified and found to depend on the amount of ice content. The higher the ice content, the larger the overestimation. The study confirmed that the combined method could accurately determine unfrozen water content and ice content in frozen soil. The results of soil column freezing experiments indicate that total water content distribution is affected by available pore space and the freezing front advance rate. It was found that there is similarity between the soil water characteristic and the soil freezing characteristic of variably saturated soil. Unfrozen water content is independent of total water content and affected only by temperature when the freezing point is reached. Abstract Copyright (2014), . American Geophysical Union. All Rights Reserved.
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15037938 Anderson, Darya (University of Arizona, Tucson, AZ); Rich, V. I.; Hodgkins, S. B.; Tfaily, Malak and Chanton, J. Mapping microbial carbon substrate utilization across permafrost thaw [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0122, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Permafrost thaw is likely to create a substantial positive feedback to climate warming, as previously frozen carbon becomes bioavailable and is released to the atmosphere. Microbes mediate this release, while also consuming "new" carbon from plant inputs and middle-aged soil carbon pools in the seasonally-thawed active layer overlying permafrost. This carbon consumption releases carbon dioxide (CO2) and methane (CH4), both potent greenhouse gases. To investigate microbial carbon cycling in this changing habitat, we examined how microbial communities' carbon substrate degradation changes along a natural permafrost thaw gradient in Stordalen Mire (68.35°N, 19.05°E), northern Sweden. At this location, intermediate thaw creates Sphagnum moss-dominated bogs, while complete thaw results in Eriophorum sedge-dominated fens. The progression of thaw results in increasing organic matter lability (Hodgkins et al, 2014), shifting microbial community composition (Mondav & Woodcroft et al 2014), and changing carbon gas emissions (McCalley et al., in review). However, the inter-relationship of the first two in producing the third remains unclear. We analyzed microbial carbon substrate utilization in the intermediate-thaw and full-thaw sites by two incubation-based methods. We used Biolog EcoPlates, which contain 31 ecologically relevant carbon substrates and a colorimetric marker of their consumption, and into which we added a soil liquid suspension. In addition, we performed mason-jar incubations of peat with carbon substrate amendments and measured CH4 and CO2 emissions. Preliminary Biolog Ecoplate incubations showed that intermediate-thaw features responded faster and more strongly overall to a wide range of substrates relative to the full-thaw features. Preliminary mason jar incubations showed that acetate amendment elicited the greatest response increase in CH4 production and the second greatest increase in CO2 production relative to the controls, in samples from both habitats. In addition, the lowest CH4 and CO2 production was seen in amendments of sphagnum acid. It is important to understand the carbon substrate utilization occurring at these initial and advanced thaw features to speculate the degree to which various carbon inputs are being metabolized to produce the observed gas emissions.
15037944 Bracho, R. G. (University of Florida, Ft. Walton Beach, FL); Webb, E.; Mauritz, Marguerite and Schuur, E. A. G. Carbon Fluxes in a sub-arctic tundra undergoing permafrost degradation [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0130, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
As an effect of climate change, temperatures in high latitude regions are increasing faster than in the rest of the world and future projections indicate it will increase between 7°C and 8°C by the end of the 21st century. Permafrost soils store around 1700 Pg of Carbon (C), which is approximately the amount of C stored in terrestrial vegetation and in the atmosphere combined. Sustained warming induces permafrost thaw, leads to a thicker seasonal active layer, and creates subsided patches in the landscape. Carbon that was previously inaccessible to decomposition is thus exposed, increasing the likelihood of positive feedback of CO2 to the atmosphere. We measured C fluxes (Net ecosystem carbon flux, NEE, and Ecosystem respiration, Re) using the eddy covariance approach in a tundra landscape (Eight Mile Lake Watershed, Alaska) undergoing permafrost degradation from the beginning of the growing season in 2008 and throughout most winters until May 2014. This interval encompassed a range of climatic variability that included a deviation of ±50% from the long term average in growing season precipitation. Active layer depth (thaw depth at the end of the growing season) and subsidence in the footprint were used as indicators of permafrost degradation. Results indicate that annual NEE ranged from a sink of 0.76 MgC ha-1 yr-1 to a source of 0.55 MgC ha-1 yr-1. NEE during the growing seasons fluctuated from 1.1 to 1.8 MgC ha-1 season-1 in net C uptake. Annual NEE was strongly affected by winter Re, which represented between 33% and 45% of the annual value regardless of of the large drop in both air and soil temperature. Parameters from the light response curve (optimum NEE, NEEopt and quantum yield, a) showed a seasonal and interannual variability and were different between the most and least degraded sites in the footprint, which affected the magnitude of the carbon cycle and may have implications for landscape C balance in sub-arctic tundra.
15037972 Christensen, Torben R. (Aarhus University, Arctic Research Centre, Aarhus, Denmark); Mastepanov, Mikhail; Lund, M.; Tamstorf, M. P.; Parmentier, Frans-Jan W.; Rysgard, S. and Lilienthal, Achim J. Reducing uncertainty in methane emission estimates from permafrost environments [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B42D-01, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Depending on factors including temperature, snow duration and soil moisture conditions, emissions of the greenhouse gas methane from permafrost wetlands can vary by factors of 2-4 between years. This variability is clear in atmospheric measurements of the gas, but a lack of ground-based data is making it hard to locate the methane sources responsible. Methane monitoring in the Arctic is expensive, requiring sophisticated analysis equipment such as power requiring laser spectrometer analysis made in remote places. This also puts demands on the logistics where infrastructures and field stations that offer line-power in the field are in high demand but very rarely found. Research projects therefore typically focus on one site, and run for a year or two. Longer term monitoring programs, which document climate, hydrology, phenology and population dynamics of birds and mammals, rarely include carbon fluxes since it is technically challenging to measure. One that does is the Greenland Ecosystem Monitoring program that started at the Zackenberg research station, which has recorded substantial methane flux variations for almost a decade in North-east Greenland. Such multi-year studies show that, while there is some connection between the amounts of methane released from one year to the next, accurate forecasting is difficult. They also highlight the importance of extending monitoring beyond the growing period into the frozen season, both in spring and autumn. A spatially distributed network of long-term monitoring stations in the Arctic, with consistency between measurements, is badly needed to improve this situation. Productive methane 'hot spots', many sporadic, have also been identified in recent studies. By ventilating surface waters, storms trigger emissions in the East Siberian Sea Shelf. Shallow lakes formed when permafrost thaws can belch methane from decomposing old organic deposits, of which there are huge amounts in the Arctic. All of these potentially important emissions are of a scale that still is in need of being reconciled with the atmospheric record. This presentation will give an overview of novel approaches including robot techniques ground-, boat- and airborne-based to reduce uncertainty in particular in relation to these 'hot spot' emissions.
15037953 Connolly, C. T. (University of Texas at Austin, Marine Science Institute, Austin, TX); Spawn, S.; Ludwig, S.; Schade, J. D. and Natali, S. The effects of permafrost thaw on organic matter quality and availability along a hill slope in northeastern Siberia [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0141, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Climate warming and permafrost thaw in northeastern Siberia are expected to change the quantity and quality of organic matter (OM) transported through watersheds, releasing previously frozen carbon (C) to biologically available pool. Hill slopes have shown to influence the distribution of OM, resulting in a downhill accumulation of available C and nutrients relative to uphill. Here we examine how future permafrost thaw will change OM quality and availability along a hill slope in a larch-dominated watershed. We collected soils from the thawed organic and mineral layers, and 1 m deep permafrost cores for dissolved organic C (DOC) and total dissolved N (TDN), C composition from measures of colored dissolved organic matter (CDOM), DOC lability from biodegradable DOC (BDOC) incubations, C and nutrient availability from extracellular-enzyme assays (EEA's), and microbial respiration from aerobic soil incubations. Here we show that organic soils (O), in comparison to mineral soils (M) and permafrost (P) are the most abundant source of C (avg O DOC: 51.6 mg/L), exhibiting low molecular complexity (avg O SUVA254: 4.05) and high quality. Evidence suggests permafrost OM may be an equally abundant, and more labile source of C than mineral soils (highest P DOC: 16.1 mg/L, lowest P SUVA254: 6.32; median M DOC: 18.5 mg/L, median M SUVA254: 24.0). Furthermore, we demonstrate that there may be a positive relationship in the rate of C mineralization and distance downhill, showing 15-30% greater CO2 production/gC downhill relative to uphill. Evidence also supports a similar relationship in permafrost DOC content and molecular complexity, showing more DOC of a lower complexity further downhill. This indicates DOC transport may have been occurring through the active layer and downhill during ice-rich permafrost formation, and may supply a labile source of carbon to lowland areas and adjacent stream networks upon thaw.
15037954 Cooper, M. D. A. (University of Exeter, United Kingdom); Estop-Aragones, C.; Fisher, J. P.; Garnett, M.; Charman, D. J.; Murton, J. B.; Phoenix, G. K.; Treharne, Rachael; Street, L. E.; Wookey, P. A. and Hartley, I. P. Methane emissions are predominantly derived from contemporary carbon from a thawing permafrost peatland in Canada [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0142, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Rapid warming at high northern latitudes is resulting in permafrost degradation. When permafrost thaws in wetlands, the peat plateaus tend to collapse, bringing the water table closer to the surface. Methane (CH4) fluxes increase post-thaw, but the extent to which this is caused by CH4 release from the decomposition of previously-frozen, old carbon, deep within the soil profile, versus waterlogging near the soil surface resulting in anaerobic decomposition of more recent inputs, is unclear. Quantifying the relative contributions of these contrasting CH4 sources is essential for predicting future rates of CH4 release from thawing permafrost wetlands. The most definitive test of whether old permafrost-derived C contributes substantially to CH4 release post thaw, would be to measure the radiocarbon (14C) content of the CH4. However, until recently this was very challenging in remote locations. Using new techniques that overcome previous limitations, we were able to measure the 14C content of CH4 being released from thawing wetlands in northern Canada. We hypothesised that time since plateau collapse would affect the amount of old CH4 being released, and so sampled in locations where collapse had occurred at different times. Samples were collected from collars that either included or excluded CH4 from deep within the peat profile, and CH-4 from a depth of 100 cm was collected by sampling soil water. We demonstrate that millennium-old CH4 was being produced at 100 cm. However, CH4 being released from the surface had contemporary 14C signatures. Using our collar treatments, we were able to calculate that deep CH4 contributed less than 10% of the surface flux, and that this contribution did not vary with time since collapse. The effect of permafrost thaw on CH4 fluxes in these peatlands appears to be more closely related to changes in near surface conditions than to increases in anaerobic decomposition of previously frozen C. This indicates permafrost thaw does not necessarily lead to increased emissions of old C via the CH4 pathway as many have assumed. This is not generally reflected in Earth system models.
15037932 de Leon, K. C. (University of Arizona, Tucson, AZ); Schwery, David; Yoshikawa, K.; Christiansen, Hanne H. and Pearce, David. The impact of climate change on microbial communities and carbon cycling in high arctic permafrost soil from Spitsbergen, Northern Norway [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0115, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Permafrost-affected soils are among the most fragile ecosystems in which current microbial controls on organic matter decomposition are changing as a result of climate change. Warmer conditions in the high Arctic will lead to a deepening of the seasonal active layer of permafrost, provoking changes in microbial processes and possibly resulting in exacerbated carbon degradation under increasing anoxic conditions. The viable and non-viable fractions of the microbial community in a permafrost soil from Adventdalen, Spitsbergen, Norway were subjected to a comprehensive investigation using culture-dependent and culture-independent methods. Molecular analyses using FISH (with CTC-DAPI) and amplified rDNA restriction analysis (ARDRA) on a 257 cm deep core, revealed the presence of all major microbial soil groups, with the active layer having more viable cells, and a higher microbial community diversity. Carbon dioxide (CO2) and methane (CH4) flux measurements were performed to show the amount of C stored in the sample. We demonstrated that the microbial community composition from the soil in the center of the core was most likely influenced by small scale variations in environmental conditions. Community structure showed distinct shift of presence of bacterial groups along the vertical temperature gradient profile and microbial counts and diversity was found to be highest in the surface layers, decreasing with depth. It was observed that soil properties driving microbial diversity and functional potential varied across the permafrost table. Data on the variability of CO2 and CH4 distribution described in peat structure heterogeneity are important for modeling emissions on a larger scale. Furthermore, linking microbial biomass to gas distribution may elucidate the cause of peak CO2 and CH4 and their changes in relation to environmental change and peat composition.
15037967 Estop-Aragones, C. (University of Exeter, College of Life and Environmental Sciences, Exeter, United Kingdom); Fisher, J. P.; Cooper, M.; Thierry, Aaron; Williams, Matthew D.; Phoenix, G. K.; Murton, J. B.; Charman, D. J. and Hartley, I. P. In situ contribution of old respired CO2 from soils in burnt and collapsed permafrost in Canada [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B41O-08, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Permafrost degradation is associated with an aggradation of the active layer thus exposing previously frozen soil carbon (C) to microbial activity. This may increase the generation of greenhouse gases and potentially increase rates of climate change. However, the rate of C release remains highly uncertain, not least because few in situ studies have measured the rate at which previously frozen C is released from the soil surface, post thaw. We quantified the contribution of this "old" C being released as CO2 from permafrost degraded soils in sporadic and discontinuous permafrost in Yukon and Northwest Territories, Canada. Firstly, we studied the effect of fire on black spruce forests as the removal of vegetation, especially mosses, may play a key role on thaw depth. Secondly, we investigated the collapse of peatland plateau after permafrost thaw which resulted in the formation of wetlands. We combined radiocarbon measurements of respired CO2 with a novel collar-design that either included or excluded CO2 released from deeper soil horizons. Our results show that, while excluding deeper layers did reduce the average age of the C being released from the soil surface, more than 90% of the CO2 came from contemporary sources, even after burnt and permafrost plateau collapse. Furthermore, soil cores dated using 210Pb show that the rapid accumulation of sedge peat after plateau collapse may more than compensate for any C losses from depth. Our results from the Canadian boreal contrast strongly with findings from other geographical areas emphasising the complexities of predicting the impact of permafrost thaw on the carbon balance of northern ecosystems.
15037919 Garnello, A. (University of Arizona, Tucson, AZ); Finnell, D.; Palace, Michael W.; Wu, J.; Lepine, Lucie C.; Crill, Patrick M. and Varner, Ruth K. Characterization of permafrost degradation and plant communities using hyperspectral reflectance [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31F-0087, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Annual temperatures in subarctic regions are increasing, resulting in rapid disappearance of long-standing permafrost. This directly affects plant community structure, increases soil active layer thickness, and changes greenhouse gas emissions. The change in carbon cycling alters climate feedback cycles, calling for accurate, efficient, permafrost degradation monitoring techniques in Earth Systems models. At Stordalen Mire, 68°21'N and 19°02'E, 50 randomized one-square meter plots were measured for vegetation composition and hyperspectral reflectance using an ASDinc FieldSpec4. Plots were classified into one of five site-types based on vegetation composition and microtopography, with each site type representing differing stages of permafrost degradation. A discrete forward multivariate model with stepwise selection successfully paired 49 of 49 plots with their site types using the reflectance values for the wavelengths centered at 1115 nm, 1190 nm, 1334 nm, 1340 nm, and 1813 nm. These wavelengths correspond to reflectance features resulting from varying plant intercellular structure (1115 nm, 1190 nm), and particular in-cell air-water interactions (1334 nm, and 1340 nm 1813 nm). A decision tree partitioning the reflectance feature at 1334 nm across all site types resulted in a 4-split tree with an R2 of .793, and a 10-fold cross-validation R2 of .712. A discrete forward multivariate analysis model successfully paired 84% of plots with their correct site types using the percent cover of five dominant species (Empetrum nigrum, Eriophorum vaginatum, Rubus chamaemorus, Sphagnum spp, Open Water). A five-split partition of site type with these five dominant species returned an R2 of .893, and a five-fold cross-validation R2 of .859. A least squares regression model used 5 species-specific spectral bands distinguishing content of plant pigment, cell-water, and physical structure to predict percent cover of four primary species: E. nigrum (R2 .82), R. chamaemorus (R2 .64), Sphagnum spp. (R2 .92), and Open Water (R2 .79). Results indicate the usefulness of hyperspectral measurements for estimating vegetative composition. Continued work will examine field spectrometer measurements with those from the EO-1 Hyperion sensor in an effort to scale-up permafrost degradation monitoring.
15037985 Hanisch, Jessica (University of Montreal, Montreal, QC, Canada); Connon, R.; Templeton, Michael; Quinton, W. L.; Olefeldt, D.; Moore, Tim R.; Roulet, Nidel T. and Sonnentag, Oliver. Characterizing dissolved organic carbon concentrations and export in a boreal forest-peatland landscape under the influence of rapidly degrading discontinuous permafrost [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43B-0235, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Our current understanding of peatland energy, water and carbon (C) cycles implies that northern peatlands are vulnerable to projected climate change, and that the perturbation of these cycles might cause a strong positive or negative net feedback to the climate system. About one third of Canada's northern peatlands contain contain perennialy frozen ground (permafrost). Boreal forest-peatland ecosystems in the discontinuous permafrost zone (50-90% of frozen ground) are especially vulnerable to rising temperatures as permafrost is ice-rich, relatively warm and thin, and thus susceptible to complete disappearance causing ground surface subsidence and a decline in forest cover in response to water-logging. Several recent studies have substantially improved our understanding of northern peatland's role in the climate system by quantifying their net ecosystem C balance which includes atmospheric and aqueous C fluxes generally dominated by the export of dissolved organic C (DOC). We characterize seasonal and diurnal variations in DOC export from five catchments (0.02-0.05 km2) at Scotty Creek, a 152 km2-watershed under the influence of rapidly degrading and disappearing discontinuous permafrost near Fort Simpson, Northwest Territories, Canada. The five catchments are characterized by different fractions of forested peat plateaus with permafrost (38-73%) and permafrost-free collapse bogs (27-62%). Dissolved organic carbon concentrations at Scotty Creek appear to be higher in catchments where the percentage of peat plateaus is higher compared to bogs, independent of catchment size. Average DOC concentration for catchments with a lower percentage of peat plateaus is lower (~43 mg/l) than for those with a higher percentage of plateaus (~60 mg/l). These preliminary results suggest that lateral C losses from this rapidly changing landscape are at least partly controlled by the peat plateau-bog ratio. Over the year, DOC export from the five catchments is limited to around a week due to the relatively dry conditions at Scotty Creek over the hot summer months: only one of the catchments produces continuous measurable surface runoff. However, as indicated through water level recordings, additional unaccounted DOC export may occur through diffuse subsurface flow.
15037971 Harden, J. W. (U. S. Geological Survey, California Water Science Center, Menlo Park, CA); Ping, C. L.; O'Donnell, Jonathan A.; Koven, C. D.; Michaelson, G. J.; Genet, H. and Xu, X. Constraining soil C loss upon thaw; comparing soils with and without permafrost [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0112, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Permafrost thaw, with its state change and increased temperature, clearly results in increased decomposition, but constraining directions and amounts of net C exchange is confounded by feedbacks among dynamic vegetation and soil layers, nutrients, and microbial communities. One way to constrain potential loss is to compare soils with and without permafrost. We compared three sets of soil profiles developed in late Pleistocene loess from various slope positions in western Iowa (no permafrost for >10 ka), south-central Alaska (no permafrost for >3550 y), and interior Alaska (current permafrost). In Iowa C where deep C was protected by loess burial, % soil C declined most precipitously with depth (down to <0.6%C at 1 m). Alaska soils with and without permafrost were similar in %C at 1 m depths (up to 2%C). However soils with permafrost had 2X to 4X more C than non-permafrost soils at 1.5 m and maintained high and highly variable (0.8 to 11%C) C contents below 150 cm. Data provide an additional line of evidence that carbon in deep permafrost is highly susceptible to loss upon thawing. Meanwhile modeling and forecasting C fate requires more insight into C protection and stabilization by burial.
15037933 Hedgpeth, A. (University of Hawaii at Manoa, Honolulu, HI); Beilman, D. and Crow, S. E. Sensitivity of Arctic permafrost carbon in the Mackenzie River basin; a substrate addition and incubation experiment [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0116, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Arctic soil organic matter (SOM) mineralization processes are fundamental to the functioning of high latitude soils in relation to nutrients, stability, and feedbacks to atmospheric CO2 and climate. The arctic permafrost zone covers 25% of the northern hemisphere and contains 1672 Pg of soil carbon (C). 88% of this C currently resides in frozen soils that are vulnerable to environmental change. For instance, arctic growing seasons may be lengthened, resulting in an increase in plant productivity and rate of below ground labile C inputs as root exudates. Understanding controls on Arctic SOM dynamics requires recognition that labile C inputs have the potential to significantly affect mineralization of previously stable SOM, also known as 'priming effects'. We conducted a substrate addition incubation experiment to quantify and compare respiration in highly organic (42-48%C) permafrost soils along a north-south transect in western Canada. Near surface soils (10-20 cm) were collected from permafrost peatland sites in the Mackenzie River Basin from 69.2-62.6°N. The surface soils are fairly young (D14C values >-140.0) and can be assumed to contain relatively reactive soil carbon. To assess whether addition of labile substrate alters SOM decomposition dynamics, 4.77-11.75 g of permafrost soil were spiked with 0.5 mg D-glucose g-1 soil and incubated at 5°C. A mass balance approach was used to determine substrate-induced respiration and preliminary results suggest a potential for positive priming in these C-rich soils. Baseline respiration rates from the three sites were similar (0.067-0.263 mg CO2 g-1 soil C) yet show some site-specific trends. The rate at which added substrate was utilized within these soils suggests that other factors besides temperature and soil C content are controlling substrate consumption and its effect on SOM decomposition. Microbial activity can be stimulated by substrate addition to such an extent that SOM turnover is enhanced, suggesting that soil C decay rates and processes are not constant, but depend on the inter-soil dynamics of other soil C pools. If these C rich soils contain ample C-resources to fuel extra microbial SOM decomposition, then possibly this enhanced use of SOM is not as a means of C acquisition, but to mobilize nutrients needed to meet microbial growth requirements.
15037976 Heslop, J. (University of Alaska Fairbanks, Water and Environmental Research Center, Fairbanks, AK); Walter Anthony, K. M.; Sepulveda-Jauregui, A. and Martinez-Cruz, K. C. Correlating permafrost organic matter composition and characteristics with methane production potentials in a first generation thermokarst lake and its underlying permafrost near Fairbanks, Alaska, USA [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B42D-06, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Thermokarst lakes, formed in permafrost-thaw depressions, are known sources of atmospheric methane (CH4) and carbon dioxide (CO2). The organic carbon (OC) utilized in the production of these greenhouse gases originates from microbial decomposition of aquatic and terrestrial organic matter (OM) sources, including soils of the lakes' watersheds and permafrost thaw beneath the lakes. OM derived from permafrost thaw is particularly important given the thickness of permafrost soils underlying some lakes (typically 10-30 m in yedoma permafrost); however, OM heterogeneity remains a significant uncertainty in estimating how microbial decomposition responds to permafrost thaw. This study correlates OM and water-extractable OC (WEOC) composition with CH4 production potentials determined from anaerobic laboratory incubations. Samples were collected from 21 depths along a 5.9-m deep thermokarst-lake sediment core and 17 depths along an adjacent 40-m deep undisturbed yedoma permafrost profile near Vault Creek, Alaska. The Vault Lake core, collected in the center of a 3230 m2 first generation thermokarst lake, includes surface lake sediments, the talik (thaw bulb), and permafrost actively thawing beneath the lake. Soil OM composition was characterized using pyrolysis-gas chromatography/mass spectrometry (py-GC/MS) and the most prevalent compounds were grouped into six indices based on their likely origin. WEOC was characterized using fluorescence spectrometry. Using stepwise multiple linear regression analyses, we found that CH4 production was negatively correlated with WEOC aromaticity (p=0.018) and fulvic acids (p=0.027). CH4 production was positively correlated with lipids and carboxylic acids (p<0.001), polysaccharides (p=0.036) and the degree of WEOC humification (p=0.013). Results suggest OM and WEOC composition can be correlated with CH4 production, indicating potential for model building to better predict greenhouse gas release from permafrost thaw.
15037941 Holden, S. R. (University of California Irvine, Irvine, CA); Welker, J. M. and Czimczik, C. I. Shrub expansion in arctic Alaska alters the sources (14C) and magnitudes of ecosystem respiration in the continuous permafrost zone [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0125, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Soils in the Arctic store up to 50% of global soil organic carbon (C) (1,672 Pg C) and more than twice the amount of C currently present in the atmosphere. At the core of this enormous C pool is the large fraction of C that has been frozen in permafrost and disconnected from the active C cycle. As the Arctic undergoes warming and wetting, permafrost C is at risk of being transferred to the atmosphere, resulting in a strong positive feedback to global climate. One of the most commonly observed responses to climate warming in the Arctic is an increase in woody shrub growth and corresponding changes in the surface energy budget and shifts in belowground processes. Increased shrub cover is accompanied by a number of soil physical and chemical changes, including decreased growing season soil temperature due to soil shading, warmer winter soil temperature due to snow accumulation around shrubs, and increased rooting depth. Therefore, shrub expansion may feedback to alter the amount of C stored in arctic ecosystems, but the direction and magnitude of this potential feedback are highly uncertain. To address this uncertainty, we established four sites across a shrub cover gradient near Toolik Lake, AK, USA, ranging from herbaceous tussock to deciduous shrub tundra. At each site we measured the rate and isotope composition (13C/12C, 14C/12C) of ecosystem, root and microbial respiration with chambers and incubations, the concentration and isotope composition of soil CO2 with wells, and the C and N concentration and isotopic composition of bulk organic matter in the active layer and upper permafrost with EA-IRMS. We used the isotope values to partition ecosystem CO2 emissions into respiration from plants, young surface soil, and old deep soil. We found that rates of ecosystem respiration increase with increasing shrub cover. Furthermore, preliminary results indicate that the proportional contribution of plants and old soil to ecosystem respiration changes with increasing shrub density. Taken together, our results suggest that ongoing shrub expansion will alter permafrost C dynamics in arctic ecosystems. Forthcoming winter measurements will provide insights into the consequences of shrub expansion for the annual C budget of the Arctic.
15037897 Holloway, Jean (Queen's University, Kingston, ON, Canada); Rudy, Ashley and Lamoureux, Scott F. Hydroclimatic and landscape controls over permafrost disturbance in the Canadian High Arctic [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31D-0045, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Unusually warm conditions during recent years in the Arctic have led to changes in the properties of the seasonal active layer and the uppermost permafrost. Deep thaw of the active layer in exceedingly warm years causes the emergence of pressurized sediment slurries at surface, called mudboils. An understanding of the processes driving mudboil formation is necessary as these features occur in proximity to and during periods when other forms of permafrost degradation and disturbance occur, particularly active layer detachments. To better improve our understanding of these features, systematic mapping of recent mudboils along with soil and water sampling was undertaken at the Cape Bounty Arctic Watershed Observatory (CBAWO), Melville Island, Nunavut in 2012 and 2013. Results indicate that these features only occur late in the melt season during especially warm years and in some cases closely follow major rainfall events. High-resolution satellite imagery for the study area was analyzed, and terrain characteristics were determined for areas with mapped mudboil activity. Notably, on a landscape scale, mudboils were significantly associated with polar semi-desert vegetation and bare soil settings, corresponding to increased active layer depth when compared to more vegetated areas. Further, fine-scale occurrence of mudboils appears to be related to differential soil moisture retention and spatially heterogeneous soil water pressurization due to thaw into the ice-rich transient layer in warm years. This research provides insights into the processes and landscape controls over these features to aid in understanding localized soil water response to deep summer thaw, with implications for surface water quality and patterns of permafrost-related degradation and disturbance.
15037951 Hough, M. (University of Arizona, Tucson, AZ); Garnello, A.; Finnell, D.; Palace, Michael W.; Rich, V. I. and Saleska, S. R. Can plant community turnover mitigate permafrost thaw feedbacks to the climate system? [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0139, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
In many parts of the Arctic, permafrost thaw due to rising temperatures results in the conversion of dry tundra to wetland bog and fen ecosystems. Such increases in anaerobic environments may have substantial feedbacks to the rate of climate change through the increased production of CH4, a greenhouse gas an order of magnitude more potent than the CO2 respired from aerobic soils. However, the total emission rates of CH4 and CO2 alone cannot predict the magnitude of feedback to the climate system since this will also depend on the ecosystem's overall carbon balance and the source of carbon (new vs old) producing the emissions. Thus, building detailed carbon budgets is essential to understanding the potential climate feedbacks of habitat changes due to permafrost thaw. We studied above-ground plant biomass and its carbon content in order to calculate the inputs of new carbon to the soil along a permafrost thaw gradient with previously well-quantified CO2 and CH4 fluxes in northern Sweden. In order to account for within-season plant community turnover, we monitored plant percent cover over the course of a growing season in three communities: areas underlain by permafrost dominated by E. vaginatum, and E. nigrum, recently thawed sphagnum dominated areas, and more established E. angustifolium dominated fen communities. Additionally, we calculated end of season biomass and percent carbon for each species and compared our findings to previously published community composition assessments from 1972/1973 and 2000. We tied our ground-based measurements to aerial remote sensing images to extrapolate biomass and percent carbon across the mire based on community type. These results allow us to calculate total carbon inputs to the mire from new above-ground biomass. By coupling these measurements with flux rates from each habitat we will be able to assess the degree to which increased biomass production might offset the increase in CH4 released from soils as a result of plant community turnover after permafrost thaw.
15037928 Hugelius, Gustaf (Stockholm University, Stockholm, Sweden); Strauss, Jens; Zubrzycki, S.; Harden, J. W.; Schuur, E. A. G.; Ping, C. L.; Schirrmeister, Lutz; Grosse, Guido; Michaelson, G. J.; Koven, C. D.; O'Donnell, Jonathan A.; Elberling, B.; Mishra, U.; Camill, P.; Yu, Z.; Palmtag, Juri and Kuhry, Peter. Improved estimates show large circumpolar stocks of permafrost carbon while quantifying substantial uncertainty ranges and identifying remaining data gaps [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0109, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Soils and other unconsolidated deposits in the northern circumpolar permafrost region store large amounts of soil organic carbon (SOC). This SOC is potentially vulnerable to remobilization following soil warming and permafrost thaw, but stock estimates are poorly constrained and quantitative error estimates were lacking. This study presents revised estimates of the permafrost SOC pool, including quantitative uncertainty estimates, in the 0-3 m depth range in soils as well as for deeper sediments (>3 m) in deltaic deposits of major rivers and in the Yedoma region of Siberia and Alaska. The revised estimates are based on significantly larger databases compared to previous studies. Compared to previous studies, the number of individual sites/pedons has increased by a factor 811 for 13 m soils, a factor 8 for deltaic alluvium and a factor 5 for Yedoma region deposits. A total estimated mean storage for the permafrost region of ca. 1300-1400 Pg with an uncertainty range of 1050-1650 Pg encompasses the revised estimates. Of this, ≤&eq;900 Pg is perennially frozen. While some components of the revised SOC stocks are similar in magnitude to those previously reported for this region, there are also substantial differences in individual components. There is evidence of substantial remaining regional data-gaps. Estimates remain particularly poorly constrained for soils in the High Arctic region and physiographic regions with thin sedimentary overburden (mountains, highlands and plateaus) as well as for >3 m depth deposits in deltas and the Yedoma region.
15037945 Jafarov, Elchin E. (University of Colorado, National Snow and Ice Data Center, Boulder, CO) and Schaefer, Kevin M. The effect of organic soil layer on simulated permafrost dynamics [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0131, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Soil organic layer controls energy exchange between the air and the ground in permafrost affected soils in the Northern Hemisphere. Organic soils contribute to an increase in soil moisture and provide a better insulation against summer heat. Better ground insulation is possible due to thermal conductivity of a thawed organic layer, which is about two times lower than thermal conductivity of a frozen organic layer. In this study, we implemented changing in time soil organic layer into the Simple Biosphere/Carnegie-Ames-Stanford Approach (SiBCASA) terrestrial ecosystem model to illustrate how the soil organic layer affects soil temperature dynamics and soil carbon dynamics. We used CRUNCEP reanalysis data to run the model for its equilibrium state with a stable climate. Our results indicate that the presence and dynamics of the organic layer allow us to better simulate active layer thickness. Moreover, dynamic carbon redistribution as a result of changing organic layer improves the simulated distribution of soil carbon with depth.
15037977 Jones, Miriam (U. S. Geological Survey, Reston, VA); Harden, J. W.; O'Donnell, Jonathan A.; Manies, K. and Jorgenson, T. Understanding carbon storage in permafrost peatlands; examples from thermokarst landscapes in interior Alaska [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B42D-07, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
As the climate at high latitudes continues to warm, permafrost is becoming increasingly vulnerable to thaw, particularly in the zone of discontinuous permafrost where mean annual air temperatures hover close to zero. Permafrost thaw has dramatic consequences on local hydrology, ecology, and the carbon (C) balance of these ecosystems. The degree to which permafrost peatlands become C sources or sinks following permafrost thaw remains a topic of much debate, owing to the difficulty in accurately dating cores from collapse-scar bogs and in understanding the vulnerability of the formerly forested peat to decomposition immediately following thaw and inundation. Here we use a combination of a chronosequence, paleoenvironmental, and modeling approaches from a permafrost peat plateau interspersed with collapse-scar bogs in Interior Alaska to address how C storage is impacted on timescales from decades to millennia following permafrost thaw. Our initial results indicate that C stocks are lowest in young (years to decades) and intermediate (decades to centuries) collapse-scar bogs, but that net C stocks in old (centuries to millennia) bogs can be as high as in permafrost plateaus. Thawed forested plateau peat is subject to rapid decomposition in the years to decades following thaw, but that rate of loss slows over time. We hypothesize that this is because the labile C pool is preferentially consumed and quickly exhausted by soil microbes. Meanwhile, post-thaw collapse-scar bog peat accumulates rapidly at the surface, and our data show that on longer centennial to millennial timescales, this near-surface C may offset initial post-thaw losses at depth. Collapse-scar bog peat accumulation rates outpace the former-plateau peat loss in a matter of years to decades. Older landscapes (i.e., those that began accumulating peat many thousands of years ago), are subject to greater C loss following thaw than are younger landscapes(i.e., those that initiated only a couple thousand years ago), leading to a much longer period of net C loss from the ecosystem in older peatlands.
15037930 Kong, W. (Chinese Academy of Sciences, ITP Institute of Tibetan Plateau Research, Beijing, China); Guo, G. and Liu Jinbo. Soil temperature and water content drive microbial carbon fixation in grassland of permafrost area on the Tibetan plateau [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0113, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Soil microbial communities underpin terrestrial biogeochemical cycles and are greatly influenced by global warming and global-warming-induced dryness. However, the response of soil microbial community function to global change remains largely uncertain, particularly in the ecologically vulnerable Tibetan plateau permafrost area with large carbon storage. With the concept of space for time substitution, we investigated the responses of soil CO2-fixing microbial community and its enzyme activity to climate change along an elevation gradient (4400-5100 m) of alpine grassland on the central Tibetan plateau. The elevation gradient in a south-facing hill slope leads to variation in climate and soil physicochemical parameters. The autotrophic microbial communities were characterized by quantitative PCR (qPCR), terminal restriction fragment length polymorphism analysis (T-RFLP) and cloning/sequencing targeting the CO2-fixing gene (RubisCO). The results demonstrated that the autotrophic microbial community abundance, structure and its enzyme activity were mainly driven by soil temperature and water content. Soil temperature increase and water decrease dramatically reduced the abundance of the outnumbered form IC RubisCO-containing microbes, and significantly changed the structure of form IC, IAB and ID RubisCO-containing microbial community. Structural equation model revealed that the RubisCO enzyme was directly derived from RubisCO-containing microbes and its activity was significantly reduced by soil temperature increase and water content decrease. Thus our results provide a novel positive feedback loop of climate warming and warming-induced dryness by that soil microbial carbon fixing potential will reduce by 3.77%-8.86% with the soil temperature increase of 1.94°C and water content decrease of 60%-70%. This positive feedback could be capable of amplifying the climate change given the significant contribution of soil microbial CO2-fixing up to 4.9% of total soil organic carbon.
15037975 Kwon, M. J. (Max Planck Institute for Biogeochemistry, Jena, Germany); Goeckede, Mathias; Wildner, Marcus; Heimann, Martin; Zimov, N. and Zimov, S. A. Impact of hydrology and vegetation community structure on CO2 and CH4 flux patterns in a permafrost ecosystem in Northeast Siberia [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B42D-04, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
A large fraction of organic carbon stored in Arctic permafrost soil is to be decomposed and released to the atmosphere under climate change. Among many drivers that influence decomposition, changes in hydrology play a pivotal role: Shifts in water table depth (WTD) often trigger modifications on soil and vegetation (e.g. soil temperature and vegetation community structure), which in turn alter carbon cycle processes. The presented study is focused on CO2 and CH4 fluxes measured with chambers in a floodplain of the Kolyma River near Cherskii, Northeast Siberia. Our study site is separated into two areas, one that has been drained since 2004, and a nearby reference site. Carbon flux (NEE, ER, methane) was measured for ~16 weeks during summer and early winter of 2013, and summer of 2014. In addition, plant-mediated CH4 transport was measured in 2014 to separate different CH4 emission pathways. Vegetation community structure was investigated in 2013 and 2014. After a decade of drainage history that lowered WTD by about 20 cm in the drained area, Eriophorum (cotton grass) that previously dominated have been much replaced by Carex (tussock-forming sedge) and shrub species. ANCOVA analysis revealed that NEE, ER, and methane flux rates were all influenced by vegetation in both summer and winter, leading to different flux patterns between two sites. WTD also influenced NEE and methane, showing little less CO2 uptake and much less CH4 emission in drained site. Plant-mediated CH4 transport through cotton grasses was correlated with diameter and length of green leaves, implying bigger plants transport more CH4 because their roots reach deeper soil layers where methanogenesis occurs. This correlation was strong at the drained site, where CH4 oxidation was dominant in shallow depths. Summarizing all effects of vegetation and WTD, the drainage results in a stronger net sink for carbon (CO2 and CH4 fluxes combined) in the growing season, but a stronger source in early winter.
15037892 Lamoureux, Scott F. (Queen's University, Kingston, ON, Canada) and Lafreniere, Melissa J. Landscape and hydrological transformation in the Canadian High Arctic; climate change and permafrost degradation as drivers of change [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31D-0036, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Recent climate warming and landscape instability arising from permafrost degradation in the Canadian High Arctic have resulted in significant changes to the hydrological system. We have undertaken an integrated watershed and permafrost research program at the Cape Bounty Arctic Watershed Observatory (75°N, 109°W) in paired watershed-lake systems to assess the impact of these changes. Research has captured hydrological changes resulting from exceptional warmth, and permafrost degradation and disturbance. Results highlight the contrasting effect of thermal (deeper soil thaw) versus physical perturbation (slope failures and permafrost degradation). Thermal perturbation applies to most of the landscape, and results indicate that ground ice melt alters flow and mobilizes solutes for a number of years following a single warm year. These effects are measureable at the slope-catchment scale, especially during baseflow. By contrast, physical disturbance is highly localized and produces high sediment and particulate carbon erosion from slopes, but downstream particulate delivery is dependent on surface connectivity. Recovery from disturbances appears to occur rapidly, and continued geomorphic change and new slope channels result in sustained delivery of particulates to channels. The result is increased long term landscape heterogeneity with respect to erosion compared to the pre-disturbance condition. Downstream channel response to particulate loading further dampens the response to physical disturbance through channel storage of material. Hence, at the larger watershed scale, the effect of physical perturbation is minimal in the initial years of recovery. These results point to a landscape that has been substantially impacted by recent hydrological and permafrost changes. Understanding and distinguishing these impacts provides a basis for systematically evaluating biogeochemical cycling and ecosystem responses in aquatic settings.
15038022 Lawrence, D. M. (National Center for Atmospheric Research, Boulder, CO); Koven, C. D.; Swenson, S. C.; Riley, W. J. and Slater, A. G. Hydrologic controls on the permafrost carbon-climate feedback [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43J-01, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Large-scale permafrost thaw is projected under unmitigated warming scenarios. Since permafrost soils contain enormous amounts of organic carbon, whose stability is contingent on remaining frozen, this permafrost thaw could lead to a significant release of carbon to the atmosphere, acting as a positive feedback to climate change. Significant uncertainty remains on the post-thaw carbon dynamics of permafrost-affected ecosystems. The large stocks of permafrost carbon have built up over time in part due to the saturated (and cold) soil conditions found across much of the permafrost domain. But, these conditions are likely to change as permafrost thaws. Here we focus on the hydrologic response. Prior research suggests that the hydrologic response may contain two phases, an initial wettening associated with ice melt and surface subsidence leading to more wetlands and lakes, followed by drying once the permafrost table has deepened enough to open up new channels to the groundwater system. Simulations to year 2300 with the Community Land Model (CLM4.5BGC) suggest that, even though Earth System Models project that Arctic climate will get wetter, soil moisture conditions will become drier both at the surface and at depth in response to projected deepening of the permafrost table. Here, we examine the relative influence of these soil moisture changes (compared to the influence of warming) on soil decomposition rates by conducting an additional model experiment in which we artificially maintain the wet 1850 soil moisture conditions through throughout the simulation. We can then assess (a) how the soil moisture drying trajectory affects the rate of soil warming (answer: not much) and (b) how a different plausible soil moisture trajectory can alter the rates of soil carbon decomposition into CO2 or CH4. We find that he drying at depth leads to faster soil carbon decomposition, while the absence of drying leads to slower decomposition rates, but higher CH4 emissions. Our results suggest that soil moisture and trends of soil moisture are an important part of the permafrost climate-carbon feedback picture and that improved understanding of impact of permafrost thaw on soil moisture dynamics is required to further constrain the amplitude of the permafrost climate-carbon feedback.
15037990 Lehn, Greg O. (Northwestern University, Evanston, IL); Jacobson, A. D.; Douglas, Thomas A.; McClelland, J. W.; Khosh, Matt S. and Barker, A. J. Seasonal variability of riverine geochemistry (87Sr/86Sr, d13CDIC, d44/40Ca, and major ions) in permafrost watersheds on the North Slope of Alaska [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43B-0240, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Global climate models predict amplified warming at high latitudes, where permafrost soils have historically acted as a carbon sink. As warming occurs, the seasonally thawed active layer will propagate downward into previously frozen mineral-rich soil, releasing carbon and introducing unique chemical weathering signatures into rivers. We use variations in the 87Sr/86Sr, d13CDIC, d44/40Ca, and major ion geochemistry of rivers to track seasonal active layer dynamics. We collected water from six streams on the North Slope of Alaska between May and October, 2009 and 2010. All rivers drain continuous permafrost but three drain tussock tundra-dominated watersheds and three drain steeper bedrock catchments with minor tundra coverage. In tundra streams, elevated 87Sr/86Sr ratios, low d13CDIC values and major ions ([Na+]+[K+]/[Ca+2]+[Mg+2]) in spring melt runoff suggest flushing of shallow soils with relatively low carbonate content. By July, 87Sr/86Sr ratios stabilize at relatively low values and d13CDIC at relatively higher values, indicating the active layer thawed into deeper carbonate-rich soils. In bedrock streams, elevated 87Sr/86Sr ratios correlate with high discharge. By late fall, bedrock stream 87Sr/86Sr ratios decrease steadily, consistent with increased carbonate weathering. Nearly constant d13CDIC values and high [SO4-2] for most of the melt season imply significant sulfuric acid-carbonate weathering in bedrock streams. d13CDIC values suggest a shift to carbonic acid-carbonate weathering in late 2010, possibly due to limited oxygen for pyrite oxidation during freezing of the active layer. d44/40Ca values in both tundra and bedrock streams increase during the seasons, suggesting increased uptake of 40Ca by plants. d44/40Ca values of rivers are at least 0.1-0.2 ppm higher than their watershed soils, rocks and sediments, suggesting significant plant uptake. Our findings show how seasonal changes in mineral weathering have potential for tracking active layer dynamics.
15037989 Lessels, Jason S. (University of Sydney, Sydney, N.S.W., Australia); Dinsmore, K. J.; Billett, M. F.; Street, L. E.; Wookey, P. A.; Tetzlaff, D.; Baxter, Robert; Subke, Jens-Arne; Dean, Joshua and Washbourne, I. J. Aquatic carbon and GHG export from a permafrost catchment; identifying source areas and primary flow paths [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43B-0239, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The aquatic pathway is increasingly being recognized as an important component of landscape scale greenhouse gas (GHG) budgets. Due to low temperatures and short residence times limiting in-stream production in northern headwater catchments, much of the exported carbon is likely to be allochthonous, transported via throughflow to the surface drainage system. Identifying sources and primary flow pathways is therefore essential in understanding and predicting changes in the aquatic flux magnitude. Arctic landscapes are now widely recognised as being particularly vulnerable to climate driven changes. The HYDRA project ("Permafrost catchments in transition: hydrological controls on carbon cycling and greenhouse gas budgets") aims to understand the fundamental role that hydrological processes play in regulating landscape-scale carbon fluxes, and predict how changes in vegetation and active layer depth in permafrost environments influence the delivery and export of aquatic carbon. In this study we present aquatic concentrations and fluxes of carbon and GHG species collected across two field seasons (2013, 2014) from an arctic headwater catchment in northern Canada. Measured species include dissolved organic (DOC) and inorganic carbon (DIC), CO2, CH4 and N2O. Measurements were made across a range of freshwater types within the tundra landscape, including lakes, ice-wedge polygons, and the 'Siksik' stream which drains the (c.a. 1 km2) primary study catchment. A nested sub-catchment approach was used along the 'Siksik' stream; 'snapshot' sampling of eight points along the stream length allowed specific vegetation communities to be targeted to assess individually their contribution to aquatic export. A combination of stable isotopes and major ion concentrations measured at each sampling point provide additional information to trace source areas and flow paths within the main study catchment. Catchment scale evasion and downstream export were calculated and an initial comparison between the relative importance of different water body types presented.
15038023 Marchenko, S. S. (University of Alaska Fairbanks, Institute of Arctic Biology, Fairbanks, AK); Nicolsky, D.; Romanovsky, V. E. and McGuire, A. D. The vulnerability of permafrost from 1960 to 2300 based on simulations of the process-based model GIPL2 across the permafrost region in the Northern Hemisphere; implications for soil carbon vulnerability [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43J-02, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Recent observations indicate a warming of permafrost in many northern regions with a resulting degradation of ice-rich and carbon-rich permafrost. In the last 30-40 years, warming in permafrost temperatures observed in Northern Eurasia, Canada, and Alaska has resulted in the thawing of permafrost in natural, undisturbed conditions in areas close to the southern boundary of the permafrost zone. The main aim of this study is to evaluate the vulnerability of permafrost under climate warming across the Permafrost Region of the Northern Hemisphere. We applied the process-based permafrost dynamics model GIPL2 (Geophysical Institute Permafrost Lab), using a historical climate forcing CRU3.1 data set for retrospective (1960-2009) and CCSM4 RCP4.5 and RCP8.5 (2009-2300) for analysis of permafrost dynamics in the future. We estimated dynamics of the area and volume of seasonally thawed soils within the three upper meters across the entire Permafrost Domain. During the last four decades of the 20th century, the simulated total area and the volume of thawed soils with Active Layer Thickness (ALT) shallower than 3 m has been varying between 11 and 13 million km2, and between 17.3 to 19.4 thousand km3 respectively. Our projections according to the CCSM4 RCP4.5 climate scenario indicate that the maximum unfrozen volume of soil within three upper meters would change between 12.8 and 20.8 thousand km3 during 2009-2300. Despite the slower rate of soil warming in peatland areas and a slower degradation of permafrost under peat soils, a considerable volume of peat (approximately 20% of the total volume of peat in the Northern Hemisphere) could be thawed by the end of the current century and 35% by 2300. The potential release of carbon and the net effect of this thawing will depend on the balance between increased productivity and respiration, and will also depend on soil moisture dynamics.
15037958 Matamala, R. (Argonne National Laboratory, Argonne, IL); Jastrow, J. D.; Calderon, Francisco; Liang, C.; Miller, R. M.; Ping, C. L.; Michaelson, G. J. and Hofmann, S. Characterizing soil organic matter degradation levels in permafrost-affected soils using infrared spectroscopy [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0147, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Diffuse-reflectance Fourier-transform mid-infrared spectroscopy (MidIR) was used to (1) investigate soil quality along a latitudinal gradient of Alaskan soils, and in combination with soil incubations, (2) to assess the relative lability of soil organic matter in the active layer and upper permafrost for some of those soils. Twenty nine sites were sampled along a latitudinal gradient (78.79N to 55.35N°). The sites included 8 different vegetation types (moss/lichen, non-acidic and acidic tundra, shrub areas, deciduous forests, mixed forests, coniferous forests, and grassland). At each site, soils were separated by soil horizons and analyzed for pH, cation exchange capacity (CEC), organic and inorganic C, and total N. Samples were also scanned to obtain MidIR spectra, and ratios of characteristic bands previously suggested as indicators of organic matter quality or degradation level were calculated. Principal component analysis showed that axis 1 explained 70% of the variation and was correlated with the general Organic:Mineral ratio, soil organic C, total N, and CEC, but not with vegetation type. Axis 2 explained 25% of the variation and was correlated with most of the band ratios, with negative values for the condensation index (ratio of aromatic to aliphatic organic matter) and positive values for all humification ratios (HU1: ratio of aliphatic to polysaccharides; HU2: ratio of aromatics to polysaccharides; and HU3 ratio of lignin/phenols to polysaccharides) suggesting that axis 2 variations were related to differences in level of soil organic matter degradation. Active organic, active mineral and permafrost layers from selected tundra sites were incubated for two months at -1, 1, 4, 8 and 16°C. The same band ratios were correlated with total CO2 mineralized during the incubations. Data from 4°C showed that the cumulative respired CO2 from the active organic layer across all sites was negatively correlated with the HU1 humification ratio, suggesting that HU1 might be a good indicator of lability for comparing active layer organic soils. We will explore correlations at the other incubation temperatures and further evaluate the utility of MidIR band ratios for predicting the potential decomposability of organic matter in permafrost-region soils.
15037952 Mauritz, M. (University of Florida, Ft. Walton Beach, FL); Schuur, E. A. G.; Bracho, R. G.; Celis, G.; Natali, S.; Hutchings, J. A.; Salmon, V. G. and Webb, E. Ecosystem carbon dynamics in response to five winters of experimental soil warming and permafrost degradation [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0140, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Arctic permafrost soils store 1700 Pg carbon (C), almost half the global soil C. For millennia permafrost soil C has been protected from decomposition by cold, waterlogged conditions. Warming temperatures will likely thaw permafrost, however the impact on arctic C balance is uncertain. Nutrient availability is predicted to increase with thaw depth and promote plant growth, potentially creating an ecosystem C sink. However, deeper thaw could also increase microbial respiration and eventually exceed C gains. Using data from a warming experiment in sub-arctic moist acidic tundra, designed to insulate soils in winter and stimulate permafrost degradation, we investigated spatial and temporal drivers of ecosystem C balance. Net ecosystem exchange (NEE) was measured continuously from May-September 2009-2013 using clear automated chambers; ecosystem respiration (Reco) was extrapolated from low light NEE and gross primary productivity (GPP) was derived (GPP = NEE-Reco). Five years of warming led to progressive increases in active layer depth. Active layer depth was positively correlated with cumulative growing season NEE, GPP and Reco. Although warming increased Reco the ecosystem remained a C sink during the growing season because high Reco was offset by increased plant growth and GPP. Eriophorum vaginatum growth accounted for most of the increased plant biomass, and was correlated with cumulative growing season GPP and Reco. NEE, GPP and Reco all peaked mid-season, and the mid-season amplitudes increased annually leading to higher cumulative NEE, GPP and Reco. In the shoulder seasons NEE and GPP were similar among years. In contrast, Reco increased at the end of the growing season each year, and high mid-season GPP was positively correlated with end season Reco. Thus, conditions that promoted plant growth also promoted C loss. These results suggest plant responses to permafrost thaw are an important driver of C dynamics. Reco associated with high biomass may result from greater autotrophic respiration as well as enhanced microbial soil decomposition. Focusing only on the growing season may overestimate the C sink of the ecosystem because high uptake appears to enhance C losses at the end of the growing season, and C loss is likely to extend beyond the observation period.
15038033 McGuire, A. D. (University of Alaska Fairbanks, Institute of Arctic Biology, Fairbanks, AK). The importance of explicitly representing soil carbon with depth over the permafrost region in Earth system models; implications for atmospheric carbon dynamics at multiple temporal scales between 1960 and 2300 [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B44A-05, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
We conducted an assessment of changes in permafrost area and carbon storage simulated by process-based models between 1960 and 2300. The models participating in this comparison were those that had joined the model integration team of the Vulnerability of Permafrost Carbon Research Coordination Network (see URL: http://www.biology.ufl.edu/permafrostcarbon/). Each of the models in this comparison conducted simulations over the permafrost land region in the Northern Hemisphere driven by CCSM4-simulated climate for RCP 4.5 and 8.5 scenarios. Among the models, the area of permafrost (defined as the area for which active layer thickness was less than 3 m) ranged between 13.2 and 20.0 million km2. Between 1960 and 2300, models indicated the loss of permafrost area between 5.1 to 6.0 million km2 for RCP 4.5 and between 7.1 and 15.2 million km2 for RCP 8.5. Among the models, the density of soil carbon storage in 1960 ranged between 13 and 42 thousand g C m-2; models that explicitly represented carbon with depth had estimates greater than 27 thousand g C m-2. For the RCP 4.5 scenario, changes in soil carbon between 1960 and 2300 ranged between losses of 32 Pg C to gains of 58 Pg C, in which models that explicitly represent soil carbon with depth simulated losses or lower gains of soil carbon in comparison with those that did not. For the RCP 8.5 scenario, changes in soil carbon between 1960 and 2300 ranged between losses of 642 Pg C to gains of 66 Pg C, in which those models that represent soil carbon explicitly with depth all simulated losses, while those that do not all simulated gains. These results indicate that there are substantial differences in responses of carbon dynamics between model that do and do not explicitly represent soil carbon with depth in the permafrost region. We present analyses of the implications of the differences for atmospheric carbon dynamics at multiple temporal scales between 1960 and 2300.
15037925 Mu, C. (Lanzhou University, Lanzhou, China) and Zhang, T. Decomposition of permafrost carbon with increasing incubation temperature on the Qinghai-Xizang (Tibetan) Plateau [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0106, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Little is currently known about the decomposition of deep-permafrost organic carbon on the Qinghai-Xizang (Tibetan) Plateau (QXP) with increasing temperature. We studied the effect of temperature on CO2 emissions from soil, from the active layer to deep permafrost (400 cm), during a 140-day incubation at temperatures of -5.0°C to +5.0°C. We found that permafrost carbon emissions on the QXP increase with soil temperature. Temperature has greater impact on soil organic carbon (SOC) decomposition in permafrost soils than in thawed soils. A temperature increase of 4.5° results in an average increase in carbon release of 482.8% (±60%) at temperature below 0°C (-5.0 to -0.5°C), and 102.0% (±37.5%) at temperatures above 0°C (0.5 to 5.0°C). Permafrost carbon has greater vulnerability at subzero temperatures than at temperature above 0°C. Moreover, the increase in permafrost carbon release in mineral soils was larger than that in organic soils at temperatures form -5.0 to -0.5°C. The released CO2 mostly came from soils at depths of 10-20 cm and deep permafrost soils at depths of 245-255 cm and 285-295 cm, based on the stable carbon isotope analysis of d13SOC and d13CO2.
15037996 Munster, J. B. (Harvard University, Cambridge, MA); Sayres, D. S.; Healy, C. E.; Dumas, Ed J.; Dobosy, Ron; Kochendorfer, John; Heuer, Mark; Meyers, Tilden P.; Baker, Bruce and Anderson, J. G. Carbon release from melting Arctic permafrost on the North Slope, AK; 12CO2 and 13CO2 concentrations and fluxes, and their relationship to methane and methane isotope concentrations measured in august 2013 [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43B-0246, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
One of the most important uncertainties in climate change is the positive feedback mechanism associated with the melting Arctic. As the Arctic permafrost destabilizes, labile carbon stored in the permafrost is subject to respiration and methanogenesis, producing greenhouse gases CO2 and CH4. Understanding the timing and rate of this release is paramount to our long-term understanding of the global climate structure, yet the remote location of the North Slope logistically precludes widespread tower measurements, necessitating airborne measurements. Presented are 12C and 13C CO2 concentration flux measurements taken via an aircraft at a height of 10-30 m during mid to late August 2013 from the north slope of Alaska. The data show different regimes for CO2 vs d-13C over regions within a roughly 100 km box, indicating heterogenous landscape with differing dominant biological processes. The data are compared to CH4 measurements that were taken simultaneously, showing highly varying concentrations of CH4 with several different archetypical relationships to the total CO2 regimes. The relationship between CO2, d-13C CO2, and CH4 concentrations provide further insight into the biological processes occurring in the melting Arctic permafrost. The data show that the dominant uptake and emission processes change by time of day and location. While the CO2 and isotopologue data alone indicates whether a region is dominant in respiration or photosynthesis, combining the data with CH4 measurements provides insight into the provenance of the CH4 as well as methanogenic biological pathways active on the North Slope, while mass balance between CH4, CO2 or d-13C CO2 determines whether the methane signature is from methanogenesis, natural hydrocarbon seeps, or methane flaring. The data show few if any cases for which increases in methane concentrations are accompanied by a deviation in CO2 or d-13C CO2 that would indicate incomplete methane flaring or natural seeps.
15038025 O'Donnell, Jonathan A. (National Park Service Fairbanks, Fairbanks, AK); Harden, J. W. and Romanovsky, V. E. The influence of organic-soil horizons on thermal dynamics in high-latitude soils; identifying thresholds for permafrost state change [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43J-04, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Organic-soil horizons exert significant control on soil temperature and permafrost dynamics in high-latitude regions. Ecosystem protection of permafrost is governed by the low thermal conductivity of organic soils, which is sensitive to changes in horizon thickness (OHT), moisture content, and decomposition extent (and thus, porosity, and density) of organic matter. At broad spatial scales, the occurrence of permafrost is positively correlated with OHT when organic horizons are relatively thin (<30 cm). Across sites where OHT is deeper, this correlation reverses and becomes negative. We hypothesize that this bi-modal relationship between OHT and permafrost occurrence is primarily governed by the contrasting thermal properties of upper organic-soil horizons and the underlying deep organic-soil and mineral-soil horizons. As documented with prior investigations on snow thermal properties, we find that that the underlying layers can have a profound impact on the insulating effect of the overlying layer. To evaluate this hypothesis, we examine the sensitivity of permafrost to soil properties (OHT, moisture content, and texture) and their variations across landscape positions and drainage class using field-based observations and generalized simulations using the Geophysical Institute Permafrost Laboratory model (GIPL). We observed significant negative correlations between minimum daily ground-surface temperature during summer and OHT across upland forest sites in interior Alaska. In peatlands, ground-surface temperature and OHT appear to be decoupled, which is likely due to variation in deposit thickness as determined by the timing of peatland formation across the region. Model results highlight the role of moisture content and water table position, both as controls on organic matter accumulation and on permafrost extent and thermal state.
15037927 Olefeldt, D. (University of Alberta, Edmonton, AB, Canada); Pelletier, Nico; Talbot, J.; Blodau, Christian and Turetsky, M. R. Peat carbon stocks and potential microbial lability of boreal peatlands with varying permafrost histories [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0108, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Large stores of C in the form of peat are stored in permafrost, particularly in the boreal discontinuous permafrost zone. Ongoing climate change is causing widespread permafrost thaw in boreal peatlands, a trend which is expected to continue this century and thus make large stores of soil C available for microbial processes and mineralization. Permafrost thaw in boreal peatlands is often associated with an ecosystem shift from dry peat plateau to wet bog surfaces, and the net C balance following thaw is determined by the balance between the mineralization of plateau peat and the new accumulation of bog peat on top. In this study we collected soil cores (~3 m deep) from one peat plateaus and four bogs that differed in time since thaw (approximately 10, 50 and 500 years since thaw). In order to assess the potential microbial lability, we incubated 25 soil samples from each core under aerobic conditions at 17.5°C. Mineralization rates were 1-2 order of magnitude higher near the surface than at depth, but near surface samples also had high variability among cores. Variability in peat microbial lability near the surface was related to thaw history and to differences in characteristics between plateau and bog peat. Mineralization rates of peat samples from below 1 m depth and down to the interface with mineral soil at 3 m were consistently low and had no difference among cores. Mineralization rates during the first 3 months of incubation for deep plateau peat samples were equivalent to 1% soil C losses per year. Relatively low microbial lability of deep peat in combination with high rates of new peat accumulation during the initial stages of bog development suggests that there is net C accumulation immediately following thaw but that the sink strength weakens or reverses during later stages when new accumulation rates diminish.
15037876 Olefeldt, D. (University of Alberta, Edmonton, AB, Canada) and Turetsky, M. R. Syntheses of wetland methane emissions at high latitudes; exploring sensitivities to climate change and permafrost thaw [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B24C-01, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Climate change and associated permafrost thaw has the potential to increase methane emissions from high latitude wetlands, thus amplifying human-caused climate change. Methane monitoring at high latitude wetlands have been carried out since the 1970s, and at this time there are published data from a large number of sites and some individual sites have data that span more than a decade. By synthesizing data both across and within sites it is possible to improve our understanding of environmental and physical controls on methane emissions. It is clear from comparing mean growing season methane emissions across sites that site wetness, soil temperature and vegetation composition have strong and interacting effects. At individual sites it is also evident that soil temperatures and wetness co-vary at inter-annual scales as a result of physical processes, with compounding influences on methane emissions. Further the presence of certain sedge species, often found in fens at high latitudes strongly influence sensitivities to soil temperature and wetness. Shifts in functional relationships as related to ecosystem structure is central for methane emissions at high latitude wetlands, given the hydrological and ecological changes that occur with permafrost thaw and thermokarst landform development. Hence, in order to more accurately project future methane emissions from high latitudes at a pan-arctic scale, it is necessary to include a spatial representation of thermokarst development as well as ecosystem-appropriate functional relationships between emissions and environmental variables.
15037896 Paquette, Cath (University of Ottawa, Department of Geography, Ottawa, ON, Canada); Lacelle, D. and Kokelj, Steve V. A watershed approach to quantify the impacts of permafrost disturbances on the hydrogeochemistry of streams in the Richardson Mountains and Peel Plateau region, northwestern Canada [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31D-0044, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Retrogressive thaw slumps are one of the most dramatic thermokarst features in ice-rich permafrost landscapes and their growth may pose significant terrestrial and aquatic impacts. In the Richardson Mountains and Lower Peel River watersheds (northwestern Canada), thaw slumps are abundant along hillslopes. Runoff from active slumps is characterized by conductivity and solute concentration nearly 1 order of magnitude higher than in pristine streams. As such, the objective of this study is to evaluate the potential cumulative impacts of thaw slumps to aquatic ecosystems and determine the watershed scale at which the impacts of slumps can be detected. This is accomplished by: i) compiling the distribution of active and stable thaw slumps in the Richardson Mountains and Peel Plateau; ii) determining the hydrogeochemistry (major ions, total dissolved solids) of pristine and slump impacted streams in this region; and iii) representing this information on watershed platforms (4th to 6th order scale). The results indicate a positive relation between slump density, cumulative surface area of slumps and average ionic concentrations within the various sub-watershed scales. Solute concentrations along streams reveal that ionic content increases immediately downstream of a slump and that for slumps with surface area greater than 5 ha, the solute concentrations remain significantly higher in impacted streams, even at the 4th-order watershed scale. The broad scale impacts of thaw slumps are indicated by a significant increase in solute concentrations in the Peel River (70,000 km2 watershed scale). These observations illustrate the nature and magnitude of hydrogeochemical changes that can be expected as ice-rich landscapes adjust to a rapidly changing climate.
15037949 Pelletier, Nico (University of Montreal, Montreal, QC, Canada); Olefeldt, D.; Turetsky, M. R.; Blodau, Christian and Talbot, J. Post-thaw carbon stock variation in a permafrost peatland of the boreal zone [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0136, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The current acceleration of permafrost thaw in the discontinuous permafrost of the boreal zone induces large uncertainties regarding the fate of soil carbon. Peatlands are believed to contain about 277 Pg of the total 1670 Pg stored in permafrost soils. In the discontinuous permafrost zone, the thawing of permafrost causes thermokarst features, leading to a succession from forested peat plateaus to non-forested sphagnum bogs. The changes in organic matter accumulation and deep carbon decomposition rates following thaw in permafrost peatlands could have an important impact on the climate system. We measured the total carbon content of peat cores along a thaw chronosequence from forested permafrost peat plateau to collapse-scar bogs. Four transect of four cores each were collected to expose the variations in carbon content at the collapse-scar feature scale as well as at the catchment scale. Loss on ignition, bulk density, carbon content of the organic matter and radiocarbon dating data reveal variability in the response of the total carbon content with time. Contrary to previous studies of this type, preliminary results do not seem to indicate an initial raise in total carbon stock following thaw. The increase in surface peat accumulation of this peatland seems to be largely offset by an increase in deep carbon loss from anaerobic decomposition.
15037955 Ramos, Erika (University of Texas at Brownsville, Brownsville, TX); Alexander, Heather D. and Natali, S. Effects of disturbances on vegetation composition and permafrost thaw in boreal forests and tundra ecosystems of the Siberian arctic [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0144, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
In Arctic ecosystems, climate-driven changes to the thermal regime of permafrost soils have the potential to create surface disturbances that influence vegetation dynamics and underlying soil properties. Disturbance-mediated changes in vegetation are important because vegetation and the accumulation of soil organic matter drive ecosystem carbon (C) dynamics and contribute to the insulation of soils and protection of permafrost from thaw. We examined the effect of two disturbance types-thermokarsts and frost boils-to determine disturbance effects on the vegetation community and soil properties in northeast Siberia. In summer 2014, we measured vegetation cover, soil moisture, soil temperature, and thaw depth in two thermokarst sites within boreal forests, two frost boil sites in tundra, and in adjacent undisturbed sites within both ecosystems. Both thermokarst and frost boils resulted in decreased vegetation cover and greater exposure of mineral soils (10-40% bare soils vs. 0% in undisturbed), and consequently, 2-3 times higher soil temperature and deeper thaw depth. Compared to undisturbed areas, soil moisture was 3-4 times higher in thermokarst areas but 1.2-2 times lower in frost boil areas, which reflected differences in microtopography between these two disturbance types. In both thermokarst and frost boil disturbed areas, deciduous and evergreen shrubs covered only 5 and 10%, respectively, compared to approximately 10 and 20%, respectively, in undisturbed areas. In general, graminoids were substantially more abundant (2-20 times) in disturbed areas than in those undisturbed. These results highlight important linkages between disturbances, vegetation communities, and permafrost soils, and contribute to our understanding of how changes in arctic vegetation dynamics as direct and/or indirect consequences of climate change have the potential to impact permafrost C pools.
15037877 Rich, V. I. (University of Arizona, Tucson, AZ); Tyson, G. W.; Woodcroft, Ben J.; Hodgkins, S. B.; Tfaily, Malak; Wik, Martin; Anderson, Darya; Crill, Patrick M.; Chanton, J.; McCalley, Carmody K.; Saleska, S. R. and Varner, Ruth K. Shifting microbiology and carbon loss across a thawing permafrost wetland-to-lake mosaic landscape [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B24C-04, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Understanding the fate of carbon (C) in thawing permafrost is an unresolved challenge of modern biogeochemistry and climate change. The associated C pools are large (~1700 PgC), and their dynamics under thaw are complex: old C decomposes as it is liberated from thawing permafrost as CO2 or CH4, even as new C accumulates due to thaw-initiated ecological succession. The interconnected wetland and aquatic landscapes commonly associated with thaw are critically important to tracing C fate, with a significant fraction cycling through lake sediments. Microbes mediate C loss across this landscape, but a mechanistic microbes-to-emissions scaling is missing. Our team is investigating in situ changes in C cycling and microbiology across a thawing permafrost mosaic palsa-bog-fen-lake landscape, at Stordalen Mire (68°21'N, 19°02'E) in Arctic Sweden. At this site, wetlands and lakes each account for roughly half of total landscape emissions (e.g., Wik et al 2013). Along the thaw gradient, vegetation shifts from ericaceous shrubs to mosses and sedges, and then aquatic plants, while organic matter becomes increasingly reduced and labile, with evidence of greater humification rates and faster decomposition (Hodgkins et al., 2014). C gas emissions peak in the fen habitat, with increasing relative production ratios of CH4 to CO2 (McCalley et al., in review, Hodgkins et al., 2014). The microbial communities mediating these transformations and losses are markedly complex, and change dramatically across the landscape. Notable community shifts include high abundances of an undescribed group of Caldiserica in intact and freshly-thawed permafrost, and of newly-identified family of hydrogenotrophic methanogens (Methanoflorentaceae) (Mondav and Woodcroft et al., 2014) in bog and fen, as well as anaerobic methane oxidizers of the ANME-2d lineage present in the lake sediments. Methanogenesis shifts both isotopically and by lineage-abundance from hydrogenotrophy in the bog to a mixture with acetoclasty in the fen. Unraveling the interconnections of microbial lineages and carbon transformations is ongoing.
15037964 Richter, Andreas (University of Vienna, Vienna, Austria); Barta, J.; Capek, Peta; Gentsch, N.; Guggenberger, G.; Kaiser, Christina; Mikutta, R.; Shibistova, Olga; Santruckova, Hana; Schnecker, Joerg and Wild, Birgit. Carbon and nutrient limitation of microbial decomposition of organic matter in permafrost soils [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B41O-05, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Cryotubated horizons of permafrost soils contain as much as 410 Pg C, a significant proportion of which may be vulnerable to climate changes through permafrost thawing and subsequent decomposition by soil microorganisms. While numerous studies have addressed temperature and soil moisture controls, very little is known on energy and nutrient constraints of microbial decomposition in permafrost soils. We investigated nutrient and carbon limitations of permafrost soils by analysing a wide range of soil samples for C:N stoichiometry and carbon isotope composition and incubating soil samples of different depths with carbon only or carbon and nitrogen amendments. Utilising the carbon isotopic composition of soil organic matter (SOM) as a proxy for the stage of decomposition, we identified a breakpoint of about 1.5% C, below which decomposition was dominated by the recycling of microbial biomass, and above which decomposition of plant derived material was the main process. This breakpoint corresponds to a threshold element ration (TERC:N) between 15-20. Soils with a C:N ratio below the TERC:N (i.e., soil that can be considered as C or energy limited) make up for a significant proportion of the overall SOM stored in permafrost soils, even in the active layer. To get more insight into the limitations of SOM decomposition, we incubated about 100 soil samples from 4 sites across Siberia with either cellulose or cellulose and protein for 180 days and calculated how the amendments affected the decomposition of native SOM. All incubated horizons, regardless of their depth or C:N ratio showed a significant increase in native SOM decomposition to a combined carbon and nitrogen amendment, that was higher than with C amendment alone. We conclude that nutrient and carbon limitations of soil microbial communities constitute important constraints on SOM decomposition and should be incorporated into models predicting future permafrost carbon storage.
15037957 Roy Chowdhury, T. (Oak Ridge National Laboratory, Oak Ridge, TN); Graham, D. E. and Wullschleger, S. D. Effects of temperature and substrate availability on methanotrophy in Arctic permafrost landscapes [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0146, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Arctic permafrost ecosystems store ~50% of global belowground carbon (C) and are a considerable source of atmospheric methane (CH4). Current estimates report that nearly 10-40 Tg yr-1 of CH4 is released from permafrost environments. In particular, topographic depressions on the landscape are predominantly anoxic and conducive to active methanogenesis. At the sediment-water interfaces of the water-saturated polygonal units, namely low- and flat-centered polygons, CH4 and oxygen gradients overlap and bacterial CH4 oxidation is an important process contributing to CH4 consumption. Methanotrophic bacteria represent the major terrestrial sinks for CH4 and can reduce CH4 emissions by ~70%. Therefore, determining how the activity and abundance of methanotrophic communities respond to warming temperature conditions is critical to predicting effects of permafrost thaw and active layer warming on CH4 emissions. As ground temperature increases in the Arctic landscape, a major impact of permafrost thaw could be draining of the active layer with resultant subsidence leading to the formation of elevated and relatively oxic high-centered polygons. These changes can impact both methanogen and methanotroph communities and affect net CH4 fluxes. To understand the controls of temperature and substrate availability on CH4 oxidation, we examined process rates and temporal dynamics of methanotroph biomass in contrasting landscape gradients. We investigated the active layer and Cryoturbated permafrost organic soils from replicate soil cores collected from high-centered and flat-centered polygonal units in the Barrow Environmental Observatory, Barrow, AK. We used quantitative PCR to quantify methanogen (mcrA) and methanotroph (pmoA) population size by functional gene analysis. We present potential methane oxidation activity in response to three incubation temperatures (-2°C, 4°C, and 10°C) that represent thaw-season ground temperatures. Our objectives were to estimate the rates of CH4 oxidation in response to seasonal fluctuations in temperature and to contrast the potential of methanogenic environments to oxidize CH4. We further compare the results with methanogenesis rates to understand the temporal dynamics of CH4 production and oxidation in warming conditions.
15037899 Rudy, Ashley (Queen's University, Kingston, ON, Canada); Holloway, Jean; Lamoureux, Scott F. and Treitz, Paul. Using permafrost disturbance susceptibility maps to understand processes that drive permafrost degradation [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31D-0048, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Continued changes to the thermal, hydrological and geotechnical conditions of permafrost have led to degradation and changes in the active layer resulting in increased permafrost disturbance across the Canadian High Arctic. Active layer detachments (ALDs) and mudboils, two forms of permafrost disturbance, are both triggered by high pore-water pressure resulting from deep active layer thaw and increased precipitation. Recent work completed at the Cape Bounty Arctic Watershed Observatory (CBAWO), in the Canadian High Arctic, has found that these two features of permafrost disturbance are associated with distinct environments; ALDs are commonly found on vegetated slopes, whereas mudboils occur on flat, less vegetated terrain. This implies that on transitional slopes pore water pressures may continue to increase resulting in ALDs in these areas over others. Mudboils act as an indicator of potentially hazardous subsurface fluid pressures that may lead to slope failure. Susceptibility maps generated using predictive modeling approaches can provide insight into landscape characteristics driving the formation of both types of features by identifying areas with high, moderate, and low susceptibility to future disturbance. Permafrost slope disturbance susceptibility models have been successfully applied to a study area at CBAWO to identify areas prone to future slope disturbance. Using a generalized additive model (GAM), the model was fitted for disturbed and undisturbed locations using GIS-derived geomorphological predictor variables including: slope, potential incoming solar radiation, wetness index, curvature, geology, and distance to water. Current modeling is underway to produce mudboil susceptibility maps using the same predictor variables, with the addition of vegetation. Comparison of the resulting susceptibility maps can be used to understand the relation between the two forms of disturbance through the assessment of their spatial distribution. Both active layer detachments and mudboils are driven by similar climatic and landscape phenomena, and as such, greater knowledge of the spatial links between them is needed to understand the nature of future permafrost degradation.
15037959 Salmon, V. G. (University of Florida, Ft. Walton Beach, FL); Mack, M. C. and Schuur, E. A. G. Carbon mineralization and nitrogen transformation during a long term permafrost incubation [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0148, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
As the limiting nutrient in warming high latitude ecosystems, nitrogen (N) is expected to play a key role in determining the future balance between permafrost carbon (C) losses and increased C sequestration by plants. During decomposition, nitrogen previously locked in soil organic matter is released into the soil solution in the form of dissolved organic molecules following depolymerization by extracellular enzymes. These dissolved organic forms of N can be consumed by the soil microbial community and incorporated in their biomass or mineralized if they are in excess of microbial demand. Once mineralized and released into the soil solutions, N can be lost from the soil system via denitrification. In well drained, low N tussock tundra, however, this pathway is unlikely. Dissolved inorganic N (DIN) and dissolved organic N (DON) are both biologically available to arctic plants. Understanding how the size of these pools changes with depth and continuing decomposition is therefore crucial to projecting the C balance of high latitude systems in a warmer future. N transformations associated with decomposition may differ greatly in surface soils, where a large labile C pool is present and soil has a high C:N ratio, versus deep soils that have a relatively small labile C pool and a lower C:N ratio. In this experiment, the relationship between N availability and C release from permafrost soils was addressed with a 225 day soil incubation performed at 15°C. Seven soil cores were collected from undisturbed, well drained tussock tundra and were partitioned into ten centimeter depth intervals to a depth of 80 cm. Carbon dioxide (CO2) fluxes were measured throughout the incubation period and were used to assess cumulative carbon losses and determine the size of the labile C pool. Destructive harvests at days 16,34,55,83, 143 and 225 were performed and pools of plant available DON and DIN were measured using 2M KCl extractions. At day 225 the microbial biomass N pool was also measured. Permafrost soils at 55-85 cm depths exhibited higher initial (4.4 mg N/gN) and late stage DIN pools (6.9 mg/gN at day 143) than active layer soils at 0-55 cm depths (0.4 mgN/gN initial DIN, 2.4 mgN/gN at day 143). The size of the labile C pool decreased with depth, and larger labile N pools delayed the release of plant available N forms from the SOM.
15037947 Sannel, Britta (Stockholm University, Stockholm, Sweden); Hugelius, Gustaf and Kuhry, Peter. Permafrost thaw in a subarctic peatland; which factors are most important? [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0134, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Permafrost peatlands cover extensive areas in the northern circumpolar permafrost region and are important soil organic carbon reservoirs. To better understand how permafrost peatlands will respond to future climate change and assess the carbon-climate feedback as a result of permafrost thaw, more knowledge about the impact and relative importance of different meteorological parameters on ground temperatures is needed. In Tavvavuoma located in the sporadic permafrost zone in northern Sweden, meteorological parameters and ground temperatures have been monitored in a peat plateau complex since 2005. Various landscape units within the peatland have different ground temperatures. In fen deposits of drained thermokarst lakes and in lake sediments permafrost is absent. In the central part of the peat plateau permafrost is present, but close to 0°C. Alongside a thermokarst lake shoreline, a maximum thermo-erosion rate of ~0.2 m/yr has been registered and ground subsidence of 0.5 m has taken place from 2102 to 2013. Despite a slight cooling trend in the air temperature record 2006-2012, ground temperatures at 2 m depth have increased by 0.05°C/yr and at 6 m depth the permafrost has started to thaw from below. According to simple linear regression analyses the mean summer temperature the present and preceding year and mean annual temperature the preceding year are variables affecting the thaw depth (p<0.1). For the ground temperature at 1 m depth the number of thawing degree-days in the summer, mean summer temperature the preceding year, mean winter temperature and snow depth are possible contributing factors (p<0.2). However, it is difficult to explain why the permafrost is getting warmer despite the overall cooling trend in air temperature (2006-2012). An explanation could be that the permafrost is relict and not in equilibrium with the current climate. A long-term increase in air temperature has been recorded at surrounding meteorological stations since the mid 20th century. If the ongoing increase in ground temperature in Tavvavuoma is a result of this continuing warming trend, short-term variability in meteorological parameters can still have an impact on the rate of permafrost degradation, but unless pronounced climate cooling would take place the overall long-term thawing of the peat plateau is inevitable.
15037929 Schaefer, Kevin M. (University of Colorado, National Snow and Ice Data Center, Boulder, CO) and Jafarov, Elchin E. Improved modeling of soil biogeochemistry in permafrost [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0110, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Modeling frozen biogeochemistry in permafrost soils is a major challenge because using observed Q10 values from incubation studies results in unrealistically high carbon emissions from permafrost. Incubation studies of frozen soil show a rapid decline in respiration as temperature decreases below freezing. Permafrost soils contain 1700 Gt of carbon, most of it frozen in permafrost below the active layer. Models with permafrost carbon in the frozen soil layers show unrealistic losses during spinup with observed Q10 values. Greatly increasing the frozen Q10 eliminates the unrealistic emissions, but suppresses winter respiration below observed values. We used a more physical approach in the Simple Biosphere/Carnegie-Ames-Stanford Approach (SiBCASA) model by separating the simulated soil carbon into three pools: thawed, thin film, and bulk frozen. Carbon transfers between thawed, thin film, and frozen pools are controlled by a curve fit of observed liquid water content in frozen soils as a function of temperature, eliminating the frozen Q10 function entirely. This restricts respiration only to the thawed pools while the frozen and thin film pools remain inactive. SiBCASA reproduces observed fluxes from incubation studies and observed winter fluxes. This new parameterization eliminated unrealistic fluxes of permafrost carbon during spinup and resulted in global total amount of frozen carbon much closer to observed values.
15037960 Schuur, E. A. G. (Northern Arizona University, Biology, Flagstaff, AZ); McGuire, A. D.; Grosse, Guido; Harden, J. W.; Hayes, D. J.; Hugelius, Gustaf; Koven, C. D.; Kuhry, Peter; Lawrence, D. M.; Natali, S.; Olefeldt, D.; Romanovsky, V. E.; Schaedel, C.; Schaefer, Kevin M.; Turetsky, M. R.; Treat, Claire C. and Vonk, Jorien. Climate change and the permafrost carbon feedback [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B41O-01, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Approximately twice as much soil carbon is stored in the northern circumpolar permafrost zone than is currently contained in the atmosphere. Permafrost thaw, and the microbial decomposition of previously frozen organic carbon, is considered one of the most likely positive feedbacks from terrestrial ecosystems to the atmosphere in a warmer world. Yet, the rate and form of release is highly uncertain but crucial for predicting the strength and timing of this carbon cycle feedback this century and beyond. New insight brought together under a multi-year synthesis effort by the Permafrost Carbon Network helps constrain current understanding of the permafrost carbon feedback to climate, and provides a framework for newly developing research initiatives in this region. A newly enlarged soil carbon database continues to verify the widespread pattern of large quantities of carbon accumulated deep in permafrost soils. The known pool of permafrost carbon is now estimated to be 1330-1580 Pg C, with the potential for ~400 Pg C in deep permafrost sediments that remain largely unquantified. Laboratory incubations of these permafrost soils reveal that a significant fraction of this material can be mineralized by microbes and converted to CO2 and CH4 on time scales of years to decades, with decade-long average losses from aerobic incubations ranging from 6-34% of initial carbon. Variation in loss rates is depended on the carbon to nitrogen ratio, with higher values leading to more proportional loss. Model scenarios show potential C release from the permafrost zone ranging from 37-174 Pg C by 2100 under the current climate warming trajectory (RCP 8.5), with an average across models of 92±17 Pg C. Furthermore, thawing permafrost C is forecasted to impact global climate for centuries, with models, on average, estimating 59% of total C emissions after 2100. Taken together, greenhouse gas emissions from warming permafrost appear likely to occur at a magnitude similar to other historically important biospheric C sources, such as land use change, but that is only a fraction of current fossil fuel emissions. Permafrost C emissions are likely to be felt over decades to centuries as northern regions warm, making climate change happen even faster than we think based on projected emissions from human activities alone.
15037942 Shelef, E. (Los Alamos National Laboratory, Los Alamos, NM); Rowland, J. C.; Wilson, C. J.; Altmann, Garrett and Hilley, G. E. Impact of downslope soil transport on carbon storage and fate in permafrost dominated landscapes [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0126, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
A large fraction of high latitude permafrost-dominated landscapes are covered by soil mantled hillslopes. In these landscapes, soil organic carbon (SOC) accumulates and is lost through lateral transport processes. At present, these processes are not included in regional or global landsurface climate models. We present preliminary results of a soil transport and storage model over a permafrost dominated hillslope. In this model soil carbon is transported downslope within a mobile layer that thaws every summer. The model tracks soil transport and its subsequent storage at the hillslope's base. In a scenario where a carbon poor subsurface is blanketed by a carbon-rich surface layer, the progressive downslope soil transport can result in net carbon sequestration. This sequestration occurs because SOC is carried from the hilllsope's near-surface layer, where it is produced by plants and is capable of decomposing, into depositional sites at the hillslope's base where it is stored in frozen deposits such that it's decomposition rate is effectively zero. We use the model to evaluate the quantities of carbon stored in depositional settings during the Holocene, and to predict changes in sequestration rate in response to thaw depth thickening expected to occur within the next century due to climate-change. At the Holocene time scale, we show that a large amount of SOC is likely stored in depositional sites that comprise only a small fraction of arctic landscapes. The convergent topography of these sites makes them susceptible to fluvial erosion and suggests that increased fluvial incision in response to climate-change-induced thawing has the potential to release significant amounts of carbon to the river system, and potentially to the atmosphere. At the time scale of the next century, increased thaw depth may increase soil-transport rates on hillslopes and therefore increase SOC sequestration rates at a magnitude that may partly compensate for the carbon release expected from permafrost thawing. Model guided field data collection is essential to reduce the uncertainty of these estimates.
15037961 Shmelev, D. (Institute of Physical Chemical and Biological Problems of Soil Science, Pushchino, Russian Federation); Veremeeva, A.; Kraev, G.; Kholodov, A. L. and Rivkina, E. Carbon pool of permafrost in Kolyma-Indigirka lowland [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B41O-02, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The original database of total carbon, bulk density and iciness and new Geological map were compiled for carbon pool permafrost estimating in Quaternary deposits of North East Yakutia. The database was based on original drilling data on the main Quaternary stratigraphic units of Kolyma-Indigirka Lowland (12 key sites, 120 boreholes, 1000 samples). New geological map was created according Landsat-7 Satellite Image (spatial resolution--30 m), the State Geological map of Quaternary Deposits (2000) and our field investigation for last 30 years in studying region. Studying area was divided into 3 regions according stratigraphy: East of Yana-Indigirka Lowland, Chukochya and Alazeya Rivers basins, East of Kolyma Lowland. Estimating was compiled for upper 25 m thickness. 4 main geomorphological levels were selected for calculation: yedoma (12,8% of total area), alasses (48%), river valley (20,9%) and coastal accumulative lowland (16,7%). Our studies shows, that distribution of yedoma was overestimated in 3,5 times by State Geological Map, mainly due to underestimating of allases (increasing area on 60%). According our assessment, inorganic carbon doesn't exceed 10% of total carbon in the studying area. Permafrost stratigraphic units contain 0.6-2.1% of TC, with the highest concentrations found in Cover Layer and Ice Complex (Yedoma). The biggest carbon pool is found in Olyor, which refers to the most widespread sediments studied and high carbon concentration (up to 18 kg.m-3). The TC pool of Yedoma was 1.5-2 times overestimated by previous studies due to less samples and underestimated iciness. The TC pool of Kolyma delta is 5-7 times overestimated because of higher total organic carbon values considered. Taking the morphology into account, the TC pool assessed is 23.4±9.5 Gt at near 95 000 km2 area. Mean specific carbon content is around 9.9 kg.m-3 in Kolyma Lowland permafrost. The stratigraphic unit-based approach used to compile the database and its analysis provides detailed study of carbon storage in Arctic permafrost. It is well organized for adequately forecasting of permafrost degradation consequences for carbon cycle, including activation of microbiological processes and greenhouse gases emissions.
15037936 Wang, Z. (McGill University, Department of Geography, and Global Environmental and Climate Change Centre, Montreal, QC, Canada); Roulet, Nigel T. and Moore, Tim R. Effects of permafrost thaw on net ecosystem carbon balance in a subarctic peatland [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0120, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
This research is to assess changes in net ecosystem carbon balance (NECB) with permafrost thaw in northern peatland: in particular how changes in C biogeochemistry influence NECB. Thawed transects associated with varying stages of permafrost thaw: from palsas with intact permafrost (P), through edge of palsa (EP), dry lawn (DL), wet lawn (WL), edge of thawed pond (ET), pond sedges (PS), to several thawed ponds (TP) in a subarctic peatland in northern Quebec were sampled in the snow free seasons of 2013 and 2014. The exchange of CO2 and CH4, vegetation, dissolved organic C (DOC) concentration and biodegradability, active layer depth, air and peat temperatures, water table depth (WT), pH, and conductivity were measured. Peat temperatures were quite similar among different locations, but the WT decreased significantly along the transect creating varied environmental conditions that supporting different plant communities. From dry to wet area, vegetation abundance and biomass showed reductions of shrubs and lichens, and increases of Sphagnum, grasses and sedges. Pore water pH increased from dry to wet area, and conductivity slightly decreased. Wet thaw area WL, ET and PS had relatively higher season gross ecosystem production (GEP) and higher season ecosystem respiration (ER), but relative similar net ecosystem CO2 exchange (NEE). Only TP had a significant higher positive season NEE. Palsa was the only CH4 sink, and quite high CH4 emissions were found after it thawed. CH4-C release significantly increased from dry to wet in thawed area, which even several times bigger than total C exchange in ET and PS. Generally, wet area had higher DOC concentration and higher DOC biodegradability indicated by lower SUVA254 (except PS which received great influence from pond). All components in the NECB (GEP, ER, CH4, DOC) increased significantly in magnitude from palsa to wet thawed area, and ecosystem C sink turned into source as palsa thawed into PS and TP. These results demonstrated WT and vegetation change lead the changes in peatland NECB with permafrost thaw. Large amount and more labile DOC produced in thawed area may indicate a 'fast' C uptake-decomposition loop was adapted in thawed peatland, and associated with the high CO2 and CH4 efflux.
15037962 Welker, J. M. (University of Alaska Anchorage, Department of Biological Sciences, Anchorage, AK); Lupascu, M.; Welker, M.; Cooper, Elisabeth and Czimczik, C. I. Ancient CO2 emissions from the High Arctic-Svalbard in winter; responses to deeper winter snow in a permafrost dominated landscape [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B41O-03, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
High Arctic tundra landscapes are underlain by globally significant pools of ancient carbon (C) in the form of permafrost that today is beginning to thaw, as evidenced by deepening active layers. The degree to which this ancient C is diffusing as CO2 into the modern atmosphere during winter is a key climate feedback uncertainty today. Quantifying the magnitude and patterns of these ancient CO2 emission are critical as we begin to fully understand how, as a consequences of climate changes, these emissions might increase even further, accelerating the rise in atmospheric CO2 concentrations and thus global temperatures. In order to do so, we measured fall and winter ecosystem respiration, soil pore space CO2 concentrations and bulk soil C at different depths along with their radiocarbon (14C) contents under ambient and experimentally manipulated deeper snow conditions in mesic tundra of Svalbard, in Adventdalen. Abiotic parameters such as air and soil temperature and water content were continuously monitored for the entire study period. Our findings reveal that: a) soils in these landscapes have permafrost that is up to 25,000 years old at 1.5 m depth; b) in late fall, once plants are dormant, CO2 emissions are dominated by ancient C with older values under deeper snow conditions c) that respiration rates are higher in winter under deeper snow, due to soils being up to 8°C warmer than ambient conditions; d) winter emissions of respired CO2 are dominated by ancient C at all times with effect of snow depth. For the first time our results show that ancient C, previously disconnected from the C cycle, is continuously emitted into the atmosphere during the long High Arctic winter. This new biosphere-atmosphere C cycle interaction may accelerate over time as permafrost active layers continue to deepen, increasing the CO2 concentration of the atmosphere, further distributing global temperatures and leading to subsequent changes in the Arctic and global climates. Our findings are integrated into a synthetic High Arctic annual cycle model of the ages and rates of CO2 emissions from the northerly most landscapes on earth.
15037987 Wickland, K. (U. S. Geological Survey, Baltimore, MD); Koch, J. C.; Crawford, J. T.; Dornblaser, M.; Kelsey, Kathy C. and Striegl, R. G. Connections among terrestrial sources of organic and inorganic carbon and surface waters in a permafrost- and wildfire-impacted headwater catchment, Alaska [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43B-0237, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
High-latitude headwater catchments commonly contain permafrost soils and are subject to disturbance by wildfire. Processes governing transport of organic and inorganic carbon from headwater catchments to surface waters, and the influence of permafrost and disturbance on those processes, remain poorly characterized. We conducted a two-year field study of a headwater catchment in interior Alaska to better understand terrestrial-aquatic linkages of carbon (C) in these systems. The 4.1 km2 catchment is underlain by permafrost, and is drained by a first-order stream. Portions of the catchment burned in 2003, resulting in localized removal of organic soils and subsequent permafrost thaw. During May-September of 2010 and 2011, we sampled stream and soil pore waters throughout the catchment on a weekly to bi-weekly basis for dissolved organic carbon (DOC), specific UV absorbance (SUVA), dissolved inorganic carbon (DIC), and dissolved carbon dioxide (CO2) and methane (CH4). Stream discharge and water chemistry were measured at two locations, reflecting drainage from the upper catchment (2.6 km2) and the entire catchment. Soil pore water sampling sites located between the two stream sampling stations included unburned hillslopes with permafrost depths ranging from 0.6 m to 0.75 m, burned hillslopes with permafrost depths to 1 m, and riparian wetland with permafrost >1 m depth. Seasonal, interannual, and spatial differences in delivery of C constituents to the stream were evident over the two study years. Mean seasonal C loads and flow-weighted mean C concentrations (FWMC) for each stream reach showed that DOC and CH4 increased, and DIC and CO2 decreased in the downstream direction. Comparing stream FWMC to mean concentrations in soil pore waters, we determined that stream DOC, SUVA, and CH4 at the downstream location matched closely with values measured in the riparian wetland and burned hillslope locations, whereas DIC concentration was most similar to unburned hillslopes. This suggests a decoupling of organic and inorganic C sources, perhaps mediated by reactivity. We use an end-member mixing model, soil hydrologic properties, and measures of DOC biodegradation to explore sources of water and C from the distinct catchment landcover types to the stream and the role of permafrost and wildfire in C delivery to streams.
15038024 Xia, J. (University of Oklahoma, Norman, OK); McGuire, A. D.; Lawrence, D. M.; Burke, Eleanor; Chen, Xiao; Delire, C. L.; Koven, C. D.; MacDougall, A. H.; Peng, Shushi; Rinke, Annette; Saito, K.; Zhang, Wenxin; Alkama, Ramdane; Bohn, Theodore J.; Ciais, Philippe; Decharme, Bertrand; Gouttevin, Isabelle; Hajima, T.; Ji Duoying; Krinner, G.; Lettenmaier, D. P.; Miller, Paul A.; Moore, John C.; Smith, Ben; Sueyoshi, Tetsuo; Shi, Zheng; Yan Liming; Liang, J.; Jiang, L. and Luo, Y. Terrestrial ecosystem model performance for net primary productivity and its vulnerability to climate change in permafrost regions [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43J-03, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
A more accurate prediction of future climate-carbon (C) cycle feedbacks requires better understanding and improved representation of the carbon cycle in permafrost regions within current earth system models. Here, we evaluated 10 terrestrial ecosystem models for their estimated net primary productivity (NPP) and its vulnerability to climate change in permafrost regions in the Northern Hemisphere. Those models were run retrospectively between 1960 and 2009. In comparison with MODIS satellite estimates, most models produce higher NPP (310±12 g C m-2 yr-1) than MODIS (240±20 g C m-2 yr-1) over the permafrost regions during 2000-2009. The modeled NPP was then decomposed into gross primary productivity (GPP) and the NPP/GPP ratio (i.e., C use efficiency; CUE). By comparing the simulated GPP with a flux-tower-based database [Jung et al. Journal of Geophysical Research 116 (2011) G00J07] (JU11), we found although models only produce 10.6% higher mean GPP than JU11 over 1982-2009, there was a two-fold disparity among models (397 to 830 g C m-2 yr-1). The model-to-model variation in GPP mainly resulted from the seasonal peak GPP and in low-latitudinal permafrost regions such as the Tibetan Plateau. Most models overestimate the CUE in permafrost regions in comparison to calculated CUE from the MODIS NPP and JU11 GPP products and observation-based estimates at 8 forest sites. The models vary in their sensitivities of NPP, GPP and CUE to historical changes in air temperature, atmospheric CO2 concentration and precipitation. For example, climate warming enhanced NPP in four models via increasing GPP but reduced NPP in two other models by decreasing both GPP and CUE. The results indicate that the model predictability of C cycle in permafrost regions can be improved by better representation of those processes controlling the seasonal maximum GPP and the CUE as well as their sensitivity to climate change.
15037923 Yang, Y. (Chinese Academy of Sciences, Institute of Botany, Beijing, China); Ding Jinzhi; Han, T.; Peng, Y.; Li, F.; Chen Ly and Chen Yongliang. Permafrost carbon-climate feedback in high-altitude ecosystems; evidence from the Tibetan Plateau [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0104, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Permafrost carbon-climate feedback has received particular interest from the global change research community. However, current evidence is mainly derived from high-latitude ecosystems, with little known about high-altitude ecosystems. In this study, we examined permafrost carbon-climate feedback in alpine grasslands on the Tibetan Plateau from the following three aspects. First, we evaluated soil carbon stock in the top 3 meter by conducting a large-scale soil survey across the study area during the summer of 2013-2014. We found that Tibetan grassland soils store 10.4 Pg C in the upper 3 meter, ~40% larger than previous estimation in the top 1 meter. Second, we examined large-scale patterns of temperature sensitivity of soil carbon decomposition in alpine ecosystems by conducting laboratory incubation experiments, and found that greater temperature sensitivity occurred in those soils with more recalcitrant components. Third, we explored the responses of carbon cycling processes in alpine grasslands to climate warming by conducting OTC experiments. We found that experimental warming stimulated ecosystem respiration, but also increased gross primary production, and thus led to the net carbon accumulation. Overall, these three lines of evidence demonstrate that carbon cycle in high-altitude ecosystems is very sensitive to climate warming.
15044039 Hubbard, Bernard E. (U. S. Geological Survey, Reston, VA); Deszcz-Pan, Maria; Smith, Bruce D.; Day, Warren C.; Gough, Larry; Kass, M. Andy; Emond, Abraham and Caine, Jonathan Saul. Correlation of Alaska Landsat image analysis with airborne geophysical survey data; a promising tool for locating outcrops, monitoring burn recovery and assessing potential permafrost thaw [abstr.]: in Geological Society of America, 2014 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 46(6), p. 780, 2014. Meeting: Geological Society of America, 2014 annual meeting & exposition, Oct. 19-22, 2014, Vancouver, BC, Canada.
Geological mapping of the bedrock in much of Alaska is very difficult, not only because of the large size and remoteness of much of the state, but also because most of the potential bedrock exposure is covered either by forest canopy, muskeg soils, and understory vegetation or coated by lichens and moss. The active layer above discontinuous permafrost and weathered rock are additional impediments in locating outcrops. Spotting outcrops from helicopters to provide support for geologists can also be difficult because brown-colored moss is often mistaken for rock. Outcrops are crucial for lithologic and structural observations and measurements needed for evaluation of mineral resources and for collecting samples for laboratory analytical work. In this study, we show that digital video data collected during airborne electromagnetic (AEM) geophysical surveys, combined with processed and visually interpreted Landsat images, can be used to interpret the location of natural outcrops and particularly bedrock exposed after large wildfires. Assuming that bedrock outcrops are electrically resistive, we correlate areas of high resistivity derived from AEM data with Landsat false-color images and known bedrock outcrops to vegetation abundance maps derived from linear spectral unmixing of the imagery. This method was tested in an unburned area near Mount Veta, Alaska in the western Fortymile mining district, where new geologic mapping was recently completed at 1:63,360-scale. AEM data was processed to estimate the electrical resistivity, and it's resolution, of layers from the surface to a depth of 50 m along flight lines. The estimated shallow resistivity (<5 m) was correlated with high-resolution video imagery and Landsat fractional abundances showing highest rock to vegetation proportions per pixel (>90% rock after normalization to shade and other featureless components). High resistivity permafrost zones can be distinguished in unburnt areas based on their high proportions of vegetation and spectral signatures dominated by white spruce and sphagnum moss. In recently burned areas, Landsat spectral unmixing allows bedrock exposures to be distinguished from dry and burnt vegetation dominated by charcoal and cellulose; as well as recovering green vegetation types such as fireweed.
15043708 Mohammed, Aaron A. (University of Calgary, Department of Geoscience, Calgary, AB, Canada); Schincariol, Robert A.; Quinton, William L. and Nagare, Ranjeet M. Mitigating permafrost degradation due to linear disturbances in sub-arctic peatlands [abstr.]: in Geological Society of America, 2014 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 46(6), p. 395, 2014. Meeting: Geological Society of America, 2014 annual meeting & exposition, Oct. 19-22, 2014, Vancouver, BC, Canada.
The presence or absence of permafrost significantly influences the hydrology and ecology of northern watersheds. Linear disturbances resulting from tree canopy removal have led to widespread permafrost degradation in sub-arctic peatlands. Seismic lines resulting from petroleum exploration can account for up to five times the natural drainage density of these basins, and affect the region's water and energy balances. As peatlands represent some of the most sensitive ecosystems to climate and human disturbances, the ability to simulate perturbations to natural systems in a controlled environment is particularly important. A method is presented that is capable of simulating natural freeze-thaw and permafrost conditions on a large variably-saturated soil monolith, housed in a two level climate chamber. The design replicates realistic thermal boundary conditions, which enables field scale rates of active-layer thaw, and presents a path forward for the large-scale experimental study of frozen ground processes. Mulching over seismic lines, using mulch of the removed tree canopy, has been proposed to reduce their environmental impact. The new set-up enabled field-scale remediation techniques to be tested, and was used to investigate the effects of the mulch on thermally mitigating permafrost thaw. Freeze-thaw cycles with and without the mulch enabled its effects to be tested. The data were assimilated into a coupled heat and water transport numerical model. An analysis was conducted on the combined effects of mulch thickness, antecedent moisture conditions and meteorological interactions. Experimental and numerical simulations show that the application of the mulch insulates the underlying soil, by decoupling the subsurface from meteorological forcing and impeding heat conduction. Net ground heat flux is reduced, which delays thaw initiation by slowing the input of energy to the subsurface. This effect prolongs the period of time the ground remains frozen during positive air temperatures and reduces frost table depths. Results indicate that mulching is an effective technique to reduce permafrost degradation and provides a scientific basis to assess the mitigation measure. This study will provide guidance in ensuring that northern exploration is performed in a more environmentally sustainable manner.
15031007 Anisimov, Oleg A. (State Hydrological Institute, Saint Petersburg, Russian Federation) and Kokorev, Vasily. Evaluating climate variables, indexes and thresholds governing Arctic urban sustainability; case study of Russian permafrost regions [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract GC11D-1024, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Addressing Arctic urban sustainability today forces planners to deal with the complex interplay of multiple factors, including governance and economic development, demography and migration, environmental changes and land use, changes in the ecosystems and their services, and climate change. While the latter can be seen as a factor that exacerbates the existing vulnerabilities to other stressors, changes in temperature, precipitation, snow, river and lake ice, and the hydrological regime also have direct implications for the cities in the North. Climate change leads to reduced demand for heating energy, on one hand, and heightened concerns about the fate of the infrastructure built upon thawing permafrost, on the other. Changes in snowfall are particularly important and have direct implications for the urban economy, as together with heating costs, expenses for snow removal from streets, airport runways, roofs and ventilation corridors underneath buildings erected on pile foundations on permafrost constitute the bulk of the city's maintenance budget. Many cities are located in river valleys and are prone to flooding that leads to enormous economic losses and casualties, including human deaths. The severity of the northern climate has direct implications for demographic changes governed by regional migration and labor flows. Climate could thus be viewed as an inexhaustible public resource that creates opportunities for sustainable urban development. Long-term trends show that climate as a resource is becoming more readily available in the Russian North, notwithstanding the general perception that globally climate change is one of the challenges facing humanity in the 21st century. In this study we explore the sustainability of the Arctic urban environment under changing climatic conditions. We identify key governing variables and indexes and study the thresholds beyond which changes in the governing climatic parameters have significant impact on the economy, infrastructure and society in the Arctic cities. We use CMIP-5 ensemble projection to evaluate future changes in these parameters and identify regions where immediate attention is needed to develop appropriate adaptation strategies.
15030897 Coon, E. (Los Alamos National Laboratory, Los Alamos, NM); Berndt, M.; Garimella, R.; Moulton, J. D.; Manzini, G. and Painter, S. L. Computational advances in the Arctic Terrestrial Simulator; modeling permafrost degradation in a warming Arctic [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract DI31A-2195, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
The terrestrial Arctic has been a net sink of carbon for thousands of years, but warming trends suggest this may change. As the terrestrial Arctic warms, degradation of the permafrost results in significant melting of the ice wedges that support low-centered polygonal ground. This leads to subsidence of the topography, inversion of the polygonal ground, and restructuring of drainage networks. The change in hydrology and vegetation that result from these processes is poorly understood. Predictive simulation of the fate of this carbon is critical for understanding feedback effects between the terrestrial Arctic and climate change. Simulation of this system at fine scales presents many challenges. Flow and energy equations are solved on both the surface and subsurface domains, and deformation of the soil subsurface must couple with both. Additional processes such as snow, evapo-transpiration, and biogeochemistry supplement this THMC model. While globally implicit coupling methods enable conservation of mass and energy on the combined domain, care must be taken to ensure conservation as the soil subsides and the mesh deforms. Uncertainty in both critical physics of each process model and in coupling to maintain accuracy between processes suggests the need for a versatile many-physics framework. This framework should allow swapping of both processes and constitutive relations, and enable easy numerical experimentation of coupling strategies. Deformation dictates the need for advanced discretizations which maintain accuracy and a mesh framework capable of calculating smooth deformation with remapped fields. And latent heat introduces strong nonlinearities, requiring robust solvers and an efficient globalization strategy. Here we discuss advances as implemented in the Arctic Terrestrial Simulator (ATS), a many-physics framework and collection of physics kernels based upon Amanzi. We demonstrate the deformation capability, conserving mass and energy while simulating soil subsidence due to bulk ice melting. Mimetic finite difference methods are used to maintain accuracy during mesh deformation. Globalization strategies similar to a local change of variables greatly extend the timestep size without requiring additional residual evaluations. Finally, ATS leverages tree structures for process kernels and data dependencies, enabling versatile combinations of processes and constitutive models and dynamic experimentation with coupling strategies. These advances are demonstrated in a series of problems coupling the thermal-mechanical-hydrological core of the ATS. This work was supported by LANL Laboratory Directed Research and Development Project LDRD201200068DR.
15040573 Douglas, Thomas A. (U. S. Army Cold Regions Research and Engineering Laboratory, Fort Wainwright, AK); Bjella, Kevin and Campbell, Seth W. What's down below? Current and potential future applications of geophysical techniques to identify subsurface permafrost conditions [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract C53C-01, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
For infrastructure design, operations, and maintenance requirements in the North the ability to accurately and efficiently detect the presence (or absence) of ground ice in permafrost terrains is a serious challenge. Ground ice features including ice wedges, thermokarst cave-ice, and segregation ice are present in a variety of spatial scales and patterns. Currently, most engineering applications use borehole logging and sampling to extrapolate conditions at the point scale. However, there is high risk of over or under estimating the presence of frozen or unfrozen features when relying on borehole information alone. In addition, boreholes are costly, especially for planning linear structures like roads or runways. Predicted climate warming will provide further challenges for infrastructure development and transportation operations where permafrost degradation occurs. Accurately identifying the subsurface character in permafrost terrains will allow engineers and planners to cost effectively create novel infrastructure designs to withstand the changing environment. There is thus a great need for a low cost rapidly deployable, spatially extensive means of "measuring" subsurface conditions. Geophysical measurements, both terrestrial and airborne, have strong potential to revolutionize our way of mapping subsurface conditions. Many studies in continuous and discontinuous permafrost have used geophysical measurements to identify discrete features and repeatable patterns in the subsurface. The most common measurements include galvanic and capacitive coupled resistivity, ground penetrating radar, and multi frequency electromagnetic induction techniques. Each of these measurements has strengths, weaknesses, and limitations. By combining horizontal geophysical measurements, downhole geophysics, multispectral remote sensing images, LiDAR measurements, and soil and vegetation mapping we can start to assemble a holistic view of how surface conditions and standoff measurements can be used to delineate subsurface permafrost geomorphology. This presentation will include examples of projects in Alaska and Greenland where a combination of geophysical and other measurement techniques have been used to identify subsurface conditions. These include projects at multiple locations around Interior Alaska where a variety of ground based and standoff measurements are being used to identify subsurface conditions, and infrastructure projects at Thule, Greenland, where geophysical measurements are being used to cut costs for new construction and maintenance. The expansion of the Cold Regions Research and Engineering Laboratories' Fox Permafrost Tunnel is to provide a three dimensional test bed for geophysical measurements, and construction is aided by geophysical measurements. The array of geophysical research tools used to interrogate the subsurface in permafrost terrains can likely provide worthwhile information in non-frozen ground terrains to support sensor development and geomorphological interpretation.
15040575 Grimm, R. E. (Southwest Research Institute, Boulder, CO) and Stillman, D. E. Advances in complex-resistivity mapping and characterization of permafrost [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract C53C-03, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Permafrost is commonly a mixture of silicates, ice, and unfrozen interfacial water. The last is always present at even small quantities of H2O but is most evident in materials with high specific surface area such as silt. Because electrical conduction occurs dominantly through the unfrozen water, high resistivity in permafrost can be associated with coarse, dry, or ice-rich materials. Complex resistivity characterizes both the transfer and storage of electrical energy in materials as a function of frequency. By sweeping a broad frequency spectrum in the laboratory (as wide as 1 mHz to 1 MHz), varying temperature, and controlling the host silicate, H2O abundance, and salt content, we have identified 10 distinct mechanisms for charge storage or transport in artificial ice-silicate mixtures. The spectra of natural samples from the US Army Permafrost Tunnel at Fox, AK were confirmed to be dominated by DC conduction and the orientational polarization of ice, with a smaller contribution from the interfacial polarizaton of unfrozen H2O. We confirmed this signature in field measurements both in and above the tunnel. At ground temperatures a few degrees below freezing, the transition between DC conduction and the orientational ice polarization is around 10-100 Hz. The conductivity is higher above this transition due to the sum of DC and AC conduction mechanisms, so we tested the difference in AC and DC conductivities normalized by the DC conductivity as a metric of ice content. This is akin to the "percent frequency effect" or PFE used in classical induced-polarization surveys. We found that this metric increases monotonically but nonlinearly with ice content in lab samples and correlated roughly with major textural zones in the tunnel. We also noted that DC resistivities previously obtained directly over the tunnel were several times higher than those derived from our survey on a nearby pathway; this difference can be ascribed to subsurface temperatures ~1 C higher beneath the pathway. Temperature also strongly affects the inferred ice content but the frequency of the dielectric relaxation gives an independent temperature estimate. Complex resistivity is therefore a promising approach to permafrost monitoring and mapping of lateral and vertical variations in ice content.
15040574 Hauck, C. (University of Fribourg, Department of Geosciences, Fribourg, Switzerland); Hilbich, C.; Marmy, A. and Scherler, M. Geophysical monitoring for validation of transient permafrost models [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract C53C-02, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Permafrost is a widespread phenomenon at high latitudes and high altitudes and describes the permanently frozen state of the subsurface in lithospheric material. In the context of climate change, both, new monitoring and modelling techniques are required to observe and predict potential permafrost changes, e.g. the warming and degradation which may lead to the liberation of carbon (Arctic) and the destabilisation of permafrost slopes (mountains). Mountain permafrost occurrences in the European Alps are characterised by temperatures only a few degrees below zero and are therefore particularly sensitive to projected climate changes in the 21st century. Traditional permafrost observation techniques are mainly based on thermal monitoring in vertical and horizontal dimension, but they provide only weak indications of physical properties such as ice or liquid water content. Geophysical techniques can be used to characterise permafrost occurrences and to monitor their changes as the physical properties of frozen and unfrozen ground measured by geophysical techniques are markedly different. In recent years, electromagnetic, seismic but especially electrical methods have been used to continuously monitor permafrost occurrences and to detect long-term changes within the active layer and regarding the ice content within the permafrost layer. On the other hand, coupled transient thermal/hydraulic models are used to predict the evolution of permafrost occurrences under different climate change scenarios. These models rely on suitable validation data for a certain observation period, which is usually restricted to data sets of ground temperature and active layer depth. Very important initialisation and validation data for permafrost models are, however, ground ice content and unfrozen water content in the active layer. In this contribution we will present a geophysical monitoring application to estimate ice and water content and their evolution in time at a permafrost station in the Swiss Alps. These data are then used to validate the coupled mass and energy balance soil model COUP, which is used for long-term projections of the permafrost evolution in the Swiss Alps. For this, we apply the recently developed 4-phase model, which is based on simple petrophysical relationships and which uses geoelectric and seismic tomographic data sets as input data.. In addition, we use continuously measured electrical resistivity tomography data sets and soil moisture data in daily resolution to compare modelled ice content changes and geophysical observations in high temporal resolution. The results show still large uncertainties in both model approaches regarding the absolute ice content values, but much smaller uncertainties regarding the changes in ice and unfrozen water content. We conclude that this approach is well suited for the analysis of permafrost changes in both, model and monitoring studies, even though more efforts are needed for obtaining in situ ground truth data of ice content and porosity.
15035195 Nyland, K. E. (George Washington University, Department of Geography, Washington, DC); Streletskiy, D. A. and Grebenets, V. I. International field school on permafrost; Yenisei, Russian Federation; 2013 [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract ED11B-0743, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
The International Field School on Permafrost was established in Russia as part of International Polar Year activities. The first course was offered in 2007 in Northwestern Siberia and attracted students from Russia, Germany, and the United States. Over the past seven years undergraduate and graduate students representing eight different countries in North America, Europe, and Asia have participated in the field school. This annual summer field course visits different regions of the Russian Arctic each year, but the three course foci remain consistent, which are to make in depth examinations of, 1) natural permafrost characteristics and conditions, 2) field techniques and applications, and 3) engineering practices and construction on permafrost. During these field courses students participate in excursions to local museums and exhibitions, meet with representatives from local administrations, mining and construction industries, and learn field techniques for complex permafrost investigations, including landscape and soil descriptions, temperature monitoring, active-layer measurements, cryostratigraphy, and more. During these courses students attend an evening lecture series by their professors and also give presentations on various regionally oriented topics of interest, such as the local geology, climate, or historical development of the region. This presentation will relate this summer's (July 2013) field course which took place in the Yenisei River region of central Siberia. The course took place along a bioclimatic transect from south to north along the Yenisei River and featured extended stays in the cities of Igarka and Noril'sk. This year's students (undergraduate, masters, and one PhD student) represented universities in the United States, Canada, and the Russian Federation. The organization of this course was accomplished through the cooperation of The George Washington University's Department of Geography and the Lomonosov Moscow State University's Department of Cryolithology and Glaciology. This course and others like it are extremely important to support and advertise to a wider audience of students studying the cryosphere because of its unique multidisciplinary nature and the hands-on experience it provides. However, this course not only provides students with an excellent field education, but also the opportunity to network and build strong relationships among their peers within the field. And hopefully these student friendships and working relationships built by this field school will continue and will foster future international research collaborations.
15040576 Parsekian, A. (University of Wyoming, Geology and Geophysics, Laramie, WY); Slater, L. D.; Nolan, J. T.; Grosse, G. and Walter Anthony, K. M. Ground penetrating radar estimates of permafrost ice wedge depth [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract C53C-04, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Vertical ground ice wedges associated with polygonal patterning in permafrost environments form due to frost cracking of soils under harsh winter conditions and subsequent infilling of cracks with snow melt water. Ice wedge polygon patterns have implications for lowland geomorphology, hydrology, and vulnerability of permafrost to thaw. Ice wedge dimensions may exceed two meters width at the surface and several meters depth, however few studies have addressed the question of ice wedge depth due to challenges related to measuring the vertical dimension below the ground. Vertical exposures where ice wedges maybe observed are limited to rapidly retreating lake, river, and coastal bluffs. Coring though the ice wedges to determine vertical extent is possible, however that approach is time consuming and labor intensive. Many geophysical investigations have noted signal anomalies related to the presence of ice wedges, but no reliable method for extracting wedge dimensions from geophysical data has been yet proposed. Here we present new evidence that ground penetrating radar (GPR) may be a viable method for estimating ice wedge depth. We present three new perspectives on processing GPR data collected over ice wedges that show considerable promise for use as a fast, cost effective method for evaluating ice wedge depth. Our novel approaches include 1) a simple frequency-domain analysis, 2) an S-transform frequency domain analysis and 3) an analysis of the returned signal power as a radar cross section (RCS) treating subsurface ice wedges as dihedral corner retro-reflectors. Our methods are demonstrated and validated using finite-difference time domain FDTD) GPR forward models of synthetic idealized ice wedges and field data from permafrost sites in Alaska. Our results indicate that frequency domain and signal power data provide information that is easier to extract from raw GPR data than similar information in the time domain. We also show that we can simplify the problem by reducing the expected output from the GPR data to a single depth parameter rather than attempting to resolve the entire ice wedge shape. This work has the potential to yield new insight into vulnerability to permafrost thaw and geomorphological processes by enabling improved estimation of ground ice volume and distribution.
15043308 Semenova, O. (Gidrotehproekt, St. Petersburg, Russian Federation); Lebedeva, Lyudmila and Volkova, N. Process-based modelling approach to assess hydrological response to wildfire in permafrost environment [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract H13A-1297, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Wildfire disturbance of river basins leads to non-linear response of hydrological systems. Though vast territories of Eastern Siberia are subject to extensive forest fires the feedbacks on permafrost and flow formation processes are still not well-known. The aim of the study was to develop modeling approach for assessment and projection of hydrological response to wildfire for the permafrost region of Eastern Siberia. The MODIS burned area data were used to identify the watersheds subject to fire during recent years. Extensive wildfires occurred in the Upper Vitim River in 2003. The region is characterized by mountainous relief and continuous permafrost. The dominant landscapes are bare rocks and sparse larch forest. The paired-watershed approach was used to detect fire-induced changes in hydrological regime. It revealed increased daily peak flood and monthly runoff within the year after the fire event. The distributed process-based Hydrograph model was used to investigate flow formation before and after the fire disturbance. The key advantage of the model that allowing its application in non-stationary post-fire conditions is explicit accounting for all main runoff formation processes and usage of observable parameters that could be changed during the modeling period. The Hydrograph model was applied to selected river basins in two stages. First, the model parameters were assessed and fixed for pre-fire conditions and the model was run for both disturbed and non-disturbed period. The agreement between observed and calculated hydrographs was the lowest in 2003, the year after the fire. In the second step the dynamic set of the model parameters was developed according to vegetation succession after the fire. The usage of the dynamic parameters allowed assessing changes of flow formation processes after the fire and projecting possible hydrological feedback to future forest fire disturbance that is expected to increase in nearest decades.
15038770 Pokrovsky, Oleg S. (University of Toulouse, Toulouse, France); Viers, J.; Prokushkin, A. S.; Mavromatis, V.; Bagard, M. L. and Chabaux, F. Basalt weathering and plant recycling in permafrost-bearing watersheds of central Siberia; a multi-isotope approach (Si, Mg, Ca, Zn, and Cu) [abstr.]: in Goldschmidt abstracts 2014, V.M. Goldschmidt Conference - Program and Abstracts, 24, p. 1973, 2014. Meeting: Goldschmidt abstracts 2014, June 8-13, 2014, Sacramento, CA.
15043476 An Shuqing (Nanjing University, Institute of Wetland Ecology, Nanjing, China); Tian Ziqiang; Cai Ying; Wen Teng; Xu Delin; Hoa Jiang; Yao Zhigang; Guan Baohua; Sheng Sheng; Yan Ouyang and Cheng Xiaoli. Wetlands of northeast Asia and High Asia; an overview: in Effects of climate change on wetlands (Junk, Wolfang J., editor), Aquatic Sciences, 75(1), p. 63-71, illus., 85 ref., January 2013. Meeting: 8th INTECOL wetland conference, July 20-25, 2008, Cuiaba, Brazil. Based on Publisher-supplied data.
This review reports background information on wetlands in the Northeast Asia and High Asia areas, including wetland coverage and type, significance for local populations, and threats to their vitality and protection, with particular focus on the relationship of how global change influenced wetlands. Natural wetlands in these areas have been greatly depleted and degraded, largely due to global climate change, drainage and conversion to agriculture and silviculture, hydrologic alterations, exotics invasions, and misguided management policies. Global warming has caused wetland and ice-sheet loss in High Asia and permafrost thawing in tundra wetlands in Northeast Asia, and hence induced enormous reductions in water-storage sources in High Asia and carbon loss in Northeast Asia. This, in the long term, will exacerbate chronic water shortage and positively feed back global warming. Recently, better understanding of the vital role of healthy wetland ecosystems to Asia's sustainable economic development has led to major efforts in wetland conservation and restoration. Nonetheless, collaborative efforts to restore and protect the wetlands must involve not only the countries of Northeast and High Asia but also international agencies. Research has been productive but the results should be more effectively integrated with policy-making and wetland restoration practices under future climatic scenarios.
15038027 Anisimov, Oleg A. (Russian State Hydrological Institute, Saint Petersburg, Russian Federation) and Kokorev, Vasily. Enhanced methane concentrations over the East Siberian Arctic shelf; explanation hypothesis based on the analysis of data from land, marine, and satellite observations [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43J-06, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
There is a lack of consensus with regard to the observed enhanced concentrations of methane at East Siberian Arctic Shelf (ESAS), as well as on the long-running effect it may have on the global climate. One group of scientists suggest that it is attributed to venting from the deep layers, and may dramatically increase in the coming decades due to thawing and increased perforation of permafrost, ultimately leading to amplification of the global warming. The other group refutes this hypothesis and supports the standpoint that the observed enhanced fluxes, up to 6-8 ppm whereas the latitude-mean is 185 ppm, are not related to recent permafrost changes but are rather attributed to the geological structure of the shelf. We analyzed data from land, marine and satellite observations and developed the conceptual model that consistently explains the atmospheric methane field in the Arctic in the context of the past, present, and future environmental changes. We explore the hypothesis, according to which enhanced concentrations of methane are associated with the geological history of ESAS. We hypothesized that observed enhanced methane venting is bound to unfrozen bottom sediments surrounding fault zones and paleo river beds, where permafrost never existed in the bottom sediments, while elsewhere on the inner shelf of ESAS sediments remain frozen and impermeable for gases since the last glacial maximum. We tested this hypothesis through analysis of the geological and paleo data, constructing the digital high resolution map of the fault zones and paleo river beds, comparing it with locations of the hydrographic stations where enhanced methane fluxes have been observed, and performing spatial statistical analysis. We demonstrated that (1) the current rate of methane concentration rise over the ESAS does not exceed that in the rest of the Arctic and in the Northern hemisphere, and (2) the probability of methane concentrations being above the average decreases with the distance to the nearest fault zone or paleo river bed. These results do not support the hypothesis of the so-called "methane bomb" at ESAS.
15037935 Behnke, M. I. (St. Olaf College, Northfield, MN); Schade, J. D.; Fiske, G. J.; Whittinghill, Kyle A. and Zimov, N. Patterns in DOC concentration and composition in tundra watersheds in the Kolyma River basin [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0119, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Much of the world's soil carbon is frozen in permafrost in the Arctic. As the climate warms and permafrost thaws, this carbon will again be actively cycled. Whether it is exported to the ocean or released as greenhouse gases to the atmosphere depends on the form of carbon compounds and conditions encountered during transport, and will determine the strength of permafrost thaw as a feedback on climate change. To better understand the fate of this carbon, we determined how and where in the landscape dissolved organic carbon (DOC) breaks down as water transports it from tundra to ocean. We compared DOC concentration and composition along flowpaths within watersheds and at the mouths of watersheds differing in drainage area. We incubated filtered water samples in light and dark, including filter-sterilized samples, to assess the interactions between light and microbial processing as mechanisms of DOC loss. Composition was assessed using optical measurements associated with the structure of organic compounds. DOC concentration declined along flowpaths within watersheds, with most loss occurring in aquatic environments high in the landscape. We also found a negative correlation between watershed size and DOC concentration. These results suggest that much of the processing of organic carbon occurs in small streams. In addition, the relationship with drainage area suggests that residence time in streams has a large impact on transformation of terrestrial carbon during transport. We found no substantial differences in optical characteristics of DOC, indicating that breakdown processes were not selective, and that light caused much of the breakdown. This conclusion is supported by the incubation experiment, which showed greater breakdown by light, and evidence that light stimulated higher rates of microbial processing. These results highlight the importance of inland aquatic ecosystems as processors of organic matter, and suggest that organic carbon from permafrost thaw is likely to be processed high in the landscape rather than transported to the ocean. Furthermore, the importance of light-induced breakdown as a mechanism for carbon loss suggests that the timing of DOC transport relative to seasonal changes in light intensity may influence the impact of permafrost thaw on climate change.
15037900 Berg, A. A. (University of Guelph, Guelph, ON, Canada); Quinton, W. L.; Huang, Jianliang; Chasmer, Laura; Ambadan, J. T.; Connon, R. and Stone, Lindsay. The relationship of increasing trends in GRACE observed total water storage to landscape changes in the Southern Taiga Plains [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31D-0050, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The southern margin of discontinuous permafrost in Canada is highly sensitive to climate change. Warming to this region causes rapid thaw and disappearance of permafrost resulting in large changes to ecological and hydrological processes. Changes in hydrology result from permafrost thaw induced subsidence and conversion of tree-covered peat plateaus into bogs and channel fens. Bogs, fens and plateaus have contrasting hydrological functions. The elevated plateaus with their shallow root zone due to frozen soils convert a relatively high proportion of hydrological input to runoff which they convey to adjacent channel fens and bogs. Bogs are largely water storage features and are typically surrounded by raised peat plateaus, while channel fens transmit water to streams and rivers. In the Scotty Creek watershed, within the southern Taiga Plains regions of Canada's Northwest Territories, numerous researchers have documented the decline of peat plateaus as a proxy for areal loss of permafrost terrain, and concomitant increases of wetland coverage. Analysis of spatial trends in global total water storage as measured by the Gravity Recovery And Climate Experiment (GRACE) satellites suggest a increasing trend of 6±1 mm/year water equivalent units over this region during the period 2003-2013. Analysis of a water budget constructed for the Scotty Creek watershed suggest that this long term trend is only weakly associated to the moderate increases to precipitation while the statistically significant increasing trends observed in discharge in this watershed would likely result in opposite sign. Further, seasonal trend analysis of the GRACE total water storage observations suggest that much of the increase in total water mass over this region occurs over the warm season suggesting that larger snowpacks are not driving the mass increase. In this presentation the changes to total water storage are compared to the trends of landscape change over this region to corroborate the rates of total water mass increase with changes in area of storage features.
15038035 Bohn, Theodore J. (Arizona State University, Tempe, AZ); Melton, Joe R.; Brovkin, Victor; Chen, G.; Denisov, S. N.; Eliseev, A. V.; Gallego-Sala, A. V.; Glagolev, M.; Ito, A.; Kaplan, Jed O.; Kleinen, Thomas; Maksyutov, Shamil S.; McDonald, K. C.; Rawlins, M. A.; Riley, W. J.; Schroeder, R.; Spahni, R.; Stocker, B.; Subin, Z. M.; Tian, Han; Zhang, B.; Zhu, Xudong and Zhuang, Q. Intercomparison of the Wetchimp-WSL wetland methane models over West Siberia; how well can we simulate high-latitude wetland methane emissions? [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B44A-08, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Wetlands are the world's largest natural source of methane, a powerful greenhouse gas. The strong sensitivity of these emissions to environmental factors such as soil temperature and moisture has led to concerns about potential positive feedbacks to climate change. This is particularly true at high latitudes, which have experienced pronounced warming and where thawing permafrost could potentially liberate large amounts of labile carbon over this century. Despite the importance of wetland methane emissions to the global carbon cycle and climate dynamics, global models exhibit little agreement as to the magnitude and spatial distribution of emissions, due to uncertainties in both wetland area and emissions per unit area driven by a scarcity of in situ observations. Recent intensive field campaigns across West Siberia make this an ideal region over which to assess the performance of large-scale process-based wetland models in a high-latitude environment. Here we present the results of a follow-up to the Wetland and Wetland CH4 Model Intercomparison Project focused on the West Siberian Lowland (WETCHIMP-WSL). We assessed 17 models and 5 inversions over this domain in terms of total CH4 emissions, simulated wetland areas, and CH4 fluxes per unit wetland area and compared these results to an intensive in situ CH4 flux dataset, several wetland maps, and two satellite inundation products. Findings include: a) estimates of total CH4 emissions from both models and inversions spanned almost an order of magnitude; b) forward models using inundation alone to estimate wetland areas suffered from severe biases in CH4 emissions; and c) aside from these area-driven biases, disagreement in flux per unit wetland area was the main driver of forward model uncertainty. We examine which forward model approaches are best suited towards simulating high-latitude wetlands and make recommendations for future modeling, remote sensing, and field campaigns to reduce model uncertainty.
15037978 Camill, P. (Bowdoin College, Brunswick, ME); Umbanhowar, C. E., Jr.; Adams, Cameron; Westervelt, Anna; Lesser, Daniel; Hall, A.; Hamley, C. and Bourakovsky, A. Climate impacts on Canadian subarctic peatland C accumulation and storage potentially mediated by moisture, peatland development, and fire [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B42D-08, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Warming climate may cause permafrost regions to become stronger sources of C due to increased decomposition or fire. However, the dynamics of soil C storage in subarctic peatlands-one of the largest sinks of high-latitude soil C-potentially complicate this hypothesis for two reasons: (1) Warming may increase C storage, presumably as productivity in temperature-limited regions is enhanced by longer growing seasons relative to losses from decomposition. (2) Regional climatic effects on C accumulation may be mediated by local processes, such as peatland development (e.g., bog vs. fen, permafrost vs. no permafrost) and associated differences in moisture and attendant response of fires to moisture. We examined 13 peat cores spanning the Holocene across a continental gradient in moisture/seasonality, from the Canadian continental interior (permafrost plateau bogs in Manitoba) to eastern coastline (unfrozen bogs along the southern boundary of permafrost in Labrador). We used 90 AMS 14C dates, percent carbon, and bulk density measurements to estimate sedimentation and C accumulation rates. Macroscopic charcoal was used to determine local fire severity. Macrofossil analysis was conducted to determine historical changes in the plant community and peatland type. The effects of past climatic changes depend on peatland development and moisture. Sites in Labrador were classified as wet, poor fens for much of their history, and fires were practically nonexistent. C accumulation rates were greatest during the Holocene Thermal Maximum and lower during more recent Neoglacial cooling. In contrast, C accumulation in Manitoba sites appeared to be greatest during initial wetter fen phases and slower during subsequent, drier bog phases. Fire was more common and severe in Manitoba during the bog phases, and the combination of drier bogs and fire slowed C accumulation rates during the HTM, thereby making C storage less sensitive to past climate. These results suggest that in regions that are potentially less moisture limited, C accumulation rates are high and may be sensitive to regional climatic changes. However, in drier regions, or where peatlands transitioned early from fen to bog, the combination of lower productivity and increased fire may constrain C accumulation response to regional climate.
15037998 Chernykh, D. (Russian Academy of Sciences, Far Eastern Branch, Pacific Oceanological Institute, Vladivostok, Russian Federation); Leifer, Ira; Shakhova, N. E. and Semiletov, Igor P. Assessment of bubble-borne methane emissions in the East Siberian Arctic Shelf via interpretation of sonar data [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43B-0249, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Arctic warming is proposed to increase methane emissions from submerged permafrost driving a positive feedback. Where emissions are from shallow seas, bubbles transport much of the methane directly, while frequent Arctic storms sparge much of the remaining dissolved methane before microbes can oxidize it. Complexity arises where emissions are small bubbles or from deeper water due to dissolution below the storm-mixed layer. Given that these emissions span a wide geographic area, a promising remote sensing technology that has been used to map and estimate emissions; however, significant uncertainties exist in sonar data interpretation due to a range of parameters affecting sonar return including bubble size distribution and spatial distribution, vertical velocity, and temperature all of which are closely inter-related in a complex and at best poorly understood manner, and change as the bubble plume rises. This process was illustrated in a series of in situ calibration experiments in the East Siberian Arctic Sea (ESAS) where controlled air bubble plumes were created and observed with sonar to quantify the relationship between sonar return and bubble plume flux for a first calibration of in situ sonar bubble plume observations in the ESAS. Results highlight the importance of bubble plume dynamics to sonar return and the absence of a simple relationship between sonar return and bubble flux. Instead sonar return related to height above seabed, even accounting for dissolution and changing hydrostatic pressure, confirming earlier laboratory studies for a deeper water column. Calibrations then were applied to field data of an area of ESAS natural seepage.
15037948 Curasi, S. R. (Colgate University, Geography, Hamilton, NY); Weber, Luis R. and Loranty, M. M. Effects of landscape position on carbon cycling in Siberian Arctic tundra [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0135, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
High latitude carbon cycling is important because shifts in climatic conditions are thawing permafrost and altering carbon uptake in ways that will impact global climate. Within arctic ecosystems variation in slope and topography lead to flows of water beneath the soil surface that increase ecosystem moisture and nutrient availability. Consequently, such differences in landscape position often alter ecosystem structure, increase vegetation productivity, and more generally alter carbon cycling, relative to adjacent upland areas. Such differences will likely result in altered ecosystem responses to continued climate change. Understanding this variability in ecosystem function will be necessary in order to accurately understand the future of the arctic carbon cycle. The objective of this study is to characterize differences in biological and environmental conditions associated with landscape position in Siberian arctic tundra, and to understand how these differences impact ecosystem carbon cycling. To quantify the impact of landscape position on tundra ecosystem carbon cycling, we selected pairs of plots in upland and low lying landscape positions with high and low shrub density. We measured CO2 flux, permafrost thaw depth, soil moisture, soil temperature, and meteorological conditions. These variables were compared relative to shrub density and landscape position in order to determine differences in gross primary productivity and ecosystem respiration associated with vegetation type and landscape position. Low-lying wet areas were more productive than adjacent upland areas, irrespective of vegetation type. We also observed shallower permafrost thaw depth, lower soil temperature, greater soil moisture, and higher ecosystem respiration in the low lying plots. The observation of higher ecosystem respiration despite lower permafrost thaw depths and soil temperatures in the low-lying areas highlights the challenges associated with understanding the arctic carbon cycle under changing biological and environmental conditions. Our results could be combined with data on variability in ecosystem type associated with landscape position across the arctic environment to better understand and model spatial variability in ecosystem scale carbon cycle dynamics.
15037895 DeBeer, Chris M. (University of Saskatchewan, Saskatoon, SK, Canada); Wheater, Howard S.; Chun, Kwok P.; Shook, Kevin and Whitfield, Paul H. The changing cold regions network; improving the understanding and prediction of changing land, water, and climate in the Mackenzie and Saskatchewan River basins, Canada [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31D-0043, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Within the cold interior of western and northern Canada, rapid and widespread environmental changes are taking place, which are of serious concern for society and have a range of implications from local to regional and global scales. From a scientific standpoint there is an urgent need to understand the changes and develop improved diagnostic and predictive modelling tools to deal with the uncertainty faced in the future. The Changing Cold Regions Network (CCRN) is a research consortium of over 50 Canadian university and government scientists and international researchers aimed at addressing these issues within the geographic domain of the Mackenzie and Saskatchewan River Basins. CCRN's primary focus is to integrate existing and new experimental data with modelling and remote sensing products to understand, diagnose and predict changing land, water and climate, and their interactions and feedbacks. To support these activities, the network utilizes a suite of 14 world-class water, ecosystem, cryosphere and climate (WECC) observatories across this region that provide exceptional opportunities to observe change, investigate processes and their dynamics, and develop and test environmental models. This talk will briefly describe the CCRN thematic components and WECC observatories, and will then describe some of the observed environmental changes and their linkages across the northern and mountainous parts of the network study domain. In particular, this will include changes in permafrost, terrestrial vegetation, snowcover, glaciers, and river discharge in relation to observed climatic changes across the region. The observations draw on a wide range of literature sources and statistical analyses of federal and provincial regional monitoring network data, while more detailed observations at some of the WECC observatories help to show how these regional changes are manifested at local scales and vice versa. A coordinated special observation and analysis period across all WECC observatories is planned for 2014-15, and this will also be briefly described.
15037994 Douglas, P. M. (California Institute of Technology, Pasadena, CA); Stolper, D. A.; Eiler, J. M.; Sessions, A. L. and Walter Anthony, K. M. The application of methane clumped isotope measurements to determine the source of large methane seeps in Alaskan lakes [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43B-0244, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Natural methane emissions from the Arctic present an important potential feedback to global warming. Arctic methane emissions may come from either active microbial sources or from deep fossil reservoirs released by the thawing of permafrost and melting of glaciers. It is often difficult to distinguish between and quantify contributions from these methane sources based on stable isotope data. Analyses of methane clumped isotopes (isotopologues with two or more rare isotopes such as 13CH3D) can complement traditional stable isotope-based classifications of methane sources. This is because clumped isotope abundances (for isotopically equilibrated systems) are a function of temperature and can be used to identify pathways of methane generation. Additionally, distinctive effects of mixing on clumped isotope abundances make this analysis valuable for determining the origins of mixed gasses. We find large variability in clumped isotope compositions of methane from seeps in several lakes, including thermokarst lakes, across Alaska. At Lake Sukok in northern Alaska we observe the emission of dominantly thermogenic methane, with a formation temperature of at least 100° C. At several other lakes we find evidence for mixing between thermogenic methane and biogenic methane that forms in low-temperature isotopic equilibrium. For example, at Eyak Lake in southeastern Alaska, analysis of three methane samples results in a distinctive isotopic mixing line between a high-temperature end-member that formed between 100-170°C, and a biogenic end-member that formed in isotopic equilibrium between 0-20°C. In this respect, biogenic methane in these lakes resembles observations from marine gas seeps, oil degradation, and sub-surface aquifers. Interestingly, at Goldstream Lake in interior Alaska, methane with strongly depleted clumped-isotope abundances, indicative of disequilibrium gas formation, is found, similar to observations from methanogen culture experiments.
15037937 Eason, Jessica (Brown University, Providence, RI); Kuhn, McKenzie A.; Dunn, Sam; Spawn, S. and Schade, J. D. Topographic variation and methane production in Siberian Arctic tundra [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0121, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Understanding the fate of soil carbon when permafrost soils begin to thaw is critical for predicting the impact of permafrost thaw on global climate change. Microbial metabolism of soil carbon can produce carbon dioxide or methane, depending on soil conditions, and which pathway dominates has great significance for the strength of climate feedbacks since methane is a much more powerful greenhouse gas than carbon dioxide. In Arctic ecosystems, methane production from upland environments is not well understood and generally assumed to be low because conditions there are generally not favorable for methanogenesis. Small changes in topography, however, can lead to great heterogeneity in soil conditions at small scales that may lead to higher methane flux than generally recognized. In this study, we investigated patterns in methane, carbon dioxide, and oxygen concentrations in in surface waters of 15 small ponds in the Kolyma River watershed in Northeast Siberia. The ponds were distributed across a topographic gradient from upland tundra high in the landscape to low-lying ponds in the floodplain of the Kolyma River. In addition, we used chambers to measured methane fluxes from a variety of topographic depressions that ranged from pools to moss-dominated saturated soils lacking surface water, to dry soils dominated by sedges. Dissolved carbon dioxide concentrations in ponds showed no trend down the topographic gradient while methane concentrations decreased downslope. The decrease in methane production may be the result of a switch from green moss to brown moss, which may act as a host for methanotrophic bacteria. Ponds with green moss had significantly higher concentrations of methane than the ponds with brown moss. In addition, we found significantly higher methane fluxes from pools and saturated soils then from drier soils, which showed very low fluxes. These results suggest that upland tundra may be a significant source of methane, and that methane fluxes are driven by a combination of soil conditions and the composition of vegetation within topographic depressions. Clearly, better understanding of small-scale patterns in gas flux and the conditions which effect it is critical to our ability to model feedbacks that may result from anthropogenic climate change.
15037931 Fisher, J. P. (University of Sheffield, Sheffield, United Kingdom); Estop-Aragones, C.; Thierry, Aaron; Hartley, I. P.; Murton, J. B.; Charman, D. J.; Williams, M. and Phoenix, G. K. Impacts of thermokarst formation and wildfire on boreal forest carbon cycling [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0114, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
At the global scale permafrost temperatures are increasing, leading to a thickening of the active layer and an increase in the amount of previously immobilised C exposed to microbial decay and subsequent release to the atmosphere. Against the backdrop of this overall trend, perturbations to permafrost systems caused by wildfires or thermokarst driven wetland formation can cause dramatic shifts in the C exchange of these ecosystems as a result of the changes in plant communities and soil thermal regimes they cause. These dynamic components of permafrost landscapes are often neglected in coupled climate-C models. However, a clear understanding of the impact of these perturbations on C cycling is crucial if we are to accurately predict future permafrost feedbacks to climate change. This is particularly pertinent given that the frequency of both forest fires and thermokarst formation is likely to increase with future climate warming. In order to assess the impact of these perturbations on C cycling we established paired burned and unburned spruce forest and paired peat plateau and thaw feature field sites near Whitehorse, YT and Yellowknife, NT within the boreal region of Canada. At each site tree photosynthetic biomass was quantified using DBH based allometric scaling equations. A combination of percentage cover surveys, biomass harvests, and leaf area determination were used to calculate understory and wetland photosynthetic biomass. Measurements of spruce and understory photosynthesis and plant and soil respiration were made using specialised acrylic chambers and an IRGA. Combining these data has allowed us to determine the impact of thermokarst formation and wildfire on C exchange with the atmosphere. This has allowed us to assess whether the dramatic increase in plant productivity between peat plateau and wetland habitats has the potential to offset thermokarst associated C losses. We have also gained an understanding of whether increases in light availability for understory vegetation in early to mid-successional post-burn sites can partially offset the loss of photosynthetic capacity caused by the lack of a tree canopy and increased soil respiration resulting from active layer thickening. Our findings provide important insights into the impact of two key perturbations on C cycling in permafrost systems.
15037918 Goswami, S. (Oak Ridge National Laboratory, Oak Ridge, TN); Hayes, D. J.; Sloan, Victoria L.; Liebig, J. A.; Norby, R. J. and Wullschleger, S. D. Spectral characteristics of vegetation functional traits across a range of thaw gradients on Alaska's Seward Peninsula [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31F-0083, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The Arctic and Boreal regions are warming rapidly, leading to the thawing of the underlying permafrost and associated changes in vegetation structure and composition. The thawing of ice-rich permafrost drives land surface dynamics called thermokarst, characterized by a variety of geomorphic surface features across high latitude landscapes. The development of these thermokarst or thermo-erosional features depends on factors such as local permafrost conditions, hydrology, geomorphology, vegetation, and climate, but their degree of dependence are not well understood across scales. The structure, functions and traits of the vegetation can work as effective indicators of these landscape changes. Our ability to characterize these vegetation characteristics across a wide range of thaw gradients at the local scale could help us to better understand the dependency as well as the impacts of thermokarst processes on them. This will also help us to develop capabilities to quantify these characteristics and dependencies from local to regional scales by using remote sensing and ecosystem modeling techniques. During the months of June-July of 2013 and 2014, we conducted field surveys at various sites across the central Seward Peninsula in Alaska covering a range of thaw gradients to collect data for vegetation functional traits, ancillary data and also hyperspectral data in the 400-2500 nm range using a field spectrometer. Data were collected from plots established along 50 m transects to capture transitional states of these thaw features from the upland zone, transition zone, and thaw lake basins as well as in polygonal features. Here we discuss the characteristics of vegetation functional traits and how they relate to the ground-based spectral measurements. Some of these findings could be scaled up using airborne and satellite remote sensing data. The findings from this study can improve our understanding of disturbance patterns and their feedbacks to local scale plant and soil dynamics. Scaling up our understanding based on multi-scale remote sensing and ecosystem models over multiple spatial and temporal scales across landscapes could help us reduce uncertainties in estimating the carbon budget from local to pan-arctic scales.
15037986 Harms, Tamara (University of Alaska Fairbanks, Fairbanks, AK); Godsey, S.; Longano, E.; Ludwig, S.; Risser, R. R. and Rushlow, C. R. Hydrology and biogeochemistry of zero-order channels draining Arctic hillslopes [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43B-0236, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Hydrologic flowpaths couple terrestrial and aquatic ecosystems and are responsive to changing climate in the arctic. However, significant uncertainty remains regarding the character and strength of links between terrestrial ecosystems and downstream aquatic ecosystems. We investigated spatial and temporal patterns in solute concentrations and stream discharge of zero-order channels, termed water tracks, draining hillslopes underlain by permafrost within the Kuparuk Basin of northern Alaska. Water tracks are ubiquitous features in this region, and may serve as a key regulator of elemental fluxes between terrestrial and aquatic ecosystems. Flow in water tracks was highly responsive to precipitation. Snowmelt dominated the annual hydrograph and in summer, rapid drying occurred between rain events. Despite widespread drying after snowmelt, isotopes of water indicated that snow-derived water contributed to flow in water tracks and the receiving river for several weeks beyond the snowmelt period, indicating capacity for storage of water in catchments even when thaw depth is shallow. In contrast, the snowmelt-derived flush of dissolved organic carbon, nitrogen, and phosphorus subsided with discharge, indicating limited supplies of these elements, or rapid uptake within catchments. After snowmelt, concentrations of nitrogen and phosphorus, the elements limiting primary production of terrestrial and aquatic ecosystems, respectively, remained low or undetectable in inorganic forms, except during large storms. Thus we expect that changes to the intensity or magnitude of precipitation will alter the availability and distribution of limiting nutrients within tundra catchments. Our observations of zero-order arctic channels indicate that changes in precipitation patterns and thaw dynamics may alter nutrient regimes of arctic ecosystems due to the key functions of nutrient delivery and distribution performed by water tracks. Strong nutrient limitation in terrestrial and aquatic ecosystems indicates potential for change in the structure and function of ecosystems under altered nutrient regimes in the arctic.
15037992 Hernes, P. (University of California-Davis, Davis, CA); Tzortziou, Maria A.; Salisbury, Joe; Mannino, Antonio; Matrai, P.; Friedrichs, M. A. and del Castillo, Carlos E. Arctic-COLORS (Coastal Land Ocean Interactions in the Arctic); a NASA field campaign scoping study to examine land-ocean interactions in the Arctic [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43B-0242, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The Arctic region is warming faster than anywhere else on the planet, triggering rapid social and economic changes and impacting both terrestrial and marine ecosystems. Yet our understanding of critical processes and interactions along the Arctic land-ocean interface is limited. Arctic-COLORS is a Field Campaign Scoping Study funded by NASA's Ocean Biology and Biogeochemistry Program that aims to improve understanding and prediction of land-ocean interactions in a rapidly changing Arctic coastal zone, and assess vulnerability, response, feedbacks and resilience of coastal ecosystems, communities and natural resources to current and future pressures. Specific science objectives include: - Quantify lateral fluxes to the arctic inner shelf from (i) rivers and (ii) the outer shelf/basin that affect biology, biodiversity, biogeochemistry (i.e. organic matter, nutrients, suspended sediment), and the processing rates of these constituents in coastal waters. - Evaluate the impact of the thawing of Arctic permafrost within the river basins on coastal biology, biodiversity and biogeochemistry, including various rates of community production and the role these may play in the health of regional economies. - Assess the impact of changing Arctic landfast ice and coastal sea ice dynamics. - Establish a baseline for comparison to future change, and use state-of-the-art models to assess impacts of environmental change on coastal biology, biodiversity and biogeochemistry. A key component of Arctic-COLORS will be the integration of satellite and field observations with coupled physical-biogeochemical models for predicting impacts of future pressures on Arctic, coastal ocean, biological processes and biogeochemical cycles. Through interagency and international collaborations, and through the organization of dedicated workshops, town hall meetings and presentations at international conferences, the scoping study engages the broader scientific community and invites participation of experts from a wide range of disciplines, to refine our science objectives and outline detailed research strategies needed to attain these objectives. The deliverable will be a comprehensive report to NASA outlining the major scientific questions, and developing the initial study design and implementation concept.
15037921 Herrick, C. (University of New Hampshire, Institute for the Study of Earth, Oceans, and Space (EOS), Durham, NH); Palace, Michael W.; Finnell, D. R.; Garnello, A.; Sullivan, F.; Anderson, S. M. and Varner, Ruth K. Use of high resolution UAS imagery to classify sub-arctic vegetation types [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31F-0089, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Sub-arctic permafrost regions are now experiencing annual warming with a resulting thaw that induces changes to the vegetative landscape. This warming trend is directly correlated to increases in annual greenhouse gas emissions including methane (CH4). Vegetation species and composition are indirect indicators of CH4 flux, and may serve as a proxy for estimating changes in CH4 emission over time. Three WorldView-2 images (2 m2 spatial resolution, 8 multispectral bands) were acquired in Jul/Aug of 2012-2014 over the Abisko region in northern Sweden. Color infrared (CIR) sub-meter imagery was also collected over a 4 km2 area in 2014 using both a multi-rotor helicopter and a fixed wing unmanned aircraft system (UAS). Fifty 1 m2 ground sample plots were established; these plots cover 5 major ground cover vegetation classes and were used in classification efforts. Texture analysis was conducted on both UAS and WV-2 imagery. Both an unsupervised k-means clustering algorithm to predict vegetation classes and a supervised classification using both random forests and neural networks were conducted; similar texture analysis and clustering were also performed on the UAS imagery. Classifications of the two imagery types were compared with promising results, thus supporting the use of UAS and high resolution satellite image collection to provide landscape level characterization of vegetation.
15037965 Jastrow, J. D. (Argonne National Laboratory, Argonne, IL); Ping, C. L.; Matamala, R.; Vugteveen, T. W.; Lederhouse, Jeremy S. and Michaelson, G. J. Variations in the horizontal and vertical distributions of organic carbon stocks across ice wedge polygons of Arctic Alaska [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B41O-06, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Estimates of the quantities of organic carbon stored in permafrost-region soils have improved immensely within the last few decades. However, uncertainties in these estimates remain high and affect our ability to reliably predict the vulnerability of the region's vast carbon stocks to remobilization caused by permafrost thaw and other perturbations related to climatic changes. Two major sources of uncertainty are (1) the uneven distributions and limited numbers of observational data, due to constraints on accessibility for much of this remote region; and (2) the high spatial heterogeneity of cryoturbated soils found in patterned ground--where freeze/thaw, frost heaving, and other cryogenic processes cause soil deformation, breaking/mixing of soil horizons, and deep burial of relatively labile organic matter. Ice wedge polygons are ubiquitous throughout Arctic coastal plains and drainage basins. These patterned ground features are large enough (~5-30 m across) that a better three-dimensional understanding of their carbon stocks might improve geospatial upscaling of observational data. We investigated the horizontal and vertical (up to 300 cm deep) distributions of soil organic matter across three polygon types on the North Slope of Alaska: low-center (LCP), flat-center (FCP), and high-center (HCP) polygons, with each type replicated three times. We found variations in the thickness and quality of surface organic horizons for different polygon types. Below the active layer, organic-rich cryoturbated horizons were located in the transition zone and fingered down into the upper permafrost. The HCPs exhibited more prominent deformation than LCPs and FCPs. The cross-sectional distribution and heterogeneity of organic carbon density differed among polygon types, which led to type variations in overall polygon carbon stocks as well. Our findings suggest that an approach based on accounting for polygon-scale (wedge to center) and/or landscape-scale (polygon type) variations, in tandem with remote sensing and geospatial tools, could help constrain the uncertainties associated with upscaling of carbon stocks for areas of patterned ground dominated by ice wedge polygons.
15038000 Joye, S. B. (University of Georgia, Athens, GA); Samarkin, V.; Shakhova, N. E. and Semiletov, Igor P. Methane concentrations and oxidation in nearshore waters of the Lena River Delta [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43B-0251, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The Arctic is warming dramatically, with potentially catastrophic impacts on climate change through rapid mobilization of labile carbon reservoirs sequestered presently in permafrost. Increasingly, Arctic feedbacks are recognized as key contributors to climate change, including cycles associated with the powerful greenhouse gas methane, whose atmospheric concentration has more than doubled since the pre-industrial epoch. Sustained methane release to the atmosphere from thawing Arctic permafrost and delivery to the coastal ocean through groundwater or riverine discharge or expulsion from the seabed is a positive and likely highly significant feedback to climate warming. Microbially-mediated methane oxidation provides a key sink and effective biofilter that can limit methane fluxes from coastal environments to the atmosphere. We examined methane dynamics on the East Siberian Arctic Shelf by determining concentrations and oxidation rates at a series of stations near the Lena River Delta and moving offshore. Methane concentrations and oxidation rates were highly elevated in and near the river mouth compared to offshore waters, except when the offshore waters were impacted by seabed methane seepage. The regulation of methane oxidation in Arctic waters appears two-fold: first, rates are strongly related to methane availability and second, in the presence of methane, nutrient availability strongly regulates methane consumption. Along the Lena river delta, elevated concentrations of both nutrients and methane create ideal conditions to support high rates of pelagic methanotrophy. Offshore, where nutrient concentrations are lower and more limiting, methane oxidation rates are considerably lower. These data suggest that, at present, nearshore waters are fairly efficient methane sinks while in offshore waters, pelagic methanotrophy is inefficient, allowing methane to escape to the atmosphere.
15038032 Kirpotin, S. (Tomsk State University, Tomsk, Russian Federation); Pokrovsky, Oleg and Gordov, E. P. Western Siberian peatlands as indicator and regulator of climate change on global scale through feedbacks with carbon effluxes [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B44A-03, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The Western Siberian plain (WSP) is the most bogged region of the World - in some parts up to 70-80% of its territory is covered by bogs, in overall 1 million km2. Western Siberia acts as a terrestrial sink of atmospheric carbon and thus plays an important role in the global cycle of carbon. For thousands of years the vast taiga forest and pristine peatland areas south of the permafrost area have been sequestrating substantial amounts of atmospheric carbon. The biggest at the World - Great Vasiugan Mire GVM (total area--7.5 million hectare settles down in its territory. This unique mire representing the object of a nature of the world value, comparable on the importance and a rank with the lake Baikal. The peat stock accumulated in the GVM is around 18 billion tons of dry organic matter, representing 16.5% of total peat stock deposits in the WSP (Vaganov etc., 2005). According to our investigations carried out in the Western Siberian Plain, contrasting processes are occurring in the Southern and Northern parts of the region. In the south, bogs are expanding in the taiga zone and there is progressive swamping which leads to forest death. As a result, in this part of Western Siberia bogs act as a kind of "global cooler" due to carbon sequestration in their peat layers. The situation in the northern part of the Western Siberian Plain is completely opposite. The bogs there are reducing their area and the forest-tundra area is being subjected to thermokarst activity and colonization of bogs by trees. Due to incredibly increased thermokarst activity, two contrast processes are observed here - a) increase of lake surface due to melting of lakes' coasts, and - b) decrease of surface area or disappearance of lakes due to water escape downstream the hydrological network. Moreover, thermokarst processes increase carbon effluxes, especially from the small lakes. This is likely to be linked to the recent climatic changes and, undoubtedly, with global warming.
15038037 Lara, M. J. (University of Alaska Fairbanks, Institute of Arctic Biology, Fairbanks, AK); McGuire, A. D.; Euskirchen, E. S.; Genet, H.; Sloan, Victoria L.; Iversen, C. M.; Norby, R. J.; Zhang, Y. and Yuan, F. Changes in landscape-level carbon balance of an Arctic Coastal Plain tundra ecosystem between 1970-2100, in response to projected climate change [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B44B-04, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Northern permafrost regions are estimated to cover 16% of the global soil area and account for approximately 50% of the global belowground organic carbon pool. However, there are considerable uncertainties regarding the fate of this soil carbon pool with projected climate warming over the next century. In northern Alaska, nearly 65% of the terrestrial surface is composed of polygonal tundra, where geomorphic land cover types such as high-, flat-, and low-center polygons influence local surface hydrology, plant community composition, nutrient and biogeochemical cycling, over small spatial scales. Due to the lack of representation of these fine-scale geomorphic types and ecosystem processes, in large-scale terrestrial ecosystem models, future uncertainties are large for this tundra region. In this study, we use a new version of the terrestrial ecosystem model (TEM), that couples a dynamic vegetation model (in which plant functional types compete for water, nitrogen, and light) with a dynamic soil organic model (in which temperature, moisture, and associated organic/inorganic carbon and nitrogen pools/fluxes vary together in vertically resolved layers) to simulate ecosystem carbon balance. We parameterized and calibrated this model using data specific to the local climate, vegetation, and soil associated with tundra geomorphic types. We extrapolate model results at a 1 km2 resolution across the ~1800 km2 Barrow Peninsula using a tundra geomorphology map, describing ten dominant geomorphic tundra types (Lara et al. submitted), to estimate the likely change in landscape-level carbon balance between 1970 and 2100 in response to projected climate change. Preliminary model runs for this region indicated temporal variability in carbon and active layer dynamics, specific to tundra geomorphic type over time. Overall, results suggest that it is important to consider small-scale discrete polygonal tundra geomorphic types that control local structure and function in regional estimates of carbon balance in northern Alaska.
15037988 Lessels, Jason S. (University of Sydney, Sydney, N.S.W., Australia); Tetzlaff, D.; Dinsmore, K. J.; Street, L. E.; Dean, Joshua; Washbourne, I. J.; Billett, M. F.; Baxter, Robert; Subke, Jens-Arne and Wookey, P. A. Utilising conservative tracers and spatial surveys to identify controls on pathways and DOC exports in an Arctic catchment [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43B-0238, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Dissolved organic carbon (DOC) is typically the predominant form of carbon exported from headwater streams, it therefore represents a major carbon export from Arctic catchments. The projected deepening of thaw depth in permafrost regions, due to an increase in air temperature, may have a significant effect on the amount of DOC exported from these systems. However, quantification of the impacts of climate driven changes on DOC export are still highly uncertain. Understanding the processes controlling DOC export is therefore crucial in predicting the potential impact of projected environmental changes. The controls of DOC production and transport are heavily influenced by soil and vegetation, which are highly variable across the landscape. To completely understand these systems information regarding spatial variability of plants, soils and thaw depths must be taken into account. In this study sub-weekly sampling of DOC was undertaken throughout 2014 in a headwater (<1 km2) catchment in the Northwest Territories, Canada. Spatial surveys of soil properties, active thaw depth and normalised difference vegetation index (NDVI) were collected and used in conjunction with conservative stable water isotopes tracers and major ions to understand sources, flow pathways and timing of DOC exports from the catchment. Stable isotope tracers act as fingerprints of water allowing sources and pathways to be assessed. Observations reveal changing DOC concentrations throughout the season as the active layer deepens and the connectivity of the soils to the stream network throughout the catchment increases. Linking the DOC data with the conservative tracer response improves the identification of carbon pathways and fluxes from the soils; preliminary analysis indicates DOC is being delivered via deeper more mineral soils later in the season. The results indicate that the active layer depth has a strong influence on the amount of DOC exported from the system, independent of the amount of carbon stored in these deeper soils.
15037956 Malhotra, Avni (McGill University, Department of Geography, and Global Environmental and Climate Change Centre, Montreal, QC, Canada) and Roulet, Nigel T. Changing environmental correlates of peatland C fluxes in a thawing landscape; do transitional thaw stages matter? [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0145, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Soils of the northern permafrost regions store 50% (1672 Pg) of the world's belowground organic carbon (C). Peatlands within this region store 277 Pg as soil C and often occur as a mosaic of wetland types, each with variable sensitivity to climate change. Permafrost thaw further increases landscape heterogeneity in peatland structure and C function. While end-member stages such as fully intact or fully thawed permafrost are well studied in peatlands, C fluxes are not well constrained in transitional thaw stages that also cover a significant area of these ecosystems. Moreover, changes in the environmental correlates of C fluxes, due to thaw, are not well described and are vital to modeling future changes to C storage of permafrost peatlands. We used 10 thaw stages in a sub-arctic peatland as a space for time substitution to measure changes in CH4 and CO2 fluxes and their correlates. Growing season mean CH4 fluxes showed a large range across the thaw gradient, increasing with thaw, from -1.1 to 370.2 mg CH4 m-2 d-1. CO2 fluxes were highly variable along the thaw gradient with GPMAX (maximum gross photosynthetic CO2 capture at maximum photosynthetically active radiation; PAR) ranging from 2.4 to 8.2 mmol CO2 m-2 s-1. Across the site, we found significant relationships of C fluxes with the correlates: water table depth, thaw depth, temperature, PAR, vascular green area and water chemistry parameters. Within individual thaw stages, strengths of bivariate environment-C flux correlations changed inconsistently as the thaw progressed. A notable exception, temperature sensitivity of CH4 fluxes, increased linearly with thaw, suggesting a shift from substrate to temperature limitation. However, C fluxes have multiple and interactive controls that are not adequately described by bivariate analyses. We found that interactive effects on C fluxes changed variably along the thaw gradient, showing that transitional stage dynamics differ unpredictably from adjacent or end-member stages. Our results suggest that transitional stages contribute to the large variability of C fluxes in a thawing landscape and may require variable parameterization in models estimating C fluxes from abiotic and biotic controls.
15037993 Matveev, Alex (Laval University, Centre d'E2.tudes Nordiques, Quebec City, QC, Canada); Vincent, Warwick F. and Laurion, Isabelle. Factors contributing to high CH4 and CO2 efflux rates from thermokarst lakes in the rapidly warming Hudson Bay region [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43B-0243, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Thermokarst lakes and ponds that form on thawing permafrost landscapes have long been recognized as biogeochemical reactors that emit significant amounts of CH4 and CO2. However, there is considerable uncertainty in the exact contribution of these water bodies to the global carbon cycle, in large part because of the paucity of observations from different ecosystem types across the circumpolar North, and the incomplete understanding of factors that control the balance between methane production (methanogenesis) and loss (methanotrophy). The aim of our research was to address these gaps by focusing on thermokarst lakes in subarctic Canada (eastern Hudson Bay), primarily at the southern limit of permafrost that is experiencing rapid warming, but where limnological changes have received little attention to date. Thermokarst lakes were sampled at five geographical locations that differed in their degree of permafrost degradation, as well as in carbon content and lability. All sampled lakes were supersaturated with CH4, with epilimnetic concentrations varying from CO2 undersaturation in turbid mineral (lithalsa) lakes of the continuous and discontinuous permafrost landscapes, to oversaturation by several orders of magnitude of both CO2 and CH4 in the organic-rich (palsa) lakes, especially in the areas of highly degraded permafrost at its southern limit. Concentrations and fluxes of CH4 and CO2 in these palsa lakes were at or above the highest values reported for thermokarst waters elsewhere. In addition, methane oxidation experiments showed high rates of methanotrophy that substantially reduced the net emission of CH4 from both lithalsa and palsa lake types. Our results imply that subarctic thermokarst lakes, especially those at the northward migrating permafrost margin, may be a major source of greenhouse gases as the circumpolar North continues to warm.
15037963 McFarlane, K. J. (Lawrence Livermore National Laboratory, Livermore, CA); Throckmorton, H. and Guilderson, T. P. Age of dissolved organic carbon across an Arctic landscape [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B41O-04, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
The Arctic is particularly vulnerable to climate change. Systems there currently experience a balance between frozen and thawed conditions and the proportion of frozen and thawed conditions are expected to change with increasing temperatures and changes in snowfall. Increased temperatures will make these frozen stocks of carbon, much of it labile, vulnerable to decomposition and translocation. Most studies on the carbon balance of terrestrial ecosystems have focused on gaseous fluxes of carbon to the atmosphere, but numerous studies have shown that production and loss of dissolved carbon can be a crucial mechanism for high-latitude ecosystem carbon loss that results in considerable export off the Arctic landscape and may reduce or eliminate terrestrial carbon sinks. In addition, hydrological vertical transport of DOC is an important process in permafrost areas. In collaboration with the NGEE-Arctic study, we measured 14C of DOC from surface waters and from shallow and deep subsurface porewater collected from various locations in the Barrow Arctic Ocean Observatory (BAO) including different drainage locations and thawed lake basins of varying age. Locations were sampled in July and September 2013 to assess changes in 14C-DOC across the landscape and from early and late summer. Preliminary results suggest that DOC in surface and pore water increases in age with depth and across the growing season. These patterns as well as patterns across the landscape will be presented and discussed.
15037939 Oshurkova, V. (Institute of Biochemistry and Physiology of Microorganisms, Russian Federation); Kholodov, A. L.; Spektor, Valentin; Sherbakova, V. and Rivkina, E. The effect of sedimentation conditions of frozen deposits at the Kolyma lowland on the distribution of methane and microorganisms activity [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0123, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Biogeochemical and microbiological investigations of methane distribution and origin in Northeastern Arctic permafrost sediments indicated that microbial methane production was observed in situ in thawed and permanently frozen deposits (Rivkina et al., 2007). To check the hypothesis about the correlation between permafrost ground type and quantity of methane, produced by microorganisms, the samples from deposits of thermokarst depression (alas), Yedoma and fluvial deposits of Kolyma floodplain for gas measurements and microbiological study were collected and the experiment with anaerobic incubation was conducted. Gas analysis indicated that alas and floodplain samples were characterized by high methane concentrations whereas Yedoma samples had only traces of methane. Two media with different substrates were prepared anaerobically for incubation. First medium contained sucrose as a substrate for hydrolytic microflora and the second one contained acetate as a substrate for methanogens. Two samples from alas, one sample from Yedoma and one from floodplain were placed in anaerobic bottles and media under gas mixture (N2, CO2 and H2) were added. The bottles were incubated for 2 weeks at room temperature. The results of the experiment showed that there was the increase of methane concentrations in the bottles with Yedoma and Floodplain samples to 52-60 and 67-90%, respectively, from initial concentrations in contrast with Alas sample inoculated bottles. At the same time the concentration of methane in control bottles, which did not include substrates, increased to 15-19%. Current research is a part of NSF funded project "The Polaris".
15037934 Phoenix, G. K. (University of Sheffield, Sheffield, United Kingdom); Fisher, J. P.; Estop-Aragones, C.; Thierry, Aaron; Hartley, I. P.; Murton, J. B.; Charman, D. J. and Williams, M. Influence of plant communities on active layer depth in Boreal forest [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0118, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Vegetation plays a crucial role in determining active layer depth (ALD) and hence also the extent that permafrost may thaw under climate change. Such influences are multifaceted and include, for example, promotion of shallow ALD by insulation from moss or shading by plant canopies in summer, or trapping of snow in evergreen tree canopies that reduces snow insulation of soil in winter. However, while the role of different vegetation components are understood at a conceptual level, quantitative understanding of the relative importance of different vegetation components and how they interact to determine active layer depth is lacking. In addition, major abiotic factors such as fire and soil hydrological properties will considerably influence the role of vegetation in mediating ALD, though again this is not well understood. To address this we surveyed multiple plots across 4 sites of contrasting vegetation and fire status, including a range of soil moisture and organic matter thickness, in the discontinuous permafrost zone near Yellowknife, NT, Canada. In each plot we measured ALD and a range of vegetation and soil parameters to understand how key characteristics of the understory and canopy vegetation, and soil properties influence ALD. Measurements included moss depth, tree canopy LAI, understory LAI, understory height, vegetation composition, soil organic matter depth, slope and soil moisture. By undertaking these surveys in sites with contrasting hydrological conditions in both burned and unburned areas we have also been able to determine which characteristics of the vegetation and soil are important for protecting permafrost, which characteristics emerge as the most important factors across sites (i.e. irrespective of site conditions) and which factors have site (ecosystem) specific influences. This work provides a major insight into how ecosystem properties influence ALD and therefore also how changes in ecosystems properties arising from climate change may influence ALD and permafrost thaw.
15037943 Schade, J. D. (St. Olaf College, Northfield, MN); Natali, S.; Spawn, S.; Sistla, S. and Schuur, E. A. G. Impact of warming and drying on microbial activity in subarctic tundra soils; inferences from patterns in extracellular enzyme activity [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0127, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Permafrost contains a large pool of carbon that has accumulated for thousands of years, and remains frozen in organic form. As climate warms, permafrost thaw will increase rates of microbial breakdown of old soil organic matter (SOM), accelerating release of carbon to the atmosphere. Higher rates of microbial decomposition may also release reactive nitrogen, which may increase plant production and carbon fixation. The net effect on atmospheric carbon, and the strength of climate feedback, depends on the balance between direct and indirect effects of increased microbial activity, which depends on changes in soil conditions and microbial responses to them. In particular, soil moisture and availability of C and N for microbes strongly influence soil respiration and primary production. Current understanding of changes in these factors as climate warms is limited. We present results from analysis of soil extracellular enzyme activities (EEA) from a long-term warming and drying experiment in subarctic Alaskan tundra (the CiPEHR experiment) as an indicator of changes in soil microbial activity and relative availability of C and N for microbes. We collected soil samples from control (C), warming (W), and warming + drying (WD) treatments and used fluorometric methods to estimate EEA in shallow (0-5 cm) and deep (5-15) soils. We measured soil moisture, SOM, and C:N, and plant tissue C:N as an indicator of N availability. Activity of N-acquiring enzymes was higher in WD soils at both depths. Carbon EEA in W soils was lower in surface, but higher in deeper soils. We also found significantly lower soil C:N in both W and WD in deeper soils, where C:N was generally lower than surface. In general, EEA results suggest drying leads to increased C availability relative to N. This may be due to lower soil moisture leading to greater aeration of soils in WD plots relative to W plots, which may be saturated due to significant land subsidence. Greater aeration may increase efficiency of carbon use by microbes, effectively increasing carbon availability for microbes in WD soils relative to W soils. This suggests that drying may reduce N recycling by microbes, potentially reducing plant production and increasing soil respiration relative to carbon fixation, increasing the likelihood that permafrost thaw will be a positive feedback on climate change.
15037926 Siewert, Matthias B. (Stockholm University, Stockholm, Sweden); Hanisch, Jessica; Weiss, Niels; Kuhry, Peter and Hugelius, Gustaf. Total storage and landscape partitioning of soil organic carbon and phytomass carbon in Siberia [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0107, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
We present results of detailed partitioning of soil organic carbon (SOC) and phytomass carbon (PC) from two study sites in Siberia. The study sites in the Tundra (Kytalyk) and the Taiga (Spasskaya Pad) reflect two contrasting environments in the continuous permafrost zone. In total 57 individual field sites (24 and 33 per study site respectively) have have been sampled for SOC and PC along transects cutting across different land covers. In Kytalyk the sampling depth for the soil pedons was 1 m depth. In Spasskaya Pad where the active layer was significantly deeper, we aimed for 2 m depth or tried to include at least the top of the permafrost. Here the average depth of soil profiles was 152 cm. PC was sampled from 1´1 m ground coverage plots. In Spasskaya Pad tree phytomass was also estimated on a 5´5 m plot. The SOC storage was calculated separately for the intervals 0-30 cm, 30-100 cm and 100-200 cm (the latter only for Spasskaya Pad), as well as for organic layer vs. mineral soil, active layer vs. permafrost and for cryoturbated soil horizons. Landscape partitioning was performed by thematic up-scaling using a vegetation based land cover classification of very high resolution (2´2 m) satellite imagery. Non-Metric Multidimensional Scaling (NMDS) was used to explore the relationship of SOC with PC and different soil and permafrost related variables. The results show that the different land cover classes can be considered distinct storages of SOC, but that PC is not significantly related to total SOC storage. At both study sites the 30-100 cm SOC storage is more important for the total SOC storage than the 0-30 cm interval, and large portions of the total SOC are stored in the permafrost. The largest contribution comes from wetland pedons, but highly cryoturbated individual non-wetland pedons can match these. In Kytalyk the landscape partitioning of SOC mostly follows large scale geomorphological features, while in Spasskaya pad forest type also has a large influence.
15038030 Smith, L. C. (University of California at Los Angeles, Los Angeles, CA). Importance of West Siberian peatlands to global carbon and water cycles [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B44A-01, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Russia's West Siberian Lowland (WSL) contains nearly 600,000 km2 of peatlands with depth >0.5 m, the most extensive such deposits in the world. These peatlands impact the global carbon cycle, representing an important CH4 source and net CO2 sink since the early Holocene. However, together with other Arctic and sub-Arcticpeatlands, the likely responses of WSL peatlands to warming climate and associated permafrost degradation are a subject of ongoing study and debate. Of prime interest is whether WSL peatlands may switch from a net carbon sink to source, especially in permafrost peatlands. Climate models predict warmer temperatures, longer growing seasons, and enhanced precipitation which should increase net primary productivity and litter production, but also soil microbial decomposition, increasing release of sequestered carbon through outgassing of CH4 and/or CO2 to the atmosphere. Projecting the net outcome of these opposing ecosystem processes on carbon sink/source status requires is difficult, and given strong N-S temperature and permafrost gradients across the WSL, the response will likely vary geographically. Hydrological status is deeply important because aerobic dry peats emit a greater fraction of CO2 whereas anaerobic wet peats predominately release CH4. A first estimate of subsurface water storage in WSL peatlands suggests they may hold ~1,200 km3 of liquid-water equivalent (~2 m), a large number that is roughly triple the annual flow of water in the Ob' River. New models, observations, and synthesis are needed to confidently project the future role of this important region to global carbon and water cycles.
15037973 Sweeney, Colm (NOAA, Earth System Research Laboratory, Boulder, CO); Dlugokencky, Ed J.; Wofsy, S. C.; Karion, Anna; Miller, Charles E.; Dinardo, Sreven J.; Bruhwiler, Lori and Miller, John B. Changes in long term CH4 fluxes from the Alaskan North Slope based on a sector analysis of Barrow CH4 mole fraction measurements [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B42D-02, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Large enhancements in CH4 over the north slope measured by the NASA Carbon in Arctic Reservoirs Vulnerability Experiment (CARVE) aircraft have motivated a detailed sector analysis of CH4 mole fraction measured by NOAA's Baseline Observatory site at Barrow, AK since 1986. This analysis shows that there is a very strong seasonal cycle in the CH4 mole fraction when winds are coming from the southern sector, which peaks in August and September each year with average enhancements of ~80 ppb. Despite many suggestions from other recent studies that CH4 emissions should be significantly enhanced in this region, our analysis indicates that emissions from the North Slope have not increased since the start of the measurement record. However, large enhancements in the CH4 mole fraction originating from the North Slope are correlated with increases in the mean air temperature coming from the same air masses, suggesting that with continued increases in North Slope surface temperatures, CH4 emissions from permafrost will increase in the North Slope as predicted.
15037940 Theberge, Julian (Western Washington University, Bellingham, WA); Schade, J. D.; Fiske, G. J.; Loranty, M. M. and Zimov, N. Changes in dissolved carbon and nitrogen concentrations along a hill slope flow path in Siberian Arctic tundra [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0124, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Permafrost soils contain a large pool of carbon that has accumulated for thousands of years, and remains frozen in organic form. As climate warms, permafrost thaw will lead to active cycling of old organic materials, possibly leading to release of carbon to the atmosphere or to export of organic carbon to the oceans. Organic matter breakdown may also release reactive forms of nitrogen, which may significantly impact ecosystem processes. We currently have limited understanding of where in Arctic landscapes breakdown of organic materials will occur, or whether this will influence the strength and direction of feedback loops that may occur in response to changes in C and N cycling. In this work, we studied changes in dissolved forms of C and N in water moving down a hillslope linking upland terrestrial environments to lowland floodplains within the Kolyma River watershed in the East Siberian Arctic tundra in July, 2014. The hill slope consisted of a mosaic of dry and saturated soils, generally with drier soils on the periphery and saturated soils in and around pools or short reaches of flowing surface water. We established transects at regular intervals downslope, installing wells in the center of the flow path and 5 meters laterally north and south. We analyzed pore-water from wells and surface water from pools at each transect for dissolved organic carbon (DOC) and total dissolved nitrogen (TDN). We used patterns in water chemistry to develop a conceptual model for biogeochemical changes as water moved downslope through soils, pools and runs. Pore-water analysis showed significantly higher DOC in lateral wells than in surface water and pore water in the center of the flow path, suggesting possible processing of C as water moves laterally towards the valley bottom. In contrast, DOC increased modestly down the center of the flow path, suggesting either higher hydrologic inputs or production of new DOC downslope. TDN concentration decreased downslope, suggesting processing by microbes or uptake by grasses which dominated the valley bottom. Together these patterns suggest N limitated microbial processes or plant production, which may increase organic C export to downstream ecosystems. If general, this pattern would have significant implications for future climate feedbacks from C released as permafrost thaws.
15038028 Tucker, C. (University of Alaska Fairbanks, Fairbanks, AK); Euskirchen, E. S.; Genet, H.; McGuire, A. D.; Rupp, S. T.; Breen, A. L.; Kurkowski, T. A.; Bennett, A. and Kofinas, Gary. Modeled changes in terrestrial C storage on the Arctic coastal plain of Alaska suggest a mid-century 21st shift from C sink to source [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43J-07, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Arctic tundra contains significant carbon (C) stocks, which are likely to change in response to climate change, depending on the balance of plant production and decomposition responses to warming and thawing permafrost. We modeled terrestrial C over the period 1901-2100 in a 67,000 km2 region of the eastern Arctic Coastal Plain of Alaska with four dominant vegetation types: wet sedge, tussock, shrub and heath tundra. The Terrestrial Ecosystem Model (TEM) is a biogeochemical model that simulates the C and N dynamics of vegetation and soils in response to climatic drivers. The version of TEM used here includes a dynamic organic soil module that allows the size of the organic soil layer to change through time. We model historical (1900-2010) and future (2010-2100) dynamics for low, intermediate and high CO2 emissions scenarios. During the period 2000-2010, modeled net primary productivity and vegetation C were significantly positively correlated with the MODIS derived normalized difference vegetation index, as were the start and end of the growing season, and the duration of the snow-covered season. Between 1900 and 2100, C storage in vegetation increased most in shrub and tussock tundra (52% and 43%, respectively) and somewhat less in wet sedge and heath tundra (15% and 21%, respectively), consistent with observed expansion of shrubby biomass across the region. Simulated terrestrial C storage for the study region changed from 40.5 kg C m-2 (soil=39.6, vegetation=1.0) in 1901 to 42.2 kg C m-2 (soil=40.9, vegetation=1.2) in 2010. In the intermediate warming scenario, by 2050, the total terrestrial C storage in the study region increased by 0.5 kg C m-2 but by 2100, 60% of this new C storage was lost, indicating a shift from net C uptake to net C loss in the study region toward the end of the century, driven by a shift in the relative magnitudes of C inputs from litter and losses from heterotrophic respiration. These changes were correlated with a 21 day increase in growing season length and ~20 cm increase in active layer depth between 2010 and 2100, yet the entire region maintained continuous permafrost. These changes suggest the eastern Arctic Coastal Plain of Alaska will serve as a net C sink for several more decades before becoming a C source later in the century.
15037950 Walter Anthony, K. M. (University of Alaska Fairbanks, Water and Environmental Research Center, Fairbanks, AK); Zimov, S. A.; Grosse, Guido; Jones, Miriam; Anthony, Peter; Chapin, Terry; Finlay, J. C.; Mack, M. C.; Davydov, S. P.; Frenzel, P. and Frolking, Steve E. Shift of thermokarst lakes from methane source to climate-cooling carbon sink [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0138, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Thermokarst lakes formed across vast regions of Siberia and Alaska during the last deglaciation and are thought to be a net source of atmospheric methane and carbon dioxide during the Holocene. However, the same thermokarst lakes can also sequester carbon, and it remains uncertain whether carbon uptake by thermokarst lakes can offset their greenhouse gas emissions. Here we use field observations of Siberian permafrost exposures, radiocarbon dating and spatial analyses to quantify Holocene carbon stocks and fluxes in lake sediments overlying thawed Pleistocene-aged permafrost. We find that carbon accumulation in deep thermokarst-lake sediments since the last deglaciation is about 1.6 times larger than the mass of Pleistocene-aged permafrost carbon released as greenhouse gases when the lakes first formed. While methane and carbon dioxide emissions following thaw lead to immediate radiative warming, carbon uptake in peat-rich sediments occurs over millennial time scales. With the help of an atmospheric perturbation model we assess thermokarst-lake carbon feedbacks to climate and find that thermokarst basins switched from a net radiative warming to a net cooling climate effect about 5000 years ago. High rates of Holocene carbon accumulation in lake sediments (47±10 g C m-2 a-1, mean ± SE, n=20 lakes) were driven by thermokarst erosion and deposition of terrestrial organic matter, by nutrient release from thawing permafrost that stimulated lake productivity and by slow decomposition in cold, anoxic lake bottoms. When lakes eventually drained, permafrost formation rapidly sequestered sediment carbon. Our estimate of about 160 Pg of Holocene organic carbon in deep lake basins of Siberia and Alaska increases the circumpolar peat carbon pool estimate for permafrost regions by over 50 percent. The carbon in perennially-frozen drained lake sediments may become vulnerable to mineralization as permafrost disappears, potentially negating the climate stabilization provided by thermokarst lakes during the late Holocene.
15037974 Weiss, Niels (Stockholm University, Stockholm, Sweden); Kuhry, Peter and Hugelius, Gustaf. The influence of thermokarst on potential decomposability of soil organic matter in a Taiga and tundra setting in NE Russia [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B42D-03, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Permafrost regions play a key role in global carbon budgets because of the size and vulnerability of their soil organic carbon (SOC) stock. Climate change is expected to raise soil temperatures resulting in an increased soil organic matter (SOM) source available for decomposition. Mineralized in the form of greenhouse gasses (GHG), this carbon can cause a positive feedback for further climate change. Thermokarst lake formation show a cyclic behaviour starting with ice melt, lowering of the permafrost table, ground surface subsidence, the formation of wetlands and eventually thermokarst lakes. In time, these lakes often drain either by proceeding permafrost degradation and talik formation, or by being cut into by another water body or drainage channel. The potential decomposition (quality) of SOM is of great importance to predict potential GHG release from permafrost regions and model global climate scenarios. Thermokarst development is often considered an important factor in permafrost degradation and increasing availability of SOM for decomposition. However, the influence of past thermokarst events and thus episodes of increased decomposition, is less understood. What is the difference in SOM between sites that have undergone former thermokarst cycles and sites that have not? Will there be a different response in decomposition upon climate change for these different land surface types? Two Siberian field sites, Spasskaya Pad (boreal forest) and Kytalyk (tundra), both with extensive active and relict thermokarst features, have been sampled. Simple geochemical characteristics that might be indicative of potential decomposition have been determined for all groups and will be compared. A comparison of results from permafrost affected and intact areas are presented and discussed.
15037966 Wu, Y. (Lawrence Berkeley National Laboratory, Berkeley, CA); Kneafsey, T. J.; Tas, N.; Bill, M.; Ulrich, C. and Hubbard, S. S. Controlled freeze-thaw experiments to study biogeochemical process and its effects on greenhouse gas release in Arctic soil columns [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B41O-07, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Greenhouse gas release associated with permafrost thawing is one of the largest uncertainties in future climate prediction. Improvement of such prediction relies on a better representation of the interactions between hydrological, geochemical and microbial processes in the Arctic ecosystem that occur over a wide range of space and time scales and under dynamic freeze-thaw conditions. As part of the Next Generation Ecosystem Experiments in the Arctic (NGEE-Arctic), we conducted controlled laboratory freeze-thaw experiments to study greenhouse gas release in vertical permafrost soil columns with vertically heterogeneous hydrological, geochemical and microbial properties. The studies were performed using soil cores collected from the NGEE Barrow, AK site. Two cores collected next to each other with very similar soil structures were used for the experiment. One of the cores was destructively sampled for baseline characterization, and the second core was used for the freeze-thaw experiments. The core extends from the ground surface into the permafrost with roughly 40 cm of active layer. The column was instrumented with various sensors and sampling devices, including thermocouples, geophysical (electrical) sensors, and sampling ports for solids and fluids. The headspace of the soil column was purged with CO2 free air and the gas samples were collected periodically for greenhouse gas analysis. Our initial tests simulated seasonal temperature variation from ~-10°C to +10°C at the ground surface. Our results demonstrated that temperature and geophysical data provided real time information on the freeze thaw dynamics of the column and the surface greenhouse gas fluxes correlated with the freeze thaw stages and associated hydrological and biogeochemical processes in the vertical soil column. For example, surface fluxes data revealed an early burst of GHG concentrations during the initial thawing of the surface ice rich layer of the soil, indicating the presence of trapped gases from previous season activities. In addition, the dynamics of the surface flux are closely related to the changes of the geochemical and microbial conditions during the freeze thaw processes.
15037946 Zhang, Y. (University of Alaska Fairbanks, Institute of Arctic Biology, Fairbanks, AK); Genet, H.; Lara, M. J.; McGuire, A. D.; Roach, J.; Patil, V.; Romanovsky, V. E.; Bolton, W. R. and Rutter, R. An assessment of thermokarst driven changes in land cover of the tanana flats wetland complex of Alaska from 2009 to 2100 in response to climate warming [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B31G-0133, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Ongoing climate warming has the potential to affect terrestrial ecosystems and the services they provide to local and regional communities, particularly in high latitude regions. Rising temperatures have increased permafrost vulnerability to thawing. In boreal region, ice-rich permafrost degradation may result in the subsidence of the ground surface and the transition from permafrost plateau forest to wetland ecosystems, with dramatic changes in ecosystem structure and function, e.g. vegetation composition, energy balance, and carbon and nutrient cycles. However, this disturbance is poorly represented in existing ecosystem models. A state-and-transition model, the Alaska Thermokarst Model (ATM), is being developed to predict thermokarst initiation and expansion and to keep track of the associated vegetation transitions in boreal and arctic regions. The drivers of these transitions in the boreal region are highly related to climate, topography, fire disturbance and forest fragmentation. In this study, we applied the ATM in a large wetland complex in Interior Alaska (the Tanana Flats) to predict changes in land cover associated to thermokarst from 2009 to 2100. Preliminary simulations over a 10 km´10 km area of the Tanana Flats suggests that permafrost plateau forests will decrease by 34.9% and collapse scar fens and bogs will increase by 88.3% in this region. After further testing and refinement of the ATM, a next step will be to couple the ATM with a process-based ecosystem model to evaluate the effects of thermokarst dynamics on carbon dynamics.
15038034 Zhuang, Q. (Purdue University, West Lafayette, IN). Quantifying net carbon exchanges between the atmosphere and terrestrial biosphere in the Arctic; what have we learned through decade regional modeling studies? [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B44A-06, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Observed Arctic warming has been projected to continue in this century. Permafrost degradation is thus expected to continue, exposing large amounts of carbon for decomposition. Dynamics of Arctic landscape and hydrology are complicated due to changing climate and thawing permafrost, affecting the carbon biogeochemical cycling in the region. Further, human activities together with changing climate transform the regional land use and land cover, including wildfires, logging, and agricultural land conversion. This presentation will review the effects of factors, controls, and processes as well as landscape types (e.g., forests vs. lakes) on carbon biogeochemistry based on regional modeling studies and observations. Specific effects on carbon dynamics to be discussed will include: 1) thawing permafrost; 2) fire disturbances; 2) atmospheric carbon dioxide; 3) inorganic and organic nitrogen uptake by plants; 4) priming; 5) aerobic and anaerobic organic matter decomposition; and 6) various complexities of microbial physiology of soils. Partitioning the contribution of these processes to regional carbon dynamics shall help us improve the terrestrial biogeochemistry models, an important component of Earth System Models that are used to project our future climate.
15037662 Blais-Stevens, Andrée (Geological Survey of Canada, Ottawa, ON, Canada); Lipovsky, Panya; Behnia, Pouran; Kremer, Marian and Smith, Sharon. Landslide inventory and susceptibility modeling for the Yukon Alaska highway corridor, Canada [abstr.]: in Geological Society of America, 2014 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 46(6), p. 608, 2014. Meeting: Geological Society of America, 2014 annual meeting & exposition, Oct. 19-22, 2014, Vancouver, BC, Canada.
As part of a research project to develop landslide susceptibility models, a landslide inventory has been updated for the Alaska Highway Corridor in the southern Yukon. The study area extends a distance of 873 km from Alaska to British Columbia (BC). It consists of a 40 km wide corridor centred on the highway and covers approximately 22,000 km2 (excluding portions extending into BC). The first step in landslide hazard analysis is compiling an inventory. A total of 1600 landslides were documented using a combination of air-photos mainly captured between the mid-1970s to 1990s, high resolution satellite imagery (2010), and field verification. A variety of landslide types were identified, including debris flows (32%), debris slides (32%), rockfalls/rock slides (14%), earth flows/slides (5%), and landslides triggered in permafrost, such as active layer detachment slides (ALD; 16%) and retrogressive thaw slumps (RTS; 1%). As with most inventories, this landslide inventory only represents a "snapshot" in time based on detectable geomorphological landslide signatures. The landslide inventory map was used to validate qualitative landslide susceptibility models for debris flows, rockfall/rockslides, and ALD. Some of the limits to validation were the signature, or lack thereof, of the deposit and/or its initiation zone. For example: ALD and RTS re-vegetate rapidly leading to a relatively short geological signature; changing permafrost conditions in recent decades may have altered the frequency of ALD and RTS; small landslides may not be visible on low resolution air photographs; and there are difficulties in resolving individual events where recurring debris flows have produced large fans which have aggraded throughout the Holocene. Nevertheless, the landslide inventory has helped characterize landslide hazards and validate the susceptibility models for the highway corridor at a preliminary level. Success rate curves, landslide susceptibility models and areas with high densities of landslides should be assessed in detail when planning infrastructure development such as roads and pipelines.
15043749 Froese, Duane G. (University of Alberta, Earth and Atmospheric Sciences, Edmonton, AB, Canada); Sanborn, Paul; Turner, Derek G.; Hidy, Alan J.; Porter, Trevor J. and Ward, Brent C. The early to middle Pleistocene transition in northwestern Canada and potential response of the Cordilleran ice sheet [abstr.]: in Geological Society of America, 2014 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 46(6), p. 654, 2014. Meeting: Geological Society of America, 2014 annual meeting & exposition, Oct. 19-22, 2014, Vancouver, BC, Canada.
One of the most remarkable features of the northern Cordilleran Ice Sheet is the record of repeated extensive glaciation in the latest Pliocene and Early Pleistocene (ca. 2.7-0.78 Ma) relative to more restricted ice during the Middle and Late Pleistocene (<780 ka). And further, the most extensive Cordilleran glaciation was also the earliest (on the basis of North Pacific ice rafting) in the late Gauss Chron (ca. 2.7-2.58 Ma). Several models have been suggested to explain these differences, including changes in atmospheric circulation and Laurentide Ice Sheet feedbacks, but the most common explanation is the influence of an uplifting Alaska Range and St. Elias Mountains to the south, forming a progressive barrier to Pacific moisture. This explanation provides a means to limit moisture to the interior during the Quaternary, but it is difficult to invoke given that the early record of permafrost (presence of periglacial structures) and multiple meteoric water isotope proxies suggest that much of the continentality of interior Alaska and Yukon was present by at least the Middle Pliocene. The most striking difference in the stratigraphic record that seems to coincide with these changes, however, is the evidence of deep weathering recorded by paleosols on drift surfaces. Paleo-Luvisols with textural B horizons (~ 20% clay) exceeding 1 m in thickness are present on multiple drift surfaces through central Yukon. These largely date to the Matuyama Chron (>0.78 Ma). Weathering of primary minerals in these relict paleosols has depleted mobile elements (Ca, Na, K) to a greater extent than in soils formed during Middle and Late Pleistocene interglacials. Other proxies, including the persistence of relict permafrost through interglacials and development of the steppe fauna, suggest more broad environmental changes across the Early to Middle Pleistocene transition across this region. The advance of the Cordilleran Ice Sheet on more deeply weathered surfaces in the late Pliocene and Early Pleistocene could have provided a means of enhancing lubrication of the bed leading to more extensive ice sheets.
15037555 Geertsema, Marten (British Columbia Ministry of Forests, Lands and Natural Resource Operations, Prince George, BC, Canada). An overview of landslide multihazard chains in British Columbia [abstr.]: in Geological Society of America, 2014 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 46(6), p. 465, 2014. Meeting: Geological Society of America, 2014 annual meeting & exposition, Oct. 19-22, 2014, Vancouver, BC, Canada.
A wide variety of common natural events in British Columbia can cause landslides. These include wildfires, rainstorms, earthquakes, permafrost degradation, sedimentation, high stream flows, and inundation. Landslides themselves, can trigger a variety of landslide types. Large landslides are often complex events. Rock falls or slides can trigger movements in soils. Rock slide-debris flow is just one example of a common complex landslide in British Columbia. Terms like "momentum transfer" and "undrained loading" are considered. Landslides can also cause other destructive non-landslide events to occur. Examples include landslide dams and their lakes, dam burst floods, and landslide displacement waves.
15031671 Porter, Trevor J. (University of Alberta, Earth and Atmospheric Sciences, Edmonton, AB, Canada); Ager, Thomas A.; Bindeman, Ilya N.; Feakins, Sarah J.; Reyes, Alberto V.; Westgate, John A. and Froese, Duane G. A similar-to-modern Pliocene climate in continental Alaska and Yukon recorded by multiple water isotope proxies; plant lipids, wood cellulose and hydrated glass shards [abstr.]: in Geological Society of America, 2014 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 46(6), p. 807, 2014. Meeting: Geological Society of America, 2014 annual meeting & exposition, Oct. 19-22, 2014, Vancouver, BC, Canada.
The Pliocene is regarded as a future climate analogue due to similar ocean-continent configurations and CO2 levels. The eastern Canadian Arctic has yielded evidence for a dramatically warmer Pliocene compared to modern, +11-16°C in some cases, but there are few records from other Arctic regions for comparison. Here we infer Pliocene temperatures in continental Alaska and Yukon from three independent water isotope proxies--leaf wax fatty acids, wood a-cellulose and hydrated glass shards. In contrast to the eastern Arctic, all lines of evidence point to a similar-to-modern Pliocene climate. A mid-Pliocene (4.3-4.6 Ma) lacustrine sequence from Fort Yukon, Alaska, yields well-preserved long-chain fatty acids (C28-C30) with dD values integrating thousands of years of annual precipitation. Likewise, the dD of hydrated glass shards of three tephra beds in the core integrate annual precipitation over millennia. Meteoric dD estimates for coeval fatty-acids and glass shards are -180 ppm (±2 ppm) and -178 ppm (±4 ppm), respectively, which equate to mean annual temperature estimates of -8°C (±7°C) and -7°C (±8°C) using a transfer function calibrated with continental North American GNIP data >50°N; reconstruction errors do not include lipid or glass fractionation uncertainties. The modern Fort Yukon mean annual temperature is -5.2°C. Wood cellulose d18O also reflects source water d18O and climate. Ch'ijee's Bluff in northern Yukon, 250 km NE from Fort Yukon, provides Pinaceae wood from Late Pliocene (ca. 3 Ma) and MIS 5e deposits with a-cellulose mean d18O values of 18.1 ppm and 18.8 ppm (±0.3 ppm), respectively, indicating comparable climates. Modern a-cellulose at the site, however, is relatively enriched with a mean of 20.5 ppm (±0.3 ppm). If the d18O offset (ca. 2 ppm) between modern and Pliocene/MIS 5e is source water-related, modern climate can be interpreted as ca. +4°C warmer, but within confidence intervals of indifference. Overall, these independent proxies argue for a regional Pliocene climate that is not appreciably different from today, consistent with sedimentological evidence for Pliocene permafrost and a predominantly boreal paleoflora in the pollen record. In turn, this suggests that the strong continentality of the region, a result of the recent uplift of the St. Elias Mountains and Alaska Range, was present by at least this time.
15040773 Barnhart, Theodore B. (University of Colorado Boulder, Institute for Arctic and Alpine Research / Department of Geography, Boulder, CO); Crosby, B. T.; Derryberry, D. R. and Rowland, J. C. Using high-temporal-resolution, repeat terrestrial LiDAR to compare topographic change detection methods and to elucidate the hydrometeorologic controls on the retreat rate and form of the Selawik retrogressive thaw slump, northwest Alaska [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract G33A-0966, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Retrogressive thaw slumps (RTS), a type of catastrophic thermokarst indicative of permafrost degradation, are forecast to increase in frequency and magnitude with a warming climate. RTS flux a disproportionate amount of sediment and nutrients to downstream ecosystems with the potential for adverse impacts. Characterizing the processes and hydrometeorologic drivers through which these features grow is necessary to better understand how these features may behave in the future. The Selawik RTS initiated in 2004 and has grown at a rate of 7-20 m/yr. In 2012, the feature was 200 m wide with a vertical headwall ~20 m high at its apex. We utilize a 58 scan repeat, ground based LiDAR data set collected over the summers of 2011 and 2012 and interval camera imagery to: (1) compare two topographic change detection methods, cloud to mesh (C2M) and the Multiscale Model to Model Cloud Comparison (M3C2) algorithm, (2) compare the error analysis techniques used with C2M and M3C2, (3) describe RTS mass loss processes, and (4) investigate the drivers of RTS retreat rate and form. We found that C2M reports higher magnitude topographic change over short time periods (~12 hours) and lower magnitude topographic change over long time periods (~20 days) when compared to M3C2. The spatially variable error analysis protocol used with M3C2 better accounts for the sources of uncertainty in point cloud data sets used for topographic change detection than C2M. TLS data from 2011 show a diel pattern in the mean retreat rate of the feature while data from 2012 show a more mixed signal. These differences are likely due to the warm, dry conditions experienced in 2011 verses the cool, wet conditions experienced in 2012. Statistical modeling indicates that RTS retreat rate and form are most sensitive to net radiation (R2 27.4%, pVal: 0.001 and R2 82.0%, pVal: <0.001, respectively). We interpret this to indicate that spallation-type mass loss processes, driven by elevated net radiation, are most effective at removing material from interstitial ice dominated RTS features. Furthermore, we find that hydrologic pathways in the tundra upslope of the feature control the cuspate form the Selawik RTS headwall.
15040577 Dou, S. (University of California, Berkeley, Earth and Planetary Science, Berkeley, CA) and Ajo Franklin, J. B. Ultrasonic measurements of unconsolidated saline sediments during freeze/thaw cycles; the seismic properties of cryopeg environments [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract C53C-05, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Saline permafrost and cryopegs (hypersaline unfrozen layers/zones within permafrost) are widespread in the Arctic coastal area as a result of marine transgression and regression in recent geological history. Owing to the freezing-point depression effect of soluble salts, they contain more unfrozen water than non-saline frozen sediments when subjected to the same permafrost temperatures (e.g., from 0 to -15 °C). Mapping subsurface cryopeg structure remains a challenging geophysical task due to the poor penetration of GPR in highly conductive fluids and related limitations for lower frequency EM techniques. Seismic profiling, particularly surface wave characterization, provides one possible approach to delineate the extent of cryopeg bodies. However, interpretation of such surveys is currently limited by the sparse database of measurements examining the seismic properties of unconsolidated materials saturated with saline fluids at sub-zero temperatures. We present the results of experiments examining seismic velocity in the ultrasonic range for both synthetic and natural permafrost sediments during freeze/thaw cycles; in these experiments, use of a range of brine salinities allows us to evaluate the properties of cryopeg sediments at in-situ conditions, a prerequisite for quantitative interpretation of seismic imaging results. Because of the abundant unfrozen water and less developed inter-granular ice structure, the seismic properties of saline permafrost typically falls between frozen and unfrozen soils. We conducted ultrasonic measurements of a freeze-thaw cycle on 20-30 Ottawa sand (grain size 590-840 mm) as well as natural mineral soils from the Barrow Environmental Observatory (BEO) saturated with brines of different salinities (0-2.5 M NaCl). For each salinity, seismic properties were measured using the ultrasonic (~1 MHz) pulse-transmission method in the temperature range from 20 to -30 °C. Similar to sediments saturated with low salinity fluids, seismic velocities increase significantly upon freezing in brine-saturated samples due to the formation of ice. However, substantial differences were observed: First, the onset of the velocity increase occurred at temperatures significantly below 0 °C (e.g., as low as -11.8 °C for 2.5 M pore-water salinity); Second, instead of having a stepwise velocity increase (temperature derivative of velocity on the order of 1000 m/s/°C) in the immediate neighborhood of the freezing-point as in non-saline samples, velocities in saline samples exhibit a gradual increase (dv/dT as low as ~70 m/s/°C) in temperatures between the freezing-point and the eutectic-point (~-25 °C) of NaCl solutions. Unusual increases in attenuation were also observed in the vicinity of freezing. Our results indicate that saline permafrost and cryopegs have distinct seismic properties when compared with their non-saline counterparts under the same thermal conditions. Moreover, the very low seismic velocities observed in this laboratory study are consistent with the low-velocity zones at Barrow, Alaska that were previously found through field-scale geophysical investigations.
15037089 Frassetto, A. (Incorporated Research Institutions for Seismology, Washington, DC); Busby, R. W.; Hafner, K.; Woodward, R. and Sauter, A. Sensor emplacement techniques and seismic noise analysis for USArray transportable array seismic stations [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract S42A-06, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
In preparation for the upcoming deployment of EarthScope's USArray Transportable Array (TA) in Alaska, the National Science Foundation (NSF) has supported exploratory work on seismic station design, sensor emplacement, and communication concepts appropriate for this challenging high-latitude environment. IRIS has installed several experimental stations to evaluate different sensor emplacement schemes both in Alaska and in the lower-48 of the U.S. The goal of these tests is to maintain or enhance a station's noise performance while minimizing its footprint and the weight of the equipment, materials, and overall expense required for its construction. Motivating this approach are recent developments in posthole broadband seismometer design and the unique conditions for operating in Alaska, where there are few roads, cellular communications are scarce, most areas are only accessible by small plane or helicopter, and permafrost underlies much of the state. We will review the methods used for directly emplacing broadband seismometers in comparison to the current methods used for the lower-48 TA. These new methods primarily focus on using a portable drill to make a bored hole three to five meters, beneath the active layer of the permafrost, or by coring 1-2 meters deep into surface bedrock. Both methods are logistically effective in preliminary trials. Subsequent station performance has been assessed quantitatively using probability density functions summed from power spectral density estimates. These are calculated for the continuous time series of seismic data recorded for each channel of the seismometer. There are five test stations currently operating in Alaska. One was deployed in August 2011 and the remaining four in October 2012. Our results show that the performance of seismometers in Alaska with auger-hole or core-hole installations can sometimes exceed that of the quietest TA stations in the lower-48, particularly horizontal components at long periods. A comparison of the performance of the various installations is discussed.
15040578 Shiklomanov, N. I. (George Washington University, Geography, Washington, DC); Streletskiy, D. A.; Nelson, F. E. and Little, J. Isotropic thaw subsidence in natural landscapes of northern Alaska [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract C53C-07, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Recent research documents warming of permafrost, increased emissions of greenhouse gases in permafrost regions, and damage to civil infrastructure induced by melting of ground ice. Particular attention has been focused on "thermokarst terrain," localized systems of irregular pits, mounds, and ponds caused by differential subsidence accompanying thaw of ice-rich permafrost. Development of thermokarst terrain is often triggered by discrete, geographically constrained disturbance of vegetative cover or hydrological patterns. Here, we describe landscape-scale, thaw-induced subsidence in northern Alaska lacking the topographic contrasts associated with thermokarst terrain. Observations in some regions of the Arctic reveal little correlation between increasing air temperature and active-layer thickness (ALT) above permafrost in undisturbed terrain. The apparent stability of ALT in many Arctic landscapes may, however, be illusory if thaw penetrates into an ice-rich layer underlying the long-term base of the active layer. The apparent stability in ALT is attributable to the presence in many permafrost regions of an ice-rich "transition layer" that resists thaw owing to the large amounts of latent heat involved in melting it. During warm summers, this layer protects underlying permafrost from thaw and creates nonlinearities in the response of the permafrost system to climatic forcing. We sought to determine whether widespread, relatively homogeneous, decadal-scale thaw subsidence, possibly attributable to climatic change, is occurring in natural, undisturbed landscapes and, if so, to estimate its magnitude and evaluate its role in the response of permafrost to atmospheric forcing. Field investigations designed to track interannual vertical movements associated with formation and ablation of ice near the permafrost table were begun in the summer of 2001 and continued annually at two 1 ha Circumpolar Active Layer Monitoring (CALM) sites representative of landscapes in the Arctic Coastal Plain and Arctic Foothills physiographic provinces of northern Alaska. Observations were conducted at the end of the thawing season with high-resolution differential GPS equipment, using a four-stage nested sampling design that provides full geographic representation of surface cover types and microtopographic elements within each sampling area. Both sampling areas experienced net subsidence of the ground surface over the period of observation. The record of temperature and vertical movement at the ground surface indicates that penetration of thaw into the transition layer has produced relatively uniform subsidence extending over entire landscapes. Without specialized observation techniques the subsidence is not apparent to observers at the surface. Integrated over extensive regions, this "isotropic thaw subsidence" may be responsible for thawing large volumes of carbon-rich substrate, and could have negative impacts on infrastructure.
15037984 Throckmorton, H. (Los Alamos National Laboratory, Los Alamos, NM); Perkins, G.; Muss, J. D.; Smith, Lydia J.; Conrad, M. E.; Torn, M. S.; Heikoop, J. M.; Newman, B. D.; Wilson, C. J. and Wullschleger, S. D. Pathways and transformations of dissolved methane and dissolved inorganic carbon in Arctic tundra soils; evidence from analysis of stable isotopes [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract B43B-0234, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
Arctic soils contain a large pool of terrestrial C and are of great interest because of their potential for releasing significant amounts of carbon dioxide (CO2) and methane (CH4) to the atmosphere. Few attempts have been made, however, to derive quantitative budgets of CO2 and CH4 budgets for high-latitude ecosystems. Therefore, this study used naturally occurring geochemical and isotopic tracers to estimate production pathways and transformations of dissolved inorganic carbon (DIC=S (total) dissolved CO2) and dissolved CH4 in soil pore waters from 17 locations (drainages) in Barrow, Alaska (USA) in July and September, 2013; and to approximate a complete balance of belowground C cycling at our sampling locations. Results suggest that CH4 was primarily derived from biogenic acetate fermentation, with a shift at 4 locations from July to September towards CO2 reduction as the dominant methanogenic pathway. A large majority of CH4 produced at the frost table methane was transferred directly to the atmosphere via plant roots and ebullition (94.0±1.4% and 96.6±5.0% in July and September). A considerable fraction of the remaining CH4 was oxidized to CO2 during upward diffusion in July and September, respectively. Methane oxidization produced <1% of CO2 relative to alternative production mechanisms in deep subsurface pore waters. The majority of subsurface CO2 was produced from anaerobic respiration, likely due to reduction of Fe oxides and humics (52±6 to 100±13%, on average) while CO2 produced from methanogenesis accounted for the remainder (0±13% to 47±6%, on average) for July and September, respectively. Dissolved CH4 and dissolved CO2 concentrations correlated with thaw depth, suggesting that Arctic ecosystems will likely produce and release a greater amount of greenhouse gasses under projected warming and deepening of active layer thaw depth under future climate change scenarios.
15038679 Hayes, L. J. (University of Wisconsin, Department of Geography, Madison, WI) and Mason, J. A. Soil development on strath terraces as influenced by terrace relative age and aeolian processes, Laramie Basin, WY [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract EP53A-0751, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Soil chronosequences were recorded for the Late Quaternary aeolian mantle capping a suite of Pleistocene strath terraces in the Laramie Basin, WY. Concurrently, samples for optically stimulated luminescence (OSL) dating were collected to constrain dates indicated by soil morphology, carbonate stages, and pedogenic observations. Results show that the measured OSL dates align with the documented degree of soil development within the aeolian mantle. Additionally, pedogenesis is related to fluctuations in soil forming factors and is not related to terrace age or height. The thickness of the mantle varies widely across the terraces and shows considerable evidence of alteration through cryoturbation, bioturbation, denudation, and re-deposition. The basin is littered with evidence of relict frost patterned ground and ice wedge casts along with blowouts, deflations structures, and small dunes. Hence, on each terrace, OSL dates fall between Late Pleistocene to Holocene (15 ka-2.5 ka) thus proving the existence of an unconformity with the suite of Early to Middle Pleistocene strath terraces (1.4 ma-400 ka). Therefore, the degree of soil morphology is also related to mantle thickness and not to terrace age or height. The results of this study show three important outcomes. Firstly, that the Laramie Basin is situated within a dynamic aeolian environment where deposition and erosion of the soil mantle is occurring at a high rate, but is not related to terrace age or height. Secondly, soil development is related to aeolian mantle thickness and not to terrace age or height. Thirdly, dates obtained provide evidence that OSL is a reliable technique for quantifying pedogenesis and, therefore, stability of a landscape cannot be assumed. Consequently, this study stresses the importance of field-based research in geomorphology.
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