July 2017 Permafrost Alert
The U.S. Permafrost Association is pleased to announce the availability of an updated searchable database on permafrost-related publications. The American Geosciences Institute, with support from the National Science Foundation, has “migrated” the previous Cold Regions Bibliography to a new platform. Included are the US Permafrost Association supported Monthly Permafrost Alerts dating back to 2011. The Bibliography is searchable at : www.coldregions.org.
Have a look for your favorite topic, location and/or author. For example, a search using “permafrost” and “Barrow” found 146 references dating back to at least 1952 and up to the more recent September 2015 Seventh Canadian Permafrost Conference.
The individual Monthly Permafrost Alerts are found on the US Permafrost Association website : http://www.uspermafrost.org/monthly-alerts.shtml.
Browse by Reference Type:
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2017064683 González-Guzmán, A. (Universidad de Córdoba, Departamento de Agronomia, Spain); Oliva, M.; Souza-Junior, V. S.; Pérez-Alberti, A.; Ruiz-Fernández, J. and Otero, X. L. Biota and geomorphic processes as key environmental factors controlling soil formation at Elephant Point, maritime Antarctica: Geoderma, 300, p. 32-43, illus. incl. 2 tables, sketch map, 94 ref., August 15, 2017.
We examined the main soil forming factors affecting the soil composition, soil properties and the associated soil-forming processes at Elephant Point, a small ice-free environment in the South Shetland Islands, Maritime Antarctica. For this purpose, we collected twenty soil samples from each of ten different sites distributed along a linear transect running from the coast to the front of the Rotch Dome glacier. The samples were obtained from surface layers (0-10 cm) and at depth (40-50 cm), although collection was limited in the moraine area by the permafrost table. We determined pH, electrical conductivity, size particle distribution, total organic carbon, total nitrogen and total concentrations of Al, Fe, Ca and P, for physical and chemical characterization of the samples. We also analysed the samples to determine the bioavailability of nutrients and Fe, Al and P partitioning and finally examined them by isotopic (d15N) and X-ray diffraction (XRD) analysis. The results of the analyses revealed two clear geochemical environments corresponding to the two most extensive geomorphological units in this peninsula: moraine and marine terraces. Soils from the moraine were characterized by alkaline reaction and high quantity of minerals with a low degree of crystallinity, whereas soils from the marine terraces showed acid reaction, high concentration of organometallic complexes and a high diversity of phosphate minerals (taranakite, minyulite, struvite, hydroxylapatite and leucophosphite), which seem to be generated by phosphatization of faecal matter deposited by seabirds and seals. Consequently, biota activity is the most relevant soil differentiating factor in the marine terraces, which add organic matter and activate geochemical cycles. On the other hand, geomorphic processes strongly affected by physical weathering processes such as glacial abrasion (by grinding process), frost shattering, and wind abrasion are the main soil-forming factors in moraine. These forces break up the parent material, transform it and translocate the products formed.
2017064685 Mishra, Umakant (Argonne National Laboratory, Environmental Science Division, Argonne, IL); Drewniak, Beth; Jastrow, Julie D.; Matamala, Roser M. and Vitharana, U. W. A. Spatial representation of organic carbon and active-layer thickness of high latitude soils in CMIP5 earth system models: Geoderma, 300, p. 55-63, illus. incl. 3 tables, sketch maps, 63 ref., August 15, 2017.
Soil properties such as soil organic carbon (SOC) stocks and active-layer thickness are used in earth system models (ESMs) to predict anthropogenic and climatic impacts on soil carbon dynamics, future changes in atmospheric greenhouse gas concentrations, and associated climate changes in the permafrost regions. Accurate representation of spatial and vertical distribution of these soil properties in ESMs is a prerequisite for reducing existing uncertainty in predicting carbon-climate feedbacks. We compared the spatial representation of SOC stocks and active-layer thicknesses predicted by the coupled Model Intercomparison Project Phase 5 (CMIP5) ESMs with those predicted from geospatial predictions, based on observation data for the state of Alaska, USA. For the geospatial modeling, we used soil profile observations (585 for SOC stocks and 153 for active-layer thickness) and environmental variables (climate, topography, land cover, and surficial geology types) and generated fine-resolution (50-m spatial resolution) predictions of SOC stocks (to 1-m depth) and active-layer thickness across Alaska. We found large inter-quartile range (2.5-5.5 m) in predicted active-layer thickness of CMIP5 modeled results and small inter-quartile range (11.5-22 kg m-2) in predicted SOC stocks. The spatial coefficient of variability of active-layer thickness and SOC stocks were lower in CMIP5 predictions compared to our geospatial estimates when gridded at similar spatial resolutions (24.7 compared to 30% and 29 compared to 38%, respectively). However, prediction errors, when calculated for independent validation sites, were several times larger in ESM predictions compared to geospatial predictions. Primary factors leading to observed differences were (1) lack of spatial heterogeneity in ESM predictions, (2) differences in assumptions concerning environmental controls, and (3) the absence of pedogenic processes in ESM model structures. Our results suggest that efforts to incorporate these factors in ESMs should reduce current uncertainties associated with ESM predictions of carbon-climate feedbacks.
2017064825 Celis, Gerardo (Northern Arizona University, Center for Ecosystem Science and Society, Flagstaff, AZ); Mauritz, Marguerite; Bracho, Rosvel; Salmon, Verity G.; Webb, Elizabeth E.; Hutchings, Jack; Natali, Susan M.; Schädel, Christina; Crummer, Kathryn G. and Schuur, Edward A. G. Tundra is a consistent source of CO2 at a site with progressive permafrost thaw during 6 years of chamber and eddy covariance measurements: Journal of Geophysical Research: Biogeosciences, 122(6), p. 1471-1485, illus. incl. 2 tables, 115 ref., June 2017.
Current and future warming of high-latitude ecosystems will play an important role in climate change through feedbacks to the global carbon cycle. This study compares 6 years of CO2 flux measurements in moist acidic tundra using autochambers and eddy covariance (Tower) approaches. We found that the tundra was an annual source of CO2 to the atmosphere as indicated by net ecosystem exchange using both methods with a combined mean of 105 ± 17 g CO2 C m-2 y-1 across methods and years (Tower 87 ± 17 and Autochamber 123 ± 14). The difference between methods was largest early in the observation period, with Autochambers indicated a greater CO2 source to the atmosphere. This discrepancy diminished through time, and in the final year the Autochambers measured a greater sink strength than tower. Active layer thickness was a significant driver of net ecosystem carbon exchange, gross ecosystem primary productivity, and Reco and could account for differences between Autochamber and Tower. The stronger source initially attributed lower summer season gross primary production (GPP) during the first 3 years, coupled with lower ecosystem respiration (Reco) during the first year. The combined suppression of GPP and Reco in the first year of Autochamber measurements could be the result of the experimental setup. Root damage associated with Autochamber soil collar installation may have lowered the plant community's capacity to fix C, but recovered within 3 years. While this ecosystem was a consistent CO2 sink during the summer, CO2 emissions during the nonsummer months offset summer CO2 uptake each year. Abstract Copyright (2017), . American Geophysical Union. All Rights Reserved.
2017064821 Dafflon, Baptiste (Lawrence Berkeley National Laboratory, Berkeley, CA); Oktem, Rusen; Peterson, John; Ulrich, Craig; Anh Phuong Tran; Romanovsky, Vladimir and Hubbard, Susan S. Coincident aboveground and belowground autonomous monitoring to quantify covariability in permafrost, soil, and vegetation properties in Arctic tundra: Journal of Geophysical Research: Biogeosciences, 122(6), p. 1321-1342, illus., 87 ref., June 2017.
Coincident monitoring of the spatiotemporal distribution of and interactions between land, soil, and permafrost properties is important for advancing our understanding of ecosystem dynamics. In this study, a novel monitoring strategy was developed to quantify complex Arctic ecosystem responses to the seasonal freeze-thaw-growing season conditions. The strategy exploited autonomous measurements obtained through electrical resistivity tomography to monitor soil properties, pole-mounted optical cameras to monitor vegetation dynamics, point probes to measure soil temperature, and periodic manual measurements of thaw layer thickness, snow thickness, and soil dielectric permittivity. The spatially and temporally dense monitoring data sets revealed several insights about tundra system behavior at a site located near Barrow, AK. In the active layer, the soil electrical conductivity (a proxy for soil water content) indicated an increasing positive correlation with the green chromatic coordinate (a proxy for vegetation vigor) over the growing season, with the strongest correlation (R = 0.89) near the typical peak of the growing season. Soil conductivity and green chromatic coordinate also showed significant positive correlations with thaw depth, which is influenced by soil and surface properties. In the permafrost, soil electrical conductivity revealed annual variations in solute concentration and unfrozen water content, even at temperatures well below 0°C in saline permafrost. These conditions may contribute to an acceleration of long-term thaw in Coastal permafrost regions. Demonstration of this first aboveground and belowground geophysical monitoring approach within an Arctic ecosystem illustrates its significant potential to remotely "visualize" permafrost, soil, and vegetation ecosystem codynamics in high resolution over field relevant scales. Abstract Copyright (2017), . American Geophysical Union. All Rights Reserved.
2017058665 Kokh, Svetlana N. (Russian Academy of Sciences, V. S. Sobolev Institute of Geology and Mineralogy, Novosibirsk, Russian Federation); Sokol, Ella V.; Deev, Evgeny V.; Ryapolova, Yuliya M.; Rusanov, Gennady G.; Tomilenko, Anatoliy A. and Bul'bak, Taras A. Post-late glacial calcareous tufas from the Kurai fault zone (southeastern Gorny Altai, Russia): Sedimentary Geology, 355, p. 1-19, illus. incl. 4 tables, geol. sketch maps, 96 ref., June 15, 2017.
Calcareous tufa deposits have been discovered in the Chibitka River valley near Lake Cheybek-Kohl, at the junction of the Kurai and Teletsk-Kurai large active faults in the southeastern Gorny Altai, Russia, at an altitude of 1800-2000 m. Fossil tufa is composed of calcite and cements Holocene grey colluvium and glacial till deposited by the Late Glacial Chibitka Glacier. Current tufa precipitation has been observed from a low-flow spring with cold (10 °C) HCO3-SO4-Ca-Mg water, rN = 6.86. The stable isotope composition of spring water is -5.8 ppm VPDB d13C of dissolved inorganic carbon and -14.5 ppm VSMOW d18O. Modern tufa consists of thin laminated Mg-calcite and Sr-aragonite crusts, with abundant algae and biofilms on their surfaces. Both modern and fossil tufas are depleted in REE (a total of 0.40-16.4 ppm and 0.40-3.80 ppm, respectively) and share similar PAAS-normalised REE + Y spectra with HREE enrichment and slight progressive LREE depletion. The modern tufas show positive d13C values of 0.1 ppm to 0.9 ppm VPDB while the fossil ones have an isotopically lighter composition of d13C = -4.1 ppm to -1.9 ppm VPDB; the d18O range is very narrow (-13.0 to -13.8 ppm VPDB). Both stable isotope and trace-element signatures (including REE patterns) of the tufas indicate precipitation from cold groundwaters subjected to prolonged interaction with a carbonate aquifer (the Baratal Group of limestone and dolostone) in a cold continental climate similar to the present conditions. Tufa deposition in the Lake Cheybek-Kohl area began with the onset of post-Late Glacial global warming and permafrost degradation. Unlike the fossil tufa formation, current precipitation of freshwater carbonates has been microbially mediated. The discovered tufa deposits provide new palaeoclimatic and active tectonic proxies in the southeastern Gorny Altai.
2017064818 Ebrahimi, Ali (Eidgenössische Technische Hochschule Zürich, Department of Environmental Systems Science, Zurich, Switzerland) and Or, Dani. Mechanistic modeling of microbial interactions at pore to profile scale resolve methane emission dynamics from permafrost soil: Journal of Geophysical Research: Biogeosciences, 122(5), p. 1216-1238, illus., 164 ref., May 2017.
The sensitivity of polar regions to raising global temperatures is reflected in rapidly changing hydrological processes associated with pronounced seasonal thawing of permafrost soil and increased biological activity. Of particular concern is the potential release of large amounts of soil carbon and stimulation of other soil-borne greenhouse gas emissions such as methane. Soil methanotrophic and methanogenic microbial communities rapidly adjust their activity and spatial organization in response to permafrost thawing and other environmental factors. Soil structural elements such as aggregates and layering affect oxygen and nutrient diffusion processes thereby contributing to methanogenic activity within temporal anoxic niches (hot spots). We developed a mechanistic individual-based model to quantify microbial activity dynamics in soil pore networks considering transport processes and enzymatic activity associated with methane production in soil. The model was upscaled from single aggregates to the soil profile where freezing/thawing provides macroscopic boundary conditions for microbial activity at different soil depths. The model distinguishes microbial activity in aerate bulk soil from aggregates (or submerged profile) for resolving methane production and oxidation rates. Methane transport pathways by diffusion and ebullition of bubbles vary with hydration dynamics. The model links seasonal thermal and hydrologic dynamics with evolution of microbial community composition and function affecting net methane emissions in good agreement with experimental data. The mechanistic model enables systematic evaluation of key controlling factors in thawing permafrost and microbial response (e.g., nutrient availability and enzyme activity) on long-term methane emissions and carbon decomposition rates in the rapidly changing polar regions. Abstract Copyright (2017), . American Geophysical Union. All Rights Reserved.
2017060553 Almeida, Ivan C. C. (Instituto Federal do Norte de Minas Gerais, Otoni, Brazil); Schaefer, Carlos Ernesto G. R.; Michel, Roberto F. M.; Fernandes, Raphael B. A.; Pereira, Thiago T. C.; de Andrade, Andre M.; Francelino, Marcio R.; Fernandes Filho, Elpidio I. and Bockheim, James G. Long term active layer monitoring at a warm-based glacier front from maritime Antarctica: in Active layer thermal regime and seasonal frost dynamics in cold climate environments (Oliva, Marc, editor; et al.), Catena (Giessen), 149(Part 2), p. 572-581, illus. incl. 5 tables, sketch map, 43 ref., February 2017.
Knowledge on active-layer dynamics and permafrost distribution is of especial importance in Maritime Antarctica, where dramatic climate warming occurred in the last decades. Few long-term studies of active-layer temperatures in this region, and no one focus on recently deglaciated areas under paraglacial conditions. This paper analyses the long-term soil thermal regime of a warm-based glacial front site located at Low Head, King George Island. The monitoring system consists of soil temperature probes connected to a datalogger that recorded data at hourly intervals. We calculated the thawing days (TD), freezing days (FD), number of isothermal days (ID), number of freeze-thaw days (FTD), thawing degree days (TDD), freezing degree days (FDD), and the apparent thermal diffusivity (ATD). The results indicate that active layer thermal regime at Low Head is similar to other periglacial environments from Maritime Antarctica, with differences associated with the influence from the nearby warm-based glacier. Surface temperatures show greater variations during the summer resulting in frequent freeze and thaw cycles, mainly (1 cm and 10 cm). The temperature profile during the studied period indicates that the active layer thickness reached a maximum of 106 cm on February 7th 2015. Soil temperature buffering was limited by the low snow cover, low soil moisture, and absence of vegetation. Based on the high interannual variability detected during the five years monitoring run, we stress that longer monitoring periods are necessary for a more detailed knowledge on how permafrost respond to climate changes in this rapidly warming zone.
2017060549 Correia, Antonio (University of Evora, Institute of Earth Sciences and Department of Physics, Evora, Portugal); Oliva, Marc and Ruiz Fernández, Jesús. Evaluation of frozen ground conditions along a coastal topographic gradient at Byers Peninsula (Livingston Island, Antarctica) by geophysical and geoecological methods: in Active layer thermal regime and seasonal frost dynamics in cold climate environments (Oliva, Marc, editor; et al.), Catena (Giessen), 149(Part 2), p. 529-537, illus. incl. 2 tables, sketch map, 53 ref., February 2017.
Geophysical surveying and geoelectrical methods are effective to study permafrost distribution and conditions in polar environments. Geoelectrical methods are particularly suited to study the spatial distribution of permafrost because of its high electrical resistivity in comparison with that of soil or rock above 0°C. In the South Shetland Islands permafrost is considered to be discontinuous up to elevations of 20-40 m a.s.l., changing to continuous at higher altitudes. There are no specific data about the distribution of permafrost in Byers Peninsula, in Livingston Island, which is the largest ice-free area in the South Shetland Islands. With the purpose of better understanding the occurrence of permanent frozen conditions in this area, a geophysical survey using an electrical resistivity tomography (ERT) methodology was conducted during the January 2015 field season, combined with geomorphological and ecological studies. Three overlapping electrical resistivity tomographies of 78 m each were done along the same profile which ran from the coast to the highest raised beaches. The three electrical resistivity tomographies are combined in an electrical resistivity model which represents the distribution of the electrical resistivity of the ground to depths of about 13 m along 158 m. Several patches of high electrical resistivity were found, and interpreted as patches of sporadic permafrost. The lower limits of sporadic to discontinuous permafrost in the area are confirmed by the presence of permafrost-related landforms nearby. There is a close correspondence between moss patches and permafrost patches along the geoelectrical transect.
2017060550 de Pablo, Miguel Angel (University of Alcala, Department of Geology, Geography and Environment, Madrid, Spain); Ramos, Miguel and Molina, A. Snow cover evolution, on 2009-2014, at the Limnopolar Lake CALM-S site on Byers Peninsula, Livingston Island, Antarctica: in Active layer thermal regime and seasonal frost dynamics in cold climate environments (Oliva, Marc, editor; et al.), Catena (Giessen), 149(Part 2), p. 538-547 (Spanish sum.), illus. incl. 1 table, sketch map, 66 ref., February 2017.
In February 2009, a new Circumpolar Active Layer Monitoring (CALM) site was established in the Limnopolar Lake drainage basin, in Byers Peninsula, Livingston Island (South Shetland Archipelago), Antarctica (62°38'59.1"S, 61°06'16.9"W). The first results from active layer thickness and thermal monitoring reported interannual variations, without relevant changes in the air temperature conditions, leaving the snow cover as the most suitable agent controlling the reported changes. Here we study in detail the snow cover evolution on thickness, timing and duration during the 2009-2014 period, by the analysis of mean daily air and ground surface temperature, as well as the snow depth monitored in a stake. Freezing indexes, n-factor, and snow indexes calculations were analyzed to establish the effects of snow cover on the ground thermal regime. The evolution of the snow cover during the 2009-2014 period resulted in about similar snow depths, with mean values of about 45 cm. The snow onset remained about constant with small variations of 10 days in early March. However, the snow offset had significant variations, increasing in more than 60 days in the last three years. This delay on the snow offset resulted in an increase in the snow cover duration from 267 (2011) to 338 (2014) days. Air temperature seems not to be strongly involved in this snow cover timing variation since the highest variation on this period of the maximum and mean annual temperatures only diminished, about 1.6° and 0.5°C respectively, but remaining constant the minimum temperatures (between -12° and -18°C). In consequence, the surface temperature evolved to become less variable along the year directly related to the annual snow layer duration, trending to longer zero curtain periods. In conclusion, the increase in the snow duration is resulting in a reduction of the thaw period in the ground, but remaining similar snow cover onset dates. The consequent decrease in the snow-free period each year could result in a thinner active layer.
2017060552 Ferreira, Alice (Universidade de Lisboa, Centre for Geographical Studies, Portugal); Vieira, Goncalo; Ramos, Miguel and Nieuwendam, Alexandre. Ground temperature and permafrost distribution in Hurd Peninsula (Livingston Island, maritime Antarctic); an assessment using freezing indexes and TTOP modelling: in Active layer thermal regime and seasonal frost dynamics in cold climate environments (Oliva, Marc, editor; et al.), Catena (Giessen), 149(Part 2), p. 560-571, illus. incl. 3 tables, sketch maps, 97 ref., February 2017.
The Western Antarctic Peninsula region shows mean annual air temperatures ranging from -4 to -2°C. Due to its proximity to the climatic threshold of permafrost, and evidence of recent changes in regional air temperatures, this is a crucial area to analyse climate-ground interactions. Freezing indexes and n-factors from contrasting topographic locations in Hurd Peninsula (Livingston Island) are analysed to assess the influence of snow cover on soil's thermal regime. The snow pack duration, thickness and physical properties are key in determining the thermal characteristics and spatial distribution of permafrost. The Temperature at the Top Of the Permafrost (TTOP) model uses freezing and thawing indexes, n-factors and thermal conductivity of the ground, as factors representing ground-atmosphere interactions and provides a framework to understand permafrost conditions and distribution. Eight sites were used to calculate TTOP and evaluate its accuracy. They encompass different geological, morphological and climatic conditions selected to identify site-specific ground thermal regime controls. Data was collected in the freezing seasons of 2007 and 2009 for air, surface and ground temperatures, as well as snow thickness. TTOP model results from sites located between 140 and 275 m a.s.l were very close to observational data, with differences varying from 0.05 to 0.4°C, which are smaller than instrumental error. TTOP results for 36 m a.s.l confirm that permafrost is absent at low altitude and thermal offsets for rock areas show values between 0.01 and 0.48°C indicating a small effect of latent heat, as well as of advection.
2017060555 Hrbacek, Filip (Masaryk University, Department of Geography, Brno, Czech Republic); Nyvlt, Daniel and Laska, Kamil. Active layer thermal dynamics at two lithologically different sites on James Ross Island, eastern Antarctic Peninsula: in Active layer thermal regime and seasonal frost dynamics in cold climate environments (Oliva, Marc, editor; et al.), Catena (Giessen), 149(Part 2), p. 592-602, illus. incl. 5 tables, geol. sketch map, 50 ref., February 2017. Includes appendices.
The active layer thermal regime was studied at two sites with different lithological properties located on James Ross Island, eastern Antarctic Peninsula, to assess the main driving factors. The Abernethy Flats site (41 m a.s.l.) is located in Cretaceous calcareous sandstones and siltstones of the Santa Marta Formation. In contrast, the Berry Hill slopes site (56 m) is composed of muddy to intermediate diamictites, tuffaceous siltstones to fine-grained sandstones of the Mendel Formation. The data of air temperature at 2 m and ground temperature at two 75-cm-deep profiles were analysed for the period 1 January 2012, to 31 December 2014. Small differences were found when comparing mean air temperatures and ground temperatures at 5, 50 and 75 cm depths, in the period 2012-2014. While the mean air temperatures varied between -7.7°C and -7.0°C, the average ground temperatures oscillated between -6.6°C and -6.1°C at 5 cm; -6.7°C and -6.0°C at 50 cm; and -6.9°C and -6.0°C at 75 cm at Abernethy Flats and Berry Hill slopes, respectively. The increasing difference of ground temperature with depth, and a significant difference in active layer thickness -52 to 64 cm at Abernethy Flats and 85 to 90 cm at Berry Hill slopes, respectively--suggests the significant effect of lithology. The higher proportion of fine particles and more thermally conductive minerals, together with higher water saturation, has been found to be fundamental for higher active layer thickness documented at Berry Hill slopes.
2017060560 Magnin, Florence (Université Savoie Mont Blanc, EDYTEM Lab., Le Bourget-du-Lac, France); Westermann, Sebastian; Pogliotti, Paolo; Ravanel, Ludovic; Deline, Philip and Malet, Emmanuel. Snow control on active layer thickness in steep alpine rock walls (Aiguille du Midi, 3842 m a.s.l., Mont Blanc Massif): in Active layer thermal regime and seasonal frost dynamics in cold climate environments (Oliva, Marc, editor; et al.), Catena (Giessen), 149(Part 2), p. 648-662, illus. incl. 4 tables, sketch map, 53 ref., February 2017.
Since the early 2000s, a remarkable amount of rockfalls has been observed in permafrost areas of the mid-latitude mountain ranges concurrently to hot summers. This study explores the seasonal thaw (ST) in permafrost rock walls of the Aiguille du Midi site (3842 m a.s.l., Mont Blanc massif). We first analyse six years of temperature records in three 10 m-deep boreholes against air temperature (AT) and a four-year time series of pictures showing the snow conditions on two rock faces. Then, we test the sensitivity of the active layer against eight snow fall scenarios using the 1-D surface energy balance and heat conduction model CryoGrid 3 forced by in-situ measurements from a vertical face. Snow falls occur all the year round at this elevation and play an important role for the active layer thickness (ALT), but the snow cover and its control are highly heterogeneous. A long-lasting of a snow cover during spring/early summer delays the ST and reduces the ALT. The thicker and the more spatially-continuous is the snow cover, the stronger are the delay and ALT reduction. Convective clouds could also reinforce this pattern. The summer AT and heat waves are the dominant controlling factors of the ALT. But summer snow falls can sometimes persist for several days on the rock surface and reduce the effect of the heat waves. Active layer can thicken during the early fall, except if the snow starts to accumulate on the rock surface and favours the refreezing. The timing of the snow fall is the most critical parameter to determine the snow effect on the ALT. This study suggests that the characteristics of the bedrock and snow accumulation (steepness, surface roughness, and sun-exposure) must be taken into account to better understand the formation and changes of the active layer and its possible implications for rockfall triggering.
2017060551 Oliva, Marc (Universidade de Lisboa, Centre for Geographical Studies, Lisbon, Portugal); Hrbacek, Filip; Ruiz Fernández, Jesús; de Pablo, Miguel Ángel; Vieira, Goncalo; Ramos, Miguel and Antoniades, Dermot. Active layer dynamics in three topographically distinct lake catchments in Byers Peninsula (Livingston Island, Antarctica): in Active layer thermal regime and seasonal frost dynamics in cold climate environments (Oliva, Marc, editor; et al.), Catena (Giessen), 149(Part 2), p. 548-559, illus. incl. 2 tables, sketch map, 53 ref., February 2017.
Topography exerts a key role in controlling permafrost distribution in areas where mean annual temperatures are slightly negative. One such case is the low-altitude environments of Maritime Antarctica, where permafrost is sporadic to discontinuous below 20-40 m asl and continuous at higher areas and active layer dynamics are thus strongly conditioned by geomorphological setting. In January 2014 we installed three sites for monitoring active layer temperatures across Byers Peninsula (Livingston Island, South Shetland Islands) at elevations between 45 and 100 m. The sites are situated in lake catchments (lakes Escondido, Cerro Negro, and Domo) that have different geomorphological and topographical conditions. Our objective was to examine the role of topography and microclimatic conditions in determining the active layer thermal regime in order to identify the factors that control geomorphic processes in these lake catchments. At each site a set of loggers was installed to monitor air temperature (AT), snow thickness (SwT) and soil temperature (ST) down to 80 cm depth. Mean annual air temperatures (MAAT) showed similar values in the three sites (-2.7 to -2.6°C) whereas soil temperatures showed varying active layer thicknesses at the three catchments. The ground thermal regime was strongly controlled by soil properties and snow cover thickness and duration, which is influenced by local topography. Geomorphological processes operating at the lake catchment scale control lacustrine sedimentation processes, and both are dependent on the combination of topographical and climatic conditions. Therefore, the interpretation of lake sediment records from these three lakes requires that soil thermal regime and snow conditions at each site be taken into account in order to properly isolate the geomorphological, environmental and climatic signals preserved in these lake records.
2017060547 Oliva, Marc; Pareira, Paulo; Ruiz Fernández, Jesús and Nieuwendam, Alexandre, editors. Active layer thermal regime and seasonal frost dynamics in cold climate environments: Catena (Giessen), 149(Part 2), p. 515-662, illus., February 2017. Individual papers within scope are cited separately.
2017060548 Ramos, Miguel (University of Alcala, Department of Physics and Mathematics, Madrid, Spain); Vieira, Goncalo; de Pablo, Miguel Angel; Molina, A.; Abramov, A. and Goyanes, G. Recent shallowing of the thaw depth at Crater Lake, Deception Island, Antarctica (2006-2014): in Active layer thermal regime and seasonal frost dynamics in cold climate environments (Oliva, Marc, editor; et al.), Catena (Giessen), 149(Part 2), p. 519-528, illus. incl. 2 tables, sketch maps, 34 ref., February 2017.
The Western Antarctic Peninsula region is one of the hot spots of climate change and one of the most ecologically sensitive regions of Antarctica, where permafrost is near its climatic limits. The research was conducted in Deception Island, an active stratovolcano in the South Shetlands archipelago off the northern tip of the Antarctic Peninsula. The climate is polar oceanic, with high precipitation and mean annual air temperatures (MAAT) close to -3°C. The soils are composed by ashes and pyroclasts with high porosity and high water content, with ice-rich permafrost at -0.8°C at the depth of zero annual amplitude, with an active layer of about 30 cm. Results from thaw depth, ground temperature and snow cover monitoring at the Crater Lake CALM-S site over the period 2006 to 2014 are analyzed. Thaw depth (TD) was measured by mechanical probing once per year in the end of January or early February in a 100´100 m with a 10 m spacing grid. The results show a trend for decreasing thaw depth from ci. 36 cm in 2006 to 23 cm in 2014, while MAAT, as well as ground temperatures at the base of the active layer, remained stable. However, the duration of the snow cover at the CALM-S site, measured through the Snow Pack Factor (SF) showed an increase from 2006 to 2014, especially with longer lasting snow cover in the spring and early summer. The negative correlation between SF and the thaw depth supports the significance of the influence of the increasing snow cover in thaw depth, even with no trend in the MAAT. The lack of observed ground cooling in the base of the active layer is probably linked to the high ice/water content at the transient layer. The pyroclastic soils of Deception Island, with high porosity, are key to the shallow active layer depths, when compared to other sites in the Western Antarctic Peninsula (WAP). These findings support the lack of linearity between atmospheric warming and permafrost warming and induce an extra complexity to the understanding of the effects of climate change in the ice-free areas of the WAP, especially in scenarios with increased precipitation as snow fall.
2017060556 Schaefer, Carlos Ernesto G. R. (Universidade Federal de Vicosa, Departamento de Solos, Vicosa, Brazil); Michel, Roberto F. M.; Delpupo, Caroline; Senra, Eduardo O.; Bremer, Ulisses F. and Bockheim, James G. Active layer thermal monitoring of a dry valley of the Ellsworth Mountains, continental Antarctica: in Active layer thermal regime and seasonal frost dynamics in cold climate environments (Oliva, Marc, editor; et al.), Catena (Giessen), 149(Part 2), p. 603-615, illus. incl. 4 tables, sketch map, 33 ref., February 2017.
The Ellsworth Mountains are located along the southern edge of the Ronne-Filchner Ice Shelf and are subdivided by the Minnesota Glacier into the Heritage Range to the east, and the Sentinel Range to the west (Figure 1). The climate of the Ellsworth Mountains is strongly controlled by proximity to the Ronne-Filchner Ice Shelf and elevation. The entire ice free area is underlain by continuous permafrost of unknown thickness, most in the form of dry permafrost. Active-layer depths in drift sheets of the Ellsworth Mountains range from 15 to 50 cm. Detailed knowledge on Antarctic permafrost is patchy, especially at the continent. Two adjacent active layer monitoring sites were installed at Mt. Dolence, Ellsworth Mountains, in the summer of 2012. Two dry-valley soils at Mt. Dolence area, on quartzite drift deposits were studied: (i) a convex-slope site exposed to the wind (Lithic Haplorthel 886 m asl, 5 cm, 10 cm, 30 cm); and a sheltered concave-slope site protected from winds (Lithic Anhyorthel 850 m asl, 5 cm, 10 cm, 30 cm). Data was recorded at hourly intervals from January 2nd 2012 until December 29th 2013. The soil climate temperature at 5 cm reaches a maximum daily mean in late December, reaching a minimum in mid July at both sites. Active layer thickness reaches a maximum of 48.4 cm at P1 on January 17th 2013 and 47.8 cm at P2 on January 7th 2012. The soil thermal regime at the dry valley of Mt. Dolence, Ellsworth Mountains is characteristic of cold desert affected by dry-frozen permafrost. Although air temperature does not reach elevated positive values, variations in soil temperature are intense, showing the soil's response to solar radiation. The origins of typical surface periglacial features and landform on the widespread Ellsworth drifts may be inherited from past events of warmer climates, since liquid water is unlikely to play any significant role under the present climate.
2017060554 Schaefer, Carlos Ernesto G. R. (Universidade Federal de Vicosa, Vicosa, Brazil); Pereira, Thiago T. C.; Almeida, Ivan C. C.; Michel, Roberto F. M.; Correa, Guilherme R.; Figueiredo, Luana P. S. and Ker, Joao C. Penguin activity modify the thermal regime of active layer in Antarctica; a case study from Hope Bay: in Active layer thermal regime and seasonal frost dynamics in cold climate environments (Oliva, Marc, editor; et al.), Catena (Giessen), 149(Part 2), p. 582-591, illus. incl. 7 tables, sketch map, 37 ref., February 2017.
Monitoring permafrost and active layer is essential for prognostic research of future climate scenarios. Although biotic factors have a prominent role in active layer behavior, apart from vegetation effects, their influence remains little investigated. It is generally assumed that frozen ground exerts influence on nesting fauna, whereas, on the other hand, land colonization by birds, such as penguins can also interfere with the soil thermal regime. However, to our knowledge, no studies report on permafrost and active layer regime changes under penguin activity. We present a comparative study of two adjacent sites located in Hope Bay, one representing an active penguin rookery-S1, and another, an adjacent abandoned site currently vegetated-S2. Soil temperature and water content, and air temperature were monitored hourly from 2009 to 2011. Current penguin activity and the resulting deposition of guano during spring and summer in S1 is an important factor for explaining the higher number of thaw degree days due to direct physical impact and chemical reactions caused by rapid guano decomposition. In the vegetated S2 site, the snow pack lasted longer, showing the highest mean minimum temperature and larger thermal insulation, as well as larger FDD than those found in the bare soil of the active rookery (S1), and lower n-F, due to greater thermal insulation. Penguins played a significant role in changing the active layer depth and thermal regime, and represent a neglected actor on the ground thermal regime in Antarctic terrestrial environments.
2017058040 Zhao Xiaodong (China University of Mining and Technology, State Key Laboratory for Geomechanics and Deep Underground Engineering, Xuzhou, China); Zhou Guoqing and Lu Guilin. Strain responses of frozen clay with thermal gradient under triaxial creep: Acta Geotechnica (Berlin), 12(1), p. 183-193, 17 ref., February 2017. Based on Publisher-supplied data.
Thermal gradient is one of the main features for the temperature distribution in artificial frozen shaft lining (FSL). The time-dependent strain responses and the corresponding heterogeneity characteristics of frozen soils with thermal gradient are of potential significance for stability assessment and prediction of FSL, especially of the FSL embedded in thick alluvium. A series of triaxial creep tests were carried out on frozen saturated clay under various thermal gradients and creep stresses. The experimental results indicated that the triaxial creep curves for frozen clay with thermal gradient exhibit viscous characteristics, and the creep rate Dea/Dt decreases with the increase in creep time t and decrease in thermal gradient. The stress-strain curve under different t showed that the creep stress has a marked growth when axial strain ea ≤&eq;1%. However, when ea>&eq; 1%, the growth rate decreases gradually. The deviation between measured radial strain erm under the middle specimen section height SSH and the calculated radial strain erc from the volumetric strain increases following a unified equation with the increase in axial strain. The radial strain erf for frozen clay with thermal gradient after experiment increases with the increase in SSH, and the slope of erf-SSH curve is significantly dependent on the thermal gradient and creep stress. The variation of erm - erc during experiment and erf distribution after experiment are the macro-responses of internal micro-heterogeneities in frozen soils induced from thermal gradient, and are closely related to strain rate and its variation. These observations and findings provide an insight into the creep mechanism and the estimation method of creep deformation for frozen soils with thermal gradient. Copyright 2016 Springer-Verlag Berlin Heidelberg
2017060565 Esper Angillieri, Maria Yanina (Universidad Nacional de San Juan, El Centro de Investigaciones de la Geósfera y la Biósfera, San Juan, Argentina). Permafrost distribution map of San Juan dry Andes (Argentina) based on rock glacier sites: Journal of South American Earth Sciences, 73, p. 42-49, illus. incl. 2 tables, sketch maps, 56 ref., January 2017.
Rock glaciers are frozen water reservoirs in mountainous areas. Water resources are important for the local populations and economies. The presence of rock glaciers is commonly used as a direct indicator of mountain permafrost conditions. Over 500 active rock glaciers have been identified, showing that elevations between 3500 and 4500 m asl., a south-facing or east-facing aspect, areas with relatively low solar radiation and low mean annual air temperature (-4 to 0 °C) favour the existence of rock glaciers in this region. The permafrost probability model, for Dry Andes of San Juan Province between latitudes 28°30'S and 32°30'S, have been analyzed by logistic regression models based on the active rock glaciers occurrence in relation to some topoclimatic variables such as altitude, aspect, mean annual temperature, mean annual precipitation and solar radiation, using optical remote sensing techniques in a GIS environment. The predictive performances of the model have been estimated by known rock glaciers locations and by the area under the receiver operating characteristic curve (AUROC). This regional permafrost map can be applied by the Argentinean Government for their recent initiatives which include creating inventories, monitoring and studying ice masses along the Argentinean Andes. Further, this generated map provides valuable input data for permafrost scenarios and contributes to a better understanding of our geosystem.
2017060821 Weber, Samuel (University of Zurich, Department of Geography, Zurich, Switzerland); Beutel, Jan; Faillettaz, Jérome; Hasler, Andreas; Krautblatter, Michael and Vieli, Andreas. Quantifying irreversible movement in steep, fractured bedrock permafrost on Matterhorn (CH): The Cryosphere (Online), 11(1), p. 567-583, illus. incl. 2 tables, 41 ref., 2017. Includes appendices.
Understanding rock slope kinematics in steep, fractured bedrock permafrost is a challenging task. Recent laboratory studies have provided enhanced understanding of rock fatigue and fracturing in cold environments but were not successfully confirmed by field studies. This study presents a unique time series of fracture kinematics, rock temperatures and environmental conditions at 3500 m a. s. l. on the steep, strongly fractured Hornligrat of the Matterhorn (Swiss Alps). Thanks to 8 years of continuous data, the longer-term evolution of fracture kinematics in permafrost can be analyzed with an unprecedented level of detail. Evidence for common trends in spatiotemporal pattern of fracture kinematics could be found: a partly reversible seasonal movement can be observed at all locations, with variable amplitudes. In the wider context of rock slope stability assessment, we propose separating reversible (elastic) components of fracture kinematics, caused by thermoelastic strains, from the irreversible (plastic) component due to other processes. A regression analysis between temperature and fracture displacement shows that all instrumented fractures exhibit reversible displacements that dominate fracture kinematics in winter. Furthermore, removing this reversible component from the observed displacement enables us to quantify the irreversible component. From this, a new metric--termed index of irreversibility--is proposed to quantify relative irreversibility of fracture kinematics. This new index can identify periods when fracture displacements are dominated by irreversible processes. For many sensors, irreversible enhanced fracture displacement is observed in summer and its initiation coincides with the onset of positive rock temperatures. This likely indicates thawing-related processes, such as meltwater percolation into fractures, as a forcing mechanism for irreversible displacements. For a few instrumented fractures, irreversible displacements were found at the onset of the freezing period, suggesting that cryogenic processes act as a driving factor through increasing ice pressure. The proposed analysis provides a tool for investigating and better understanding processes related to irreversible kinematics.
2017064037 Siewert, Matthias Benjamin (Stockholm University, Department of Physical Geography, Stockholm, Sweden); Hugelius, Gustaf; Heim, Birgit and Faucherre, Samuel. Landscape controls and vertical variability of soil organic carbon storage in permafrost-affected soils of the Lena River delta: Catena (Giessen), 147, p. 725-741, illus. incl. 4 tables, sketch maps, 83 ref., December 2016. Includes appendices.
To project the future development of the soil organic carbon (SOC) storage in permafrost environments, the spatial and vertical distribution of key soil properties and their landscape controls needs to be understood. This article reports findings from the Arctic Lena River Delta where we sampled 50 soil pedons. These were classified according to the U.S.D.A.. Soil Taxonomy and fall mostly into the Gelisol soil order used for permafrost-affected soils. Soil profiles have been sampled for the active layer (mean depth 58 ± 10 cm) and the upper permafrost to one meter depth. We analyze SOC stocks and key soil properties, i.e. C%, N%, C/N, bulk density, visible ice and water content. These are compared for different landscape groupings of pedons according to geomorphology, soil and land cover and for different vertical depth increments. High vertical resolution plots are used to understand soil development. These show that SOC storage can be highly variable with depth. We recommend the treatment of permafrost-affected soils according to subdivisions into: the surface organic layer, mineral subsoil in the active layer, organic enriched cryoturbated or buried horizons and the mineral subsoil in the permafrost. The major geomorphological units of a subregion of the Lena River delta were mapped with a land form classification using a data-fusion approach of optical satellite imagery and digital elevation data to upscale SOC storage. Landscape mean SOC storage is estimated to 19.2 ± 2.0 kg C m-2. Our results show that the geomorphological setting explains more soil variability than soil taxonomy classes or vegetation cover. The soils from the oldest, Pleistocene aged, unit of the delta store the highest amount of SOC per m2 followed by the Holocene river terrace. The Pleistocene terrace affected by thermal-degradation, the recent floodplain and bare alluvial sediments store considerably less SOC in descending order.
2017063973 Temme, Arnaud J. A. M. (Wageningen University, Environmental Sciences, Netherlands); Heckmann, Tobias and Harlaar, Piet. Silent play in a loud theatre; dominantly time-dependent soil development in the geomorphically active proglacial area of the Gepatsch Glacier, Austria: Catena (Giessen), 147, p. 40-50, illus. incl. table, sketch maps, 83 ref., December 2016.
Climate change over the last century, expressed as temperature increase, is substantially stronger in the European Alps than the average for the Northern Hemisphere. This leads to fast glacial retreat and permafrost degradation, and hence to increased rates and risks of mass wasting, more extreme floods in spring and lower base flow in summer. We do not know enough about the interplay between increased proglacial mass wasting and geomorphic activity on the one hand, and soil development on proglacial areas on the other hand. Both processes affect the attenuation of storm flow, provision of base flow and the future geo-, pedo- and biodiversity of Alpine valleys. However, despite the known importance of soil-landscape interactions, soils and landscapes have so far only been studied in isolation. Our objective was to assess whether soil development (the silent play) in a geomorphically active proglacial area (the loud theater) was nonetheless dominantly a function of time since glacial retreat--as often observed in geomorphically inactive proglacial areas. We used conditional Latin Hypercube sampling to select 97 locations in the Gepatsch glacier proglacial area in the west of Austria that best cover variation in soil age and topographic position. Standard soil observations were done in all locations. Soil development indicators were then related to time since glacial retreat and a range of geomorphic variables. Results indicate that time since glacial retreat indeed remains an important explanatory variable, and that soil development in the Gepatsch glacier proglacial area roughly equals that in some other well-studied valleys. Geomorphic variables were found to be significant co-determinants of soil development, with a strong scale-dependency. Variation in soil properties increased over time, and the storage of organic matter in the proglacial area is currently in the order of 330 kg per year.
2017063927 Farquharson, L. M. (University of Alaska Fairbanks, Department of Geosciences, Fairbanks, AK); Mann, D. H.; Grosse, G.; Jones, B. M. and Romanovsky, V. E. Spatial distribution of thermokarst terrain in Arctic Alaska: Geomorphology, 273, p. 116-133, illus. incl. 4 tables, geol. sketch map, 79 ref., November 15, 2016. Includes appendices.
In landscapes underlain by ice-rich permafrost, the development of thermokarst landforms can have drastic impacts on ecosystem processes and human infrastructure. Here we describe the distribution of thermokarst landforms in the continuous permafrost zone of Arctic Alaska, analyze linkages to the underlying surficial geology, and discuss the vulnerability of different types of landscapes to future thaw. We identified nine major thermokarst landforms and then mapped their distributions in twelve representative study areas totaling 300-km2. These study areas differ in their geologic history, permafrost-ice content, and ground thermal regime. Results show that 63% of the entire study area is occupied by thermokarst landforms and that the distribution of thermokarst landforms and overall landscape complexity varies markedly with surficial geology. Areas underlain by ice-rich marine silt are the most affected by thermokarst (97% of total area), whereas areas underlain by glacial drift are least affected (14%). Drained thermokarst-lake basins are the most widespread thermokarst landforms, covering 33% of the entire study region, with greater prevalence in areas of marine silt (48% coverage), marine sand (47%), and aeolian silt (34%). Thermokarst-lakes are the second most common thermokarst landform, covering 16% of the study region, with highest coverage in areas underlain by marine silt (39% coverage). Thermokarst troughs and pits cover 7% of the study region and are the third most prevalent thermokarst landform. They are most common in areas underlain by deltaic sands and gravels (18% coverage) and marine sand (12%). Alas valleys are widespread in areas of aeolian silt (14%) located in gradually sloping uplands. Areas of marine silt have been particularly vulnerable to thaw in the past because they are ice-rich and have low-gradient topography facilitating the repeated development of thermokarst-lakes. In the future, ice-rich aeolian, upland terrain (yedoma) will be particularly susceptible to thaw because it still contains massive concentrations of ground ice in the form of syngenetic ice-wedges that have remained largely intact since the Pleistocene.
2017063931 Moran, Andrew P. (University of Innsbruck, Institute of Geography, Innsbruck, Austria); Ivy Ochs, Susan; Vockenhuber, Christof and Kerschner, Hanns. Rock glacier development in the Northern Calcareous Alps at the Pleistocene-Holocene boundary: Geomorphology, 273, p. 178-188, illus. incl. 6 tables, sketch maps, 109 ref., November 15, 2016.
Relict rock glaciers provide information on past discontinuous permafrost and former mean annual air temperatures. A lack of records showing former permafrost distribution along the northern Alpine fringe prompted the investigation and numerical dating of a belt of relict rock glaciers in the Karwendel Mountains of the Northern Calcareous Austrian Alps. In two neighbouring cirques that were still glaciated during the early Younger Dryas, eleven 36Cl exposure ages from boulder surfaces were obtained. The ages imply the onset of rock glacier activity around ~ 12.3 ka with subsequent stabilization and permafrost melt out no later than ~ 10.1 ka. Hence, rock glacier formation coincided with glacier retreat in the cirques around the mid-Younger Dryas and continued into the early Holocene. As permafrost induced features, the rock glacier termini indicate the local past lower limit of discontinuous permafrost in open cirque floors at ~ 2000 m asl, which is around 400 m lower than during the mid-twentieth century at comparable locations in the Karwendel Mountains. Thus, a mean annual air temperature reduction of ~- 2.6 to - 3.8°C relative to the mid-twentieth century is inferred. Based on a minimum glacier equilibrium line altitude in the cirques, a summer temperature reduction of less than - 2.6 to - 1.8°C is shown, suggesting an increased seasonality at the time of rock glacier activity.
2017063909 Murton, Julian B. (University of Sussex, Department of Geography, Brighton, United Kingdom); Ozouf, Jean-Claude and Peterson, Rorik. Heave, settlement and fracture of chalk during physical modelling experiments with temperature cycling above and below 0°C: Geomorphology, 270, p. 71-87, illus. incl. 2 tables, 40 ref., October 2016. Includes appendices.
To elucidate the early stages of heave, settlement and fracture of intact frost-susceptible rock by temperature cycling above and below 0 °C, two physical modelling experiments were performed on 10 rectangular blocks 450 mm high of fine-grained, soft limestone. One experiment simulated 21 cycles of bidirectional freezing (upward and downward) of an active layer above permafrost, and the other simulated 26 cycles of unidirectional freezing (downward) of a seasonally frozen bedrock in a non-permafrost region. Heave and settlement of the top of the blocks were monitored in relation to rock temperature and unfrozen water content, which ranged from almost dry to almost saturated.In the bidirectional freezing experiment, heave of the wettest block initially occurred abruptly at the onset of freezing periods and gradually during thawing periods (summer heave). After the crossing of a threshold marked by the appearance of a macrocrack in the upper layer of permafrost, summer heave increased by an order of magnitude as segregated ice accumulated incrementally in macrocracks, interrupted episodically by abrupt settlement that coincided with unusually high air temperatures. In the unidirectional freezing experiment, the wet blocks heaved during freezing periods and settled during thawing periods, whereas the driest blocks showed the opposite behaviour. The two wettest blocks settled progressively during the first 15 freeze-thaw cycles, before starting to heave progressively as macrocracks developed.Four processes, operating singly or in combination in the blocks account for their heave and settlement: (1) thermal expansion and contraction caused heave and settlement when little or no water-ice phase change was involved; (2) volumetric expansion of water freezing in situ caused short bursts of heave of the outer millimetres of wet rock; (3) ice segregation deeper in the blocks caused sustained heave during thawing and freezing periods; and (4) freeze-thaw cycling caused consolidation and settlement of wet blocks prior to macrocracking in the unidirectional freezing experiment. Rock fracture developed by growth of segregated ice in microcracks and macrocracks at depths determined by the freezing regime. Overall, the heave, settlement and fracture behaviour of the limestone is similar to that of frost-susceptible soil.
2017060148 Alexeev, Vladimir A. (University of Alaska Fairbanks, International Arctic Research Center, Fairbanks, AK); Arp, Christopher D.; Jones, Benjamin M. and Cai, Lei. Arctic sea ice decline contributes to thinning lake ice trend in northern Alaska: Environmental Research Letters, 11(7), Paper no. 074022, illus. incl. 1 table, 23 ref., July 2016.
Field measurements, satellite observations, and models document a thinning trend in seasonal Arctic lake ice growth, causing a shift from bedfast to floating ice conditions. September sea ice concentrations in the Arctic Ocean since 1991 correlate well (r=+0.69, p<0.001) to this lake regime shift. To understand how and to what extent sea ice affects lakes, we conducted model experiments to simulate winters with years of high (1991/92) and low (2007/08) sea ice extent for which we also had field measurements and satellite imagery characterizing lake ice conditions. A lake ice growth model forced with Weather Research and Forecasting model output produced a 7% decrease in lake ice growth when 2007/08 sea ice was imposed on 1991/92 climatology and a 9% increase in lake ice growth for the opposing experiment. Here, we clearly link early winter 'ocean-effect' snowfall and warming to reduced lake ice growth. Future reductions in sea ice extent will alter hydrological, biogeochemical, and habitat functioning of Arctic lakes and cause sub-lake permafrost thaw. Copyright (Copyright) 2016 IOP Publishing Ltd
2017060119 Gadek, Bogdan (University of Silesia, Faculty of Earth Sciences, Sosnowiec, Poland); Grabiec, Mariusz; Kedzia, Stanislaw and Raczkowska, Zofia. Reflection of climate changes in the structure and morphodynamics of talus slopes (the Tatra Mountains, Poland): Geomorphology, 263, p. 39-49, illus. incl. 3 tables, sketch maps, 89 ref., June 15, 2016.
Talus slopes beside glaciers are among the best objects to research on climate change. In the Tatra Mountains, the highest mountains of central Europe, no glaciers remain, only glacierets and permafrost. For that reason a complex investigation of talus slopes was conducted there in the years 2009-2010. This paper presents the results of GPR and lichenometric measurements of the talus slopes in six glacial cirques located in the High and Western Tatras. The thickness and internal structure of talus slopes were identified along with the variability and conditions of their development. Maximum thickness of the talus slopes ranges from 20 to 35 m, reaching higher values in the High Tatras. The diversity of the thickness of the talus slopes within the Tatras is mostly explained by differences in the relief conditioned by lithology. The diverse altitudinal locations of the talus slopes, and the exposure and inclinations are not reflected in the size and thickness. The thickness of the studied slopes depends primarily on the activity of the processes supplying rock material and on the size and shape of the sediment supply area. The results of the lichenometric testing together with the analysis of the long-term precipitation data imply a several hundred-year-long deterioration of the climate during the Little Ice Age, which is reflected in the increased activity of morphogenetic processes on the talus slopes across the whole massif of the Tatras. In the last 200 years, the talus slopes of the Tatras were most active in three periods: at the end of the Little Ice Age, in the 1930s and 1940s, and in the early 1970s. Abstract Copyright (2016) Elsevier, B.V.
2017060050 Colucci, R. R. (Istituto di Scienze Marine, Department of Earth System Sciences and Environmental Technologies, Trieste, Italy); Fontana, D.; Forte, E.; Potleca, M. and Guglielmin, M. Response of ice caves to weather extremes in the southeastern Alps, Europe: Geomorphology, 261, p. 1-11, illus. incl. sketch maps, 41 ref., May 15, 2016.
High altitude karstic environments often preserve permanent ice deposits within caves, representing the lesser-known portion of the cryosphere. Despite being not so widespread and easily reachable as mountain glaciers and ice caps, ice caves preserve much information about past environmental changes and climatic evolution. We selected 1111 ice caves from the existing cave inventory, predominantly but not exclusively located in the periglacial domain where permafrost is not dominant (i.e., with mean annual air temperature < 3 °C but not in a permafrost environment). The influence of climate and topography on ice cave distribution is also investigated. In order to assess the thickness and the inner structure of the deposits, we selected two exemplary ice caves in the Canin massif (Julian Alps) performing several multifrequency GPR surveys. A strong influence of global and local climate change in the evolution of the ice deposits has been particularly highlighted in the dynamic ice cave type, especially in regard to the role of weather extremes. The natural response of ice caves to a warming climate could lead to a fast reduction of such ice masses. The increased occurrence of weather extremes, especially warmer and more intense precipitation caused by higher mean 0 °C-isotherms, could in fact be crucial in the future mass balance evolution of such permanent ice deposits. Abstract Copyright (2016) Elsevier, B.V.
2017065981 Lampe, Reinhard (Universität Greifswald, Institut für Geographie und Geologie, Greifswald, Germany); Janke, Wolfgang; Schult, Manuela; Meng, Stefan and Lampe, Matthias. Multiproxy-Untersuchungen zur Paläoökologie und -hydrologie eines spätglazial- bis frühholozänen Flachsees im nordostdeutschen Küstengebiet (Glowe-Paläosee, Insel Rügen) [Multiproxy investigations on the palaeoecology and hydrology of a late glacial to early Holocene shallow lake on the northeastern German Baltic Coast (Glowe Palaeolake, Rugen Island)]: Eiszeitalter und Gegenwart - Quaternary Science Journal, 65(1), p. 41-75 (English sum.), illus. incl. sects., 3 tables, sketch map, 152 ref., 2016.
The paper presents results of multiproxy-investigations of a 3 m long sediment section from the Glowe Palaeolake, covering the period Pre-Bolling to the middle of the Preboreal. The Lateglacial and early Holocene landscape development comprising climate fluctuations, lake evolution, lake-level variations and vegetation history is reconstructed using pollen, diatom, macrofossil, molluscs as well as sedimentological and geochemical data based on 14C-dating. The palaeolake appeared due to the decay of the permafrost during the Bolling and developed in the Allerod into a 3-4 m deep, species-poor and macrophyte-rich stillwater. The submerse vegetation and fauna decreased during the Younger Dryas, but returned fast and with higher density in the Preboreal. Phases of cooler climate can be parallelized with the Gerzensee oscillation, the Younger Dryas and the Rammelbeek oscillation, which each are palynologically bipartite. In contrast, indications for the Older Dryas were only scarce. The cooler phases were characterized by intensified allochthonous clastic input into the lake. During the Younger Dryas the input was dominated by solifluction processes, while during the Allerod and the Preboreal predominantly fluvial processes occurred. The most significant changes in the palaeoecology of the lake were caused by the rapid warming at the onset of the Preboreal. During the phases of warmer climate the vegetation development was influenced by the vicinity to the Baltic Ice Lake, which caused, compared to more southerly regions, a delayed spread of Pinus. Also, the long term climate changes determined the alterations in the chemical sediment composition, the diatom flora and the macrophyte vegetation. Short term variations, which caused the closely spaced sediment layering mainly in the older part of the sediment section cannot be explained so far. The course of the outcropping stratigraphic units was used to construct a lake-level curve. It shows a rapid rise in the early Allerod and a subsequent slower rise until the highstand in the Younger Dryas. In the early Preboreal, a fast lake-level fall occurred, the palaeolake silted up and dried out in the middle of the Preboreal.
2017065977 Zheleznyak, Il'ya Iosifovich (Russian Academy of Sciences, Siberian Division, Institute of Natural Resources, Ecology and Cryosphere, Chita, Russian Federation) and Mal'chikova, Irina Yur'yevna. Issledovaniye l'doobrazovaniya v glybovykh massivakh gornykh porod kriolitozony severnogo Zabaykal'ya [Studies of ice formation in boulder terrains within permafrost zone of northern Transbaikalia]: Izvestiya Ural'skogo Gosudarstvennogo Gornogo Universiteta = Izvestiya of the Ural State Mining University, 43(3), p. 64-66 (English sum.), 13 ref., 2016.
Authors present information about the conditions of ice formation in the natural and technogenic clumpy rock masses in the climatic conditions of the mountain regions of Subarctic in the Northern Transbaikalia. This research substantiates actuality of the study of ice formation in such clumps for the purpose of developing methods and technical means for their engineering and geological study, determination of physical and mechanical properties, development of approaches to the solution of a wide range of geo-ecological and geotechnical problems and, in general, the problem of ensuring the stability of constructions of various purposes. One can find basic differences of their properties, which determine the radiation balance of the surface of clumpy rock masses depending on the situation on the terrain and the orientation to the cardinal. The authors also analyze of the impact of seasonal fluctuations in temperature, humidity and precipitation on the particular ice formations in clumpy rock massifs as a result of convective heat transfer in interclumpy spaces. The results of studies show relations of the formation and accumulation of ice from the structure of clumpy massifs. Authors obtained types and main genetic characteristics of ice in clumpy rock masses. Moreover, authors determined the conditions for forming the structure of the crystal lattice, water crystallization, crystal growth, chemical composition, physical and mechanical properties and other characteristics of ice, in the surface and underground rock clumpy massifs. One can see their dependence on dynamics of the changing in the winter low daily and seasonal temperature of crystallization and the rapid growth of ice crystals. Authors present conclusions of the scientific and practical importance in solving practical problems of economic development of the territories with local and areal extent of clumpy rock massifs.
2017061671 Falaschi, Daniel (Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales, Mendoza, Argentina); Tadono, Takeo and Masiokas, Mariano. Rock glaciers in the Patagonian Andes; an inventory for the Monte San Lorenzo (Cerro Cochrane) Massif, 47°S: Geografiska Annaler. Series A: Physical Geography, 97(4), p. 769-777, illus. incl. 3 tables, sketch map, 47 ref., December 2015.
Although rock glaciers in the Central and Desert Andes of Argentina and Chile have been previously studied in detail, much less attention has been paid to the occurrence of these permafrost forms in Patagonia. Recently, however, the establishment of the Argentinean Glacier Inventory program, which intends to inventory and monitor all ice masses along the Argentinean Andes, has started a large amount of new geocryological research. The project is designed to provide reliable and worldwide comparable results, supported by well established technical procedures and background information. Presented here is the first rock glacier inventory of the Monte San Lorenzo (Cerro Cochrane) region in the southern Patagonian Andes. A total of 130 intact (9.86 km2) and 47 fossil (1.45 km2) landforms were inventoried using two 2.5 m resolution ALOS Panchromatic Remote-sensing Instruments for Stereo Mapping images. Since the Argentinean federal initiative described above legally protects all rock glaciers in the country as water reserves, and due to the little scientific knowledge concerning rock glaciers in the vast majority of the Patagonian Andes, this inventory provides an important basis for political decision-making and opens further geocryological research avenues for the Patagonian region in general. Abstract Copyright (2015), Swedish Society for Anthropology and Geography.
2017061670 Luethi, Rachel (University of Zurich, Glaciology, Geomorphodynamics & Geochronology, Zurich, Switzerland); Gruber, Stephan and Ravanel, Ludovic. Modelling transient ground surface temperatures of past rockfall events; towards a better understanding of failure mechanisms in changing periglacial environments: Geografiska Annaler. Series A: Physical Geography, 97(4), p. 753-767, illus. incl. 3 tables, sketch maps, 66 ref., December 2015.
Despite the rising interest in mountain permafrost due to climatic changes and a noticed increase of registered rockfall events in the European Alps and other mountain ranges, little is known about transient thermal conditions in the detachment areas of rockfalls. Temperature conditions prior to the rockfall events of 144 past events in the European Alps were modelled with a physically based ground temperature model. To minimise the impact that uncertainty has on interpretations, only relative values were used, that is, percentiles obtained from cumulative distribution functions of the modelled ground surface temperatures from the beginning of the meteorological measurement series up to the event dates. Our results suggest that small and mid-sized rockfalls (volumes up to 100 000 m3) from high elevation occurred mainly during short-term periods of unusually high temperatures. This was neither found to be a result of the seasonal distribution (most analysed events in higher elevations occurred from July to September) nor of the longer-term temporal distribution (most analysed events occurred after 2000) only. Plausible explanations are either a destabilisation related to advective thaw or failure due to stress redistribution caused by large temperature variations. Large deep-seated rock slope failures (>&eq;100000 m3) in high elevation occurred all year round. Abstract Copyright (2015), Swedish Society for Anthropology and Geography.
2017059495 Yu Qihao (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Fan Kai; You Yanhui; Guo Lei and Yuan Chang. Comparative analysis of temperature variation characteristics of permafrost roadbeds with different widths: Cold Regions Science and Technology, 117, p. 12-18, illus. incl. 3 tables, September 2015. Based on Publisher-supplied data.
According to Expressway Network Plan of China, an expressway is to be constructed in the permafrost regions on the Qinghai-Tibet Plateau. The understanding of the heat transfer characteristics of the subgrade in expressways with wide pavements is crucial for damage prevention and control, and the long-term stability of the roadbed. Based on the monitored data from the Qingshuihe section of the Qinghai-Tibet Highway (QQTH) and Qinghai-Tibet Test Expressway (QTTE) in the permafrost regions on the Qinghai-Tibet Plateau, the heat-transfer process and the ground temperature response of highways and expressways with different embankment widths were analyzed. The results from QQTH showed that during the past 17 years, the variation of the ground temperature of QQTH embankment was mainly affected by the solar radiations and heat absorption process of pavement surface. The intensity of heat absorption of the soil at the base of the roadbed was much more than that in natural conditions, and it resulted in a more rapid and continuous increase of the temperature under the embankment, which could reach up to 0.8 °C/a. Comparing with QQTH in the initial period after its reconstruction, the variation characteristics of the ground temperature in embankment of the QTTE was generally the same, but the intensity of heat absorption in embankment increased by nearly 30% in the QTTE, and permafrost degeneration was further accelerated. The increase in ground temperatures at different depths and the maximum thawing speed of permafrost were nearly doubled as that on the QQTH. On the QTTE, the effect of sunny-shady slope in the embankment was identified. During the observation period of 4 years, the sunny-shady effect caused the ground temperature to be offset by about 2 m from the axis of symmetry to the sunny slope direction, and longitudinal cracks of roadbed have been resulted. Stricter technical standards for future expressways, will mean that the permafrost issues will become more important and serious, and corresponding research is more urgent and significant. Abstract Copyright (2015) Elsevier, B.V.
2017059391 Yang, Zhaohui (University of Alaska Anchorage, College of Engineering, Anchorage, AK); Still, Benjamin and Ge, Xiaoxuan. Mechanical properties of seasonally frozen and permafrost soils at high strain rate: Cold Regions Science and Technology, 113, p. 12-19, illus. incl. 2 tables, May 2015. Based on Publisher-supplied data.
Frozen soils, especially seasonally frozen soils, have a great impact on the seismic performance of bridge pile foundations. To account for this impact on pile foundations during seismic events, it is necessary to evaluate the mechanical properties of naturally frozen soil samples. This paper focuses on the mechanical properties of naturally frozen silty soils at a relatively high strain rate. High quality specimens of both permafrost and seasonally frozen soils were prepared by block sampling and machining. Both horizontal and vertical specimens were prepared to investigate the effect of specimen orientation. Unconfined compression tests were performed at temperatures ranging from - 0.7 °C to - 11.6 °C, at a constant deformation rate corresponding to a strain rate of 0.001/s. Testing results including soil characteristics and mechanical properties such as stress-strain curves, compressive strength, yield strength, modulus of elasticity, strain values at unconfined compressive and yield strength, and strain value at which 50% of the compressive strength is achieved are presented. The impact of temperature, dry density, water content, and specimen orientation on the mechanical properties is discussed. For permafrost, the ultimate compressive strength of horizontal specimens is substantially higher than that of vertical specimens at the same testing temperature and this strength anisotropy is likely due to ice wedge formation, commonly observed in lowland permafrost. In general, the ultimate compressive strength of naturally frozen specimens is lower than that found in previous studies for remolded frozen silty soils. Abstract Copyright (2015) Elsevier, B.V.
2017059394 Zhou Guoqing (State Key Laboratory for Geomechanics and Deep Underground Engineering, Xuzhou, China); Hu Kun; Zhao Xiaodong; Wang Jianzhou; Liang Hengchang and Lu Guilin. Laboratory investigation on tensile strength characteristics of warm frozen soils: Cold Regions Science and Technology, 113, p. 81-90, illus. incl. 2 tables, May 2015. Based on Publisher-supplied data.
The tensile strength characteristics of warm frozen soils have significant influences on slope stabilities in permafrost regions and on the establishment of ice segregation criterion under frozen fringe conditions. Tensile experiments were carried out on two frozen soils, e.g., frozen clay (FC) and frozen silty clay (FSC), under various temperatures warmer than - 2 °C using the indirect tensile method of Brazilian Splitting Method (BSM). The experimental results indicated that the relationship between tensile strength and corresponding negative temperature can be described by power function both for FC and FSC, but that can be written as linear function for pure ice. The analysis of the factors affecting tensile strength under a warm temperature ranging from 0°C to - 2°C indicated that the pore ice content and pore ice strength dominate the total tensile strength, and the contribution of which to total tensile strength for FC and FSC is approximately 95%. Abstract Copyright (2015) Elsevier, B.V.
2017059340 Li Bo (Chinese Academy of Sciences, Guangzhou Institute of Energy Conversion, Guangzhou, China); Li Xiaosen; Li Gang and Chen Zhaoyang. Evaluation of gas production from Qilian Mountain permafrost hydrate deposits in two-spot horizontal well system: Cold Regions Science and Technology, 109, p. 87-98, January 2015. Based on Publisher-supplied data.
In 2008-2009, gas hydrate deposits were confirmed to exist in the Qinghai-Tibet Plateau permafrost (QTPP) during the Scientific Drilling Project of Gas Hydrate in Qilian Mountain permafrost. Gas hydrate samples were successfully collected from three drilling sites: DK-1, DK-2, and DK-3. Based on the limited geological data from site measurements, gas was produced from the hydrate deposits of DK-2 zone in a two-spot well system through numerical simulation, and its commercial viability was evaluated. The two wells were placed on the same horizontal plane in the middle of the hydrate-bearing layer (HBL), and the depressurization and thermal stimulation methods were employed simultaneously in this system. Simulation results showed that desirable gas production performance could be obtained under suitable operation conditions when using this kind of well design. During the production process, large amount of free gas accumulated in the vicinity of the injection well until the flow channels between the two wells were gradually opened. It was found that the gas production performance was more favored with larger depressurization driving force, while the heat injection rate should be determined cautiously. Dependences of gas production performance on the various properties of hydrate deposits were also assessed. Abstract Copyright (2015) Elsevier, B.V.
2017059339 Wang Lanmin (Lanzhou University, School of Civil Engineering and Mechanics, Lanzhou, China); Wang Wenli and Yu Fan. Thaw consolidation behaviours of embankments in permafrost regions with periodical temperature boundaries: Cold Regions Science and Technology, 109, p. 70-77, January 2015. Based on Publisher-supplied data.
A modified simulation method based on large strain thaw consolidation theory was proposed for the thaw consolidation behaviours of permafrost embankment. It was verified using monitored data that the new method has a good performance in simulating seasonal changes of thaw settlement. For permafrost embankment with different thermal and mechanical properties, the consolidation process in the post-thawed layer of top ground surface will accomplish during initial operating period. After that, thaw consolidation degree will decrease continuously. The decreasing rate of thaw consolidation degree (Dr ) is proportional to thaw consolidation ratio (R) of deep permafrost layer. Regression analysis indicates that Dr is a power function of R. Abstract Copyright (2015) Elsevier, B.V.
2017059338 Wang Tao (China University of Mining and Technology, State Key Laboratory for Geomechanics and Deep Underground Engineering, Xuzhou, China); Zhou Guoqing; Wang Jianzhou; Zhao Xiaodong; Yin Qixiang; Xia Lijiang and Liu Yuyi. Stochastic analysis model of uncertain temperature characteristics for embankment in warm permafrost regions: Cold Regions Science and Technology, 109, p. 43-52, January 2015. Based on Publisher-supplied data.
For embankments in cold regions, the soil properties and the upper boundary conditions are stochastic because of complex geological processes and changeable atmospheric environment. In this study, we model the soil properties as random fields and the upper boundary conditions as stochastic processes. A triangular local average (TLA) method is used to discretize the two-dimensional (2D) random fields. The random temperature fields of an embankment in a cold region are investigated by Neumann stochastic finite element method (NSFEM), and the computational formulas of mean and standard deviation are developed. In the calculation flow chart, a stochastic finite element (FE) program has been compiled by Matrix Laboratory (MATLAB) software. The results show that TLA method perfectly matches with triangular FE method. The randomness of soil properties and boundary conditions lead to the randomness of temperature. The results will improve our understanding of the random temperature field of embankments in cold regions. The proposed method can be used to solve other uncertain thermodynamic problems. Abstract Copyright (2015) Elsevier, B.V.
2017061494 Ghobadi, M. H. (Bu-Ali Sina University, Department of Geology, Hamedan, Iran) and Babazadeh, R. Experimental studies on the effects of cyclic freezing-thawing, salt crystallization, and thermal shock on the physical and mechanical characteristics of selected sandstones: Rock Mechanics and Rock Engineering, 48(3), p. 1001-1016, 48 ref., 2015.
Rocks are used in engineering works as monuments, building stones, and architectural covering stones. Their weathering behaviors and physical and mechanical properties are the most important factors controlling their suitability as building stones. The aim of this study is to evaluate the weathering behaviors of sandstones from the Qazvin area (western Iran). In total, nine sandstones (A, B, C, CG, S, S1, Min, Tr, and Sh) were analyzed. Accelerated weathering processes, namely freezing-thawing (F-T), salt crystallization (SC), heating-cooling (H-C), and heating-cooling-wetting (H-C-W), were used. Sandstones were subjected to 60 cycles of F-T, H-C, and H-C-W and 20 cycles of SC, and changes in characteristics including weight loss (%), P-wave velocity loss (%), and changes in uniaxial compressive strength (UCS) and point load strength were recorded after different numbers of cycles. The results from our laboratory studies indicate that rocks from the same stratigraphic layer can show major differences in weathering properties, and their sensitivity to these processes are different. Also, it was found that the thermal behavior of sandstones under wet and dry conditions were different. In the next stage of this study, a decay function model was used to statistically evaluate the disintegration rate. This model showed that the disintegration rate was higher for salt recrystallization compared with F-T, H-C, and H-C-W processes. Copyright 2014 Springer-Verlag Wien
2017065811 Grube, Alf (Geologisches Landesamt, Behörde für Umwelt und Energie, Hamburg, Germany). Periglaziäre, polygonal-verzweigte rinnenförmige Bildungen und glazitektonische Strukturen in Saale-Till am Elbe-Urstromtalrand bei Wedel (Schleswig-Holstein) [Periglacial polygonal-dendritic channelized forms and glaciotectonic structures in Saalian till at the rim of the Elbe spillway in Wedel (Schleswig-Holstein)]: Eiszeitalter und Gegenwart - Quaternary Science Journal, 64(1), p. 3-13 (English sum.), 59 ref., 2015.
Remarkable polygenetical structures were observed at a refinery rehabilitation site in Wedel/Holstein. The polygonal shaped, channel-like structures are incised in mid-Saalian clayey, chalk-rich till. They are symmetrically semicircular shaped and filled with calcareous, silty sands that can be interpreted as sandy reworked till with aeolian components. The width reaches from approx. 0.3 to 1.5 metres, the depth up to approx. 0.8 metres. Horizontal cracks up to more than 10 meters in lengths, occurring as narrow belts of sand with reddish colour, are often centrally aligned in the channel-like structures. The present-day red colour is not natural but related to pollution. These belts reach down to the bottom of the channel like structures. At the lower site of the channel-like structures glacitectonic fissures with a width up to a few centimetres were to be traced into a depth of several metres to the basis of the excavat ion. The genesis of the channel-like structures is discussed, e.g., a possible relation with the pre-existing glacitectonic joints resp. the expected periglacial paleohydrogeological setting.
2017065913 Richter, Detlev Konrad (Ruhr-Universität Bochum, Institut für Geologie, Mineralogie und Geophysik, Bochum, Germany); Goll, Kristina; Grebe, Witold; Niedermayr, Andrea; Platte, Alexander and Scholz, Denis. Weichselzeitliche Kryocalcite als Hinweise für Eisseen in der Hüttenbläserschachthöhle (Iserlohn, NRW) [Weichselian cryogenic calcites indicating former ice pools in Huttenblaserschacht Cave (Iserlohn, North Rhine-Westphalia)]: Eiszeitalter und Gegenwart - Quaternary Science Journal, 64(2), p. 67-81 (English sum.), 56 ref., 2015.
C/O-stable isotope composition (VPDB) of speleothems from the Makkaronihalle of the Hüttenbläserschacht Cave in Iserlohn shows a clear separation between glacial and interglacial calcites. In contrast to normal speleothems (stalagmites, excentriques, crystals in cave ponds, draperies; d18O: -4.0 to -6.1 per mill, d13C: -4.9 to -10.9 per mill), rhombohedral crystal sinter and spherulitic speleoparticles are characterised by lower d18O (-8.9 to -17.9 per mill) and higher d13C values (+0.7 to -6.1 per mill). This suggests that these speleogenetic particles were formed in slowly freezing waterpools on ice during the transition from a stadial to an interstadial phase. Precise 230Th/U-dating shows younger Weichselian ages of 28.6 to 33.0 ka for these speleogenetic particles from north-west Germany. These formation periods indicate freezing conditions overlain by 34 m of host rock and provide the minimum depth of permafrost penetration for the younger Weichselian in the area of the northern Sauerland (north-west Germany).
2017059333 Feng Qiang (China University of Mining and Technology, State Key Laboratory for Geomechanics and Deep Underground Engineering, Xuzhou, China); Jiang Binsong; Zhang Qiang and Wang Liping. Analytical elasto-plastic solution for stress and deformation of surrounding rock in cold region tunnels: Cold Regions Science and Technology, 108, p. 59-68, illus. incl. 2 tables, December 2014. Based on Publisher-supplied data.
In recent years, the construction of cold-region tunnels has increased in western China. However, the studies of the analytical elasto-plastic solution for the stress and deformation of surrounding rock in cold-region tunnels are limited. To solve this engineering problem and propose new theoretical insights for analysis and design, the elasto-plastic calculation model for surrounding rock in cold-region tunnels is established in this paper. In this model, the entire surrounding rock is divided into four zones, namely, the unfrozen elastic zone, the frozen elastic zone, the frozen plastic zone and the support zone. The frozen surrounding rock is assumed to conform to the ideal elasto-plastic model and the Mohr-Coulomb yield criterion. The stress and deformation fields in each zone are solved according to continuity conditions. A case is introduced to obtain the distribution of stress and strain in the surrounding rock of cold-region tunnels. The reason that the circumferential stress is less than the radial stress in the unfrozen zone is explained and the range of that is also addressed. Moreover, the location in which no displacement is generated is determined in the freezing circle. The produced high stress is mainly influenced by the linear frost strain. The results of stress field and strain field are verified by the existing elastic solution. At last, parameter analysis is performed to obtain the influence of the related parameters on plastic radius and the surrounding rock stresses at the inner and outer edges of the freezing circle. The results can guide for numerical simulations and field engineering practice. Abstract Copyright (2014) Elsevier, B.V.
2017063517 Luo Xuedong (China University of Geosciences, Department of Engineering, Wuhan, China); Jiang Nan; Zuo Changqun; Dai Zhenwei and Yan Suntao. Damage characteristics of altered and unaltered diabases subjected to extremely cold freeze-thaw cycles: Rock Mechanics and Rock Engineering, 47(6), p. 1997-2004, 15 ref., November 2014.
Altered and unaltered diabases are commonly deposited on hydrothermally mineralized slopes. To study their damage characteristics during freeze-thaw cycles, they were sampled from Cihai iron ore mine located in an extremely cold region, Xinjiang, China and examined using acoustic and X-ray diffraction experiments to analyze the differences in their main mineral components and explore their damage characteristics under freeze-thaw conditions. Based on the results of these experiments, their damage and degradation patterns were obtained and the evolution of their physical characteristics including the rock mass loss rate (LF), rock strength loss rate (Rs), P-wave velocity loss rate (Vl), and freeze-thaw coefficient (Kf) was analyzed. In addition, two groups of equations were established to characterize the relationships of these physical and mechanical properties of the rock specimens with the number and temperature of freeze-thaw cycles. The results show that the mineral composition of diabase changes during its alteration, showing increased clay and calcite, and the degradation and evolution patterns of the physical and mechanical parameters (LF, Rs, Vl, and Kf) of the altered rocks during freeze-thaw cycles are different from those of diabase, with the altered diabase exhibiting greater damage than the diabase. Copyright 2013 Springer-Verlag Wien
2017059331 Pei Wansheng (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Zhang Mingyi; Lai Yuanming; Jin Long and Harbor, Jon. Thermal stability analysis of crushed-rock embankments on a slope in permafrost regions: Cold Regions Science and Technology, 106-107, p. 175-182, illus. incl. 1 table, October 2014. Based on Publisher-supplied data.
Highways/railways often pass across slope areas and their embankments are often built on the slopes in permafrost regions. It is difficult to ensure the thermal stability of the embankments at the slopes due to the effect of slopes. To protect the underlying permafrost, the crushed-rock embankments are often used in the slope areas. Therefore, it is very necessary to explore the thermal state of crushed-rock embankments located on the slopes. In this study, we studied numerically the temperature characteristics of three kinds of crushed-rock embankments located on a slope under global warming, i.e. crushed-rock interlay embankment, crushed-rock interlayer-revetment embankment and crushed-rock base embankment. Numerical results indicate that the crushed-rock interlayer embankment and the crushed-rock interlayer-revetment embankment, located on a slope with a ratio of 1:3.73 (about 15° from the horizontal), cannot effectively eliminate the negative effect of climate warming and construction-induced warming, and the effect of slope is still obvious on the thermal stability of permafrost under the crushed-rock interlayer embankment. However, the crushed-rock base embankment can significantly reduce the temperature of underlying permafrost and keep the underlying permafrost table stable for a long term; furthermore, the ground temperatures under the long side slope are far lower than those under the short side slope, and this will be more advantageous to control the slide of the embankment located on a slope and increase its stability. We also find that the three kinds of embankments cannot all remove the thermal effects of construction from themselves in a short term. Generally speaking, the crushed-rock base embankment structure can be very advantageous to the thermal stability of the embankment on a slope. Abstract Copyright (2014) Elsevier, B.V.
2017059330 Xie Qijun (Southwest Jiaotong University, School of Mechanics and Engineering, Chengdu, China); Zhu Zhiwu and Kang Guozheng. Dynamic stress-strain behavior of frozen soil; experiments and modeling: Cold Regions Science and Technology, 106-107, p. 153-160, illus. incl. 4 tables, October 2014. Based on Publisher-supplied data.
The dynamic stress-strain behavior of artificial frozen soil (with a moisture content of 30%) was tested using a split Hopkinson pressure bar (SHPB) under various impact compressive loading conditions. The tests were performed at strain rates 400-1000 s-1 and different temperatures (i.e., - 3, - 8, - 18, and - 28°C). The experimental results show that the dynamic stress-strain responses of the artificial frozen soil exhibit a positive strain rate sensitivity and negative temperature dependence. An energy-based dynamic constitutive model was constructed to simulate the dynamic stress-strain behavior of the frozen soil. It is shown that the proposed model can describe the positive strain-rate sensitivity and negative temperature dependence of the artificial frozen soil reasonably, and predict the dynamic stress-strain curves of the frozen soil well. Abstract Copyright (2014) Elsevier, B.V.
2017059277 Byun, Yong-Hoon (Korea University, School of Civil, Environmental and Architectural Engineering, Seoul, South Korea); Yoon, Hyung-Koo; Kim, Young Seok; Hong, Seung Seo and Lee, Jong-Sub. Active layer characterization by instrumented dynamic cone penetrometer in Ny-Alesund, Svalbard: Cold Regions Science and Technology, 104-105, p. 45-53, illus. incl. 2 tables, sketch map, August 2014. Based on Publisher-supplied data.
Global warming may induce an increase of active layer thickness in the Arctic region. The freezing and thawing of the active layer can damage infrastructures such as roads, railways, and embedded pipe lines in cold regions. A few methods, however, have been proposed to characterize the active layer. The objective of this study is to evaluate the characteristics of the active layer by laboratory and field tests, especially using the instrumented dynamic cone penetrometer (IDCP). Geographical and geological characteristics of Ny-Alesund, Svalbard are introduced, and the geotechnical properties, microstructure observations, and thermal properties of the Ny-Alesund soils are investigated. In addition, subsurface temperatures monitored for a year are discussed. The IDCP, which is able to measure the energies transferred into the rod head and the cone tip, is applied to the evaluation of the strength variation and the thickness of the active layer in Ny-Alesund. During dynamic penetration tests, the IDCP can produce profiles of the corrected cone tip resistance as well as the dynamic cone penetration index (DCPI). The results show that the active layer thickness estimated from the DCPI and corrected cone tip resistance profiles is approximately 1700 mm. Furthermore, the bottom of the active layer significantly corresponds to that estimated by the maximum ground temperature profile with a soil thermal diffusivity of 5.5 · 10-7 m2·s-1. This study represents the characteristics of Ny-Alesund soils investigated with a variety of laboratory tests, and suggests that the IDCP may be effectively used for active layer characterization. Abstract Copyright (2014) Elsevier, B.V.
2017059280 Dong Yuanhong (China Communications Construction Company First Highway Consultants Company, Xi'an, China); Pei Wansheng; Liu Ge; Jin Long and Chen Donggen. In-situ experimental and numerical investigation on the cooling effect of a multi-lane embankment with combined crushed-rock interlayer and ventilated ducts in permafrost regions: Cold Regions Science and Technology, 104-105, p. 97-105, illus. incl. 1 table, August 2014. Based on Publisher-supplied data.
For the multi-lane expressway embankment constructed in permafrost regions, the width is always over 20 m and asphalt-concrete pavement is adopted, both of which would largely increase the heat absorption of underlying permafrost compared with ordinary highway embankment. The increased heat absorption would result in more severe warming and thawing in underlying permafrost and threat the stability of the embankment. So, traditional cooling measures would not be effective enough to protect the underlying permafrost or to ensure the thermal stability of multi-lane expressway embankment. Based on this, a combined cooling measure composed of crushed-rock interlayer and ventilated ducts at its top was presented by the authors, the cooling mechanism of which was validated under laboratory condition. However, it is of necessity to further investigate the cooling effect of the new combined cooling measure under actual condition and its long-term cooling effect under global warming background. In this study, firstly, the observed temperature data from an in-situ test embankment of the new combined cooling measure were collected and analyzed. The observed data illustrated that the new cooling measure was effective in protecting underlying permafrost under actual condition of the Qinghai-Tibetan Plateau. Secondly, a numerical model was validated by the in-situ test data. Finally, the temperature distributions of ordinary multi-lane embankment, multi-lane embankment with crushed-rock interlayer and multi-lane embankment with combined crushed-rock interlayer and ventilated ducts after 20 years of construction were numerically simulated under global warming background. According to the numerical study result, the long-term cooling effect of single crushed-rock in multi-lane embankment was limited. After the ventilated ducts were added at the top of the crushed-rock interlayer, the cooling effect was greatly enhanced and was effective enough to protect the underlying permafrost. Abstract Copyright (2014) Elsevier, B.V.
2017059275 Liu Jiankun (Beijing Jiaotong University, School of Civil Engineering, Beijing, China); Lu Peng; Cui Yinghui and Liu Jingyu. Experimental study on direct shear behavior of frozen soil-concrete interface: Cold Regions Science and Technology, 104-105, p. 1-6, illus. incl. 2 tables, August 2014. Based on Publisher-supplied data.
In order to study the mechanical behavior of frozen soil-concrete interfaces, a series of direct shear tests were conducted on a large-scale temperature-controlled direct shear test system (TZJ-150). Synchronous variations were found in both the shear stress-displacement and vertical displacement-shear displacement curves. The whole shear process can be divided into five stages: the elastic deformation part, the plastic deformation part, the whole slide part, the strain hardening part, and the stable residual strength part. The influence rules of normal pressure, temperature, and water content on the shear strength of the interface were obtained by a series of sample tests with different parameters. Fitted equations between factors and shear strength were presented. The peak shear strength had linear relationships with the normal pressure and temperature, but a nonlinear relationship with the water content, which had a much greater effect on the peak shear strength. The residual shear strength also had linear relationships with the normal pressure and temperature, but was basically unrelated with the water content. A reasonable explanation about the changes of peak shear strength and residual shear strength was proposed. Abstract Copyright (2014) Elsevier, B.V.
2017059276 Zhou Jiazuo (Chinese Academy of Sciences, Institute of Rock and Soil Mechanics, Wuhan, China); Wei Changfu; Li Dongqing and Wei Houzhen. A moving-pump model for water migration in unsaturated freezing soil: Cold Regions Science and Technology, 104-105, p. 14-22, illus. incl. 2 tables, August 2014. Based on Publisher-supplied data.
This paper presents a new approach for simulating the water migration in freezing soils, in which the pore water migration and heat transfer are characterized using an imaginary pump attached with a small imaginary reservoir. The pump moves with the freezing front as temperature decreases, sucks the liquid water from the unfrozen zone and then stores it in the frozen zone. The reservoir is used to gather the sucked water and store it in the form of pore ice through phase change. Explicit governing equations are developed for describing the water migration, crystallization and/or heat transfer in the soil, the pump and the reservoir. The proposed model is numerically implemented into a commercial code. Compared to the previous approaches used to simulate the soil freezing processes, application of the new approach avoids remeshing and recalculating the moving boundaries, and this feature can drastically simplify the numerical implementation of the theoretical model. The new approach is used to analyze the one-dimensional freezing process in soils. The simulated results are compared with the experimental data available in the literature and the simulations based on other approaches, showing that the new approach is capable of effectively simulating the freezing process of soils. Abstract Copyright (2014) Elsevier, B.V.
2017059278 Zhou Jiazuo (Chinese Academy of Sciences, Institute of Rock and Soil Mechanics, Wuhan, China); Wei Changfu; Wei Houzhen and Tan Long. Experimental and theoretical characterization of frost heave and ice lenses: Cold Regions Science and Technology, 104-105, p. 76-87, illus. incl. 2 tables, August 2014. Based on Publisher-supplied data.
A series of freezing experiments were conducted to simulate the frost heave in saturated silt samples with variable thermal boundaries. It is shown that before the frost heave occurs, a small amount of pore water is discharged out of the soil due to the sudden freezing of the super-cooled pore water, and that once the frost heave occurs, the total amount of frost heave is approximately equal to the amount of frost heave due to water intake. A formulation is developed which can be used to determine the initiation time of frost heave. The location of the freezing front and the amount of frost heave are calculated, and the calculated results agree well with the experimental measurements. A criterion for ice lens initiation/growth is presented, according to which an ice lens initiates or grows if the volumetric water content is equal to or greater than 1. It is demonstrated that the predicted ice lenses are similar to the observed ones, showing the validity of the criterion. Abstract Copyright (2014) Elsevier, B.V.
2017059274 Tian Huihui (Chinese Academy of Sciences, Institute of Rock and Soil Mechanics, Wuhan, China); Wei Changfu; Wei Houzhen and Zhou Jiazuo. Freezing and thawing characteristics of frozen soils; bound water content and hysteresis phenomenon: Cold Regions Science and Technology, 103, p. 74-81, illus. incl. 1 table, July 2014. Based on Publisher-supplied data.
The freezing/thawing characteristics of three soils with different compositions are investigated based on the nuclear magnetic resonance (NMR) proton spin spin relaxation time (T2) distribution and free-induction decay (FID) measurements. A threshold value of T2 is identified for defining the bound water, and the bound water contents in the soils are calculated. It is demonstrated that the bound water content varies insignificantly with temperature in all the tested soils. The hysteretic characteristics of soils are analyzed during a freezing/thawing cycle, and possible mechanisms for the hysteresis are discussed. It is found that the hysteresis loop can be divided into three distinct zones, in which the hysteresis can be accounted for by metastable nucleation, capillary and adsorption effects, and adsorption effect, respectively. A NMR-based procedure is proposed for determining the unfrozen pore water content. In particular, it is shown that the thickness of the water films decreases with the temperature in the fully-saturated frozen soils. Abstract Copyright (2014) Elsevier, B.V.
2017059272 Zhao Lianzhen (Nanjing Forestry University, Department of Civil Engineering, Nanjing, China); Yang Ping; Wang, J. G. and Zhang, Lai-Chang. Cyclic direct shear behaviors of frozen soil-structure interface under constant normal stiffness condition: Cold Regions Science and Technology, 102, p. 52-62, June 2014. Based on Publisher-supplied data.
The frozen soil-structure interface is the key connecting component between structures and the soil in the permafrost regions. The soil-structure interface is usually subjected to seismic or wind loadings; consequently the cyclic shear properties of the interface are the key parameters of concern when considering the safety and durability of the structures in these permafrost regions. In this paper we present the results of measuring and analyzing the cyclic shear properties of an artificially frozen soil-structure interface; the experimental work being conducted on our self-developed, large-scale multi-functional direct shear apparatus (DDJ-1). These direct shear tests were conducted under conditions of constant normal stiffness, having a specific initial value for normal stresses (either 300, 500, or 700 kPa), and at a constant frozen temperature (i.e. -6, -10, or -14°C) or a rising temperature (from -14°C to -2°C). Their cyclic shear stress and normal displacement were measured in 30 cycles for each of the constant frozen temperature settings, and in 13.25 cycles for the rising temperature. These test results show that: (1) The maximum shear stress is observed in the first cycle. This maximum shear stress is higher for lower frozen temperature and higher initial normal stress. Furthermore, the internal friction angle of the frozen soil-structure interface decreases with shear cycle and higher frozen temperature. (2) Under constant frozen temperature, the rates of increase of the normal displacement and normal stress slow down with cyclic loading time. However, these rates of increase are fast at the beginning, slow down, and then speed up again under the rising temperature. (3) The reversible normal displacement, expressed by the peak-to-trough distance of normal displacement, linearly increases with the initial normal stress when the frozen temperature is constant. Abstract Copyright (2014) Elsevier, B.V.
2017059271 Mu Cuicui (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Zhang Tingjun; Schuster, Paul F.; Schaefer, Kevin; Wickland, Kimberly P.; Repert, Deborah A.; Liu, Lin; Schaefer, Tim and Cheng Guodong. Carbon and geochemical properties of cryosols on the North Slope of Alaska: Cold Regions Science and Technology, 100, p. 59-67, April 2014. Based on Publisher-supplied data.
Cryosols contain roughly 1700Gt of Soil organic carbon (SOC) roughly double the carbon content of the atmosphere. As global temperature rises and permafrost thaws, this carbon reservoir becomes vulnerable to microbial decomposition, resulting in greenhouse gas emissions that will amplify anthropogenic warming. Improving our understanding of carbon dynamics in thawing permafrost requires more data on carbon and nitrogen content, soil physical and chemical properties and substrate quality in cryosols. We analyzed five permafrost cores obtained from the North Slope of Alaska during the summer of 2009. The relationship between SOC and soil bulk density can be adequately represented by a logarithmic function. Gas fluxes at -5°C and 5°C were measured to calculate the temperature response quotient (Q10). Q10 and the respiration per unit soil C were higher in permafrost-affected soils than that in the active layer, suggesting that decomposition and heterotrophic respiration in cryosols may contribute more to global warming. Abstract Copyright (2014) Elsevier, B.V.
2017061590 Curtaz, M. (Fondazione Montagna Sicura, Courmayeur, Italy); Ferrero, A. M.; Roncella, R.; Segalini, A. and Umili, G. Terrestrial photogrammetry and numerical modelling for the stability analysis of rock slopes in high mountain areas; Aiguilles Marbrées case: Rock Mechanics and Rock Engineering, 47(2), p. 605-620, 42 ref., March 2014.
Several high-altitude slope instability phenomena, involving rock blocks of different volumes, have been observed in recent years. The increase in these phenomena could be correlated to climatic variations and to a general increase in temperature that has induced both ice melting with consequent water seepage and glacial lowering, with a consequent loss of support of the rock face. The degradation of the high-altitude thermal layer, which is known as "permafrost", can determine the formation of highly fractured rock slopes where instabilities can concentrate. The present research has developed a methodology to improve the understanding and assessment of rock slope stability conditions in high mountain environments where access is difficult. The observed instabilities are controlled by the presence of discontinuities that can determine block detachments. Consequently, a detailed survey of the rock faces is necessary, both in terms of topography and geological structure, and in order to locate the discontinuities on the slope to obtain a better geometric reconstruction and subsequent stability analysis of the blocky rock mass. Photogrammetric surveys performed at different times allow the geostructure of the rock mass to be determined and the rock block volumes and detachment mechanisms to be estimated, in order to assess the stability conditions and potential triggering mechanisms. Photogrammetric surveys facilitate both the characterisation of the rock mass and the monitoring of slope instabilities over time. The methodology has been applied in a case study pertaining to the North Face of Aiguilles Marbrées in the Mont Blanc massif, which suffers from frequent instability phenomena. A slope failure that occurred in 2007 has been back-analysed using both the limit equilibrium method (LEM) and 3D distinct element modelling (DEM). The method has been supported and validated with traditional in situ surveys and measurements of the discontinuity orientation and other rock mass features. Copyright 2013 Springer-Verlag Wien
2017059268 Chen Tuo (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Institute, Lanzhou, China); Ma Wei; Wu Zhijian and Mu Yanhu. Characteristics of dynamic response of the active layer beneath embankment in permafrost regions along the Qinghai-Tibet Railroad: Cold Regions Science and Technology, 98, p. 1-7, illus. incl. 2 tables, February 2014. Based on Publisher-supplied data.
Dynamic response characteristics and stability of embankment are of primary importance for railroad operation in permafrost regions. The strong motion tests are carried out on a traditional sand gravel embankment at the Beilu River segment along the Qinghai-Tibet Railroad, and the acceleration waveforms at the shoulder and the slope toe of the embankment, when passenger train and freight train pass, are collected through strong motion tests. There is an obvious attenuation effect during the waveform transfer process from the shoulder to slope toe, and the natural frequency of the embankment is between 30-40 Hz. Based on the tests in situ, the nonlinear dynamic finite element analysis is applied for numerical simulations on dynamic response of the traditional sand gravel embankment to train load, and the influences of underlying active layer on the dynamic response of the embankment at different seasons are analyzed. The results show that the vibration attenuation of the train load is obvious at different seasons, which presents a linear decrease tendency in summertime, but a nonlinear decrease tendency in wintertime. Both of the two decrease tendencies mainly occur within the soil layer above the permafrost table, but the attenuation effect in summertime, when the active layer is thawed, is slightly greater than that in wintertime when the active layer is frozen. Soil deformation induced by train vibrations occurs mainly above the permafrost table in summertime, but in wintertime, it mainly occurs above the natural surface. Meanwhile, the amount of deformation at the same location in summertime is far more than that in wintertime. Abstract Copyright (2014) Elsevier, B.V.
2017059270 Cui Zhendong (China University of Mining and Technology, School of Mechanics and Civil Engineering, Jiangsu, China); He Pengpeng and Yang Weihao. Mechanical properties of a silty clay subjected to freezing-thawing: Cold Regions Science and Technology, 98, p. 26-34, illus. incl. 4 tables, February 2014. Based on Publisher-supplied data.
The structure of soil will change a lot after freezing and thawing. The mechanical properties and the microstructures are quite different from those of the undisturbed soil. Based on the static triaxial tests and dynamic triaxial tests, this paper studied the mechanical characteristics of a silty clay and quantitatively analyzed the scanning electron microscopy (SEM) images of the silty clay before and after freezing and thawing. According to the static triaxial test and the disturbed state concept (DSC), the constitutive relationship of the thawing soil was investigated. The dynamic triaxial tests were conducted to study the dynamic constitutive relationship of the thawing soil and the mechanical parameters were compared with those of the undisturbed soil. The parameters of the microstructures of silty clay were extracted to analyze the influences of the freezing and thawing on silty soil. Abstract Copyright (2014) Elsevier, B.V.
2017059269 Wang Pingkang (China Geological Survey, Oil and Gas Survey, Beijing, China); Zhu Youhai; Lu Zhenquan; Huang Xia; Pang Shouji and Zhang Shuai. Gas hydrate stability zone migration occurred in the Qilian Mountain permafrost, Qinghai, northwest China; evidences from pyrite morphology and pyrite sulfur isotope: Cold Regions Science and Technology, 98, p. 8-17, illus. incl. 2 tables, February 2014. Based on Publisher-supplied data.
Fracture-filling pyrites, which semi-filled or fully filled rock fractures, were commonly found in the cores from all hydrate testing well in the Qilian mountain permafrost. The occurrence of the pyrites is very similar to the "fracture-filling" gas hydrate that occurred in this area, and whose distribution mainly concentrated below the hydrate layer or layer of hydrate associated anomaly. This paper carried out the study in morphology and sulfur isotope for the fracture-filling pyrites. The results show that fracture-filling pyrites consisted of cube form pyrite crystals, directionally spread in a step-like fashion along the fracture surface, and associated with a circular structure; the value of d34SCDT ranges from 6.761 ppm to 41.846 ppm, and the most positive excursion exists below the deepest layer of hydrate associated anomaly. The characters in pyrite crystal morphology, sulfur isotopic composition and spatial distribution closely related with the secondary change of metastable gas hydrate reservoir. The permafrost degeneration resulting from climate warming is the most direct cause for gas hydrate stability zone (GHSZ) migration that occurred in the Qilian mountain. The zone between the shallowest and the deepest distribution of the fracture-filling pyrite recorded the possible largest original GHSZ. The top and the bottom of GHSZ have moved downward and upward to a certain extent, respectively, further inferring that the depth of permafrost has decreased about 10m in the boreholes. Abstract Copyright (2014) Elsevier, B.V.
2017065000 Aydan, Omer (Tokai University, Institute of Oceanic Research and Development, Shizuoka, Japan); Sato, Akira and Yagi, Masatoshi. The inference of geo-mechanical properties of soft rocks and their degradation from needle penetration tests: Rock Mechanics and Rock Engineering, 47(5), p. 1867-1890, 37 ref., 2014.
Needle penetration tests (NPTs) are used for inferring the uniaxial compressive strength of soft rocks, particularly in tunneling through squeezing rocks and foundations on weathered rocks in Japan. The device measures the applied load and the penetration depth of its needle. The ratio of applied load to penetration depth was originally called the needle penetration index (NPI). In this study, this device has been used to infer the geo-mechanical properties of soft rocks from Japan, Turkey, Indonesia, and Egypt. Various equations are presented to infer the geo-mechanical properties in terms of the NPI and compared with the experimental results. The possibility of evaluating the anisotropy of geo-mechanical properties is shown. Furthermore, the characterization of geo-mechanical properties of fault/fracture and slip (shear) surfaces is explained. Some additional equations are given to consider the degradation of geo-mechanical properties as a function of water content, weathering state, and number of cycles of freezing-thawing. Furthermore, the possibility of evaluating the time-dependency characteristics of soft rocks by needle penetration testing is discussed through experiments. It is shown that the effects of water content, weathering state, and number of cycles of freezing-thawing and time-dependency can be evaluated using the NPT technique. Copyright 2013 Springer-Verlag Wien
2017059491 Haeberli, Wilfried (University of Zurich, Geography Department, Zurich, Switzerland). Mountain permafrost; research frontiers and a special long-term challenge: in Contaminants in freezing ground and cold ecosystems (Margesin, Rosa, editor; et al.), Cold Regions Science and Technology, 96, p. 71-76, December 2013. Based on Publisher-supplied data.
Advanced methodologies such as core drilling, borehole logging/monitoring, geophysical tomography, high-precision photogrammetry, laser altimetry, GPS/SAR surveying, miniature temperature data logging, geotechnical laboratory analyses, numerical modelling, or GIS-based simulation of spatial distribution patterns in complex topography at regional to global scales have created a rapidly increasing knowledge basis concerning permafrost in cold mountain ranges. Based on a keynote presentation about mountain permafrost at CFG8 in Obergurgl 2012, a brief summary is provided concerning primary research frontiers and the long-term challenge related to the increasing probability of far-reaching flood waves in high-mountain regions originating at newly forming lakes as a consequence of large rock falls and landslides from destabilising steep rock walls with conditions of warming and degrading permafrost often in combination with de-buttressing by vanishing glaciers. Research is especially intense in the densely populated European Alps. Abstract Copyright (2013) Elsevier, B.V.
2017059490 Margesin, Rosa (University of Innsbruck, Innsbruck, Austria) and Snape, Ian, editors. Contaminants in freezing ground and cold ecosystems: Cold Regions Science and Technology, 96, p. 69-137, illus., December 2013. Individual papers within scope are cited separately.
2017059265 Pei Wansheng (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Yu Wenbing; Li Shuangyang and Zhou Jiazuo. A new method to model the thermal conductivity of soil-rock media in cold regions; an example from permafrost regions tunnel: Cold Regions Science and Technology, 95, p. 11-18, November 2013. Based on Publisher-supplied data.
Thermal conductivity of soil-rock media is an important index for analyzing the temperature field of cold region engineering. As a kind of mixed media, the thermal conductivity is determined by many factors, e.g. porosity, dry density, saturation degree, temperature, water content and so on. In this study, the thermal conductivity model of soil-rock media is established by multiple linear regression method based on the basic parameters of soil-rock samples. The significant testing (correlation coefficient R2, F-test and probability-of-F-to-enter) shows that the regression effect is well. To validate the multiple linear regression model, a comparison of the calculated values from the model with the tested data not used in the construction of the model shows that this model can effectively calculate thermal conductivity of soil-rock media. Additionally, compared with the other three general models, i.e. BP neural model, physical model and CK model, the multiple linear regression model is more reasonable and effective. Finally, based on the apparent heat capacity theory, a general regression model for soil-rock media in cold regions is obtained. It is hoped that a parameter basis can be provided for the temperature field simulation of cold region engineering from the study. Abstract Copyright (2013) Elsevier, B.V.
2017059267 Sheng Daichao (Central South University, School of Civil Engineering, National Engineering Laboratory for High-Speed Railway Construction, Hunan, China); Zhang Sheng; Yu Zhiwu and Zhang Jiasheng. Assessing frost susceptibility of soils using PCHeave: Cold Regions Science and Technology, 95, p. 27-38, November 2013. Based on Publisher-supplied data.
This paper first presents a simple frost heave model. Frost heave is assumed to be caused by the formation of ice lenses in a freezing soil. The formation of ice lenses is governed by the Clapeyron equation of thermodynamics and relies on the existence of a frozen fringe between the frozen and unfrozen zones. Both unfrozen water and ice co-exist in pores of the frozen fringe. The suction at the water-ice interface is the driving force for the water flow that feeds the growth of the ice lens. The initiation of a new ice lens is governed by a simple effective stress concept. The frost heave model contains only a few soil parameters and can be used to compute frost heave and frost penetration in stratified soil profiles. The second part of the paper illustrates the application of the frost heave model in assessing the frost susceptibility of different soils. It is shown that the frost susceptibility of a soil must be assessed together with environmental conditions such as overburden pressure, temperature gradient, cooling rate and the depth of groundwater table. A soil that is only mildly susceptible to frost according to classification can still generate a significant amount of heave or heaving pressure under favourable environmental conditions. Abstract Copyright (2013) Elsevier, B.V.
2017061148 Thienpont, Joshua R. (Queen's University, Paleoecological Environmental Assessment and Research Laboratory, Kingston, ON, Canada); Kokelj, Steven V.; Korosi, Jennifer B.; Cheng, Elisa S.; Desjardins, Cyndy; Kimpe, Linda E.; Blais, Jules M.; Pisaric, Michael F. J. and Smol, John P. Exploratory hydrocarbon drilling impacts to Arctic lake ecosystems: PLoS One, 2013(e78875), illus. incl. sketch map, 37 ref., November 6, 2013.
Recent attention regarding the impacts of oil and gas development and exploitation has focused on the unintentional release of hydrocarbons into the environment, whilst the potential negative effects of other possible avenues of environmental contamination are less well documented. In the hydrocarbon-rich and ecologically sensitive Mackenzie Delta region (NT, Canada), saline wastes associated with hydrocarbon exploration have typically been disposed of in drilling sumps (i.e., large pits excavated into the permafrost) that were believed to be a permanent containment solution. However, failure of permafrost as a waste containment medium may cause impacts to lakes in this sensitive environment. Here, we examine the effects of degrading drilling sumps on water quality by combining paleolimnological approaches with the analysis of an extensive present-day water chemistry dataset. This dataset includes lakes believed to have been impacted by saline drilling fluids leaching from drilling sumps, lakes with no visible disturbances, and lakes impacted by significant, naturally occurring permafrost thaw in the form of retrogressive thaw slumps. We show that lakes impacted by compromised drilling sumps have significantly elevated lakewater conductivity levels compared to control sites. Chloride levels are particularly elevated in sump-impacted lakes relative to all other lakes included in the survey. Paleolimnological analyses showed that invertebrate assemblages appear to have responded to the leaching of drilling wastes by a discernible increase in a taxon known to be tolerant of elevated conductivity coincident with the timing of sump construction. This suggests construction and abandonment techniques at, or soon after, sump establishment may result in impacts to downstream aquatic ecosystems. With hydrocarbon development in the north predicted to expand in the coming decades, the use of sumps must be examined in light of the threat of accelerated permafrost thaw, and the potential for these industrial wastes to impact sensitive Arctic ecosystems.
2017063346 Pommerol, A. (Universität Bern, Physikalisches Institut, Bern, Switzerland); Thomas, N.; Jost, B.; Beck, P.; Okubo, C. and McEwen, A. S. Photometric properties of Mars soils analogs: Journal of Geophysical Research: Planets, 118(10), p. 2045-2072, illus. incl. 8 tables, 87 ref., October 2013.
We have measured the bidirectional reflectance of analogs of dry, wet, and frozen Martian soils over a wide range of phase angles in the visible spectral range. All samples were produced from two geologic samples: the standard JSC Mars-1 soil simulant and Hawaiian basaltic sand. In a first step, experiments were conducted with the dry samples to investigate the effects of surface texture. Comparisons with results independently obtained by different teams with similar samples showed a satisfying reproducibility of the photometric measurements as well as a noticeable influence of surface textures resulting from different sample preparation procedures. In a second step, water was introduced to produce wet and frozen samples and their photometry investigated. Optical microscope images of the samples provided information about their microtexture. Liquid water, even in relatively low amount, resulted in the disappearance of the backscattering peak and the appearance of a forward-scattering peak whose intensity increases with the amount of water. Specular reflections only appeared when water was present in an amount large enough to allow water to form a film at the surface of the sample. Icy samples showed a wide variability of photometric properties depending on the physical properties of the water ice. We discuss the implications of these measurements in terms of the expected photometric behavior of the Martian surface, from equatorial to circum-polar regions. In particular, we propose some simple photometric criteria to improve the identification of wet and/or icy soils from multiple observations under different geometries. Abstract Copyright (2013), . American Geophysical Union. All Rights Reserved.
2017059263 Kanevskiy, M. (University of Alaska Fairbanks, Fairbanks, AK); Shur, Y.; Krzewinski, T. and Dillon, M. Structure and properties of ice-rich permafrost near Anchorage, Alaska: Cold Regions Science and Technology, 93, p. 1-11, illus. incl. 2 tables, sketch map, September 2013. Based on Publisher-supplied data.
Geotechnical investigations in the vicinity of Anchorage, Alaska revealed a body of ice-rich permafrost up to 12m thick and approximately 150m long. Mean annual air temperature in Anchorage is +2.2°C which is unfavorable to the existence of permafrost. However, isolated masses of relic permafrost exist at temperatures close to 0°C protected from rapid thawing by a thick layer of peat and soils with high ice content. Frozen soils found at the study site include silty clay of glacio-lacustrine origin with numerous layers of segregated ice up to 70cm in thickness. The average volume of visible ice is 42.5%; and total gravimetric water content is 68%. With an average permafrost thickness of 9.5m and an average thaw strain of 40%, the thaw settlement of the surface is expected to be at least 3.8m after degradation of permafrost, an unacceptable deformation for any engineered structure on these soils. Abstract Copyright (2013) Elsevier, B.V.
2017059264 Olgun, Murat (Selcuk University, Department of Civil Engineering, Konya, Turkey). The effects and optimization of additives for expansive clays under freeze-thaw conditions: Cold Regions Science and Technology, 93, p. 36-46, illus. incl. 8 tables, September 2013. Based on Publisher-supplied data.
This article reports on the optimization of additives to improve the geotechnical properties of an expansive clay soil subject to freeze-thaw effect, and the effects on soil behavior are evaluated. Lime and rice husk ashes, which are waste materials, were used in stabilization, and randomly distributed fiber was used as reinforcement. The response surface methodology was used for experimental design and optimization. The ranges of additives used in the experimental design were selected as 2.0-8.0% lime, 0.0-15.0% rice husk ash, and 0.0-0.8% fiber. The experiments were conducted on both soil samples before and after freeze-thaw cycle. The non freeze-thaw subjected samples were subjected to only 28-day curing, whereas freeze-thaw subjected samples were subjected to 28-day curing followed by seven freeze-thaw cycles. At the end of these periods, unconfined compressive strength and swelling tests were conducted on the samples, the results were evaluated via response surface methodology, and scanning electron microscopy images were produced for some samples. According to the experimental results, the most influential parameter on compressive strength values in non freeze-thaw subjected samples was lime percentage, whereas it was rice husk ash percentage in freeze-thaw subjected samples. Fiber and lime were effective on axial strain value in both cases. While only the lime amount was effective on the swelling pressure values in the non freeze-thaw subjected samples, the lime and the rice husk ash amount were effective in the freeze-thaw subjected samples. In the optimization of three response variables in combination, desirability levels were 0.85 and 0.94, respectively, in non freeze-thaw subjected and freeze-thaw subjected samples. In the non freeze-thaw subjected samples, the optimum percentages for lime, rice husk ash and fiber additives were calculated as 7.39%, 5.78-5.91% and 0.8%, respectively. In the freeze-thaw subjected samples, the optimum percentages were 6.46%, 14.94-15.0% and 0.78-0.79%, respectively. The optimum rice husk ash amount increased under the freeze-thaw effect and it was especially effective, whereas the lime percentage decreased. Abstract Copyright (2013) Elsevier, B.V.
2017059262 Yao Xiaoliang (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Qi Jilin; Yu Fan and Ma Ling. A versatile triaxial apparatus for frozen soils: Cold Regions Science and Technology, 92, p. 48-54, illus. incl. 1 table, August 2013. Based on Publisher-supplied data.
Settlement and damage to infrastructures in permafrost regions depend in part on the mechanical properties of permafrost layers. In order to get a better understanding of the mechanical behavior of frozen soils, a triaxial apparatus was developed with three new features in addition to the traditional functions. The first is the accurate temperature control, which allows temperature to fluctuate within ±0.1°C during the loading period, and ±0.02°C before loading, so as to get a better understanding of the mechanical properties of frozen soils under temperatures close to thawing point. The second feature is used to measure K0 of frozen soils. A highly-sensitive radial strain measurement device was designed and the K0 state can be accurately maintained by automatically adjusting the radial pressure when radial deformation changes more than ±10mm. The third is the precise measurement of the volumetric strain through the displacement of axial and radial loading pistons. The capabilities of the triaxial apparatus are shown using a series of test results. It is considered to be a promising tool to investigate the mechanical properties of frozen soils. Abstract Copyright (2013) Elsevier, B.V.
2017063404 Aydan, Omer (Tokai University, Ocean Research Institute, Shizuoka, Japan) and Ulusay, Resat. Geomechanical evaluation of Derinkuyu antique underground city and its implications in geoengineering: Rock Mechanics and Rock Engineering, 46(4), p. 731-754, 60 ref., July 2013.
Derinkuyu Underground City, located in the Cappadocia Region of Turkey, is an important structure not only for its antique and archaeological characteristics, but also as a structure in terms of the long-term stability of underground rock structures excavated by mankind. The authors carried out some observational, experimental and theoretical rock mechanics studies in the region from 1996 in the context of a research project supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan for the assessment of the long-term behaviour of Derinkuyu Underground City, and these studies are still continuing. In addition to the monitoring of the environmental conditions such as temperature, moisture and air pressure, they also installed acoustic emission (AE) and electrical potential (EP) measurement systems to monitor the behaviour and response of the surrounding rock at the fifth and seventh floors of the underground city. In this article, the geology, seismicity and state of stress of the Cappadocia Region, climatic conditions in the underground city and its vicinity, short- and long-term behaviours of the surrounding rock, its index and mechanical properties, and effects of water content and freezing-thawing processes were investigated. The stability of Derinkuyu Underground City was also evaluated using theoretical and numerical methods, and the results were presented. Furthermore, its implications in modern geoengineering are also discussed. Copyright 2013 Springer-Verlag Wien and Springer-Verlag
2017059238 Bray, Matthew T. (University of Alaska Fairbanks, Department of Civil and Environmental Engineering, Fairbanks, AK). Secondary creep approximations of ice-rich soils and ice using transient relaxation tests: Cold Regions Science and Technology, 88, p. 17-36, illus. incl. 8 tables, April 2013. Based on Publisher-supplied data.
This paper serves two purposes: 1) it presents a simple empirical approach based on relaxation tests, from which secondary creep parameters can be approximated with significant practical time savings and 2) provides secondary creep observations and parameters for ice-rich soils as a function of cryostructure and massive ice facies. The form of test presented consists of a relaxation test in which the strain varies with time. Empirical evidence indicates that the onset of a secondary creep phase in ice-rich soils and ice is connected to the strain. Under increasing or decreasing stepped constant stress creep (CSC) tests, the initiation of secondary creep rates occurs very quickly upon a step change in the applied stress. The relaxation condition represents a continuously decreasing stepped creep tests. Once secondary creep conditions are initiated, the relaxation test can be used to approximate secondary creep. Secondary creep characteristics determined from relaxation tests agree well with CSC tests. Tests were conducted on ice-rich frozen silt from a Pleistocene age Yedoma permafrost composed of uniform windblown loess (Fairbanks silt). In addition to frozen soils, a number of samples of massive wedge ice and Matanuska glacial and basal ice were tested. Relaxation tests were conducted at temperature between -1°C and -5°C. Analysis of secondary creep parameters indicates that cryostructure has an influence on the secondary creep behavior of frozen soils. It is shown the volumetric unfrozen water has a significant impact on secondary creep parameters. With increasing unfrozen water content, parameters A and n approach the values observed for polycrystalline ice. It was shown for temperatures warmer than -2°C and stresses between 200 kPa and 1000 kPa, ice-rich soils creep at a faster rate than polycrystalline ice facies. This relates to unfrozen water. For temperatures colder than -3°C, the creep rates of polycrystalline ice are greater than undisturbed frozen soils for stresses less 200 kPa. The creep characteristics of remolded Fairbanks silt are not representative of undisturbed ice-rich samples and provide non-conservative creep estimates of undisturbed frozen soils. Abstract Copyright (2013) Elsevier, B.V.
2017059239 Rudy, Ashley C. A. (Queen's University, Department of Geography, Kingston, ON, Canada); Lamoureux, Scott F.; Treitz, Paul and Collingwood, Adam. Identifying permafrost slope disturbance using multi-temporal optical satellite images and change detection techniques: Cold Regions Science and Technology, 88, p. 37-49, illus. incl. 3 tables, April 2013. Based on Publisher-supplied data.
Active layer detachments (ALDs) are a common form of permafrost slope disturbance that pose a serious risk for infrastructure and can impact environmental and ecological stability in Arctic regions. Effective recognition and detection of slope disturbances are critical for future hazard analysis. Historically, this has primarily been done through manual image interpretation and field mapping, both of which are cost-intensive. Semi-automatic detection techniques have been successfully applied in more temperate regions to identify slope failures, however, little work has been done to map permafrost disturbances. In this paper we present a methodology to detect and map ALDs using multi-temporal IKONOS satellite imagery in combination with vegetation index differencing and object-based image analysis, to semiautomatically identify landscape change associated with ALDs. A normalized difference vegetation index (NDVI) was computed for each of the two dates (2004 and 2010) and then subtracted generating a NDVI difference surface. Using areas where vegetation was removed as a proxy for the presence of ALDs, a multi-resolution segmentation algorithm was used to threshold the NDVI difference map into objects to demarcate regions of similarity (i.e., potential ALDs). To discriminate between disturbed and undisturbed zones a NDVI threshold was applied removing false positives. The thresholded image was then verified with a disturbance inventory collected from the field. These methods were successfully applied to the study area achieving 43% detection accuracy when identifying all ALDs. Morphometric characteristics were used to separate ALDs into two forms, elongate and compact, with accuracies assessed for each. Elongate ALDs, with a detection accuracy of 67%, are typically more destructive, moving substantially more material downslope over longer distances and posing a greater risk for infrastructure. By contrast, compact ALDs are associated with minimal downslope sliding distances (<1m to several meters) and result in little to no extension in the scar zone and thus limited downslope material movement. The method used in this study detected only 7% of compact disturbances indicating that morphology and size are important variables when detecting ALDs. These results collectively show promise for the semi-automated detection of slope disturbances (i.e., elongate ALDs) in permafrost settings and a cost-effective method to delineate areas for more detailed hazard assessment methods. Abstract Copyright (2013) Elsevier, B.V.
2017059237 Yi Xiangsheng (Chinese Academy of Sciences, Institute of Geographic Sciences and Natural Resources Research, Beijing, China); Li Guosheng and Yin Yanyu. Comparison of three methods to develop pedotransfer functions for the saturated water content and field water capacity in permafrost region: Cold Regions Science and Technology, 88, p. 10-16, illus. incl. 4 tables, April 2013. Based on Publisher-supplied data.
In this study, pedotransfer functions (PTFs) for predicting the soil saturated water content (SWC) and field water capacity (FWC) from basic soil properties were developed by using multiple-linear regression (MLR), artificial neural network (ANN) and Rosetta method. A soil data set (N=488 samples) in the Three-River Headwaters Region (Qinghai Province in China), was randomly divided into a training data set (N1=400 samples) for the prediction, and a testing data set (N2=88 samples) for the validation. The general performance of PTFs was evaluated based on the coefficient of determination (R2), root mean square error (RMSE) and mean error (ME) between the observed and predicted values. Some important conclusions were obtained from this research, which mainly contained three aspects as follows. (1) The general prediction effect of the MLR method was good. The absolute value of ME and RMSE for the SWC was below 0.0509, and the R2 was 0.9031. However, the absolute value of ME and RMSE for the FWC were bigger, and the R2 was lower than the ANN and Rosetta method respectively. (2) The performance of ANN was the best in three methods. The absolute value of ME and RMSE for the SWC and FWC was all below the 0.0386, and their R2 were above 0.8593. (3) The absolute value of ME and RMSE of the Rosetta method for the SWC were larger than other two methods, and the R2 was lower than the ANN but higher than MLR. The prediction effect for the FWC was fairly good for its relatively high R2 and low ME, RMSE. This research could provide the scientific basis for the study of soil hydraulic properties in the Three-River Headwaters Region of Qinghai Province and be helpful for the estimation of soil water retention in regional scale. Abstract Copyright (2013) Elsevier, B.V.
2017059236 Xiao Yao (Chinese Academy of Sciences, State Key Laboratory of Cryospheric Science, Lanzhou, China); Zhao Lin; Dai Yongjiu; Li Ren; Pang Qiangqiang and Yao Jimin. Representing permafrost properties in CoLM for the Qinghai-Xizang (Tibetan) Plateau: Cold Regions Science and Technology, 87, p. 68-77, illus. incl. 4 tables, March 2013. Based on Publisher-supplied data.
Most land surface models (LSMs) used in climate models do not perform well in modeling the permafrost processes. Due to the complex permafrost distribution characteristics and landscapes of the Qinghai-Tibet Plateau (QTP), the LSMs simulations over QTP are even worse. In this study, we revised the permafrost scheme in the original Common Land Model (CoLM) to improve its capability of simulating permafrost processes. We adopted a new frozen soil parameterization scheme, in which maximum unfrozen water content is defined as a function of soil matric potential. In addition, we extended the model's bottom to a depth below that without annual variations in temperature and replaced the zero-flux lower boundary condition with a constant geothermal heat flux based on literature and temperature gradient measurements in a 34.5-m-deep borehole. What's more, we revised the original snow cover fraction parameterization scheme of CoLM according to the special snow cover distribution characteristics over QTP. We calibrated and validated the modified model against observations from 2005 to 2008. The results indicate that the modified model produced more reasonable simulations of radiation balance components and significantly improved the simulation of soil liquid water content. It also shows an improved capability of reproducing soil temperatures from the top to the bottom of soil layers. The modified CoLM provides a useful tool for understanding and predicting the fate of permafrost in QTP under a warming climate. Abstract Copyright (2013) Elsevier, B.V.
2017059235 You Yanhui (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Yu Qihao; Pan, Xicai; Wang Xinbin and Guo Lei. Application of electrical resistivity tomography in investigating depth of permafrost base and permafrost structure in Tibetan Plateau: Cold Regions Science and Technology, 87, p. 19-26, illus. incl. 1 table, March 2013. Based on Publisher-supplied data.
The changes in the thickness of permafrost and the distribution characteristics of ground ice are of great importance for engineering and environmental issue research in permafrost regions. This study was conducted in the permafrost observation field in Qumahe in the east of the Tibetan Plateau by using electrical resistivity tomography (ERT) for investigating the depth of permafrost base and the structure of permafrost. The results demonstrated that the ERT can detect the depth of permafrost base, identify the characteristics of ground ice and the variation of permafrost types in Qumahe. Also, the effects and accuracy of ERT were evaluated combining the information provided by borehole and ground temperature monitoring. The comprehensive analysis of the data shows that the distribution of permafrost and ground ice in this area is strongly influenced by geographical, topographical and other local factors. The depth of the permafrost base within the observation field differs by 30m. Aspect, surface water and vegetation conditions have the most significant influence on the thickness of permafrost. A seasonal stream in the low-lying area of the observation field also brings strong influence to permafrost thermal disturbance and thickness. Meanwhile, different geomorphic unit and surface conditions significantly influence the development of ground ice. To be specific, the massive ground ice is mainly developed in the flat swamping wetland, especially the low-lying wetland. In terms of depth, the massive ground ice is mainly developed within 5 to 10m below the permafrost table. Abstract Copyright (2013) Elsevier, B.V.
2017059231 Ling Xianzhang (Harbin Institute of Technology, Centre of Subgrade and Prevention Engineering, Harbin, China); Li Qionglin; Wang Lina; Zhang Feng; An Lingshi and Xu Pengju. Stiffness and damping radio evolution of frozen clays under long-term low-level repeated cyclic loading; experimental evidence and evolution model: Cold Regions Science and Technology, 86, p. 45-54, illus. incl. 2 tables, February 2013. Based on Publisher-supplied data.
The dynamic properties of frozen clays under repeated cyclic loading is changing with the increasing number of loading cycles. Compared with the short-term low-level repeated cyclic loading, the variation of the dynamic properties of frozen clays under long-term low-level repeated cyclic loading should not be ignored. So far, the evolutions of the dynamic properties as well as the stiffness and damping ratio of frozen clays under long-term low-level repeated cyclic loadings have rarely been studied. In this study, a series of cyclic tri-axial tests were carried out and the influence of the dynamic loading amplitudes, the confining pressures, the temperatures, the moisture contents and the salt contents of the specimens on the dynamic properties were studied. Thereby, the observation that stiffness increased and damping ratios decreased with the increasing number of repeated loading cycles were obtained. Based on the experimental evidence, the conclusion that the evolutions of the dynamic properties under long-term low-level repeated cyclic loading were related to the accumulative axial strain was achieved. The accumulative axial strains were normalization through introducing the accumulative axial strain ratio. A subsequent work focused on establishing the stiffness and damping ratio evolution models. Combined with the Hardin-Drnevich hyperbolic model, the evolutions models can be used to calculate the dynamic response of the frozen clays which had experienced long-term low-level repeated cyclic loading. Abstract Copyright (2013) Elsevier, B.V.
2017059233 Talalay, Pavel G. (Jilin University, Polar Research Center, Changchun City, China). Subglacial till and bedrock drilling: Cold Regions Science and Technology, 86, p. 142-166, illus. incl. 3 tables, February 2013. Based on Publisher-supplied data.
Drilling to till and bedrock of ice sheets and glaciers offers unique opportunities for examining processes acting at the bed. Samples of basal and subglacial material contain important paleo-climatic and paleo-environmental records and provide a unique habitat for life, give significant information on sediment deformation beneath glaciers and its coupling to the subglacial hydraulic system, subglacial geology, and tectonics. Retrieving bedrock samples under ice sheets and glaciers is a very difficult task. Drilling operations are complicated by extremely low temperature at the surface of, and within glaciers, and by glacier flow, the absence of roads and infrastructures, storms, winds, snowfalls, etc. Nevertheless, borehole drilling might be considered as the optimal method to access beds of the glaciers and to sample subglacial material. Four types of subglacial drilling technologies are considered: (1) non-rotary sampling; (2) non-core penetrating; (3) pipe-string rotary drilling; (4) electromechanical cable-suspended drilling. The most simple and effective systems for sampling in subglacial soft sediments or unfrozen till from pre-drilled access holes are non-rotary devices like gravity corer and piston corer. The maximal thickness of ice is determined by the length of wire rope attached to the corer and could possibly be more than 4000m. Potentially, piston sampling can reach a maximal depth of 25m in soft subglacial lake sediments. In stiffer sediments a hammer corer or vibrocorer should be used. To install different sensors and markers into the soft till beneath glaciers and to measure basal sliding, different types of sediment non-core penetrators were used. Typically the boreholes are pre-drilled by hot-water systems as well. To recover core of the true bedrock the rotary drilling systems are used. The experience of pipe-string rotary drilling in subglacial environment showed that drilling operations were very unstable, and the recovery of subglacial sediment was generally poor. Commercial drilling rigs for drilling up to the depth of 3000m or more tend to be very heavy and require a large logistical load to move and support. They also require more equipment for the circulation system. Taking into account that they are not adapted for extremely unfavorable conditions in Polar Regions and also need high power consumption, these drill rigs were not considered for subglacial exploration. Electromechanical cable-suspended systems are widely used for core drilling in pure and debris-containing ice. The main feature of these systems is that an armored cable with a winch is used instead of a pipe-string to provide power to the down-hole motor system and to retrieve the down-hole unit. The use of armored cable allows a significant reduction in power and material consumption, a decrease in the time of round-trip operations, and a simplification in the cleaning of the hole from the cuttings. To penetrate frozen till and bedrock the electomechanical drills can be adapted for coring bedrock. This was confirmed by four successful penetrations into the bedrock carried out by U.S. and Russian specialists. The procedure of till and bedrock drilling and the geological description of retrieved debris-containing ice and bedrock cores are given. Abstract Copyright (2013) Elsevier, B.V.
2017059227 Kanevskiy, M. (University of Alaska Fairbanks, Institute of Northern Engineering, Fairbanks, AK); Shur, Y.; Jorgenson, M. T.; Ping, C. L.; Michaelson, G. J.; Fortier, D.; Stephani, E.; Dillon, M. and Tumskoy, V. Ground ice in the upper permafrost of the Beaufort Sea coast of Alaska: Cold Regions Science and Technology, 85, p. 56-70, illus. incl. 1 table, sketch map, January 2013. Based on Publisher-supplied data.
Ground ice in the upper permafrost of the Beaufort Sea coast of Alaska was studied from 2005 to 2008 at 65 field sites located between Point Barrow and the Canadian border. The main terrain units in the studied area include (1) the primary surface of the coastal plain; (2) drained-lake basins; (3) low foothills (yedoma); (4) deltas and tidal flats; and (5) sand dunes. Wedge ice is the main type of massive ground ice, and ice-wedge polygons occurred on nearly all land surfaces. The volumetric content of wedge ice for the area varies from 3% to 50% between various terrain units with average value of about 11% for the entire coast. The highest content of wedge ice (about 50%) is typical of yedoma terrain, which occurred in a small segment at the coast of the Camden Bay. At the primary surface of the western region of the Arctic Coastal Plain, wedge-ice content reached almost 30%, with an average value of about 14%. Slightly smaller values were estimated for the primary surface of the eastern region of the Arctic Coastal Plain and for old drained-lake basins. Other types of massive ground ice included thermokarst-cave ice, ice cores of pingos, and a rare occurrence of folded massive ice at Barter Island. The content of segregated ice in organic and mineral soils between ice wedges was very high at most of the study sites. The total average volumetric ice content (due to wedge, segregated, and pore ice) for the whole area was 77%, ranging from 43% in eolian sand to 89% in yedoma. Abstract Copyright (2013) Elsevier, B.V.
2017059229 Yu Fan (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Qi Jilin; Yao Xiaoliang and Liu Yongzhi. Degradation process of permafrost underneath embankments along Qinghai-Tibet Highway; an engineering view: Cold Regions Science and Technology, 85, p. 150-156, illus. incl. 1 table, January 2013. Based on Publisher-supplied data.
Embankment settlement is closely related to the process of degrading of underling permafrost. Previous studies have focused on the process of permafrost degradation under natural ground surfaces, and the degradation process under roadway embankments has yet to be investigated. With the influence of climate warming, this study becomes more and more important in the analysis of embankment settlement. In this paper, based on the in-situ geothermal data of up to 15 years of 5 typical sections along the Qinghai-Tibet Highway (QTH), the characteristics of permafrost degradation are extensively investigated. According to the characteristics, the trends of thawing and temperature rise in the process of permafrost degradation are analyzed. Corresponding to the tendencies, four stages are defined according to the mean annual ground temperature (MAGT). Combining the features of permafrost degradation in each stage with the in-situ data of embankment settlements along QTH, the sources of the embankment settlement are identified. The main results are as follows. The permafrost degrades extensively in the five typical sections with different characteristics. With the increase in MAGT, the thawing rate firstly increases and then fluctuates as temperature rise rate increases and then decreases at MAGT of about -0.5°C. The four stages are divided: initial degradation stage, for MAGT ≤&eq; -2.5°C; the intensive degradation stage, for -2.5°C<MAGT ≤&eq; -0.5°C; the vertical talik stage, for -0.5°C<MAGT ≤&eq; 0°C; and the quasi-disappearance stage, for MAGT>0°C. When MAGT is less than about -1.2°C, the main contribution of total settlement is probably thawing settlement, with the negligible creep of permafrost; when MAGT higher than -1.2°C, creep of permafrost starts to have an increasing share in the total settlement. Abstract Copyright (2013) Elsevier, B.V.
2017067013 Lebedeva, Lyudmila (Nansen Environmental and Remote Sensing Centre, St. Petersburg, Russian Federation) and Semenova, Olga. Use of soil thaw/freeze depth data to verify hydrological modelling at poor gauged basins in permafrost regions: in Schwerpunktausgabe Umwelt-Wasser; hydrologische Prozessstudien in Forschungseinzugsgebieten; Herausforderungen und Ausblick, Die Bodenkultur (Wien), 64(3-4), p. 53-59 (German sum.), 21 ref., 2013.
The distributed process-based runoff formation model hydrograph was applied and tested against soil thaw/freeze depth and runoff data in different permafrost landscapes of the Kolyma Water-Balance station (KWBS). The parameterization describing different permafrost conditions was elaborated. Soil thaw/freeze depths were simulated for three sites comprising rocky talus, mountainous tundra and larch forest landscapes. The runoff model was applied and calibrated for the Kontaktovy Creek watershed (21.2 km2), which is covered by these respective land cover types. Runoff simulations were carried out for three poorly-gauged river basins (areas ranging from 1820 to 9560 km2) using the same soil and vegetation parameters of the calibrated model. The results have shown that the Hydrograph model can be reliably applied in the conditions of data limitation considering permafrost-related hydrological processes.
URL: http://www.boku.ac.at/diebodenkultur/volltexte/sondernummern/band-64/heft-3-4/le ...
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2017057939 Banville, David-Roy. Modélisation cryohydrogéologique tridimensionnelle d'un bassin versant pergélisolé; une étude cryohydrogéophysique de proche surface en zone de pergélisol discontinu à Umiujaq au Québec Nordique [Three-dimensional cryohydrogeological modeling of a permafrost drainage basin; a cryohydrogeological study of a shallow depth discontinuous permafrost zone at Umiujaq in northern Quebec]: 256 p., illus. incl. sects., 7 tables, geol. sketch maps, 104 ref., Master's, 2016, Université Laval, Quebec, QC, Canada. Includes 8 appendices.
2017057940 Ducharme, Marc-André Caractérisation du pergélisol; application d'une nouvelle méthode afin d'estimer la conductivité thermique à l'aide de la tomodensitométrie [Characterization of permafrost; application of a new method to estimate thermal conductivity using computed tomography]: 101 p. (English sum.), illus. incl. 17 plates, 5 tables, sketch maps, 68 ref., Master's, 2016, Université Laval, Quebec, QC, Canada. Includes appendices.
When building in the Arctic, design considerations require precise knowledge of the thermal and geotechnical properties of the permafrost. Computed tomography provides visualization of the cryostructure of permafrost. Previous studies showed great potential in using this technology for classification and volume measurements of permafrost components, i.e. sediment (solid), ice and gas (void) contents. The aims of this study are (1) to develop an innovative and non-destructive approach using CT scan to compute the thermal conductivity of undisturbed permafrost samples and (2) to validate the results computed from CT scan image analysis with proven experimental thermal conductivity data. The very good results obtained so far show that CT scan thermal conductivity measurements yield results comparable to other existing methods. The new approach could still be significantly improved by the use of a higher resolution CT scanner.
2017057952 Gagnon, Samuel. Measurement of permafrost greenhouse gas emissions through a new automated system of closed chambers: 99 p. (French sum.), illus. incl. 11 tables, sketch map, 190 ref., Master's, 2015, Université Laval, Quebec, QC, Canada. Accessed on April 28, 2017; includes appendix.
Warming in the Arctic has the potential to affect the global climate through permafrost thaw leading to increased greenhouse gas (GHG) emissions. However, these emissions are difficult to quantify because the methods conventionally used are often prohibitively expensive and time-consuming. With a new automated system of closed chambers developed for this study, this project aimed to measure permafrost GHG emissions in a polygonal peatland located near Salluit, Nunavik. The emissions were quantified under different environmental conditions in order to simulate climate warming and to determine the effect of spatial variability on GHG emissions. Results show that the new system yields results comparable to those obtained with an existing commercial system. Temperature was the principal factor influencing ecosystem respiration variability and the largest GHG emissions were measured on the water-saturated plot.
2017057946 Pelletier, Maude. Geomorphological, ecological and thermal time phase of permafrost degradation, Tasiapik, Nunavik (Québec, Canada): 69 p. (French sum.), illus. incl. 4 tables, sketch maps, 106 ref., Master's, 2015, Université Laval, Quebec, QC, Canada. Accessed on April 28, 2017; includes 3 appendices.
Six plots, representative of the regional ecological time sequence associated with permafrost degradation, were selected on a silty ice-rich permafrost plateau near Umiujaq, Nunavik. The objective of the present work is to determine the changes that occur in the flow of energy between the three layers of the ecosystem (vegetation / snow cover, active layer, permafrost) and the feedbacks that occur during the degradation of permafrost and to quantify the rate of the transition using time-lapse aerial photographs and tree ring analysis. In order to respond to these objectives, the methodology follows the ADAPT (Arctic Development and Adaptation on Permafrost in Transition) protocol, including ecological, climate, stratigraphic and thermal data analysis. The results show exponential evolution of permafrost degradation factors over a period of time of about 90 years; slowly during the first 60 years, and significantly faster during the last 30 years.
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2017058009 Gooseff, Michael N. (University of Colorado at Boulder, Institute of Arctic and Alpine Research, Boulder, CO); Wlostowski, Adam; McKnight, Diane M. and Jaros, Chris. Hydrologic connectivity and implications for ecosystem processes; lessons from naked watersheds: in Connectivity in geomorphology (Wohl, Ellen, editor; et al.), Geomorphology, 277, p. 63-71, illus. incl. sketch map, 41 ref., January 15, 2017. Meeting: 47th Binghamton geomorphology symposium, Sept. 16-19, 2016, Fort Collins, CO.
Hydrologic connectivity has received great attention recently as our conceptual models of watersheds and water quality have evolved in the past several decades. However, the structural complexity of most temperate watersheds (i.e. connections among shallow soils, deep aquifers, the atmosphere and streams) and the dynamic seasonal changes that occur within them (i.e., plant senescence which impacts evapotranspiration) create significant challenges to characterizing or quantifying hydrologic connectivity. The McMurdo Dry Valleys, a polar desert in Antarctica, provide a unique opportunity to study hydrologic connectivity because there is no vegetative cover (and therefore no transpiration), and no deep aquifers connected to surface soils or streams. Glacier melt provides stream flow to well-established channels and closed-basin, ice-covered lakes on the valley floor. Streams are also connected to shallow hyporheic zones along their lengths, which are bounded at ~ 75 cm depth by ice-cemented permafrost. These hydrologic features and connections provide water for and underpin biological communities. Hence, exchange of water among them provides a vector for exchange of energy and dissolved solutes. Connectivity is dynamic on timescales of a day to a flow season (6-12 weeks), as streamflow varies over these timescales. The timescales over which these connections occur is also dynamic. Exchanges between streams and hyporheic zones, for example, have been estimated to be as short as hours to as long as several weeks. These exchanges have significant implications for the biogeochemistry of these systems and the biotic communities in each feature. Here we evaluate the lessons we can learn about hydrologic connectivity in the MDV watersheds that are simplified in the context of processes occurring and water reservoirs included in the landscape, yet are sensitive to climate controls and contain substantial physical heterogeneity. We specifically explore several metrics that are simple and/or commonly employed in hydrologic analyses and interpret them in the context of connectivity between and among hydrologic features.
2017066145 Aragones, Cristian Estop (University of Alberta, Edmonton, AB, Canada); Heffernan, Liam and Olefeldt, David. Potential rates of anaerobic decomposition and experimental priming effects in thawed peats from discontinuous permafrost in western Canada [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0612, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Recent climate change has led to increased rates of warming and wildfire in the circumpolar region. It is predicted that this will promote the widespread thawing of permafrost and the development of thermokarst bogs in the peatlands of western Canada. Previously frozen deep organic matter becomes available to microbial activity with thermokarst with the potential loss of C stocks while liberating greenhouse gases to the atmosphere and creating a positive feedback to climate change. Although anoxic conditions in these waterlogged systems may reduce peat decomposition, fresh plant derived C inputs associated with high vegetation productivity post-thaw could increase peat decomposition. The effect of this potential mechanism on enhanced peat decomposition is poorly investigated though. We are measuring anaerobic CO2 and CH4 production rates from a peat plateau, an adjacent young and an old thermokarst feature in the discontinuous permafrost. Samples were selected from depths where peat has been exposed to seasonal thaw (active layer) and from deeper, previously frozen organic matter along 5 m profiles. Preliminary results indicate that most CO2 production is driven by the top meter of peat, especially in the recent thermokarst where the highest rates of CH4 production are also measured due to high vegetation productivity post-thaw. Data suggests that the decomposition of deeper peat is more temperature sensitive. We are considering a 13C labelling experiment to investigate the priming effects on heterotrophic respiration of organic matter heterotrophic respiration once the labile C pool has been depleted and production rates have become stable over time. Fourier transform infrared (FTIR) spectroscopy will be used to determine how peat quality is related to anaerobic decomposition rates, its temperature dependency, and priming effects. These measurements aim to constrain the fate of C through anaerobic decomposition upon permafrost thaw.
2017064397 Beck, M. A. (University of New Hampshire Main Campus, Earth Sciences, Durham, NH); Hamilton, B. T.; Spry, E.; Johnson, J. E.; Palace, M. W.; McCalley, C. K.; Varner, R. K. and Bothner, W. A. Tracking organic carbon transport from the Stordalen mire to glacial Lake Tornetrask, Abisko, Sweden [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B23B-0571, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
In subarctic regions, labile organic carbon from thawing permafrost and productivity of terrestrial and aquatic vegetation are sources of carbon to lake sediments. Methane is produced in lake sediments from the decomposition of organic carbon at rates affected by vegetation presence and type as well as sediment temperature. Recent research in the Stordalen Mire in northern Sweden has suggested that labile organic carbon sources in young, shallow lake sediments yield the highest in situ sediment methane concentrations. Ebullition (or bubbling) of this methane is predominantly controlled by seasonal warming. In this project we sampled stream, glacial and post-glacial lake sediments along a drainage transect through the Stordalen Mire into the large glacial Lake Tornetrask. Our results indicate that the highest methane and total organic carbon (TOC) concentrations were observed in lake and stream sediments in the upper 25 centimeters, consistent with previous studies. C/N ratios range from 8 to 32, and suggest that a mix of aquatic and terrestrial vegetation sources dominate the sedimentary record. Although water transport occurs throughout the mire, major depositional centers for sediments and organic carbon occur within the lakes and prohibit young, labile TOC from entering the larger glacial Lake Tornetrask. The lack of an observed sediment fan at the outlet of the mire to the lake is consistent with this observation. Our results suggest that carbon produced in the mire stays in the mire, allowing methane production to be greater in the mire bound lakes and streams than in the larger adjacent glacial lake.
2017064261 Blazewicz, Steven (Lawrence Livermore National Laboratory, Livermore, CA); White, Richard A., III; Tas, Neslihan; Euskirchen, Eugene Susanne; McFarland, Jack W.; Jansson, Janet and Waldrop, Mark P. Life in ice; microbial growth dynamics and greenhouse gas production during winter in a thermokarst bog revealed by stable isotope probing targeted metagenomics [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B11I-04, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Permafrost contains a reservoir of frozen C estimated to be twice the size of the current atmospheric C pool. In response to changing climate, permafrost is rapidly warming which could result in widespread seasonal thawing. When permafrost thaws, soils that are rich in ice and C often transform into thermokarst wetlands with anaerobic conditions and significant production of atmospheric CH4. While most C flux research in recently thawed permafrost concentrates on the few summer months when seasonal thaw has occurred, there is mounting evidence that sizeable portions of annual CO2 and CH4 efflux occurs over winter or during a rapid burst of emissions associated with seasonal thaw. A potential mechanism for such efflux patterns is microbial activity in frozen soils over winter where gasses produced are partially trapped within ice until spring thaw. In order to better understand microbial transformation of soil C to greenhouse gas over winter, we applied stable isotope probing (SIP) targeted metagenomics combined with process measurements and field flux data to reveal activities of microbial communities in 'frozen' soil from an Alaskan thermokarst bog. Field studies revealed build-up of CO2 and CH4 in frozen soils suggesting that microbial activity persisted throughout the winter in soils poised just below the freezing point. Laboratory incubations designed to simulate in-situ winter conditions (-1.5°C and anaerobic) revealed continuous CH4 and CO2 production. Strikingly, the quantity of CH4 produced in 6 months in frozen soil was equivalent to approximately 80% of CH4 emitted during the 3 month summer 'active' season. Heavy water SIP targeted iTag sequencing revealed growing bacteria and archaea in the frozen anaerobic soil. Growth was primarily observed in two bacterial phyla, Firmicutes and Bacteroidetes, suggesting that fermentation was likely the major C mineralization pathway. SIP targeted metagenomics facilitated characterization of the primary metabolic pathways in growing organisms that likely drove C mineralization. Results indicate that winter microbial activities can play an important role in controlling seasonal C flux in recent thawed permafrost and characterization of growing organisms leads to stronger mechanistic linkages between the soil microbial community and ecosystem processes.
2017064497 Bouskill, Nicholas (Lawrence Berkeley National Laboratory, Berkeley, CA); Riley, William J.; Mekonnen, Zelalem Amdie and Grant, Robert. Sensitivity of soil permafrost to winter warming; modeled impacts of climate change. [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B53G-0603, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
High-latitude tundra soils are warming at nearly twice the rate of temperate ecosystems. Changes in temperature and soil moisture can feedback on the processes controlling the carbon balance of tundra soils by altering plant community composition and productivity and microbial decomposition rates. Recent field manipulation experiments have shown that elevated soil and air temperatures can stimulate both gross primary productivity and ecosystem respiration. However, the observed soil carbon gains following summer time stimulation of plant productivity have been more than offset by elevated decomposition rates during the rest of the year, and particularly over winter. A critical uncertainty is whether these short-term responses also represent the long-term trajectory of tundra ecosystems under chronic disturbance. Herein we employ a mechanistic land-model (ecosys) that represents many of the key above- and belowground processes regulating the carbon balance of tundra soils to simulate a winter warming experiment at Eight Mile Lake, Alaska. Using this model we examined the short-term (5-10 year) influence of soil warming through the wintertime by mimicking the accumulation of a deeper snow pack. This deeper snow pack was removed to a height equal to that of the snow pack over control plots prior to snow melt. We benchmarked the model using physical and biological measurements made over the course of a six-year experiment at the site. The model accurately represented the effect of the experimental manipulation on thaw depth, N mineralization, winter respiration, and ecosystem gross and net primary production. After establishing confidence in the modeled short-term responses, we extend the same chronic disturbance to 2050 to examine the long-term response of the plant and microbial communities to warming. We discuss our results in reference to the long-term trajectory of the carbon and nutrient cycles of high-latitude permafrost regions.
2017064396 Burke, S. A. (University of New Hampshire, Institute for the Study of Earth, Oceans, and Space, Durham, NH); Wik, M.; Lang, A.; Crill, P. M. and Varner, R. K. Thaw stage and incoming solar radiation influence ebullitive methane fluxes from peatland ponds [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B23B-0569, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Arctic regions are experiencing the most rapid warming, leading to a destabilization of permafrost and an increase in available carbon (C) for decomposition to carbon dioxide (CO2) and methane (CH4). Peatlands in the Northern Hemisphere alone are estimated to contain around 50% of the Earth's store of soil organic C. Due to lack of long-term measurements uncertainty remains whether these systems will remain sinks of atmospheric C for much longer. Studies have found that small water bodies can release a significant amount of CH4 per square meter to the atmosphere. These water bodies can form rapidly due to permafrost thaw in combination with changes in hydrology. Our research focus is on understanding the seasonal and interannual controls on CH4 ebullitive flux (bubbling) and how thaw stage and hydrology influence the annual release of CH4 from these systems. Over four field seasons (2012-2015), measurements of CH4 ebullition have been made from eight ponds at Stordalen Mire in northernmost Sweden. Between 2012 and 2015, we have made 1294 measurements of CH4 ebullition with an average emission of 20 mg m-2d-1 and a range of 0-1257 mg m-2d-1. These data are the longest set of observations of CH4 flux from small thaw ponds to date. In order to explain the observed within year variability in CH4 emissions, we've developed a conceptual model of thaw stage, which is defined by vegetation type and abundance, pond water depth, and hydrological connectedness. Our observations also indicate interannual variability in CH4 ebullition is controlled by average shortwave radiation input which could potentially be used as a proxy to estimate emission in other pond systems and to predict changes in future emissions.
2017066143 Chen Leiyi (Chinese Academy of Sciences, Institute of Botany, Beijing, China); Ding Jinzhi and Yang Yuanhe. Linking temperature sensitivity of soil CO2 release to substrate, environmental and microbial properties across alpine permafrost ecosystems [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0610, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Our knowledge on fundamental drivers of temperature sensitivity (Q10) of soil carbon dioxide (CO2) release is crucial for improving the predictability of soil carbon dynamics among Earth System Models. However, patterns and determinants of Q10 over a broad geographic scale have not been fully understood, especially in alpine permafrost ecosystems. Here we addressed this issue by incubating surface soils (0-10 cm) obtained from 156 sites across Tibetan alpine permafrost region. Q10 was estimated from the dynamics of soil CO2 release rate under varying temperatures of 5-25°C. Structure equation modeling (SEM) was performed to evaluate the relative importance of substrate, environmental and microbial properties in regulating soil CO2 release rate and Q10. Our results indicated that steppe soils had significantly lower CO2 release rate but higher Q10 than meadow soils. The combination of substrate properties and environmental variables could predict 52% of the variation in soil CO2 release rate across all grassland sites, and explained 37% and 58% of the variation in Q10 across the steppe and meadow sites, respectively. Of them, precipitation was the best predictor of soil CO2 release rate. Basal microbial respiration rate (B) was the most important predictor of Q10 in steppe soils, while soil pH outweighed B as the major regulator in meadow soils. These results demonstrate that carbon quality and environmental variables co-regulate Q10 across alpine permafrost region, implying that modelers can rely on 'carbon-quality temperature' hypothesis for estimating apparent temperature sensitivities, but relevant environmental factors, especially soil pH should be considered in higher productivity alpine regions.
2017066181 Coble, Ashley A. (University of New Hampshire Main Campus, Durham, NH); Rodriguez-Cardona, Bianca; Wymore, Adam; Prokishkin, Anatoly Stanislavovich; Kolosov, Roman and McDowell, William H. Dissolved organic matter composition and biodegradability in a permafrost-dominated watershed network in central Siberia [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43G-03, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Thawing permafrost soils can mobilize large quantities of dissolved organic matter (DOM) from soils to headwater streams, and DOM may undergo rapid transformations in streams and rivers in transit to the Arctic Ocean. With climate change an increased frequency of fire is also expected, which will further alter the DOM entering streams, and may contribute to changes in its biodegradability. Elucidating how DOM composition varies across a fire gradient within a river network underlain by continuous permafrost will therefore improve our understanding of the impact of climate change on Arctic ecosystems and its role in the global carbon cycle. To determine DOM composition we measured optical properties via excitation-emission matrices (EEMs) and subsequent parallel factor analysis across a spatially extensive collection of sites in central Siberia. Within a subset of streams in the Nizhnyaya Tunguska watershed network, we also measured biodegradable dissolved organic carbon (BDOC) incubated at in situ temperatures over a 7 day period during spring freshet on two dates in early June. Despite clear changes in optical properties of DOM and background DOC concentration along the fire gradient (range: 3 to >100 y since burn) BDOC did not vary systematically with years since fire for either incubation date. In the first incubation conducted near peak flow BDOC ranged from negligible to 7.6% (BDOC concentration = negligible to 1.4 mg C L-1) within a 7 day period. In the second incubation conducted 5 days later BDOC was negligible across all sites (as both a percentage and a concentration). Our results suggest that DOC exported from permafrost soils in the central Siberian plateau is relatively unreactive at in situ temperatures over 7 day time scales, which contrasts with previous studies conducted in watersheds underlain with Yedoma outcrops where biodegradability comprises a large fraction of DOC. Our preliminary results suggest that melting of permafrost soils in central Siberia may export large quantities of C to the Arctic Ocean that are not rapidly degraded in streams and rivers.
2017064567 Cohen, Denis (Iowa State University, Ames, IA); Zwinger, Thomas; Haeberli, Wilfried and Fischer, Urs Heinrich. A fully coupled transient thermomechanical ice-flow/permafrost model of the Rhine Glacier, Switzerland; effects of permafrost on basal conditions [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract C21B-0672, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
The safe disposal of radioactive wastes in deep geological repositories requires their containment and isolation for up to one million years. Over that time period, the performance of the repositories in mid- and high-latitude regions can be impacted by future ice-age conditions which may cause deep glacial erosion, permafrost development, and changes in groundwater fluxes. In Switzerland, repositories are planned in the northern Swiss lowlands near the marginal zone of the former Rhine Glacier that repeatedly formed two extensive piedmont lobes (the Rhine and Linth lobes) over the Swiss Plateau. There, overdeepenings formed by glacial erosion indicate that the glacier was warm-based. Yet the Last Glacial Maximum (LGM) occurred under cold conditions: central Europe experienced extremely cold and dry conditions caused by the penetration of winter sea ice to low latitudes in the Atlantic Ocean and the corresponding closure of the primary humidity source north of the Alps. At the LGM, flat and extended lobes of large piedmont glaciers spreading out over much of the Swiss Plateau were polythermal, characterized by low driving stresses (typically around 30 kPa) and surrounded by continuous periglacial permafrost up to 150 m thick. Subsurface temperatures and groundwater flow conditions were strongly influenced by the presence of extended surface and subsurface ice. Using numerical models we explore the effects of permafrost on basal conditions of the piedmont lobes during the build-up of the Rhine Glacier. We apply a two-dimensional transient fully coupled thermomechanical full stress ice-flow and permafrost model along a flowline characterizing the Rhine lobe. The energy equation is solved in both ice and rock and permafrost is modeled using an effective heat capacity formulation to account for phase transitions. Transient effects during ice advances and permafrost build-up up to the LGM are resolved by modeling the full glacial cycle using reconstructed temperature and mass balance gradients from either Greenland or Antarctic ice cores. We explore how climate parameterization (temperature offset, mass balance gradients in the accumulation and ablation zones, climate signals) affect the development of temperate basal conditions necessary for significant erosion to occur.
2017066183 Connolly, Craig T. (University of Texas at Austin, Austin, TX); Spencer, Robert G.; Cardenas, M. Bayani; Bennett, Philip C.; McNichol, Ann P. and McClelland, James W. Characterizing groundwater sources of organic matter to arctic coastal waters [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43G-06, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
The Arctic is projected to transition from a runoff-dominated system to a groundwater-dominated system as permafrost thaws due to climate change. This fundamental shift in hydrology is expected to increase groundwater flow to Arctic coastal waters, which may be a significant source of dissolved organic matter (DOM) to these waters-even under present conditions-that has been largely overlooked. Here we quantify and elucidate sources of groundwater DOM inputs to lagoons along the eastern Alaskan Beaufort Sea coast using an approach that combines concentration measurements and radiocarbon dating of groundwater, soil profiles, and soil leachable dissolved organic carbon (DOC). Samples were collected in late summer, when soil thaw depths (active layer) were near their maximum extent. As anticipated, the radiocarbon age of bulk soil organic matter increased with depth (modern - 6,100 yBP), while the amount of extractable DOC decreased with depth within the active layer. However, amounts of extractable DOC increased dramatically in thawed permafrost samples collected directly below the actively layer. Concentrations of DOM in groundwater (ranging from 902 to 5,118 mmol L-1 DOC) are one to two orders of magnitude higher than those measured in lagoons and nearby river water. In contrast, the 14C-DOC ages of groundwater (1,400±718 s.d. yBP), lagoon water (1,750 yBP), and river water (1,610 yBP) are comparable. Together these results suggest that: (1) groundwater provides a highly concentrated input of old DOC to Arctic coastal waters; (2) groundwater DOM is likely sourced from organic matter spanning the entire soil profile; and (3) the DOM in rivers along the eastern Alaskan Beaufort Sea coast during late summer is strongly influenced by groundwater sources, but is much lower in concentration due to photo-mineralization and/or biological consumption. These results are key for assessing how changes in land-ocean export of organic matter as permafrost thaws will change into the future with clear ramifications for Arctic coastal environments.
2017064600 Cuozzo, Nicolas (University of Washington, Isotope Laboratory, Department of Earth and Space Sciences, Seattle, WA); Sletten, R. S.; Hu, Y. and Teng, F. Z. Tracing salt provenance in McMurdo Dry Valley soils by using magnesium isotopes [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract V51A-3046, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
The McMurdo Dry Valleys (MDV) are a hyper-arid polar desert that contain a rich geologic record in permafrost that has been preserved over millions of years. Soluble salts accumulate through the surface and subsurface of MDV soils. Sources of salt accumulation include mineral weathering, transport of marine aerosols, and possible glacial meltwater. This project seeks to study the provenance of these salts in a 30-meter ice cemented permafrost core collected in Beacon Valley. The ice-rich core was thawed and water extracted by centrifugation using a double bottom centrifuge tube. The extracted water was analyzed for ionic composition, pH, and Mg isotopes (d26Mg), which are useful in interpreting provenance. The ionic and d26Mg values show a disconformity at around 7 meters. Above 7 meters, d26Mg values vary between -0.76 to -0.52, indicating rock-water interactions. These samples are isotopically heavier than the lower section of the core and can be explained by a slow accumulation of sediment and warmer near-surface temperatures that allow for greater chemical weathering of dolerite in the ice-cemented, debris-rich permafrost core. This interpretation is also supported by the more alkaline pH values (7.07 - 7.54) above 7 meters, which is consistent with chemical weathering of dolerite. In comparison, salt samples below 7 meters have d26Mg values between -0.95 to -0.84, which overlaps with modern seawater (d26Mg = -0.83 ± 0.09) and is fairly consistent throughout the rest of the core. Furthermore, below a depth of 7 meters, Mg/Na and Mg/K ratios are also similar to modern seawater. In summary, these results indicate differing sources of salts along the depth of the Dry Valley permafrost core, changing from a marine-dominant signature in the deeper section to a stronger weathered signal in the upper section. Additional work dating the sediment using cosmogenic nuclides provides a history for the burial of the sediments in the permafrost core and may provide broad scale paleoclimatic implications.
2017064422 Egan, J. E. (Dalhousie University, Earth Sciences, Halifax, NS, Canada); Natali, S.; Risk, D. A.; Schade, J. D.; Holmes, R. M. and Mann, P. J. Short-term impacts from the 2015 Yukon-Kuskokwim River delta tundra fire on permafrost vulnerability and C loss [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B23D-0621, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Fire frequency and areal extent have been increasing for the past several decades in carbon-rich boreal and tundra ecosystems. The summer of 2015 was the second worst fire year on record in Alaska. One of these 2015 Alaskan fires burned within the Yukon-Kuskokwim Delta (YK Delta), where more area was burned in 2015 than in the previous 74 years combined. The goal of this project was to examine the immediate effects of fire on carbon storage and export from the YK Delta and, by extension, to gain critical insights into how the carbon balance of arctic deltas will change over the coming decades. One year after the fire, in June 2016, we measured terrestrial and aquatic carbon outputs associated with the burn event, from three areas within the burn scar, and three non-burnt areas nearby. Here we present ecosystem respiration (Reco) partitioning results from this campaign, which was done using a dual-isotope approach to determine how the fire has altered the contribution of autotrophic and heterotrophic respiration sources from the active layer, and heterotrophic respiration sources from permafrost. Reco gas samples were collected from static chambers, and Reco sources (organic and mineral layer soils, above and belowground vegetation, and permafrost soil) were incubated and sampled for their isotopic composition (both d13C and D14C). Removal of insulating soil organic layers by the fire significantly increased permafrost thaw in the burn scar compared to control areas, and thus, we expect that this will increase the contribution of "old" permafrost carbon to Reco. Ultimately, these results will inform long-term trajectories of the vulnerability and fate of delta carbon pools.
2017066182 Ewing, Stephanie A. (Montana State University, Bozeman, MT); O'Donnell, Jonathan A.; Koch, Joshua C.; Paces, James B.; Aiken, George and Striegl, Robert G. Radiocarbon and uranium isotopes in surface waters reveal enhanced hydrologic connection with permafrost thaw [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43G-05, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
The residence time of ice in permafrost is an indicator of past climate history, and of the resilience and vulnerability of high-latitude ecosystems to global change. Development of geochemical indicators of ground-ice residence times in permafrost will advance understanding of permafrost formation, preservation, and thaw in response to climate warming and other disturbance. We used uranium activity ratios (234U/238U) and radiocarbon (14C) to evaluate the signal of permafrost thaw at two gaged locations (upstream and downstream) on Beaver Creek, a central Alaskan stream that flows from rocky uplands to terraces and lowlands mantled by thick, ice-rich loess permafrost (yedoma). Uranium activity ratios in surface waters provide a tracer of transit time and source (permafrost thaw water, supra- and sub-permafrost groundwater), but must be interpreted in the context of parent material and hydrology. Previous work has shown that dissolved organic carbon (DOC) from yedoma in the age range of 10-100 ky is highly labile, suggesting ongoing production in permafrost and potential carbon (C) loss upon thaw with increasing permafrost age. Uranium activity ratios were inversely correlated with DOC-14C values in streamwater at the upstream gages throughout the year, and at the downstream gage during summer, indicating aged C that co-occurs with increased nitrate-N in winter baseflow at the upstream site, but not at the downstream site. In the context of observations at a number of sites in central Alaska, these patterns suggest enhanced hydrologic connection of the downstream site in summer that may be facilitated by permafrost thaw and may result in capture of young DOC in the floodplain. In regional streams, mineral substrate dictates hydrologic connection with permafrost thaw, with enhanced mixing of source waters from supra- and sub-permafrost groundwater as thaw progresses.
2017066279 Frederick, Jennifer Mary (Sandia National Laboratories, Albuquerque, NM); Bull, Diana L.; Jones, Craig; Roberts, Jesse and Thomas, Matthew Anthony. Evaluating approaches to a coupled model for arctic coastal erosion, infrastructure risk, and associated coastal hazards [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract EP13C-1043, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Arctic coastlines are receding at accelerated rates, putting existing and future activities in the developing coastal Arctic environment at extreme risk. For example, at Oliktok Long Range Radar Site, erosion that was not expected until 2040 was reached as of 2014 (Alaska Public Media). As the Arctic Ocean becomes increasingly ice-free, rates of coastal erosion will likely continue to increase as (a) increased ice-free waters generate larger waves, (b) sea levels rise, and (c) coastal permafrost soils warm and lose strength/cohesion. Due to the complex and rapidly varying nature of the Arctic region, little is known about the increasing waves, changing circulation, permafrost soil degradation, and the response of the coastline to changes in these combined conditions. However, as scientific focus has been shifting towards the polar regions, Arctic science is rapidly advancing, increasing our understanding of complex Arctic processes. Our present understanding allows us to begin to develop and evaluate the coupled models necessary for the prediction of coastal erosion in support of Arctic risk assessments. What are the best steps towards the development of a coupled model for Arctic coastal erosion? This work focuses on our current understanding of Arctic conditions and identifying the tools and methods required to develop an integrated framework capable of accurately predicting Arctic coastline erosion and assessing coastal risk and hazards. We will present a summary of the state-of-the-science, and identify existing tools and methods required to develop an integrated diagnostic and monitoring framework capable of accurately predicting and assessing Arctic coastline erosion, infrastructure risk, and coastal hazards. The summary will describe the key coastal processes to simulate, appropriate models to use, effective methods to couple existing models, and identify gaps in knowledge that require further attention to make progress in our understanding of Arctic coastal erosion. Co-authors listed in alphabetical order. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.
2017066144 Fuchs, Matthias (Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Potsdam, Potsdam, Germany); Grosse, Guido; Jones, Benjamin M.; Maximov, Georgy and Strauss, Jens. Soil organic carbon storage in five different arctic permafrost environments [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0611, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Arctic river deltas and ice-rich permafrost regions are highly dynamic environments which will be strongly affected by future climate change. Rapid thaw of permafrost (thermokarst and thermo-erosion) may cause significant mobilization of organic carbon, which is assumed to be stored in large amounts in Arctic river deltas and ice-rich permafrost. This study presents and compares new data on organic carbon storage in thermokarst landforms and Arctic river delta deposits for the first two meters of soils for five different study areas in Alaska and Siberia. The sites include the Ikpikpuk river delta (North Alaska), Fish Creek river delta (North Alaska), Teshekpuk Lake Special Area (North Alaska), Sobo-Sise Island (Lena river delta, Northeast Siberia), and Bykovsky Peninsula (Northeast Siberia). Samples were taken with a SIPRE auger along transects covering the main geomorphological landscape units in the study regions. Our results show a high variability in soil organic carbon storage among the different study sites. The studied profiles in the Teshekpuk Lake Special Area--dominated by drained thermokarst lake basins--contained significantly more carbon than the other areas. The Teshekpuk Lake Special Area contains 44±9 kg C m-2 (0-100 cm, mean value of profiles±Std dev) compared to 20±7 kg C m-2 kg for Sobo-Sise Island--a Yedoma dominated island intersected by thaw lake basins and 24±6 kg C m-2 for the deltaic dominated areas (Fish Creek and Ikpikpuk). However, especially for the Ikpikpuk river delta, a significant amount of carbon (25±9 kg C m-2) is stored in the second meter of soil (100-200 cm). This study shows the importance of including deltaic and thermokarst-affected landscapes as considerable carbon pools, but indicates that these areas are heterogeneous in terms of organic carbon storage and cannot be generalized. As a next step, the site-level carbon stocks will be upscaled to the landscape level using remote sensing-based land cover classifications to calculate the carbon storage potential for Arctic deltas and larger thermokarst regions, to estimate mobilization potentials from thermokarst and thermo-erosion, and to provide input data for future permafrost carbon feedback models.
2017066147 Gagne, Kristin (University of Alaska Fairbanks, Water and Environmental Research Center, Fairbanks, AK); Anthony, Katey M. Walter and Guerard, Jennifer. Survey of permafrost thaw influence on surface water dissolved organic matter in sub-arctic Alaska [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0614, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
The chemical and functional group composition of permafrost organic matter largely remains unknown. Characterizing dissolved organic matter (DOM) chemical composition offers insight into the quality and extent of the permafrost carbon pool that may mobilize and transform into smaller components or greenhouse gasses upon thaw. The Goldstream watershed in interior Alaska is underlain by discontinuous permafrost with varying stage of talik (thaw bulb) development, allowing for the comparison of thaw stage on DOM composition. Surface water samples were collected from lakes and streams in regions of the watershed with varying degrees of permafrost thaw in order to investigate seasonal variability and associated trends in DOM composition. Additionally, select permafrost cores were obtained and utilized in leachate experiments to identify the fraction and reactivity of the soil organic carbon pool leached from active layer and permafrost soil upon thaw. Leached organic moieties were compared to the total permafrost organic carbon pool and the DOM of the overlying surface water. Extracted isolates from both permafrost and active layer were characterized by 3D excitation-emission fluorescence, UV-vis spectroscopy, PARAFAC, SPR-W5-WATERGATE 1H-NMR, total organic carbon, ICP-MS, and ion chromatography, coupled with photolysis experiments to determine reactive oxygen species production to characterize potential reactivity. Differences in carbon pool composition were resolved between seasons and with the extent of permafrost thaw. This is a key first step to determine how permafrost degradation influences DOM pool composition on a molecular level, which is essential for assessing permafrost organic matter impact on biogeochemical cycling and other ecological functions as it becomes incorporated into a warming landscape.
2017066142 Gandois, Lure (EcoLab France, Castanet Tolosan, France); Hoyt, Alison; Xu, Xiaomei; Hatte, Christine; Teisserenc, Roman and Tananaev, Nikita. Origin of carbon released from ecosystems affected by permafrost degradation in Northern Siberia [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0609, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Permafrost soils and peatlands store half of the soil organic carbon stock worldwide, and are rapidly evolving as a result of permafrost thaw. Determining the origin (permafrost or recent photosynthesis) of carbon which is released to surface waters and the atmosphere is crucial to assess Arctic ecosystems' potential feedback to climate change. In order to evaluate it, we investigated the stable and radioactive content of carbon in solid organic matter, dissolved organic matter (DOM) and dissolved CO2 and CH4 in a discontinuous permafrost area of Siberia affected by permafrost degradation (Igarka, Graviyka catchment (67°27'11"N, 86°32'07"E)). We collected samples from the active layer, permafrost, surface water and bubbles from thermokarst lakes. We further investigated DOM and dissolved CO2 and CH4 in porewater profiles, streams and the catchment outlet. In thermokarst lakes, DOM of surface water as well as CO2 and CH4 from bubbles from lake sediments predominantly originate from modern carbon. In two locations, CO2 and CH4 from bubbles have relatively low 14C contents, with ages greater than 700 yr BP, but still younger that what was previously reported in Eastern Siberia. In all samples the D14C of CH4 and CO2 were strongly correlated, with CH4 being consistently older than CO2, indicating strong interrelation between CO2 and CH4 cycles. In our study, permafrost influenced CO2 and CH4 is found in small ponds where palsa collapse and the resulting bank erosion has mobilized sequestered carbon. In peatland porewater, the D14C of DOM, CO2 and CH4 increases with depth (DOM: 1385 ±45 yr BP at 2 m), indicating a contribution from Holocene peatlands affected by permafrost. In deep layers, CO2 reduction is the dominant pathway of CH4 production, whereas acetate fermentation dominates in thermokarst lakes. In summary, the majority of dissolved CO2 and CH4 analyzed from thermokarst lakes and degraded peatlands is modern and originates from recently fixed carbon. Additionally, the DOM exported in small streams draining peatlands is also modern. However, at the catchment scale, an additional contribution from deep groundwater or thawing permafrost results in an intermediate D14C of DOM (300-400 yr BP) at the outlet of the Graviyka River.
2017066160 Garnello, Anthony (University of Arizona, Ecology and Evolutionary Biology, Tucson, AZ); Dye, Dennis G.; Bogle, Rian; Hough, Moira; Raab, Nicole; Dominguez, Sky; Rich, Virginia Isabel; Crill, Patrick M. and Saleska, Scott R. Investigating the relationship between peat biogeochemistry and above-ground plant phenology with remote sensing along a gradient of permafrost thaw. [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0631, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Global climate models predict a 50%-85% decrease in permafrost area in northern regions by 2100 due to increased temperature and precipitation variability, potentially releasing large stores of carbon as greenhouse gases (GHG) due to microbial activity. Linking below ground biogeochemical processes with observable above ground plant dynamics would greatly increase the ability to track and model GHG emissions from permafrost thaw, but current research has yet to satisfactorily develop this link. We hypothesized that seasonal patterns in peatland biogeochemistry manifests itself as observable plant phenology due to the tight coupling resulting from plant-microbial interactions. We tested this by using an automated, tower-based camera to acquire daily composite (red, green, blue) and near infrared (NIR) images of a thawing permafrost peatland site near Abisko, Sweden. The images encompassed a range of exposures which were merged into high-dynamic-range images, a novel application to remote sensing of plant phenology. The 2016 growing season camera images are accompanied by mid-to-late season CH4 and CO2 fluxes measured from soil collars, and by early-mid-late season peat core samples of the composition of microbial communities and key metabolic genes, and of the organic matter and trace gas composition of peat porewater. Additionally, nearby automated gas flux chambers measured sub-hourly fluxes of CO2 and CH4 from the peat, which will also be incorporated into analysis of relationships between seasonal camera-derived vegetation indices and gas fluxes from habitats with different vegetation types. While remote sensing is a proven method in observing plant phenology, this technology has yet to be combined with soil biogeochemical and microbial community data in regions of permafrost thaw. Establishing a high resolution phenology monitoring system linked to soil biogeochemical processes in subarctic peatlands will advance the understanding of how observable patterns in plant phenology can be used to monitor permafrost thaw and ecosystem carbon cycling.
2017064493 Gibson, Carolyn (University of Alberta, Edmonton, AB, Canada); Olefeldt, David; Flannigan, Mike; Chasmer, Laura and Thompson, Dan K. Long term effects of wildfire on permafrost stability and carbon cycling in peatlands [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B53G-0584, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Permafrost soils in boreal and arctic ecosystems store almost twice as much carbon as is currently present in the atmosphere and are therefore important players in the global carbon cycle. Wildfire can act as an important trigger of permafrost thaw (laterally through thermokarst development and vertically though active layer deepening), and due to increasing fire frequency and more severe fires with a changing climate, rates of permafrost thaw are expected to accelerate in the future. However, there remains much uncertainty about the extent and timing to which wildfire affects permafrost stability. This study aims to assess the role of wildfire on future permafrost stability and carbon storage in permafrost peatlands by exploring the hypothesis that wildfire increases ground heat flux which leads to permafrost destabilization and changes in ecosystem respiration that spans decades until vegetation recovery occurs. Research has been conducted in a series of sites that burned 2-48 years ago in the Northwest Territories, Canada. Thaw depths, soil thermal regimes and ecosystem respiration have been monitored. Satellite imagery has been used to determine the area of recent permafrost thaw within fire scars and adjoining unburned areas. We show that for approximately thirty years sites that experienced fire had deeper active layers than their paired unburned sites. Surprisingly, the effect of fire was most pronounced ~10-15 years following fire with about a doubling of active layer during this time period. With increased active layer deepening we found that permafrost stability along the edges of peat plateaus was drastically affected. Using remote sensing approaches, the rate of new thermokarst development approximately doubled over 30 years following fire. These results suggest that increasing fire frequency and lengthening of the fire season will lead to increased fire-induced permafrost thaw which has long term implications for carbon cycling and land use.
2017066140 Heffernan, Liam (University of Alberta, Edmonton, AB, Canada); Aragones, Cristian Estop; Blodau, Christian and Olefeldt, David. Contrasting approaches to determine the impact of permafrost thaw on C cycling in northern peatlands [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0607, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Northern peatlands are a globally significant pool of terrestrial carbon (C) and have acted as a major C sink since the last deglaciation. The peatland complexes found in western Canada are a mosaic of peat plateaus underlain by permafrost interspersed with permafrost free thermokarst bogs. Recent climate change has led to increased rates of thermokarst bog expansion due to permafrost thaw. In order to understand whether permafrost thaw causes net C loss or uptake, we studied both the variation in C stocks and of surface greenhouse gas fluxes along a pair of thermokarst chronosequences located in thick (>6 m) peatlands in the discontinuous permafrost zone of western Canada. Each zone of a chronosequence is characterized by permafrost conditions, including a zone where permafrost is still present (peat plateau), a zone of recent thermokarst development (dominated by Sphagnum riparium and sedges), and a mature thermokarst zone (dominated by Sphagnum fuscum and woody shrubs) where permafrost thaw occurred >50 years ago. Each zone has distinct hydrological conditions, with the recent thermokarst being much wetter. Increased wetness causes increased heat conduction and average July to November soil temperatures at 50, 100, and 200 cm were 1.6, 2.2, and 1.7°C warmer, respectively, in the recent than in the mature thermokarst zone. This difference likely increases respiration rates at depth substantially. Our study aims to reconcile findings from other sites where investigations of C stock and greenhouse gas emissions have yielded disparate conclusions. By combining C stocks and C emissions along a thaw chronosequence, and highlighting the differences in C cycling between recently and older thawed thermokarst features, this current work aims to reconcile these contrasting views.
2017064484 Hiemstra, Christopher A. (U. S. Army Cold Regions Research and Engineering Laboratory, Fort Wainwright, AK); Newman, Stephen D.; Douglas, Thomas A.; Gelvin, Arthur B. and Bjella, Kevin. Lidar detection of permafrost change [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B52C-07, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Permafrost is a dominant feature of Arctic and boreal landscapes, and permafrost surfaces are changing. Beyond gradual warming, water-driven heat transfer has the potential to change permafrost dominated landscapes dramatically and quickly. Due to record (2014) and near-record (2016) wet summers, permafrost landscapes near Fairbanks Alaska have undergone a substantial localized transformation from elevated runoff and resultant thermokarst development. When ground ice thaws, volume displacements occur and the surface subsides or erodes entirely. These developments have dramatic implications for water routing and infrastructure. Before mechanistic analyses can occur regarding drivers of surface change the magnitude and location of change must be detected, but this is a sizeable challenge. Our objective was to detect surface changes and identify where they occur to assess the potential for permafrost thaw and attendant terrain subsidence elsewhere. A short (less than 3 years) time series of repeat airborne LiDAR measurements were used to investigate permafrost-geomorphology interactions at three permafrost-dominated sites near Fairbanks, Alaska. Distinct and relatively rapid localized changes in surface elevation were tied to record precipitation received in summer 2014. Aerial imagery was also assessed to see if these surface changes were identifiable using other means and more universally available coarser-scale datasets. Readily identifiable changes resulting from surface subsidence and inundation were observed along with inchoate plant vigor decline. These results suggest multi-temporal LiDAR collections at the local to regional scales are particularly useful in detecting landscape change. Challenges were identified in utilizing disparate LiDAR datasets where some datasets were of higher resolution than others. Hydrologic events and the landscape's response to them are a growing concern for infrastructure design and development in areas with permafrost.
2017066293 Holland, Amanda (University of Sussex, Brighton, United Kingdom); Moses, Cherith; Sear, David Ayres and Cope, Sam. Mixed sand and gravel beaches; accurate measurement of active layer depth and sediment transport volumes using PIT tagged tracer pebbles [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract EP14A-01, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
As sediments containing significant gravel portions are increasingly used for beach replenishment projects globally, the total number of beaches classified as 'mixed sand and gravel' (MSG) increases. Calculations for required replenishment sediment volumes usually assume a uniform layer of sediment transport across and along the beach, but research into active layer (AL) depth has shown variations both across shore and according to sediment size distribution. This study addresses the need for more accurate calculations of sediment transport volumes on MSG beaches by using more precise measurements of AL depth and width, and virtual velocity of tracer pebbles. Variations in AL depth were measured along three main profile lines (from MHWS to MLWN) at Eastoke, Hayling Island (Hampshire, UK). Passive Integrated Transponder (PIT) tagged pebbles were deployed in columns, and their new locations repeatedly surveyed with RFID technology. These data were combined with daily dGPS beach profiles and sediment sampling for detailed analysis of the influence of beach morphodynamics on sediment transport volumes. Data were collected over two consecutive winter seasons: 2014-15 (relatively calm, average wave height <1 m) and 2015-16 (prolonged periods of moderate storminess, wave heights of 1-2 m). The active layer was, on average, 22% of wave height where beach slope (tanb) is 0.1, with variations noted according to slope angle, sediment distribution, and beach groundwater level. High groundwater levels and a change in sediment proportions in the sandy lower foreshore reduced the AL to 10% of wave height in this area. The disparity in AL depth across the beach profile indicates that traditional models are not accurately representing bulk sediment transport on MSG beaches. It is anticipated that by improving model inputs, beach managers will be better able to predict necessary volumes and sediment grain size proportions of replenishment material for effective management of MSG beaches.
2017064518 Hu Guojie (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, Lanzhou, China); Zhao Lin; Wu Xiaodong; Wu Tonghua; Li Ren; Xie Changwei and Zou Defu. A mathematical investigation of the air-ground temperature relationship in permafrost regions on the Tibetan Plateau [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract C11C-0782, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Air and soil temperatures are important factors which contribute to hydro-thermal processes and ecosystem dynamics in permafrost regions. However, there is little research about soil thermal dynamics during freeze-thaw processes in regions with thermal orbits on the Tibetan Plateau. Thermal orbits can provide simplified illustrations of relationships between air and ground temperatures. The paper presents a new quantitative analysis for thermal orbit by combining the characteristics of ellipse and linear regression theories. A sensibility analysis of thermal orbits was conducted with different air and ground temperatures and vegetation types on the Tibetan Plateau. Results indicated that the thermal orbit regression slopes and intercepts can show the variation characteristics between air and ground temperatures at different depths. These two temperatures demonstrate a homologous variation with increasing depth. Thermal orbits were shown to provide useful tool for understanding the thermal properties of the permafrost related to soil moisture, climate change and vegetation effects in permafrost regions on Tibetan Plateau.
2017064511 Hwang, Cheinway (National Chiao Tung University, Hsinchu, Taiwan); Hsieh, Chia-En and Cheng, Yung-Sheng. Permafrost thawing-induced land subsidence and lake level drop in northern Alaska detected by ENVISAT and SARAL/Altika altimeters [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract C11A-0740, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Recent technical improvements in post-processing radar altimeter data have made possible the application of radar altimetry to land subsidence detection, coastal sea surface height recovery and tide model improvement. Here we show elevation changes detected by ENVISAT (2002-2010) and SRARL/Altika (2013-present) over permafrost-covered areas in northern Alaska. Useful waveforms are selected and retracked to improve the ranging accuracy to detect land and lake level changes. Subwaveforms are retracked by a threshold retracker with an optimal threshold value of 0.1. We assess the accuracy of elevation changes from the two altimeters using change rates at crossovers of ascending and descending tracks on both land surface and Teshekpuk Lake and by comparison with ICESat-derived rates over Teshekpuk. The standard error of elevation change rate from the altimeters is below one cm/year. The subsidence rates from ENVISAT are ~2 cm/year and ~10 cm/year in coastal area and in the sloping, southern study area. SRARL/Altika detects subsidence rates larger than 10 cm/year. Lake level of Teshekpuk dropped at a rate of 5 cm/year. The subsidence and lake level drop are likely caused by permafrost thawing. Using the temperature highs from four weather stations and the seasonal elevation lows from altimeters and a simplified thermal dynamics, we estimate the thicknesses of active layers. This presentation shows the value of radar altimeter in permafrost study.
2017066162 Jastrow, Julie D. (Argonne National Laboratory, Environmental Science Division, Argonne, IL); Ping, Chien-Lu; Deck, Clara B.; Matamala, Roser; Vugteveen, Timothy W.; Lederhouse, Jeremy S. and Michaelson, Gary J. Distribution and degradation state of soil organic carbon stocks in ice wedge polygons of the Arctic Coastal Plain, Alaska [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0634, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Estimates of the amount of organic carbon (C) stored in permafrost-region soils and its susceptibility to mobilization with changing climate are improving but remain high, affecting the ability to reliably predict regional C-climate feedbacks. In lowland permafrost soils, much of the organic matter exists in a poorly degraded state and is often weakly associated with soil minerals due to the cold, wet environment and cryoturbation. Thus, the impacts of warming and permafrost thaw likely will depend, at least initially, on the past history of soil organic matter (SOM) degradation. Ice wedge polygons are ubiquitous, patterned ground features throughout Arctic coastal plain regions and are large enough (5-30 m across) that a better three-dimensional understanding of their C stocks and relative degradation state could improve geospatial upscaling of observational data and contribute benchmarks for constraining model parameters. We investigated the distribution and existing degradation state of SOM to a depth of 2 meters across three polygon types on the Arctic Coastal Plain of Alaska: flat-centered (FCP), low-centered (LCP), and high-centered (HCP) polygons, with each type replicated 3 times. To assess the relative degradation state of SOM, we used particle size fractionation to isolate fibric (coarse) from more degraded (fine) particulate organic matter and separated mineral-associated organic matter into silt- and clay-sized fractions. We found variations in the thickness and quality of surface organic layers for different polygon types. Below the active layer, organic-rich cryoturbated layers were located in the transition zone and fingered down into the upper permafrost. Soil organic C stocks varied across individual polygons and differed among polygon types, with HCPs generally having the largest C stocks. The relative degradation state of SOM also varied spatially and vertically within polygons and differed among polygon types. Our findings suggest that accounting for polygon-scale (wedge to center to wedge) and landscape-scale (polygon type) variations could help reduce the uncertainties in observational estimates of soil C stocks and their degradation state for areas dominated by ice wedge polygons.
2017064485 Jorgenson, Janet C.; Jorgenson, Mark T.; Boldenow, Megan and Orndahl, Kathleen M. Landscape change detected over a 60 year period in the Arctic National Wildlife Refuge, Alaska, using high resolution aerial photographs and satellite images [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B52C-09, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
We documented landscape change over a 60 year period in the Arctic National Wildlife Refuge in northeastern Alaska using aerial photographs and satellite images. We used a stratified random sample to allow inference to the whole refuge (78,050 km2), with five random sites in each of seven ecoregions. Each site (2 km2) had a systematic grid of 100 points for a total of 3500 points. We chose study sites in the overlap area covered by acceptable imagery in three time periods: aerial photographs from 1947-1955 and 1978-1988, Quick Bird and IKONOS satellite images from 2000-2007. At each point a 10 meter radius circle was visually evaluated in ARC-MAP for each time period for vegetation type, disturbance, presence of ice wedge polygon microtopography and surface water. A landscape change category was assigned to each point based on differences detected between the three periods. Change types were assigned for time interval 1, interval 2 and overall. Additional explanatory variables included elevation, slope, aspect, geology, physiography and temperature. Overall, 23% of points changed over the study period. Fire was the most common change agent, affecting 28% of the Boreal Forest points. The next most common change was degradation of soil ice wedges (thermokarst), detected at 12% of the points on the North Slope Tundra. The other most common changes included increase in cover of trees or shrubs (7% of Boreal Forest and Brooks Range points) and erosion or deposition on river floodplains and at the Beaufort Sea coast. Changes on the North Slope Tundra tended to be related to landscape wetting, mainly thermokarst. Changes in the Boreal Forest tended to involve landscape drying, including fire, reduced area of lakes and tree increase on wet sites. The second time interval coincided with a shift towards a warmer climate and had greater change in several categories including thermokarst, lake changes and tree and shrub increase.
2017064380 Jorgenson, T. (Alaska Ecoscience, Fairbanks, AK); Wickland, K.; Ewing, S. A.; Johnston, C. E.; Kanevskiy, M. Z.; Harden, J. W.; Koch, J. C.; O'Donnell, J. A. and Striegl, Robert G. Patterns and controls of methane fluxes across permafrost and ice-wedge degradation wetland chronosequences in Arctic and boreal Alaska [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B21L-07, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Arctic and boreal landscapes can undergo major restructuring when ice-rich permafrost and ground ice thaws in response to changing climate conditions or disturbance. In lowland areas, this commonly results in formation of thermokarst wetlands that produce and emit methane. Many studies have investigated the controls and magnitude of methane emissions from thermokarst wetlands, generally considering these wetlands as static over timescales of interest to methane flux assessments. However, thermokarst wetlands are dynamic features that undergo successional changes driven by positive and negative feedbacks associated with changing hydrology, vegetation, energy balance, and carbon accumulation--all of which are key controls on methane emission. To better understand how thermokarst wetland methane emissions change over decadal to centurial time scales, we quantified methane fluxes at sites in Arctic and boreal Alaska where numerous thermokarst wetlands have formed over time, creating chronosequences that allow for study of multiple wetland successional stages in a single landscape. We measured seasonal methane fluxes and associated variables across three to four successional stages of wetlands, and undegraded areas, at an Arctic site near Prudhoe Bay, Alaska, and at a boreal site in the Innoko Flats National Wildlife Refuge, Alaska. The Arctic site is affected by ice-wedge degradation and re-aggradation, and the boreal site is undergoing permafrost thaw with no evidence of re-aggradation. Seasonal methane emissions were greatest from late-successional stage wetlands formed ~20 years after ice-wedge degradation at Prudhoe Bay (4.3 ± 3.7 mg C-CH4 m-2 hr-1), and from middle-successional stage wetlands formed ~30-70 years post-permafrost thaw at Innoko Flats (2.9 ± 2.2 mg C-CH4 m-2 hr-1). At Prudhoe Bay, the variables associated with differences in methane emission across all successional stages were percent cover of graminoids, water table height, and seasonal surface heat flux; at Innoko Flats, soil temperature and dominant moss species were key. The recognition and incorporation of changing methane emissions from Arctic and boreal thermokarst wetlands during succession from formation through stabilization will improve projections of future methane emissions from high latitude systems.
2017066245 Jorgenson, Torre (Alaska Ecoscience, Fairbanks, AK) and Shur, Yuri. Tale of two deltas; permafrost dynamics on the Colville and Yukon-Kuskokwim deltas [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract EP12B-04, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Arctic deltas are the predominant coastline in the Arctic and are greatly modified by permafrost aggradation and degradation. In comparing the Colville Delta (CD) along the Beaufort Sea (MAAT -11°C) with the Yukon-Kuskokwim Delta (YKD) along the Bering Sea (MAAT -1°C), permafrost characteristics respond to differences in climate, flooding, salinization, and vegetation-soil development. Both deltas have an inner zone dominated by fluvial processes and nonsaline ecosystems, and an outer zone affected by both tidal and fluvial processes and has salt-affected ecosystems. In the CD, closed taliks develop under the deeper channels and surface permafrost starts to form on channel bars where water is <2 m deep. During early floodplain development with active sedimentation, syngenetic permafrost is climate driven, ice-poor, and dominated by pore and lenticular cryostructures. On inactive floodplains, where flooding is infrequent and fine-grained sedimentation is greatly diminished, climate-driven, ecosystem-modified permafrost aggrades upward in response to thickening organics and thinning active layer. Here a ~2-m-thick intermediate layer develops that is ice-rich and dominated by reticulate and ataxitic cryostructures. On the oldest abandoned floodplains, permafrost becomes sufficiently ice rich from segregated and wedge ice that thermokarst lakes develop. Large storm surges up to 3 m amsl, such as those in 1963 and 1970, have caused extensive salt killed and ice-wedge degradation. Thus, thermokarst is abundant even at low temperatures. In the YKD, permafrost develops only during late floodplain stages in response to sphagnum accumulation and creates extensive permafrost plateaus that rise ~1 m above the floodplain. This ecosystem-driven permafrost is epigenetic, ice-poor, and dominated by pore and lenticular cryostructures. Permafrost develops around existing water bodies, but thermokarst lakes are uncommon. Large storm surges up to 3.5 m amsl, such those in 1974 and 2005, damaged vegetation along the plateaus margins and created shallow thermokarst moats. In response to expected climate warming of 4-6°C over the next century, permafrost dynamics in the CD should remain similar to current conditions, while in the YKD permafrost likely will be eliminated in the next 30-50 years.
2017066149 Kholodov, Alexander L. (University of Alaska Fairbanks, Fairbanks, AK); Natali, Susan; Loranty, Michael M. and Romanovsky, Vladimir E. Mechanisms of vegetation protective effect on thermal state of permafrost in Alaska. [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0619, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
To understand the effect of vegetation on ground temperature, we measured plant and soil properties at 24 locations across Alaska. The following factors were determined to be most important in terms of their influence on surface energy balance: trees density, understory vegetation biomass and soil carbon pool in active layer. These sites are located in boreal and tundra ecosystems and span a recent mean annual air temperature ranging from -3 to -12°C. These ecosystem measurements were combined with an examination of temperature differences at the air-ground surface and ground surface-permafrost table levels. The first index gives us information about the influence of snow during the snow-covered period and insulation effect of vegetation during the growing season. Combination of the second one with measurements of soil physical properties provides the data for an estimation of the relationship between active layer temperature and soil organic content. Results of our investigation show that highest gradient in system atmosphere-ground surface-permafrost corresponds to the above ground level. Difference between mean annual air and ground surface temperatures ranges from 1.5 to 9°C and is mostly caused by the warming impact of snow during winter season which consists of 3 to 13°C. In the boreal forest zone the cooling effect of vegetation during the growing season due to shading effect and surface insulation can be as high as -5°C. It leads to lower values of mean annual gradient in the boreal forest zone in comparison with tundra. Processes of heat transfer within the active layer generate negative mean annual temperature gradient between the ground surface and the permafrost table for all investigated ecotypes. This difference value varies from -2.8°C in boreal forest to -0.7°C in tundra and has strong positive correlation with carbon content in the active layer soil. Research was supported by US NSF projects ARC-1304271 and PLR-1417908.
2017066180 Longo, William M. (Brown University, Earth, Environmental and Planetary Science, Providence, RI); Huang, Yongsong; Russell, James M.; Giblin, Anne E.; McNichol, Ann P.; Xu, Li and Daniels, William. Differential millennial-scale responses of terrestrial carbon cycling dynamics to warming from two contrasting lake catchments in arctic Alaska [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43G-02, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Earth's permafrost carbon (C) reservoir is more than twice as large as global atmospheric C and its vulnerability to warming makes it a significant potential feedback to climate change. Predicted rates of warming could result in the release of 5 to 15% of permafrost C to the atmosphere by 2100 (Schuur et al., 2015); however the uncertainty around this estimate hinders our ability to quantify the arctic temperature-carbon feedback. To elucidate the long-term response of terrestrial C to warming in regions underlain by continuous permafrost, we present geologic records of changes in temperature and terrestrial C cycling dynamics from sediment cores from two contrasting lake catchments in arctic Alaska. The sediment records feature independent chronologies, biomarker-based temperature reconstructions, and geochemical measurements of vascular plant biomarkers (lignin phenols) that provide insight into terrestrial carbon quality, its release from permafrost soils and its transit time on the landscape. Our results indicate that both abrupt and sustained increases in temperature over the past 20,000 years resulted in increased carbon normalized yields of lignin phenols (L8, L6), which indicate increased mobilization of terrestrial organic carbon from permafrost soils. Lignin phenol indicators of terrestrial carbon quality (Ad:Al(s), Ad:Al(v)), indicated that carbon quality decreased with increasing temperature. These results demonstrate covariation between temperature and both the decay of terrestrial organic matter and lignin alteration resulting from dissolution and sorption processes. Compound specific radiocarbon analyses of lignin phenols and their offsets from depositional ages quantify transit times of terrestrial carbon on the landscape. These measurements revealed the presence of a persistent "pre-aged" terrestrial organic carbon pool, which is likely sourced from degrading permafrost. We also observe different responses of terrestrial organic carbon cycling to temperature that depend on landscape characteristics. C cycling responses are pronounced in the low-relief, Pleistocene-aged catchment of lake E5, and more muted in Lake Fog 2, which exists in a higher-relief and younger catchment. Mechanisms differentiating the responses of these catchments are discussed.
2017064421 Ludwig, S. (University of Alaska Fairbanks, Biology and Wildlife, Fairbanks, AK); Natali, S.; Holmes, R. M.; Mann, P. J.; Sanderman, J. and Schade, J. D. Fire effects on vegetation community, carbon pools, and permafrost vulnerability in subarctic tundra [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B23D-0615, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Fire frequency and severity are increasing in high latitudes as a result of global climate change. The last decade has seen unprecedented tundra fires, such as the fires that occurred in the Yukon-Kuskokwim River Delta (YKD), which burned 424 km2 in 2015. The effects of fire are of particular importance in tundra ecosystems, which store large quantities of carbon (C) in soil organic matter (SOM). SOM is also an effective insulator that protects permafrost from thawing. Burning of the organic layer can therefore cause both direct and indirect C losses. Our objective was to measure the direct C losses from the Kuka Creek fire, one of the largest areas that burned in the 2015 YKD fires, and the consequences on soil C, vegetation recovery, and permafrost thaw. The area of the 2015 YKD fires is dominated by lichen and dwarf shrub, and with average organic layer depth of 39 cm and active layer depth of 56 cm. In September 2015 and June 2016, we assessed the effects of the Kuka Creek fire on above and below ground C pools, as well as changes in vegetation community and soil environmental properties. In burned areas, organic layer depth was reduced by 50% and active layer depths increased by 50%. The remaining organic layers in burned areas were drier and contained 20% less SOM. FTIR analysis showed SOM contained an average of 20% char in burned soils (top XX cm). One year after the fire, burned ground comprised 60% of ground cover, and recovering vegetation comprised 40%. Frozen soil cores sampled down to 1.5 m exhibited buried organic layers and ice content often exceeding 50%. The Kuka Creek fire combusted more than half of the C in vegetation and surface organic soil, representing a positive feedback to climate. The changes in thaw depth and organic layer depth may exacerbate this by thawing previously frozen soil C and causing ground subsidence. However, changes in soil moisture and char content could decrease post-fire soil respiration, and the recovering vegetation community could offset some C losses. The short-term effects of the Kuka Creek fire demonstrate large C losses, while the net effects of thawing permafrost and the recovering vegetation and SOM layer have the potential to likely augment but possibly mitigate these losses.
2017066158 Malhotra, Avni (Oak Ridge National Laboratory, Oak Ridge, TN); Roulet, Nigel T.; Moore, Tim R. and Limpens, Juul. Effect of permafrost thaw on carbon fluxes, litter decomposition and ecohydrology in a sub-Arctic peatland; increased uncertainty from transitional dynamics [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0629, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Carbon (C) release from thawing permafrost in ice-rich peatlands is spatially and temporally heterogeneous due to abrupt localized changes following initial thaw. We investigated the contribution of transitional thaw areas to variability in C loss by evaluating changes in moisture regimes, vegetation, litter decomposition and C fluxes. In a thaw chronosequence at Stordalen mire in northern Sweden, we found that adjacent thawed and unthawed areas had unrelated water table fluctuations. These abrupt hydrological changes were associated with a weakened link between water table depth and above-ground plant abundance, and with non-linear shifts in the partitioning of gaseous effluxes between CO2 and CH4. Inclusion of soil temperature along with ecohydrological variability improved predictions of non-linear changes in C flux after permafrost thaw. Structural heterogeneity across the thaw gradient also decreased the predictability of litter decomposition rates by its key theoretical controls (moisture and temperature). Instead, litter decomposition was well predicted by surface elevation. We will present the key mechanisms by which transitional thaw stages increase landscape scale C flux uncertainty and provide suggestions for modeling and upscaling C loss from thawing ice-rich peatlands.
2017064417 Manies, K. (U. S. Geologcial Survey, Western Regional Offices, Menlo Park, CA); Fuller, C. and Jones, M. Modeling peat ages using 7Be data to account for downwash of 210Pb [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B23C-0597, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
In order to determine the amount of peat, and thus carbon, which has accumulated since the last thaw event, we are interested in dating the surface layers of boreal thermokarst bogs. However, there can often be a mismatch by several decades between dates obtained using 210Pb, 14C, or 137Cs. We found that 210Pb-based dates were almost always younger than 14C-based dates. One of the limitations often cited regarding the use of 210Pb dating for peatlands is the potential for this radionuclide to be transported down the soil profile, biasing the mean accumulation rate (MAR) towards higher values which, in turn, results in younger ages at a specific horizon. 7Be, which has similar depositional behaviors as 210Pb but a much shorter half-life (53.22 days), can be used to help determine if there is movement of 210Pb through surface layers and the depths to which 210Pb-bearing particles are transported (over the mean life of 7Be). These data can then be used in new models, such as the Linked Radionuclide aCcumulation model (LRC; Landis et al., 2016, URL: http://dx.doi.org/10.1016/j.gca.2016.02.2013), which account for 210Pb downwash when calculating soil horizon ages. To this end, we measured 7Be within a bog four times over the growing season. 7Be was found to 4 cm in May, reached its maximum depth of penetration in July (7 cm), and then receded again to 4 cm. The maximum integrated 7Be activity was also found in July. This pattern is similar to other studies which found 7Be deposition decreased over the rainy season. Next, we will calculate peat ages with models that include downwash of 210Pb, the depths of which will be based on the penetration depth of 7Be. These ages will be compared to 210Pb ages obtained with both the Constant Rate of Supply (CRS) and Constant Flux-Constant Sedimentation (CF:CS) models and to 137Cs- and 14C-derived ages. We anticipate that dates based on models that include some transport of 210Pb into the soil profile will provide more accurate peat formation dates and allow for more accurate carbon accumulation rates.
2017064508 McGuire, Anthony David (U. S. Geological Survey, Fairbanks, AK). Evaluation of offline models used to simulate components of the permafrost carbon feedback; experience from the permafrost carbon network model integration group [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B54F-01, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
The Model Integration Group of the Permafrost Carbon Network (see URL: http://www.permafrostcarbon.org/) has conducted studies to evaluate the sensitivity of offline terrestrial permafrost and carbon models to both historical and projected climate change. These studies indicate that there is a wide range of (1) initial states permafrost extend and carbon stocks simulated by these models and (2) responses of permafrost extent and carbon stocks to both historical and projected climate change. In this study, we synthesize what has been learned about the variability in initial states among models and the driving factors that contribute to variability in the sensitivity of responses. We conclude the talk with a discussion of efforts needed by (1) the modeling community to standardize structural representation of permafrost and carbon dynamics among models that are used to evaluate the permafrost carbon feedback and (2) the modeling and observational communities to jointly develop data sets and methodologies to more effectively benchmark models.
2017066190 Meyer, Franz J. (University of Alaska Fairbanks, Water and Environmental Research Center, Fairbanks, AK); Anthony, Katey M. Walter; Regmi, Prajna; Engram, Melanie J.; Wirth, Lisa and Grosse, Guido. Characterizing methane emission response to the past 60 years of permafrost thaw in thermokarst lakes [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B44D-08, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
In this NASA ABoVE-funded project, we combine geospatial data products derived from airborne and spaceborne remote sensing (RS) data with targeted field observations and modeling in order to quantify ecosystem responses to Arctic and boreal environmental change. Specifically, we quantify methane (CH4) ebullition (bubbling) emissions associated with 60 years of permafrost thaw in thousands of Alaskan and NW Canadian lakes by direct observation with RS systems. To achieve our goals, we have developed statistically-significant models that are using SAR, optical and infrared RS data in order to detect and quantify CH4 ebullition emissions at intra-, whole- and regional-lake scales. We also established a relationship between observed CH4 ebullition and average annual soil organic carbon (SOC) inputs to a handful of Alaskan lakes via thermokarst-margin expansion during recent decades using field data, radiocarbon dating and modeling. Our paper we will provide an overview of the goals, datasets, and methods used for the various components of this project. We will present on (1) the collection of new and synthesis of existing field data on CH4 ebullition, thaw-bulbs and SOC; (2) the analysis of existing data from aerial surveys, SAR and optical RS of CH4 in lake ice; (3) the orthorectification of historic aerial photos for comparison to high-resolution satellite imagery to produce fine-scale regional maps of lake area change, (4) the modelling of permafrost SOC quantities eroded into lakes; (5) the radiocarbon dating of CH4 and SOC, (6) GIS modeling to produce multi-temporal regional maps of historic lake area change, associated CH4 emissions, and permafrost SOC stocks; and (7) outreach to stakeholders at Alaska village and rural community field sites. To demonstrate the scientific relevance of our work we will also showcase a set of research results that we have been able to achieve so far. These will include (1) first regional-scale RS-based estimates of lake-borne CH4 ebullition emissions; (2) regional scale estimates of lake area change from an analysis of 50 years of remote sensing data; and (3) regression models linking lake area change to CH4 emissions.
2017066139 Olefeldt, David (University of Alberta, Edmonton, AB, Canada); Aragones, Cristian Estop; Burd, Katheryn; Gibson, Carolyn and Heffernan, Liam. Long term effects of permafrost thaw and wildfire on peatland carbon cycling [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0606, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Boreal peatland complexes in the discontinuous permafrost zone of western Canada are mosaics of treed, permafrost affected peat plateaus interspersed with Sphagnum dominated thermokarst bogs where permafrost is absent. In a series of studies, we have assessed the implications and interactions of wildfire and permafrost thaw for peatland C cycling in this region. Carbon cycling in recently formed thermokarst bogs is of particular interest, as development of thermokarst bogs have been suggested to both cause substantial losses and gains in C storage. In order to reconcile disparate findings, we combined the monitoring of greenhouse gas fluxes with the study of peat cores in recently formed and mature thermokarst bogs. Preliminary results suggest that the mature thermokarst bogs are greater C sinks than recently formed thermokarst bogs during summer. Increased heat conduction in the wetter recently formed bogs caused substantially higher soil temperatures even at 3 m depth. Anaerobic laboratory incubations of deep peat showed that even moderate changes in temperature increased mineralization rates substantially. Furthermore, we found that mineralization rates of dissolved organic carbon (DOC) in near surface pore water was nearly ten times faster in recent than in mature thermokarst bogs. To assess to what degree wildfire accelerates permafrost thaw and thermokarst bog expansion, we combined a remote sensing landscape classification with in-situ monitoring of soil thermal regimes in sites that varied with regards to time since fire. Soil temperatures and active layer measurements indicated that the effect of wildfire on peat plateaus was most pronounced 10-15 years following the fire, and that it takes 30 to 40 years before soil thermal regimes of burned peat plateaus fully recover. In accordance, we found that peatland complexes affected by wildfire 20 to 30 years ago had twice as fast expansion rates of thermokarst bogs than nearby unburned peatland complexes. Our studies show that it is vital to account for the effects and interactions of wildfire and permafrost thaw in order to understand C cycling at the landscape scale.
2017066159 Pegoraro, Elaine (Northern Arizona University, Flagstaff, AZ); Bracho, Rosvel G. and Schuur, Edward. Long-term priming-induced changes in permafrost soil organic matter decomposition [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0630, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Warming of tundra ecosystems due to climate change is predicted to thaw permafrost and increase plant biomass and litter input to soil. Additional input of easily decomposable carbon can stimulate microbial activity, consequently increasing soil organic matter decomposition rates. This phenomenon, known as the priming effect, can exacerbate the effects of climate change by releasing more CO2 from permafrost soils; however, the extent to which it could decrease soil carbon stocks in the Arctic is unknown. Most priming incubation studies are conducted for a short period of time, making it difficult to assess if priming is a short-term phenomenon, or could persist over the long-term. We incubated permafrost soil from a moist acidic tundra site in Healy, Alaska for 456 days at 15°C. Soil from surface and deep layers were amended with three pulses of uniformly 13C labeled glucose, a fast decomposing substrate, every 152 days. We also quantified the proportion of old carbon respired by measuring 14CO2. Substrate addition resulted in higher respiration rates in glucose amended soils; however, positive priming was only observed in deep layers, where on average 9%, 57%, and 25% more soil-derived C was respired at 45-55, 65-75, and 75-85 cm depth increments for the duration of the experiment. This suggests that microbes in deep layers are limited in energy, and the addition of easily decomposable carbon increases native soil organic matter decomposition.
2017066154 Persson, Andreas (Lund University, Department of Physical Geography and Ecosystem Science, Lund, Sweden) and Connolly, John. Detecting changes in a permafrost peatland from 1943 to 2013 with historical and recent remote sensing data. [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0624, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Peatlands or mires contain about one third of the global terrestrial carbon pool and are located on between 3-6% of the global land area. In boreal and sub-arctic permafrost peatlands the soil organic carbon (SOC) pools are stable and decomposition is suspended only as long as the soil is frozen. Climate warming is projected to be greater in the high latitudes, observed mean annual air temperatures in northern Sweden have increased by 2-3°C since the 1950s. Thawing permafrost leads to new hydrological regimes potentially leading to increased production of methane. In this study, two sets of data were analysed: (i) a stereo-pair of black and white aerial photographs acquired in August 1943 by the Swedish Airforce, with a spatial resolution of 50 cm, and (ii) a geo-rectified Worldview2 (WV2) multispectral image acquired on the 24th of July, 2013. The aerial photographs were digitized using a very high resolution camera, georeferenced and incorporated into a geodatabase. The analysis of image areas was performed by heads-up visual interpretation both on a computer monitor and through stereoscopes. The aim was to identify wet and dry areas in the palsa peatland. Feature Analyst (FA) object oriented image analysis (OBIA) was used with the WV2 dataset to extract features that are related to the hydrological state of the mire. Feature Analyst is an extension to ArcGIS. The method uses a black box algorithm that can be adjusted with several parameters to aid classification and feature extraction in an image. Previous studies that analysed aerial photographs from 1970 and 2000 showed that there was an increase in the amount of wet areas on the Swedish palsa bog mire Stordalen. In this study we determine the change in wet areas over a seventy-year period. The central part of the palsa mire has been extensively studied as it has been presumed that it has collapsed due to warmer temperatures in recent decades. However, our analysis shows that much of the internal hydrological patterns on this part of the palsa bog seem to be temporally stable, at least since 1943. Macro changes not identified in previous studies are observed here where it can be seen that the extent of the palsa has retreated, in areas contiguous to streamflow, possibly in response to contact with relatively warmer streamflow.
2017066153 Plaza, César (Spanish National Research Council (CSIC), Madrid, Spain); Pegoraro, Elaine and Schuur, Edward. Response of organic matter quality in permafrost soils to warming [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0623, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Global warming is predicted to thaw large quantities of the perennially frozen organic matter stored in northern permafrost soils. Upon thaw, this organic matter will be exposed to lateral export to water bodies and to microbial decomposition, which may exacerbate climate change by releasing significant amounts of greenhouse gases. To gain an insight into these processes, we investigated how the quality of permafrost soil organic matter responded to five years of warming. In particular, we sampled control and experimentally warmed soils in 2009 and 2013 from an experiment established in 2008 in a moist acidic tundra ecosystem in Healy, Alaska. We examined surface organic (0 to 15 cm), deep organic (15 to 35 cm), and mineral soil layers (35 to 55 cm) separately by means of stable isotope analysis (d13C and d15N) and solid-state 13C nuclear magnetic resonance. Compared to the control, the experimental warming did not affect the isotopic and molecular composition of soil organic matter across the depth profile. However, we did find significant changes with time. In particular, in the surface organic layer, d13C decreased and alkyl/O-alkyl ratio increased from 2009 to 2013, which indicated variations in soil organic sources (e.g., changes in vegetation) and accelerated decomposition. In the deep organic layer, we found a slight increase in d15N with time. In the mineral layer, d13C values decreased slightly, whereas alkyl C/O-alkyl ratio increased, suggesting a preferential loss of relatively more degraded organic matter fractions probably by lateral transport by water flowing through the soil. Acknowledgements: This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No. 654132. Web site: URL: http://vulcan.comule.com
2017066151 Qu, Bin (Lappeenranta University of Technology, Laboratory of Green Chemistry, Mikkeli, Finland); Sillanpaa, Mika; Kang Shichang; Stubbins, Aron; Li Chaoliu; Yan Fangping; Aho, Kelly Sue and Raymond, Peter A. Aged dissolved organic carbon exported from rivers of the Third Pole [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0621, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Global river export of dissolved organic carbon (DOC) to the oceans (250 Tg-C yr-1; Tg=1012 g) is a key component of the global carbon cycle and is subject to climate forcing. Polar ecosystems are experiencing dramatic warming in the recent decades, potentially mobilizing large amounts of ancient permafrost carbon into contemporary rivers. However, no information is available for rivers of the climate sensitive Tibetan Plateau, which is the highest plateau on earth, water tower of Asia, and another region with extensive permafrost cover. We present the radiocarbon age and export of dissolved organic carbon from the Tibetan headwaters of three large Asian rivers (Yellow, Yangtze and Brahmaputra) during high flow. Dissolved organic carbon concentrations were lower than for Arctic rivers. Consequently, the carbon yield (0.41 gC m-2 yr-1) was lower than for Arctic rivers (1.6 gC m-2 yr-1), despite Tibetan rivers having higher annual discharge (280 kg m-2 yr-1 vs 215 kg m-2 yr-1). Average radiocarbon ages (511±294 years before present) were older in the Tibetan rivers than for Arctic and tropical rivers. Explanations were sought for Tibetan river carbon's old age. A positive correlation between radiocarbon age and permafrost watershed coverage was observed, indicating that old carbon (656±177 years before present) is exported during high flow from permafrost regions of the Tibetan Plateau. Additionally, Inputs of fossil carbon (2,265±1009 years before present) from polluted South and East Asia may also contribute to the old age of Tibetan river carbon.
2017064509 Rasmussen, Laura Helene (University of Copenhagen, Department of Geosciences, Center for Permafrost (CENPERM), Copenhagen, Denmark); Zhang, Wenxin; Elberling, Bo and Cable, Stefanie. Experimental and ecosystem model approach to assessing the sensitivity of High Arctic deep permafrost to changes in surface temperature and precipitation [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B54F-02, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Permafrost affected areas in Greenland are expected to experience large temperature increases within the 21st century. Most previous studies on permafrost consider near-surface soil, where changes will happen first. However, how sensitive the deep permafrost temperature is to near-surface conditions through changes in soil thermal properties, snow depth and soil moisture, is not known. In this study, we measured the sensitivity of thermal conductivity (TC) to gravimetric water content (GWC) in frozen and thawed deep permafrost sediments from deltaic, alluvial and fluvial depositional environments in the Zackenberg valley, NE Greenland. We also calibrated a coupled heat and water transfer model, the "CoupModel", for the two closely situated deltaic sites, one with average snow depth and the other with topographic snow accumulation. With the calibrated model, we simulated deep permafrost thermal dynamics in four scenarios with changes in surface forcing: a. 3 °C warming and 20% increase in precipitation; b. 3°C warming and 100% increase in precipitation; c. 6°C warming and 20% increase in precipitation; d. 6°C warming and 100% increase in precipitation. Our results indicated that frozen sediments had higher TC than thawed sediments. All sediments showed a positive linear relation between TC and soil moisture when frozen, and a logarithmic one when thawed. Fluvial sediments had high sensitivity, but never reached above 12% GWC, indicating a field effect of water retention capacity. Alluvial sediments were less sensitive to soil moisture than deltaic and fluvial sediments, indicating the importance of unfrozen water in frozen sediment. The deltaic site with snow accumulation had 1°C higher annual mean ground temperature than the average snow site. The soil temperature at the depth of 18 m increased with 1.5°C and 3.5 °C in the scenarios with 3°C and 6°C warming, respectively. Precipitation had no significant additional effect to warming. We conclude that below-ground sediment properties affect the sensitivity of TC to GWC, that surface temperature changes can significantly affect the deep permafrost within a short period, and that differences in snow depth affect surface temperatures. Geology, pedology and precipitation should thus be considered if estimating future High arctic deep permafrost sensitivity.
2017064477 Reum, F. (Max Planck Institute for Biogeochemistry, Jena, Germany); Goeckede, M.; Miller, S. M.; Michalak, A. M.; Henderson, J.; Miller, C. E. and Heimann, M. Methane emissions from the East Siberian Arctic Shelf [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B31I-02, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
The East Siberian Arctic Shelf (ESAS) may be emitting large amounts of methane to the atmosphere. The hypothesized sources are degrading subsea permafrost, as well as methane hydrates and free gas pools below the permafrost layer. Existing estimates of methane emissions from the ESAS are based on upscaling of local measurements or on the synoptic variability of atmospheric methane signals around the Arctic Ocean. These estimates vary from zero to 17 Tg CH4 yr-1, which is a substantial magnitude and uncertainty given that the largest methane source in northern high latitudes is considered to be boreal wetlands with estimated emissions of 20-50 Tg CH4 yr-1.Here, we estimate methane emissions from the ESAS using a geostatistical inverse model and atmospheric observations of methane mixing ratios. These observations include data from a new measurement station located at the coast of the ESAS (Ambarchik, 69.6N, 162.3E), as well as data from other stations around the Arctic Ocean. The modeling approach is designed to identify important methane emission drivers in the region by determining spatiotemporal methane flux patterns which are not only consistent with the atmospheric data, but also correlate with key environmental covariates that represent major methane emission processes. These covariates include, among others, ocean depth and sea-ice concentration as proxies for oceanic methane fluxes, and mechanistic model estimates of methane sources on land, such as wetlands and lakes.
2017066157 Reuss-Schmidt, Kassandra (University of Sheffield, Animal and Plant Sciences, Sheffield, United Kingdom) and Zona, Donatella. Evaluating spatiotemporal differences in methane fluxes on the North Slope of Alaska via eddy covariance footprint modelling [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0628, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Arctic permafrost soils store 1300-1370 Pg of organic carbon, twice the current atmospheric stock. This region is warming at approximately 1°C per decade, and permafrost soils could lose 381-616 Pg C by 2300, with a large portion potentially being released as the potent greenhouse gas methane (CH4). Despite intensive investigation, uncertainty estimates of CH4 emissions have significantly increased since the first estimates in 1974. Two main difficulties in creating a baseline flux estimate is the region's remote nature and the high spatiotemporal variability in methane fluxes. This project examines fluxes from three eddy covariance sites in Barrow, Alaska by applying the Kormann and Meixner (2001) footprint model to investigate the spatio-temporal variability in fluxes across the arctic polygonal tundra throughout the year. A LiDAR digital elevation model collected by NGEE Arctic at a very fine resolution (0.25 m) and WorldView2 data have been used to give quantitative metrics for vegetation and microtopographic differences over these three sites. Preliminary results show significant differences (p-value <0.05) in CH4 emission patterns in the footprints that could bias flux estimates by 20%. Furthermore, the pattern of footprint variability shows divergent spatial patterns between summer and winter fluxes. The largest mean summer fluxes were observed in a low lying sedge-dominated drained lake basin (7.74 mg CH4 m-2 day-1) with the less degraded, more polygonal area having an average flux of (5.82 mg CH4 m-2 day-1). In the winter "zero curtain" period, the pattern reversed with higher fluxes coming from the polygonal area (3.58 mg CH4 m-2 day-1) and slightly lower fluxes (3.35 mg CH4 m-2 day-1) observed from the lake basin. This highlights that flux drivers differ by season and that these dynamics should be considered for estimating annual and regional fluxes.
2017066282 Richmond, Bruce M. (U. S. Geological Survey, Pacific Coastal and Marine Geology Science Center, Santa Cruz, CA); Gibbs, Ann; Johnson, Cordell D.; Swarzenski, Peter W.; Oberle, Ferdinand J.; Tulaczyk, Slawek M. and Lorenson, Thomas D. Coastal permafrost bluff response to summer warming, Barter Island, Ne Alaska [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract EP13C-1046, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Observations of warming air and sea temperatures in the Arctic are leading to longer periods of permafrost thaw and ice-free conditions during summer, which lead to increased exposure to coastal storm surge, wave impacts, and heightened erosion. Recently collected air and soil (bluff) temperatures, atmospheric pressure, water levels, time-lapse photography, aerial photography and satellite imagery, and electrical resistivity tomography (ERT) surveys were used to document coastal bluff morphological response to seasonal warming. Data collection instruments and time-lapse cameras installed overlooking a bluff face on the exposed open ocean coast and within an erosional gully were used to create an archive of hourly air temperature, pressure, bluff morphology, and sea-state conditions allowing for documentation of individual bluff failure events and coincident meteorology. Permafrost boreholes as deep as 6 m from the upper bluff tundra surface were fitted with thermistor arrays to record a high resolution temperature record that spanned an initial frozen state, a summer thaw cycle, and subsequent re-freezing. Late summer ERT surveys were used to link temperature observations to subsurface electrical resistivities and active-layer dynamics. Preliminary observations suggest surface warming and active layer growth are responsible for a significant amount of bluff face failures that are exacerbated in the shore perpendicular gullies and along the exposed ocean coast. Electrical resistivity surveys and geochemical data reveal concentrated brines at depth, which likely contribute to enhanced, localized erosion in weakened strata.
2017064496 Rupp, Danielle (Michigan Technological University, School of Forest Resources and Environmental Sciences, Houghton, MI); Kane, Evan S.; Keller, Jason; Turetsky, Merritt R. and Meingast, Karl Michael. Long-term effects of hydrologic manipulations on pore water dissolved organic carbon in an Alaskan rich fen [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B53G-0602, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Boreal peatlands are experiencing rapid changes due to temperature and precipitation regime shifts in northern latitudes. In areas near Fairbanks, Alaska, thawing permafrost due to climatic changes alters peatland hydrology and thus the biogeochemical cycles within. Pore water chemistry reflects the biological and chemical processes occurring in boreal wetlands. The characterization of dissolved organic carbon (DOC) within pore water offers clues into the nature of microbially-driven biogeochemical shifts due to changing hydrology. There is mounting evidence that organic substances play an important role in oxidation-reduction (redox) reactivity of peat at northern latitudes, which is closely linked to carbon cycling. However, the redox dynamics of DOC are complex and have not been examined in depth in boreal peatlands. Here, we examine changes in organic substances and their influences on redox activity at the Alaska Peatland Experiment (APEX) site near Fairbanks, Alaska, where water table manipulation treatments have been in place since 2005 (control, raised water table, and lowered water table). With time, the altered hydrology has led to a shift in the plant community to favor sedge species in the raised water table treatment and more shrubs and non-aerenchymous plants in the lowered water table treatment. The litter from different plant functional types alters the character of the dissolved organic carbon, with more recalcitrant material containing lignin in the lowered water table plot due to the greater abundance of shrubs. A greater fraction of labile DOC in the raised treatment plot likely results from more easily decomposed sedge litter, root exudates at depth, and more frequently waterlogged conditions, which are antagonistic to aerobic microbial decomposition. We hypothesize that a greater fraction of phenolic carbon compounds supports higher redox activity. However, we note that not all "phenolic" compounds, as assayed by spectrophotometry, have the same redox activity. We report these results in the context of previous observations of higher methane fluxes from the raised water table plot. Taken together, these findings provide the mechanistic details needed to understand residual error in modeling efforts of anaerobic carbon evasion (methane and carbon dioxide) in boreal wetlands.
2017066155 Shu, Shijie (University of Illinois at Urbana Champaign, Department of Atmospheric Sciences, Urbana, IL); Mishra, Umakant; Randerson, James Tremper; He, Yujie; Koven, Charles; Hoffman, Forrest M. and Jain, Atul K. Estimating potential damping of cryoturbation on permafrost carbon emissions using a perturbed parameters approach in a land surface model [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0626, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Permafrost soils in the northern hemisphere contain about half of the world's total soil organic carbon (SOC), which has the potential to be a large carbon source as a consequence of anticipated climate changes. However, divergent estimates of the magnitude and the trend of soil carbon emission between different global land surface models with simple representation of permafrost processes highlighted the demand to understand the influence of processes that are most likely to affect the permafrost carbon cycle feedbacks (PCF), including cryoturbation, oxygen limitation and microbial dynamics. Here we use a land surface model, the Integrated Science and Assessment Model with one-dimensional soil biogeochemistry (ISAM-1DSB), to examine how the response of cryoturbation to a changing thermal and hydrological regime will affect the PCF under the IPCC RCP8.5 climate scenario. ISAM-1DSB contains an extended permafrost representation, a 1-D frost heave model that resolves ice lens formation and growth to represent cryoturbation and a gas diffusion model to estimate oxygen availability in poorly-drained soil. To validate the model's ability to capture the vertical variability of SOC profiles, ISAM-1DSB has been forced with CRU-NCEP reanalysis to build up quasi-equilibrium contemporary SOC storage and compared to a set of permafrost soil profiles from three different permafrost soil suborders: Histel, Turbel and Orthel. For the first time, soil D14C profiles across the pan-arctic region has been utilized to constrain the key uncertain parameter linking ice lens velocity to the cryoturbation rate in the frost heave scheme by matching model estimated D14C profiles with observations. The estimated range of the cryoturbation rate has been utilized to represent the uncertainty of the cryoturbation under future climate change. Finally, ISAM-1DSB has been forced with future climate projections from CMIP5 model outputs for the entire permafrost region to perform three simulation cases with the lower, the median and the upper bound of the parameter. These experiments estimate the permafrost carbon emission till 2100 to test a hypothesis: the accumulated permafrost SOC emission will be smaller with consideration of cryoturbation, but this trend will be enhanced once the cryoturbation stalls.
2017066156 Soom, Florian (Lawrence Berkeley National Laboratory, Berkeley, CA); Ulrich, Craig; Dafflon, Baptist; Wu, Yuxin; Kneafsey, Timothy J.; López, Robin D.; Peterson, John and Hubbard, Susan S. Estimating the spatial distribution of soil organic matter density and geochemical properties in a polygonal shaped Arctic Tundra using core sample analysis and X-ray computed tomography [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0627, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
The Arctic tundra with its permafrost dominated soils is one of the regions most affected by global climate change, and in turn, can also influence the changing climate through biogeochemical processes, including greenhouse gas release or storage. Characterization of shallow permafrost distribution and characteristics are required for predicting ecosystem feedbacks to a changing climate over decadal to century timescales, because they can drive active layer deepening and land surface deformation, which in turn can significantly affect hydrological and biogeochemical responses, including greenhouse gas dynamics. In this study, part of the Next-Generation Ecosystem Experiment (NGEE-Arctic), we use X-ray computed tomography (CT) to estimate wet bulk density of cores extracted from a field site near Barrow AK, which extend 2-3m through the active layer into the permafrost. We use multi-dimensional relationships inferred from destructive core sample analysis to infer organic matter density, dry bulk density and ice content, along with some geochemical properties from nondestructive CT-scans along the entire length of the cores, which was not obtained by the spatially limited destructive laboratory analysis. Multi-parameter cross-correlations showed good agreement between soil properties estimated from CT scans versus properties obtained through destructive sampling. Soil properties estimated from cores located in different types of polygons provide valuable information about the vertical distribution of soil and permafrost properties as a function of geomorphology.
2017064398 Spry, E. (University of Minnesota Morris, Morris, MN); Beck, M. A.; Hamilton, B. T.; Johnson, J. E.; Palace, M. W.; McCalley, C. K.; Varner, R. K. and Bothner, W. A. Linking discharge to carbon transport within an arctic stream network in Stordalen Mire, Abisko, Sweden [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B23B-0572, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Permafrost soils hold an appreciable amount of the world's soil carbon; release of carbon from these soils is vulnerable to climate warming. Research has shown that high latitude wetlands situated on the discontinuous permafrost boundary are responding to increases in temperature, releasing large amounts of methane. Dissolved and particulate carbon within these ecosystems can be transported within stream networks and connect to glacial and post-glacial lakes with relatively unknown consequences. This project aims to investigate the role discharge plays between water bodies and its relationship to carbon dispersal throughout a drainage system in a subarctic mire. We investigate the transport and mobilization of carbon within a large summertime, low flow stream network in Stordalen Mire near Abisko, Sweden. Connectivity of Stordalen Mire to the large glacial Lake Tornetrask was also examined. Samples of surface water were taken at fifteen sites along a drainage transect and analyzed for methane, dissolved inorganic carbon, total organic carbon (POC and DOC), pH, temperature, and dissolved oxygen. Concentrations of methane in surface waters averaged 0.33 mM in stream sites versus 1.02 mM in lakes, but also decreased along the transect from the mire to glacial Lake Tornetrask. Our results indicate that although a significant amount of water passes through the mire and into Lake Tornetrask, very little methane and dissolved inorganic carbon is carried into the lake; this implies that the carbon contribution of low-flow streams to larger glacial lakes may be less than previously indicated.
2017066179 Tank, Suzanne E. (University of Alberta, Edmonton, AB, Canada); Kokelj, Steve V.; Bulger, Cara A.; Shakil, Sarah; Zolkos, Scott; St. Louis, Vincent L.; St. Pierre, Kyra; McClelland, James W. and Striegl, Robert G. Rapid changes in biogeochemical cycling across multiple scales in stream and river networks of the western Canadian Arctic [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43G-01, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
The flux and processing of biogeochemical constituents within stream and river networks is intricately linked to current, and changing, processes on land. In the western Canadian Arctic, recent work has documented a significant change in these land-to-freshwater connections, with a near 20% increase in the combined flux of dissolved organic, and inorganic carbon (DOC, DIC) at the mouth of the Mackenzie River over the past 40 years. This change is occurring over a potentially vast spatial scale: the Mackenzie watershed drains 1.5 M km2 of permafrost-affected terrain. To understand the mechanisms underlying these large-scale observations, direct investigations at the sub-catchment scale are required. Within the greater Mackenzie catchment, one region undergoing rapid climate-induced change is the Peel Plateau, where the ubiquity of massive ground ice causes permafrost thaw to manifest as large retrogressive thaw slump (RTS) features, which can mobilize millions of cubic meters of sediment downslope and downstream. Soils in this region are comprised of deep, mineral-rich glacial tills, which appears to combine with significant RTS sediment mobilization to cause the effects of permafrost thaw to be strongly mediated by particle- and mineral-associated processes. At a direct level, these effects are striking: particulate organic carbon (POC) concentrations increase by up to two orders of magnitude downstream of slumps, while a similar increase in dissolved minerals is accompanied by a decrease in CO2, suggesting an important role for mineral weathering in this region's changing carbon cycle. However, these direct effects also have important indirect implications for biogeochemical change. For example, while RTSs release DOC of low aromaticity and high degradeability--as found in other permafrost-affected landscapes--the presence of mineral-rich suspended sediment appears to sequester DOC downstream of slumps. Beyond the carbon cycle, RTS sediment mobilization is accompanied by a marked increase in methyl mercury transport, with fluxes almost entirely associated with the particulate phase. Overall, these findings from the Peel Plateau highlight the importance of assessing permafrost thaw effects across multiple biogeochemical constituents, and a broad diversity of Arctic landscape types.
2017064494 Tran, Anh Phuong (Lawrence Berkeley National Laboratory, Berkeley, CA); Dafflon, Baptiste and Hubbard, Susan S. Coupled land surface-subsurface inverse modeling to investigate arctic hydrological and thermal dynamics and soil organic content using geophysical data [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B53G-0596, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Quantification of soil surface-subsurface hydro-thermal processes in permafrost regions is essential as they influence many biogeochemical processes. Recently, coupled hydrogeophysical inversion that inverts geophysical data to estimate subsurface hydro-thermal properties and processes has become an important approach. However, this approach is suffered from non-uniqueness because it typically relies on only geophysical datasets. This approach is also focuses on quantifying subsurface processes only. We extend previous coupled hydrogeophysical inversion approach to include multiple types of above- and below-ground datasets, and also to account for interactions between the land and subsurface. The joint inversion of multiple geophysical and non-geophysical datasets helps to reduce non-uniqueness. We focus our study in the Arctic region, where surface-subsurface hydro-thermal regimes are both influenced by soil organic carbon and mineral content. In our inversion scheme, the CLM model serves as a forward model to simulate the land-surface processes and subsurface hydro-thermal dynamics. We developed an advanced optimization technique that combines the deterministic and stochastic optimization algorithms to obtain both model parameters and their uncertainties. The stochastic optimization estimates the posterior distribution (pdf) of the model parameters by using the Bayesian inference and Delayed Rejection Adaptive Metropolis (DRAM) Markov Chain Monte Carlo (MCMC) techniques. The deterministic optimization algorithm is used to approximate the start point of model parameters and proposal covariance matrix for the stochastic optimization. We will describe the new coupled inversion approach and its ability to provide accurate estimates of soil hydro-thermal and physical properties, the latter including vertical distribution of organic, clay and sand content. We will also describe analysis of the modeling results, including: 1) evaluation of the relationship between measurement errors and uncertainties of model parameters, 2) investigation of the improvement in parameter estimation when joint inverting liquid, soil temperature and electrical resistivity data and 3) examination of the effect of parameter uncertainties on the accuracy of hydro-thermal variables.
2017064401 Varner, R. K. (University of New Hampshire Main Campus, Durham, NH); McCalley, C. K.; Clarizia, P. E.; Verbeke, B. A.; Werner, S. L.; Burke, S. A.; Malhotra, A. and Rocci, K. Using carbon isotopes of methane from porewater to understand methane emissions across a permafrost thaw gradient [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B23B-0577, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Methane (CH4) emissions from high latitude ecosystems are controlled in part by the presence/absence of permafrost and concomitant modifications in vegetation composition. Rapid transitions in habitat impact CH4 emissions both by changing the moisture regime as well as the production and emission pathways. Measurement of the isotopic composition of CH4 in porewater in these thawed ecosystems can indicate shifts in production pathways of CH4. We measured CH4 and carbon dioxide (CO2) emission, belowground CH4 concentration and 13CH4 of porewater, vegetative type, and vascular greenness area (VGA) along a thaw gradient during summers 2012-2016 in Stordalen Mire, Sweden. Concentrations of CH4 belowground showed positive correlation with aboveground emissions. Carbon isotopic signatures of CH4 varied varied between sites with more hydrogenotrophic signatures in sites dominated by Sphagnum spp. and acetate fermentation signatures in sedge dominated sites (Carex and Eriophorum spp.). These data indicate that these ecosystems transition from thaw, their 13CH4 emissions will change and therefore need to be accounted for in global atmospheric budgets and models.
2017066146 Vining, Sarah Rose (University of Arizona, Tucson, AZ); Hough, Moira; McClure, Amelia; Saleska, Scott R. and Rich, Virginia Isabel. Thawing permafrost in arctic peatlands leads to changing vegetation composition, decline in plant biodiversity, but little change in biomass [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0613, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
As permafrost thaws over the next century due to a rapidly changing climate, the shifting nature and amount of bioavailable soil organic matter (SOM) are causing ecosystem-level changes in carbon dioxide (CO2) and methane (CH4) fluxes. These greenhouse gases could drive a positive feedback to climate change, increasing the rate of permafrost thaw. The change in SOM is due to (a) new availability of previously frozen permafrost carbon (C), and (b) shifting plant communities. Appreciable study has focused on the former; we focus here on the latter, at a 'natural' permafrost thaw gradient in Arctic Abisko, Sweden. As previously frozen soil destabilizes and collapses into a waterlogged habitat, dominant vegetation type shifts from smaller, woodier plants to moss-dominated sites, then to taller, leafier sedges. This plant community succession is associated with increased CO2 uptake, which could partially offset the thaw-associated C release from soils if it resulted in greater C storage. We tested the hypothesis that C stored in plant biomass increases spatially across the thaw gradient by sampling both above and below ground biomass. We also took time points from the early and peak-growing season (early June to late July) to test if differences in plant growth seasonality impacted our biomass measures. Surprisingly, we found that total above and below ground biomass together do not significantly change from the intact to the fully-thawed habitats, despite previous research showing that productivity appears to be higher in the fully water-logged fen. However, biodiversity significantly decreased from the intact to waterlogged sites. The lack of observed biomass increase despite the increase in NPP observed in other studies from this site could be explained if the C taken up by sedges in fen sites is deposited in SOM at increased rates either through root exudates or annual litter deposition. Since the shift in plant community composition is associated with the observed loss of plant biodiversity across the gradient, these results suggest that plant community succession alters the quantity, type, and diversity of plant litter inputs to the soil. Such changes in litter quantity and type are important drivers of decomposition rates and therefore the status of the ecosystem as a source versus sink for atmospheric carbon.
2017066152 Waldrop, Mark P. (U. S. Geological Surveys, Menlo Park, CA); Neumann, Rebecca Bergquist; Jones, Miriam; Manies, Kristen; McFarland, Jack W.; Blazewicz, Steven and Turetsky, Merritt R. Accelerated rates of in situ microbial activity after permafrost collapse estimated from a porewater isotope model [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0622, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Permafrost thaw is expected to become widespread in interior Alaska over the coming century, resulting in increased CO2 and CH4 fluxes from soils and a positive feedback to global warming. However much of our understanding of the microbial response to thaw is predicated on simple laboratory incubations that preclude the multitude of interactions occurring in soils under field situations. Here, we utilize a time series of 13CO2 and 13CH4 measured in porewater collected from thermokarst bogs of different ages to estimate in-situ reaction rates of microbial respiration, methanogenesis from acetate, methanogenesis from CO2, homoacetogenesis, and methane oxidation from porewater concentrations and 13CO2 and 13CH4. We utilized this modeling technique to test the hypothesis that microbial activities are stimulated soon after permafrost thaw and this effect declines over time. Our field site is a chronosequence of thermokarst bogs at the Alaska Peatland Experiment (APEX) in interior AK where we have observed significant losses of peatland carbon since permafrost collapse over the last half century. Concentrations of dissolved CO2 and CH4 in porewater increased with depth, and were higher in the youngest bog compared to the older bogs. With increasing depth 13CH4 became more depleted while 13CO2 became more enriched. Preliminary modeling results, based upon these porewater gas concentrations and isotope values, indicate that microbial activities are higher in the youngest bogs compared to the older bogs, supporting the hypothesis that accelerated rates of microbial activities in young thermokarst features are responsible for high rates of C losses from these systems. Additionally, model results will be compared to variation in the abundance of methanogens, methane oxidizers, and acetogens as well as process rates measured in lab incubations, providing insights into the mechanisms responsible for these losses.
2017066150 Wang Yinhui (Peking University, Beijing, China) and Xu Yunping. Chemical characterization of dissolved organic matter in an alpine stream from thawing and collapsing permafrost to Qinghai Lake [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0620, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
The Tibetan Plateau is the world's largest and highest plateau, approximately two thirds of which is covered by permafrost. Due to recent climate warming, large organic carbon stored in the permafrost is thawing and becomes available for transport to aquatic ecosystems (i.e., stream and lake) as dissolved organic matter (DOM) and fine particulate organic matter (POM). These DOM and POM are not only important food sources for the aquatic food web, but also a significant feedback if remineralized during transport. In this work, we collected water samples along a stream from the headwater in the Permafrost region to the downstream in the Qinghai Lake. The concentration and composition of DOM were determined using high temperature combustion analysis, UV- Vis absorption spectroscopy and fluorescence spectroscopy. The concentration of dissolved organic carbon decreased sharply from 13.87 mg/L to 4.32 mg/L from collapsing permafrost area (3850 m a.s.l.) to the foot of the mountain (3200 m a.s.l.), and then fluctuated in a narrow range between 3.00 mg/L and 4.50 mg/L. The DOM with high humic-like fluorescence, specific UV absorbance (SUVA254), and low spectral slope ratio (S275-295) and fluorescence index (FI) was observed in the headwater, which was distinct difference from that at the middle and downstream area where the DOM are less aromatic and low molecular weight. Meanwhile, the freshness index (b/a) increased slightly in mid and down-stream. This increasing trend for FI and b/a indicated a contribution of recently in situ produced DOM by aquatic bacteria and algae in the stream. We speculate that the biological process is an important way to cause the chemical change of DOM composition and concentration, and therefore the thawing and transport of permafrost carbon may play a key role in sustaining the alpine stream ecosystem.
2017066148 Wilson, Emily Lynn (NASA, Goddard Space Flight Center, Greenbelt, MD); DiGregorio, Anthony J.; Carter, Lynn M.; Euskirchen, Eugene Susanne; Edgar, Colin; Hoffman, Christine; Ramanathan, Anand K.; Mao, Jianping; Duncan, Bryan N.; Ott, Lesley E.; Liang, Qing; Melocik, Katherine A. and Tucker, Compton J. Methane and carbon dioxide emissions during the seasonal permafrost thaw at the Bonanza Creek Research Forest; results from the May 2016 field campaign [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0618, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
We present field measurements from a May 2016 campaign funded under NASA's Interdisciplinary Science (IDS) program to track methane (CH4) and carbon dioxide (CO2) emissions above thawing permafrost at three sites near Fairbanks, AK. Each of the sites, located in the Bonanza Creek Research Forest, represent a different ecosystem including black spruce with cold soils and stable permafrost, collapse scar bog with thermokarst formation, and a site with moderately rich fen lacking near surface permafrost. Field experiments were carried out in May during the seasonal ground thaw of the active layer. Measurements included permafrost depth and subsurface structure using ground penetrating radar, meteorological variables (air and soil temperature, net radiation, albedo, precipitation, snow depth, vapor pressure, etc.), eddy covariance data from a 3-D sonic anemometer, and surface and column concentrations of CH4 and CO2 with an open-path infrared gas analyzer (LICOR) and Miniaturized Laser Heterodyne Radiometer (Mini-LHR) respectively. We have referred to this effort as a pilot study because our intent is to expand our observational network in the future to other sites in North America, which will aid in the monitoring of changes in GHG emissions in the Arctic as well as complement and help interpret data collected by space-borne instruments, such as GOSAT, IASI, and AIRS. This is the first time that these types of measurements have been combined to provide a holistic view of the evolution of, and the atmospheric response to permafrost thaw. The final year of this effort will focus on estimating a global source of GHG emissions from thawing permafrosts. We will use MODIS and Landsat-8 Operational Land Imager and Thermal Infrared Sensor data to "scale up" the data collected at the three sites on the basis of land surface type information. Based on the data collected at the three sites and a variety of existing satellite data sets, we will develop a computationally-efficient parameterization of emissions from thawing permafrosts for use in the NASA GEOS-5 Atmospheric General Circulation Model (AGCM), thus benefiting ongoing efforts in the NASA Global Modeling and Assimilation Office (GMAO) to build an Earth System Model which is used for both retrospective and predictive simulations of important GHGs.
2017066141 Yang Yuanhe (Chinese Academy of Sciences, Institute of Botany, Beijing, China); Ding Jinzhi; Li Fei; Yang Guibiao and Chen Leiyi. The permafrost carbon inventory on the Tibetan Plateau; a new evaluation using deep sediment cores [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0608, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
The permafrost organic carbon (OC) stock is of global significance because of its large pool size and potential positive feedback to climate warming. However, due to the lack of systematic field observations and appropriate upscaling methodologies, substantial uncertainties exist in the permafrost OC budget, which limits our understanding on the fate of frozen carbon in a warming world. In particular, the lack of comprehensive estimation of OC stock across alpine permafrost means that the current knowledge on this issue remains incomplete. Here we evaluated the pool size and spatial variations of permafrost OC stock to 3 meters depth on the Tibetan Plateau by combining systematic measurements from a substantial number of pedons (i.e., 342 three-meter-deep cores and 177 50-cm-deep pits) with a machine learning technique (i.e., support vector machine, SVM). We also quantified uncertainties in permafrost carbon budget by conducting Monte Carlo simulation. Our results revealed that the combination of systematic measurements with the SVM model allowed spatially explicit estimates. The OC density (OC amount per unit area, OCD) exhibited a decreasing trend from the southeastern to the northwestern plateau, with the exception that OCD in the swamp meadow was substantially higher than that in surrounding regions. Our results also demonstrated that Tibetan permafrost stored a large amount of OC in the top 3 meters, with the median OC pool size being 15.31 Pg C (interquartile range: 13.03-17.77 Pg C). Of them, 44% occurred in deep layers (i.e., 100-300 cm), close to the proportion observed across the northern circumpolar permafrost region. The large carbon pool size, together with significant permafrost thawing implies a risk of carbon emissions and positive climate feedback across the Tibetan alpine permafrost region.
2017066218 Yi, Yonghong (University of Montana, College of Forestry & Conservation, Numerical Terradynamic Simulation Group, Missoula, MT); Kimball, John S.; Moghaddam, Mahta and Reichle, Rolf H. Characterizing permafrost active layer dynamics and sensitivity to landscape spatial heterogeneity; a case study in Alaska [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B52C-06, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
An important feature of the Arctic is the large spatial heterogeneity in permafrost and active layer conditions, which are generally poorly represented in global climate and carbon models and can lead to large uncertainties in predicting regional ecosystem responses and feedbacks to climate change. In this study, we developed a spatially integrated analysis and modeling framework to investigate the sensitivity of permafrost active layer processes to sub-grid heterogeneity in vegetation, terrain and disturbance factors. The model framework combines detailed field measurements of vegetation, microclimate and active layer properties with local scale (~100 m resolution) soil active layer retrievals from airborne radar remote sensing, and landscape level (>&eq;1-km resolution) environmental observations from satellite microwave and optical-infrared sensors. Satellite observations, including land surface temperature, snow cover extent and soil moisture from the MODIS and SMAP sensors, are used as primary model drivers for estimating snow/soil thermal conductivity and soil temperature profiles. The model estimates regional patterns and recent changes (2001-present) in permafrost extent (PE) and ALT across Alaska at landscape scale (~1-km resolution). Local scale maps of active layer conditions and additional land parameters include soil moisture and surface organic layer thickness from combined low frequency (L+P-band) airborne radar backscatter from the NASA UAVSAR and AirMOSS sensors will be used to inform the coarser landscape model simulations and quantify the effects of surface organic layer and soil moisture spatial heterogeneity on the estimated soil active layer dynamics. These results are used to clarify regional patterns and recent changes in permafrost active layer conditions, and underlying environmental controls across Alaska.
2017066184 Zhang, Xiaowen (University of Florida, Department of Geological Sciences, Ft. Walton Beach, FL); Bianchi, Thomas S.; Cui, Xingqian; Rosenheim, Brad E.; Ping, Chien-Lu; Kanevskiy, Mikhail Z.; Hanna, Andrea Miller and Allison, Mead A. Permafrost mobilization from the watershed to the Colville River delta; evidence from biomarkers and 14C ramped pyrolysis [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43G-08, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
As temperatures in the Arctic rise abnormally fast, permafrost in the region is vulnerable to extensive thawing. This could release previously frozen organic carbon (OC) into the contemporary carbon cycle, giving a positive feedback on global warming. Recent research has found the presence of particulate permafrost in rivers, deltas, and continental shelves in the Arctic, but little direct evidence exists on the mechanism of transportation of previously frozen soils from watershed to the coast. The Colville River in northern Alaska is the largest North American Arctic River with a continuous permafrost within its watershed. Previous work has found evidence for the deposition of previously frozen soils in the Colville River delta (Schreiner et al., 2014). Here, we compared the bulk organic carbon thermal properties, ages of soils and river and delta sediments from the Colville River drainage system using 14C Ramped Pyrolysis and chemical biomarkers. Our data show that deep permafrost soils as well as river and delta sediments had similar pyrograms and biomarker signatures, reflecting transport of soils from watershed to the delta. Surface soil had pyrograms indicative of less stable (more biodegradable) OC than deeper soil horizons. Similarity in pyrograms of deep soils and river sediment indicated the limited contribution of surface soils to riverine particulate OC inputs. Sediments in the delta showed inputs of yedoma (ice-rich syngenetic permafrost with large ice wedges) from the watershed sources (e.g., river bank erosion) in addition to peat inputs, that were largely from coastal erosion.
2017064237 Zhao Hui (Chinese Academy of Sciences, Institute of Mountain Hazards and Environment, Chengdu, China); Wang Xiaodan; Lu Xuyang and Cai Yanjiang. Large methane emission during onset of freezing from natural wetlands in the high altitude permafrost region [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B11C-0464, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Methane (CH4) emission from natural wetlands is critically important due to its high warming potential. The freeze-thaw transition has been confirmed to play an important role in annual CH4 budget, yet the magnitude of this effect is uncertain in Qinghai-Tibet Plateau. An intensive field monitoring experiment was carried out in the Northern Tibet (altitude 4750 m) to estimate the CH4 emission in the late autumn and early winter. We find that emissions fall to a low steady level after the growing season but then increase significantly during the freeze-in period. The observation concluded that a large CH4 source was caused by freezing thaw; the maximum emission rate was 4.45 mg m2 h-1, more than that in the growing season. The winter freezing effect contributed to a large CH4 source, which is approximately 45% of the previously calculated annual CH4 emission in the study area. If our results are typical for natural wetlands in the northern Tibet, we estimate a CH4 emission of 0.05-0.1 Tg C (1 Tg=1012 g) caused by winter freezing effect in the Tibet region in 2014. Our findings suggest that permafrost-associated freeze-in bursts of methane emissions in the high altitude permafrost regions could be an important and so far unrecognized component of the seasonal distribution of CH4 emissions.
2017064517 Zhao Lin (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, Lanzhou, China); Zou Defu; Sheng Yu; Chen Ji; Wu Tonghua; Wu Jichun; Pang Qiangqiang and Wang Wu. Modelling the permafrost extent on the Tibetan Plateau [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract C11C-0778, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
The Tibetan Plateau (TP) possesses the largest areas of permafrost terrain in mid- and low-latitude regions of the world. Permafrost plays significant role in climatic, hydrological, and ecological systems, and has great influences on landforms formation, slope and engineering construction. Detailed database of distribution and characteristics of permafrost is crucial for engineering planning, water resource management, ecosystem protection, climate modeling, and carbon cycle research. Although some permafrost distribution maps were compiled in previous studies and proved very useful, due to the limited data source, ambiguous criteria, little validation, and the deficiency of high-quality spatial datasets, there are a large uncertainty in the mapping permafrost distribution. In this paper, a new permafrost map was generated mostly based on freezing and thawing indices from modified MODISland surface temperatures (LSTs), and validated by various ground-based dataset. Soil thermal properties of five soil types across the TP estimated according to the empirical equation and in situ observed soil properties (water content and bulk density) which were obtained during the field survey. Based on these data sets, the model of Temperature at the Top Of Permafrost (TTOP) was applied to simulate permafrost distribution over the TP. The results show that permafrost, seasonally frozen ground, and unfrozen ground covered areas of 106.4´104 km2, 145.6´104 km2, and 2.9´104 km2. The ground based observations of permafrost distribution across the five investigated regions (IRs) and three highway transects (across the entire permafrost regions from north to south) have been using to validate the model. Result of validation shows that the kappa coefficient vary from 0.38 to 0.78 in average 0.57 at the five IRs and from 0.62 to 0.74 in average 0.68 within three transects. The result of TTOP modeling shows more accuracy to identify thawing regions in comparison with two maps, compiled in 1996 and 2006 and could be better represent the detailed permafrost distribution than other methods. Overall, the results are providing much more detailed maps of permafrost distribution, which could be a promising basic data set for further research on permafrost on the Tibetan Plateau.
2017066161 Zheng, Jianqiu (Oak Ridge National Laboratory, Oak Ridge, TN). Biogeochemical controls on microbial CH4 and CO2 production in Arctic polygon tundra [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract B43C-0633, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Accurately simulating methane (CH4) and carbon dioxide (CO2) emissions from high latitude soils is critically important for reducing uncertainties in soil carbon-climate feedback predictions. The signature polygonal ground of Arctic tundra generates high level of heterogeneity in soil thermal regime, hydrology and oxygen availability, which limits the application of current land surface models with simple moisture response functions. We synthesized CH4 and CO2 production measurements from soil microcosm experiments across a wet-to dry permafrost degradation gradient from low-centered (LCP) to flat-centered (FCP), and high-centered polygons (HCP) to evaluate the relative importance of biogeochemical processes and their response to warming. More degraded polygon (HCP) showed much less carbon loss as CO2 or CH4, while the total CO2 production from FCP is comparable to that from LCP. Maximum CH4 production from the active layer of LCP was nearly 10 times that of permafrost and FCP. Multivariate analyses identifies gravimetric water content and organic carbon content as key predictors for CH4 production, and iron reduction as a key regulator of pH. The synthesized data are used to validate the geochemical model PHREEQC with extended anaerobic organic substrate turnover, fermentation, iron reduction, and methanogenesis reactions. Sensitivity analyses demonstrate that better representations of anaerobic processes and their pH dependency could significantly improve estimates of CH4 and CO2 production. The synthesized data suggest local decreases in CH4 production along the polygon degradation gradient, which is consistent with previous surface flux measurements. Methane oxidation occurring through the soil column of degraded polygons contributes to their low CH4 emissions as well.
2017061836 Ji, Yoonmi (Seoul National University, Seoul, South Korea); Park, Ji-Suk and Ro, Hee-Myong. Effect of repeated freeze-thaw cycles on the fluxes of CO2 and CH4 along a soil profile in subarctic tundra [abstr.]: in Goldschmidt abstracts 2016, V.M. Goldschmidt Conference - Program and Abstracts, 26, p. 1342, 2016. Meeting: Goldschmidt 2016, June 26-July 1, 2016, Yokohama, Japan.
2017061838 Jia, Jihui (Kyoto University, Graduate School of Engineering, Kyoto, Japan); Liang, Y.; Murata, S.; Tsuji, T. and Matsuoka, T. P-T diagram of elastic moduli of CH4 and CO2 hydrate [abstr.]: in Goldschmidt abstracts 2016, V.M. Goldschmidt Conference - Program and Abstracts, 26, p. 1344, 2016. Meeting: Goldschmidt 2016, June 26-July 1, 2016, Yokohama, Japan.
2017057458 Davidson, Scott J. (University of Sheffield, Department of Animals and Plant Sciences, Sheffield, United Kingdom); Sloan, Victoria; Phoenix, Gareth; Wagner, Robert; Oechel, Walter and Zona, Donatella. Improving understanding of controls on spatial variability in methane fluxes in Arctic tundra [abstr.]: in European Geosciences Union general assembly 2015, Geophysical Research Abstracts, 17, Abstract EGU2015-500, 1 ref., 2015. Meeting: European Geosciences Union general assembly 2015, April 12-17, 2015, Vienna, Austria.
The Arctic is experiencing rapid climate change relative to the rest of the globe, and this increase in temperature has feedback effects across hydrological and thermal regimes, plant community distribution and carbon stocks within tundra soils. Arctic wetlands account for a significant amount of methane emissions from natural ecosystems to the atmosphere and with further permafrost degradation under a warming climate, these emissions are expected to increase. Methane (CH4) is an extremely important component of the global carbon cycle with a global warming potential 28.5 times greater than carbon dioxide over a 100 year time scale (IPCC, 2013). In order to validate carbon cycle models, modelling methane at broader landscape scales is needed. To date direct measurements of methane have been sporadic in time and space which, while capturing some key controls on the spatial heterogeneity, make it difficult to accurately upscale methane emissions to the landscape and regional scales. This study investigates what is controlling the spatial heterogeneity of methane fluxes across Arctic tundra. We combined over 300 portable chamber observations from 13 micro-topographic positions (with multiple vegetation types) across three locations spanning a 300 km latitudinal gradient in Northern Alaska from Barrow to Ivotuk with synchronous measurements of environmental (soil temperature, soil moisture, water table, active layer thaw depth, pH) and vegetation (plant community composition, height, sedge tiller counts) variables to evaluate key controls on methane fluxes. To assess the diurnal variation in CH4 fluxes, we also performed automated chamber measurements in one study site (Barrow) location. Multiple statistical approaches (regression tree and multiple linear regression) were used to identify key controlling variables and their interactions. Methane emissions across all sites ranged from -0.08 to 15.3 mg C-CH4 m 2 hr 1. As expected, soil moisture was the main control determining the direction and magnitude of methane flux, with methane emissions occurring in saturated micro-topographic locations and drier sites showing low rates of uptake. An interesting exception was in tussock sedge vegetation, which had a deep water table (approximately 20 cm-40 cm below the soil surface) but which emitted methane in comparable quantities to saturated communities late in the growing season. This highlights the importance of plant transport and of understanding temporal variation in fluxes. Automated chamber measurements from peak and late growing season showed minimal diurnal trends in methane fluxes, indicating that short-term chamber measurements are representative of average diurnal CH4 fluxes. The breadth of environmental and vegetation variables measured across a wide spatial extent of arctic tundra vegetation communities within this study highlights the overriding controls on methane emissions and will significantly help with upscaling methane emissions from the plot scale to the landscape scale. Reference: IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T. F., D. Qin, G. K. Plattner, M. Tignor, S. K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P. M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp, doi:10.1017/CBO97811074153 [Copyright Author(s) 2015. CC Attribution 3.0 License: URL: http://meetingorganizer.copernicus.org/EGU2015/EGU2015-500.pdf">https://creativecommons.org/licenses/by/3.0/legalcode]
2017057484 Lim, Edward (University of Sheffield, Department of Animal and Plant Sciences, Sheffield, United Kingdom) and Zona, Donatella. The temperature response of methane emission in Arctic wet sedge tundra [abstr.]: in European Geosciences Union general assembly 2015, Geophysical Research Abstracts, 17, Abstract EGU2015-561, 2 ref., 2015. Meeting: European Geosciences Union general assembly 2015, April 12-17, 2015, Vienna, Austria.
Since the last glacial maximum Arctic tundra soils have acted as an important carbon sink, having accumulated carbon under cold, anaerobic conditions (Zona et al. 2009). Several studies indicate that recent climate warming has altered this balance, with the Arctic tundra now posited to be a significant annual source of atmospheric methane (CH4) (McGuire et al. 2012). Nonetheless, the response of Arctic tundra CH4 fluxes to continued climate warming remains uncertain. Laboratory and field studies indicate that CH4 fluxes are temperature sensitive, thus accurate calculation of the temperature sensitivity is vital for the prediction of future CH4 emission. For this, the increase in reaction rate over a 10°C range (Q10) is frequently used, with single fixed Q10 values (between 2 and 4) commonly incorporated into climate-carbon cycle models. However, the temperature sensitivity of CH4 emission can vary considerably depending on factors such as vegetation composition, water table and season. This promotes the use of spatially and seasonally variable Q10 values for accurate CH4 flux estimation under different future climate change scenarios. This study investigates the temperature sensitivity (Q10) of Arctic tundra methane fluxes, using an extensive number of soil cores (48) extracted from wet sedge polygonal tundra (Barrow Experimental Observatory, Alaska). 'Wet' and 'dry' cores were taken from the centre and raised perimeter of ice-wedge polygons, where the water tables are 0 cm and -15 cm respectively. Cores were incubated in two controlled environment chambers (University of Sheffield, UK) for 12 weeks under different thaw depth treatments (control and control +6.8 cm), water tables (surface and -15 cm), and CO2 concentrations (400 ppm and 850 ppm) in a multifactorial manner. Chamber temperature was gradually increased from -5°C to 20°C, then gradually decreased to -5°C, with each temperature stage lasting one week. Average CH4 fluxes from 'dry' cores were consistently low and did not change significantly with temperature, indicating that CH4 emission from drier Arctic tundra soils is not particularly temperature sensitive. Average CH4 emission from 'wet' cores increased with increasing temperature between -5°C and 20°C. Interestingly, continued increases in average CH4 emission as chamber temperature decreased (20°C to 0°C) were observed. Importantly, when chamber temperature was increased (-5°C to 20°C), average CH4 emission in the 'wet' cores was consistently lower at the end of each week-long temperature stage compared to at the start. This suggests that the response of CH4 emission to climate warming might acclimate. Overall, this study is critical for refining the temperature sensitivity of Arctic tundra CH4 emission, and thus improving model predictions of the response of CH4 fluxes to climate change. References McGuire, AD; Christensen, TR; Hayes, D. et al. (2012). An assessment of the carbon balance of Arctic tundra: comparisons among observations, process models, and atmospheric inversions. Biogeosciences. Vol. 9, p. 3185- 3204, doi:10.5194/bg-9-3185-2012. Zona, D; Oechel, WC; Kochendorfer, J. et al. (2009). Methane fluxes during the initiation of a large-scale water table manipulation experiment in the Alaskan Arctic tundra. Global Biogeochemical Cycles. Vol. 23, GB2013, doi:10.1029/2009GB003487. [Copyright Author(s) 2015. CC Attribution 3.0 License: URL: http://meetingorganizer.copernicus.org/EGU2015/EGU2015-561.pdf">https://creativecommons.org/licenses/by/3.0/legalcode]
2017063861 Miller, Clint. Low methane concentrations in sediment along the Siberian slope; inference from pore water geochemistry: in 65th annual convention of the Gulf Coast Association of Geological Societies, American Association of Petroleum Geologist sectional meeting and the 62nd annual meeting of the Gulf Coast Section of the Society of Economic Paleontologists and Mineralogists (Levine, Steve, editor; et al.), Transactions - Gulf Coast Association of Geological Societies, 65, p. 817-818, 2015. Meeting: 65th annual convention of the Gulf Coast Association of Geological Societies, American Association of Petroleum Geologist sectional meeting and the 62nd annual meeting of the Gulf Coast Section of the Society of Economic Paleontologists and Mineralogists, Sept. 20-22, 2015, Lafayette, LA. Addendum.
The Eastern Siberian Arctic Ocean (ESAO) is experiencing some of the fastest rates of climate warming. Additionally, the ESAO hosts 80% of the world's subsea permafrost, and presumably holds large amounts of methane in sediments as gas hydrate and free gas. Despite these vast stores of vulnerable carbon, the ESAO is sparingly explored. Here, we present pore water geochemistry results from cores taken during the SWERUS-C3 international expedition and along five transects. Four of these are along the slopes of Arlis Spur, Central East Siberia, Henrietta Island-Makarov Basin, and Eastern Lomonosov Ridge; one is along the shelf in Herald Trough. Upward methane flux toward the seafloor, as inferred from dissolved sulfate and alkalinity profiles, is negligible on slopes the Arlis Spur, Central East Siberia, and Eastern Lomonosov Ridge. Methane flux from slopes near Henrietta Island and Makarov Basin ranged from 13.7 (367 m water depth) to 16.2 mmol/m2-kyr (964 m water depth). The highest flux on the slope, located at the intersection with Lomonosov Ridge, is 25.8 mmol/m2-kyr. In contrast to the generally low methane fluxes of the continental slope, the shelf sediments in Herald Trough have high upward methane fluxes, with measured rates up to 156.9 mmol/m2-kyr. These methane results are the first of their kind in this climatically sensitive region, and contradict previous assumptions regarding high methane flux rates along the slope.
2017059486 Pastukhov, Alexander (Russian Academy of Sciences, Urals Division, Institute of Biology, Syktyvkar, Russian Federation); Kaverin, Dmitry and Marchenko-Vagapova, Tatiana. Evolution and genesis of permafrost peatlands in southern limit of cryolithozone in European north-east [abstr.]: in European Geosciences Union general assembly 2015, Geophysical Research Abstracts, 17, Abstract EGU2015-451, 2015. Meeting: European Geosciences Union general assembly 2015, April 12-17, 2015, Vienna, Austria.
The North-East of the European part of Russia is currently experiencing a degradation of permafrost due to climate warming. Permafrost peat plateaus extending only about 20% of the territory contain almost 50% of stocks of soil organic carbon (Pastukhov & Kaverin, 2013). Currently in the region extreme southern limit of the permafrost zone with permafrost temperature 0 ... -1DGC is the far north taiga. Sporadic island permafrost is preserved only in peat plateaus, which are an ideal object for assessing climate change impacts in the event of further thawing of permafrost. On the basis of the macrofossil, palynological and 14C data of peat, Holocene evolution and current state of permafrost peatlands were studied in the extreme southern limit of the East European Cryolithozone. Palynological and radiocarbon data provides evidence of the start of peat accumulation in the early Holocene, about 8000 years ago, in the late boreal (BO-2). Then the accumulation of peat first significantly slowed down, and then almost stopped between 2500-850 years ago. I.e. about 2500 years ago permafrost was aggradated, which manifested itself in the heave of peatland mounds and a sharp decline in peat accumulation due to dry conditions in raised surface peat. There was the formation of permafrost peat plateaus of modern appearance. Fens occurred from the late-modern Subatlantic (SA-3-SA-R) Holocene period, i.e. after the Little Ice Age and the beginning of the small climatic optimum (about 850 years ago), when the permafrost partially degraded, and formed non-permafrost sphagnum bogs. At the same time (SA-3-SA-R), the gradual and slower peat accumulation proceeded. Vegetation of peat mounds prevents permafrost thawing in the current climate warming. As mounds surface dry out, lichens succeed mosses and bare peat circles are formed. But dry peat has higher insulating properties and prevents from further thawing. Thawing of permafrost peatlands starting from the surface occurs only as their destruct or on condition of hindered surface runoff with possible formation of lakes and fens. A relatively closed hydrological regime of peat plateaus explains widespread peat mounds with permafrost-affected soils-Cryic Histosols (40% of the area). Thus, permafrost peatlands could be considered as rather stable ecological systems. The study was supported by the RFBR 14-05-31111 and UNDP/GEF ClimaEast 00059042 projects. [Copyright Author(s) 2015. CC Attribution 3.0 License: URL: http://meetingorganizer.copernicus.org/EGU2015/EGU2015-451.pdf">https://creativecommons.org/licenses/by/3.0/legalcode]
2017059472 Recio, Cayetana Blitz (Universidad de Alcala, Alcala, Spain); de Pablo, Miguel Ángel; Ramos, Miguel and Molina, Antonio. The state of permafrost surrounding "Gabriel de Castilla" Spanish Antarctic Station (Deception Island, Antarctica); studying the possible degradation due to the infrastructures heating effect [abstr.]: in European Geosciences Union general assembly 2015, Geophysical Research Abstracts, 17, Abstract EGU2015-420, 2015. Meeting: European Geosciences Union general assembly 2015, April 12-17, 2015, Vienna, Austria.
Permafrost degradation is one of the effects of the global warming. Many studies reveal the increase of active layer and reduction on permafrost table thickness, also in Antarctica. However, these trends on permafrost can be accelerated by the human activities, as the heating produced by the Antarctic stations infrastructures when they are not properly isolated from the ground. In Deception island, South Shetland Archipelago, we started 3 years ago a monitoring program at the 26 years old "Gabriel de Castilla" Spanish Antarctic Station (SAS), It is focused on characterizing the state of permafrost, since in the coastal scarps at tens of meters from the station an increase on erosion had been detected. Although the main cause of the erosion of this coastal volcanoclastic materials is the 2 meters thick icefield which forms during the winter in the inner sea of this volcanic island, we want to detect any possible contribution to the coastal erosion caused by the permafrost degradation related to the SAS presence. We present our preliminary analysis based on three years of continuous ground temperature data, monitored at a shallow borehole (70 cm deep) in the SAS edge, together with the active layer thickness measured around the station and their vicinities in two thawing seasons. We complete this study with the analysis of the continuous temperature data taken inside the SAS and the air and ground temperatures below the station, acquired during the last Antarctic Campaign (December 2014-February 2015). These preliminary results are fundamental 1) to discard any contribution from the SAS presence, and to help to improve its thermal isolation, 2) to help improve our knowledge about the thermal state of permafrost in the area, and 3) to help to understand the causes of the coastal erosion in the volcanic Deception Island. [Copyright Author(s) 2015. CC Attribution 3.0 License: URL: http://meetingorganizer.copernicus.org/EGU2015/EGU2015-420.pdf">https://creativecommons.org/licenses/by/3.0/legalcode]
2017057485 Shapovalova, Elizaveta (Russian Academy of Sciences, Oil and Gas Research Institute, Moscow, Russian Federation). The role of modern geodynamics in the transformation of the local erosion basis in the Arctic river systems [abstr.]: in European Geosciences Union general assembly 2015, Geophysical Research Abstracts, 17, Abstract EGU2015-565, 2015. Meeting: European Geosciences Union general assembly 2015, April 12-17, 2015, Vienna, Austria.
To assess the impact of modern geodynamic processes in the erosion of river channels in the area of oil and gas field, located in the permafrost region the following studies were made: interpretation of satellite images to identify fault zones in the structure of the landscape oil and gas field, located in the subarctic zone; mathematical modeling of extensive and local subsidence in the found faults areas; field measurements within the territory of the field. These studies led to conclusions about influence of modern geodynamic processes on activization of erosive processes. Dimensions of the studied field is approximately 40 60 km. As a result of extensive sagging modeling on its territory for the period of the end of the development the sag depth of the Earth's surface equal to 90 cm was obtained. In this case, the slope of the Earth's surface with respect to the central part of the study area will be 4.5 10 5. This slope is comparable with the values of the average slope of lowland rivers. For example, for the Ob River it is 4 10 5. This case shows that the river flowing through the field, due to changes in the local erosion basis may be experiencing channel deformation in its central part. According to the observations and model calculations local subsidence of the Earth's surface in fault zones induced by mining, lead to the Earth's surface inclines order 7´10-5 - 1.2´10-3. Field observations in 2014 in areas where active faults identified revealed a number of factors of changes in the river channel. There were areas overdeepened channel, tear off and slipped down blocks of rocks, leading to the subsequent transformation of the channel, as well as additional thermal erosion gullies that increase the accumulation of sediments and alter the structure of the river network. The combination of modern geodynamics with thermokarst processes in perennial permafrost layer enhances erosion. This investigations have shown that the factor of modern geodynamics of natural or man-made influences on the transformation of the river system at the present stage of its development. This is a new factor. Previously, it was not taken into account, among other geomorphological factors in the analysis of structure changes of the Earth's surface. [Copyright Author(s) 2015. CC Attribution 3.0 License: URL: http://meetingorganizer.copernicus.org/EGU2015/EGU2015-565.pdf">https://creativecommons.org/licenses/by/3.0/legalcode]
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2017058247 Kerr, D. E.; Morse, P. D. and Wolfe, S. A. Reconnaissance surficial geology, Willow Lake, Northwest Territories, NTS 85-L: Geological Survey of Canada, Canadian Geoscience Map, Geological Survey of Canada, Ottawa, ON, Canada, Rep. No. 304, 1 sheet (French sum.), illus. incl. color surficial geology map, 1:125,000, 6 ref., 2017. ISBN: 978-0-660-06895-4. Preliminary edition.
Glaciolacustrine sediments, associated with glacial Lake McConnell, were deposited as veneers over till in the broad, poorly drained low-lying areas of the northern, central and southeastern regions of the map area, below 290 m a.s.l. They are commonly overlain by organics and exhibit thermokarst activity. Glaciofluvial sediments and some bedrock ridges were reworked into glaciolacustrine beaches in the eastern lowlands. These beaches, occurring between 220 to 290 m a.s.l., mark the decreasing elevation of the glacial lake over time due to isostatic rebound. In the south, the Horn Plateau, rising to over 700 m, and consisting of till blanket, hummocky till, moraine complex, and colluvium on its slopes, remained above the limit of glaciolacustrine inundation. Crag-and-tails, drumlins and drumlinoids record a westward ice flow during the last glaciation, with local northwestward and southwestward diversions around the Plateau. A series of small moraine ridges on the Plateau may mark the retreat of ice margins or stagnating lobes during deglaciation about 11-10 ka BP.
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