15091653 Connon, R. F. (Wilfrid Laurier University, Centre for Cold Regions and Water Science, Waterloo, ON, Canada); Quinton, William L.; Craig, J. R.; Hanisch, J. and Sonnentag, O. The hydrology of interconnected bog complexes in discontinuous permafrost terrains: in Canadian Geophysical Union; Hydrology Section, 2015 (Quinton, William L., editor; et al.), Hydrological Processes, 29(18), p. 3831-3847, illus. incl. sect., 2 tables, sketch map, 48 ref., August 30, 2015.
In the zone of discontinuous permafrost, the cycling and storage of water within and between wetlands is poorly understood. The presence of intermittent permafrost bodies tends to impede and re-direct the flow of water. In this region, the landscape is characterized by forested peat plateaus that are underlain by permafrost and are interspersed by permafrost-free wetlands. These include channel fens which convey water to the basin outlet through wide, hydraulically rough channels and flat bogs which are typically thought to retain moisture inputs as storage. Field studies conducted at a peatland-dominated landscape near Fort Simpson, Northwest Territories, Canada, indicate the presence of ephemeral drainage channels that form a cascade of connected bogs that ultimately discharges into a channel fen. Consequently, understanding bogs as dynamic transmitters of surface and subsurface flows, rather than simple storage regions, calls for further examination. Whether bogs act as either storage features or flow through features has a direct impact on the runoff contributing area in a basin. Here, two adjacent series of bog cascades were gauged over two consecutive years to determine spatial and temporal changes in effective runoff contributing areas. It was found that runoff varies significantly between two adjacent bog cascades with one cascade producing 125 mm of runoff over the 2-year period, while the other yielded only 25 mm. The bog cascades are primarily active during the snowmelt season when moisture conditions are high; however flows can also be generated in response to large rain events. It is proposed that bog cascades operate under an 'element threshold concept' whereby in order for water to be transmitted through a bog, the depression storage capacity of that bog must first be satisfied. Our work indicates that whether bogs act as storage features or flow-through features has a direct impact on the runoff contributing area in a basin. Neglecting to represent connected bogs as dynamic transmission features in the landscape is shown to underestimate water available for streamflow by between 5 and 15%, and these systems are therefore a key component of the water balance in discontinuous permafrost regions. Copyright Copyright 2015 John Wiley & Sons, Ltd.
15086430 Dymov, A. A. (Institute of Biology Komi, Syktyvkar, Russian Federation); Zhangurov, E. V. and Hagedorn, F. Soil organic matter composition along altitudinal gradients in permafrost affected soils of the subpolar Ural Mountains: Catena (Giessen), 131, p. 140-148, illus. incl. 4 tables, sketch map, 55 ref., August 2015.
Soil organic matter (SOM) in high-latitude soils is assumed to be highly vulnerable to climate changes. Relative little information exists from soils of mountain ecosystems which might respond differently to permafrost melt than in flat terrain due to a better drainage. In this study, we measured SOM composition of six typical soils along an altitudinal gradient of the remote Subpolar Urals, reaching from alpine tundra to the forest zone. The SOM characteristics was estimated by applying 13C nuclear magnetic resonance (13C NMR) spectroscopy, electron paramagnetic resonance (ESR), elemental analysis and amino acid composition of humic acid (HA) extracts from soils. Result showed that SOM stocks ranged between 8 and 13 kg C m-2 but reached up to 40 kg C m-2 in a Stagnic Podzol in the alpine tundra. In the mineral soil, 13C NMR indicated that the contribution of alkyl-C was 60% in the forest and 50% in the tundra, while aromaticity was 5% in the tundra, but 19% in the forest. This shows that SOM of mineral soils in alpine tundra was more aliphatic but less aromatic than in the Podzols of the forested zone. In contrast to mineral soils, SOM characteristic in organic layers was very similar among all soil types despite different vegetation types. Consequently, we suggest that the large difference in SOM quality in the mineral soil between tundra and forest can primarily be attributed to abiotic soil conditions in the deeper soil with a stronger waterlogging and a lower permafrost depth in the tundra soils. The low status of oxidative SOM degradation in the mineral soil of the tundra is also an indication that SOM of tundra is highly vulnerable to an improved aeration associated with permafrost melt in drained mountain soils. Abstract Copyright (2015) Elsevier, B.V.
15091654 Gibson, J. J. (Alberta Innovates Technology Futures, Victoria, BC, Canada); Birks, S. J.; Yi, Y. and Vitt, D. H. Runoff to boreal lakes linked to land cover, watershed morphology and permafrost thaw; a 9-year isotope mass balance assessment: in Canadian Geophysical Union; Hydrology Section, 2015 (Quinton, William L., editor; et al.), Hydrological Processes, 29(18), p. 3848-3861, illus. incl. 6 tables, sketch map, 37 ref., August 30, 2015.
Stable isotopes of oxygen and hydrogen were measured in water samples collected annually from a representative suite of 50 lakes in northeastern Alberta over a 9-year period and are interpreted using a steady-state isotope mass balance model to determine water yield and runoff ratios for the lake watersheds and residence time of the lakes. This isotopic perspective on hydrology of the region provides new insight into the role of land cover, watershed morphometry, climatic drivers and permafrost thaw on lakes. Bog cover, permafrost and presence of thaw features in bogs are found to be the dominant hydrologic drivers, although morphometric properties such as elevation, lake area and drainage basin area are also influential. In addition to quantifying the hydrologic fluxes, the analysis establishes contrasting conditions in more southerly lakes, located in the Stony Mountains and west of Fort McMurray, as compared with more northerly sites in the Birch Mountains, Caribou Mountains and northeast of Fort McMurray, mainly because of contributions from thawing permafrost at the northerly sites. Distinct hydrologic conditions are also noted for Shield systems north of Lake Athabasca where bogs and permafrost are absent. While permafrost thaw is not directly labelled by oxygen and hydrogen isotope composition, isotope mass balance calculations suggest that contributions of up to several hundred millimetres per year are occurring in 14 of the 50 lake watersheds under study. Several of these lakes have water yields in excess of precipitation in some years, and regional groups of lakes display significant correlations between water yield and percentage of bogs that have collapsed. Copyright Copyright 2015 John Wiley & Sons, Ltd.
15086808 Heikoop, Jeffrey M. (Los Alamos National Laboratory, Earth and Environmental Sciences Division, Los Alamos, NM); Throckmorton, Heather M.; Newman, Brent D.; Perkins, George B.; Iversen, Colleen M.; Roy Chowdhury, Taniya; Romanovsky, Vladimir; Graham, David E.; Norby, Richard J.; Wilson, Cathy J. and Wullschleger, Stan D. Isotopic identification of soil and permafrost nitrate sources in an Arctic tundra ecosystem: Journal of Geophysical Research: Biogeosciences, 120(6), p. 1000-1017, illus. incl. sects., 3 tables, sketch maps, 98 ref., June 2015.
The nitrate (NO3-) dual isotope approach was applied to snowmelt, tundra active layer pore waters, and underlying permafrost in Barrow, Alaska, USA, to distinguish between NO3- derived from atmospheric deposition versus that derived from microbial nitrification. Snowmelt had an atmospheric NO3- signal with d15N averaging -4.8 ± 1.0 ppm (standard error of the mean) and d18O averaging 70.2 ± 1.7 ppm. In active layer pore waters, NO3- primarily occurred at concentrations suitable for isotopic analysis in the relatively dry and oxic centers of high-centered polygons. The average d15N and d18O of NO3- from high-centered polygons were 0.5 ± 1.1 ppm and -4.1 ± 0.6 ppm, respectively. When compared to the d15N of reduced nitrogen (N) sources, and the d18O of soil pore waters, it was evident that NO3- in high-centered polygons was primarily from microbial nitrification. Permafrost NO3- had d15N ranging from approximately -6 ppm to 10 ppm, similar to atmospheric and microbial NO3-, and highly variable d18O ranging from approximately -2 ppm to 38 ppm. Permafrost ice wedges contained a significant atmospheric component of NO3-, while permafrost textural ice contained a greater proportion of microbially derived NO3-. Large-scale permafrost thaw in this environment would release NO3- with a d18O signature intermediate to that of atmospheric and microbial NO3. Consequently, while atmospheric and microbial sources can be readily distinguished by the NO3- dual isotope technique in tundra environments, attribution of NO3- from thawing permafrost will not be straightforward. The NO3- isotopic signature, however, appears useful in identifying NO3- sources in extant permafrost ice. Abstract Copyright (2015), . American Geophysical Union. All Rights Reserved.
15086434 Kokelj, S. V. (Northwest Territories Geological Survey, Yellowknife, NT, Canada); Tunnicliffe, J.; Lacelle, D.; Lantz, T. C.; Chin, K. S. and Fraser, R. Increased precipitation drives mega slump development and destabilization of ice-rich permafrost terrain, northwestern Canada: Global and Planetary Change, 129, p. 56-68, illus. incl. 4 tables, sketch map, 45 ref., June 2015.
It is anticipated that an increase in rainfall will have significant impacts on the geomorphology of permafrost landscapes. Field observations, remote sensing and historical climate data were used to investigate the drivers, processes and feedbacks that perpetuate the growth of large retrogressive thaw slumps. These "mega slumps" (5-40 ha) are now common in formerly glaciated, fluvially incised, ice-cored terrain of the Peel Plateau, NW Canada. Individual thaw slumps can persist for decades and their enlargement due to ground ice thaw can displace up to 106m3 of materials from slopes to valley bottoms reconfiguring slope morphology and drainage networks. Analysis of Landsat images (1985-2011) indicate that the number and size of active slumps and debris tongue deposits has increased significantly with the recent intensification of rainfall. The analyses of high resolution climatic and photographic time-series for summers 2010 and 2012 shows strong linkages amongst temperature, precipitation and the downslope sediment flux from active slumps. Ground ice thaw supplies meltwater and sediments to the slump scar zone and drives diurnal pulses of surficial flow. Coherence in the timing of down valley debris tongue deposition and fine-scaled observations of sediment flux indicate that heavy rainfall stimulates major mass flow events. Evacuation of sediments from the slump scar zone can help to maintain a headwall of exposed ground ice, perpetuating slump growth and leading to larger disturbances. The development of debris tongue deposits divert streams and increase thermoerosion to initiate adjacent slumps. We conclude that higher rainfall can intensify thaw slump activity and rapidly alter the slope-sediment cascade in regions of ice-cored glaciogenic deposits. Abstract Copyright (2015) Elsevier, B.V.
15086807 Overduin, Pier Paul (Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Potsdam, Germany); Liebner, Susanne; Knoblauch, Christian; Günther, Frank; Wetterich, Sebastian; Schirrmeister, Lutz; Hubberten, Hans-Wolfgang and Grigoriev, Mikhail N. Methane oxidation following submarine permafrost degradation; measurements from a central Laptev Sea shelf borehole: Journal of Geophysical Research: Biogeosciences, 120(5), p. 965-978, illus. incl. sketch maps, strat. col., 74 ref., May 2015.
Submarine permafrost degradation has been invoked as a cause for recent observations of methane emissions from the seabed to the water column and atmosphere of the East Siberian shelf. Sediment drilled 52 m down from the sea ice in Buor Khaya Bay, central Laptev Sea revealed unfrozen sediment overlying ice-bonded permafrost. Methane concentrations in the overlying unfrozen sediment were low (mean 20 mM) but higher in the underlying ice-bonded submarine permafrost (mean 380 mM). In contrast, sulfate concentrations were substantially higher in the unfrozen sediment (mean 2.5 mM) than in the underlying submarine permafrost (mean 0.1 mM). Using deduced permafrost degradation rates, we calculate potential mean methane efflux from degrading permafrost of 120 mg m-2 yr-1 at this site. However, a drop of methane concentrations from 190 mM to 19 mM and a concomitant increase of methane d13C from -63 ppm to -35 ppm directly above the ice-bonded permafrost suggest that methane is effectively oxidized within the overlying unfrozen sediment before it reaches the water column. High rates of methane ebullition into the water column observed elsewhere are thus unlikely to have ice-bonded permafrost as their source. Abstract Copyright (2015), . American Geophysical Union. All Rights Reserved.
15091648 Fritz, M. (Alfred Wegener Institute, Deprtment of Periglacial Research, Potsdam, Germany); Deshpande, B. N.; Bouchard, F.; Hogstrom, E.; Malenfant-Lepage, J.; Morgenstern, A.; Nieuwendam, A.; Oliva, M.; Paquette, M.; Rudy, A. C. A.; Siewert, M. B.; Sjoberg, Y. and Weege, S. Future avenues for permafrost science form the perspective of early career researchers: The Cryosphere (Online), 9(4), p. 1715-1720, illus., 21 ref., 2015.
Accelerating climate change and increased economic and environmental interests in permafrost-affected regions have resulted in an acute need for more directed permafrost research. In June 2014, 88 early career researchers convened to identify future priorities for permafrost research. This multidisciplinary forum concluded that five research topics deserve greatest attention: permafrost landscape dynamics, permafrost thermal modeling, integration of traditional knowledge, spatial distribution of ground ice, and engineering issues. These topics underline the need for integrated research across a spectrum of permafrost-related domains and constitute a contribution to the Third International Conference on Arctic Research Planning (ICARP III).
15083784 Bockheim, James G. (University of Wisconsin, Department of Soil Sciences, Madison, WI) and Munroe, Jeffrey S. Organic carbon pools and genesis of alpine soils with permafrost; a review: Arctic, Antarctic, and Alpine Research, 46(4), p. 987-1006, illus. incl. 6 tables, sketch map, 120 ref., November 2014.
Soils with mountain permafrost occupy 3.5 million km2 worldwide, with 70% in central Asia. High-mountain environments have "warm" permafrost, with surface permafrost temperatures of -0.5 to -2°C and deep active layers (2 to 8 m). From a global database of 41 sites and 312 pedons, alpine soils with permafrost are strongly acid (pH=5.0 to 5.5), have intermediate cation-exchange capacities (20 to 25 cmolc/kg) and base saturation (44% to 85%), and commonly have an isotic mineral class. Soil organic carbon is concentrated in the upper 30 to 40 cm, with profile density averaging 15.2±1.3 kg m2 (range=<1.0 to 88.3 kg m2), which is comparable to temperate grasslands (13 kg m2) but substantially less than moist arctic tundra (32 kg m2). Mountain soils with permafrost contain 66.3 Pg of soil organic carbon (SOC), which constitutes 4.5% of the global pool. In contrast, the SOC pool in the Arctic is 496 Pg (33% of the global pool). Alpine soils with deep active layers contrast strongly with high-latitude soils in areas of continuous permafrost. Permafrost in the upper 2 m induces cryoturbation in the profile, acts as a barrier to water movement, and generates cooler temperatures resulting in greater SOC levels. High-elevation and high-latitude soils are experiencing warming of air temperature and permafrost and a thickening of the active layer.
15084106 Bai Yuchun (Hydrogeology and Engineering Geology Prospecting Institute of Heilongjiang Province, Harbin, China); Li Yongli; Dong Xueliang and Zhao Lei. Analysis and prevention measures for typical geological disaster formation and mechanisms within permafrost zone of Greater Khingan Range: Journal of Groundwater Science and Engineering, 2(3), p. 85-93, illus. incl. geol. sketch maps, 6 ref., September 2014.
The types, factors and formation conditions of typical geological disasters within the permafrost zone in the Greater Khingan Range area of Heilongjiang province were analysed in the paper. The formation mechanism behind geological disasters was illustrated, and the development trend, prevention programs and effects of the typical disaster on communities, agricultural lands and landscapes were reviewed.
15083427 Spötl, C. (University of Innsbruck, Institute of Geology, Innsbruck, Austria) and Cheng, H. Holocene climate change, permafrost and cryogenic carbonate formation; insights from a recently deglaciated, high-elevation cave in the Austrian Alps: Climate of the Past, 10(4), p. 1349-1362, illus. incl. 1 table, 48 ref., 2014.
Cryogenically formed carbonate particles represent a rather new class of speleothems whose origin is directly linked to the presence of perennial ice in the subsurface. Recent studies concluded that dating these deposits provides important time constraints on the presence and the thickness of permafrost, e.g., during the last glacial period. More precisely, these carbonates record episodes of progressive karst water freezing. Such conditions have been associated with periods of permafrost thawing allowing the infiltration of meltwater into formerly dry, frozen caves. To shed more light on the origin of the coarsely crystalline variety of these cryogenic cave carbonates - CCCcoarse for short - we examined a high-elevation cave site in the western part of the Austrian Alps which is located in an area dominated by permafrost features and transformed from an ice cave into an essentially ice-free cave during the past decade. Two side chambers of the main gallery revealed cryogenic calcite deposits whose isotopic composition indicates that they formed in individual pools of water carved in ice which underwent very slow freezing under closed-system conditions, i.e., enclosed in ice. 230Th dating shows that most of these carbonates formed ca. 2600 yr BP. Based on comparisons with other palaeoclimate archives in the Alps this thawing episode did not occur during a climate optimum, nor did CCCcoarse form in this cave during, e.g., the Roman or the Medieval Warm Periods. Our results suggest that the occurrence of CCCcoarse, at least in mountain regions characterized by discontinuous permafrost, may be more stochastic than previously thought. Given the inherent heterogeneity of karst aquifers and the important role of localized water infiltration in modifying the thermal structure of the subsurface, we caution against attributing CCCcoarse occurrences solely to peak warming conditions, while confirming the unique significance of these deposits in providing robust age constraints on permafrost thawing episodes.
15089898 Opitz, Stephan (Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany); Ramisch, Arne; Mischke, Steffen and Diekmann, Bernhard. Holocene lake stages and thermokarst dynamics in a discontinuous permafrost affected region, northeastern Tibetan Plateau: Journal of Asian Earth Sciences, 76, p. 85-94, illus. incl. 1 table, sketch map, 60 ref., October 25, 2013.
Sediments of a thermokarst system on the north-eastern Tibetan Plateau were studied to infer changes in the lacustrine depositional environment related to climatic changes since the early Holocene. The thermokarst pond with a length of 360 m is situated in a 14.5´6 km tectonically unaffected intermontane basin, which is underlain by discontinuous permafrost. A lake sediment core and bankside lacustrine onshore deposits were analysed. Additionally, fossil lake sediments were investigated, which document a former lake-level high stand. The sediments are mainly composed of marls with variable amounts of silt carbonate micrite, and organic matter. On the basis of sedimentological (grain size data), geochemical (XRF), mineralogical (XRD) and micropaleontological data (ostracods and chironomide assemblages) a reconstruction of a paleolake environment was achieved. Lacustrine sediments with endogenic carbonate precipitation suggest a lacustrine environment since at least 19.0 cal ka BP. However, because of relocation and reworking processes in the lake, the sediments did not provide distinct information about the ultimate formation of the lake. The high amount of endogenic carbonate suggests prolonged still-water conditions at about 9.3 cal ka BP. Ostracod shells and chironomid head capsules in fossil lake sediments indicate at least one former lake-level high stand, which were developed between the early and middle Holocene. From the late Holocene the area was possibly characterized by a lake-level decline, documented by a hiatus between lacustrine sediments and a reworked loess or loess-like horizon. After the lake-level decline and the following warming period, the area was affected by thermally-induced subsidence and a re-flooding of the basin because of thawing permafrost. Abstract Copyright (2013) Elsevier, B.V.
15091646 Chadburn, S. E. (University of Exeter, Earth System Sciences Department, Exeter, United Kingdom); Burke, E. J.; Essery, R. L. H.; Boike, J.; Langer, M.; Heikenfeld, M.; Cox, P. M. and Friedlingstein, P. Impact of model developments on present and future simulations of permafrost in a global land-surface model: The Cryosphere (Online), 9(4), p. 1505-1521, illus. incl. 4 tables, sketch map, 73 ref., 2015.
15091440 Xu Zhiwei (Nanjing University, School of Geographic and Oceanographic Sciences, Nanjing, China); Lu Huayu; Yi Shuangwen; Vandenberghe, Jef; Mason, Joseph A.; Zhou Yali and Wang Xianyan. Climate-driven changes to dune activity during the last glacial maximum and deglaciation in the Mu Us dune field, north-central China: Earth and Planetary Science Letters, 427, p. 149-159, illus. incl. 1 table, sketch maps, 74 ref., October 1, 2015. Includes appendices.
One significant change of terrestrial landscapes in response to past climate change has been the transformation between activity and stability of extensively distributed wind-blown sand dunes. The relations between the dynamics of the aeolian landscape and its drivers are not yet completely understood, however. Evidence of aeolian sand deposition during the Last Glacial Maximum (LGM) is scarce in many mid-latitude dune fields, whereas abundant evidence exists for aeolian sand accumulation during the deglaciation, i.e. after about 15 ka. Whether this contrast actually reflects changes in dune activity is still unclear, making paleoclimatic interpretation uncertain. Comprehensive field investigation and luminescence dating in the Mu Us dune field, north-central China, demonstrates that aeolian sands deposited during the LGM are preserved as fills in periglacial sand wedges and beneath loess deposits near the downwind dune field margin. The scarcity of LGM dune sand elsewhere in the dune field is interpreted as the result of intensive aeolian activity without substantial net sand accumulation. Increasing sand accumulation after 15 ka, reflected by much more extensive preservation, signals a change in sand supply relative to sand transportation through the dune field. Reduced wind strength and other environmental changes including regional permafrost degradation after 15 ka transformed the dune field state from net erosion to net accumulation; the dunes, however, remained largely mobile as they were in the LGM. Similar diverging patterns of dune sand accumulation and preservation before and after 15 ka in many mid-latitude dune fields imply broad climatic controls linked to the changes in high-northern-latitude forcing. Abstract Copyright (2015) Elsevier, B.V.
15091657 Williams, Tyler J. (University of Saskatchewan, Centre for Hydrology, Saskatoon, SK, Canada); Pomeroy, John W.; Janowicz, J Richard; Carey, Sean K.; Rasouli, Kabir and Quinton, William L. A radiative-conductive-convective approach to calculate thaw season ground surface temperatures for modelling frost table dynamics: in Canadian Geophysical Union; Hydrology Section, 2015 (Quinton, William L., editor; et al.), Hydrological Processes, 29(18), p. 3954-3965, illus. incl. 3 tables, sketch map, 45 ref., August 30, 2015.
The frost table depth is a critical state variable for hydrological modelling in cold regions as frozen ground controls runoff generation, subsurface water storage and the permafrost regime. Calculation of the frost table depth is typically performed using a modified version of the Stefan equation, which is driven with the ground surface temperature. Ground surface temperatures have usually been estimated as linear functions of air temperature, referred to as 'n-factors' in permafrost studies. However, these linear functions perform poorly early in the thaw season and vary widely with slope, aspect and vegetation cover, requiring site-specific calibration. In order to improve estimation of the ground surface temperature and avoid site-specific calibration, an empirical radiative-conductive-convective (RCC) approach is proposed that uses air temperature, net radiation and antecedent frost table position as driving variables. The RCC algorithm was developed from forested and open sites on the eastern slope of the Coastal Mountains in southern Yukon, Canada, and tested at a high-altitude site in the Canadian Rockies, and a peatland in the southern Northwest Territories. The RCC approach performed well in a variety of land types without any local calibration and particularly improved estimation of ground temperature compared with linear functions during the first month of the thaw season, with mean absolute errors <2 °C in seven of the nine sites tested. An example of the RCC approach coupled with a modified Stefan thaw equation suggests a capability to represent frozen ground conditions that can be incorporated into hydrological and permafrost models of cold regions. Copyright Copyright 2015 John Wiley & Sons, Ltd.
15084780 de Haas, Tjalling (Utrecht University, Faculty of Geosciences, Utrecht, Netherlands); Kleinhans, Maarten G.; Carbonneau, Patrice E.; Rubensdotter, Lena and Hauber, Ernst. Surface morphology of fans in the high-Arctic periglacial environment of Svalbard; controls and processes: Earth-Science Reviews, 146, p. 163-182, illus. incl. 2 tables, sketch map, 139 ref., July 2015. Includes appendices.
Fan-shaped landforms occur in all climatic regions on Earth. They have been extensively studied in many of these regions, but there are few studies on fans in periglacial, Arctic and Antarctic regions. Fans in such regions are exposed to many site-specific environmental conditions in addition to their geological and topographic setting: there can be continuous to discontinuous permafrost and snow avalanches and freeze-thaw cycles can be frequent. We study fans in the high-Arctic environment of Svalbard to (1) increase our fundamental knowledge on the morphology and morphometry of fans in periglacial environments, and (2) to identify the specific influence of periglacial conditions on fans in these environments. Snow avalanches have a large geomorphic effect on fans on Svalbard: the morphology of colluvial fans is mainly determined by frequent snow avalanches (e.g., flattened cross-profiles, exposed fine-grained talus on the proximal fan domain, debris horns and tails). As a result, there are only few fans with a rockfall-dominated morphology, in contrast to most other regions on Earth. Slush avalanches contribute significant amounts of sediment to the studied alluvial fans. The inactive surfaces of many alluvial fans are rapidly beveled and leveled by snow avalanches, solifluction and frost weathering. Additionally, periglacial reworking of the fan surface often modifies the original morphology of inactive fan surfaces, for example by the formation of ice-wedge polygons and hummocks. Permafrost lowers the precipitation threshold for debris-flow initiation, but limits debris-flow volumes. Global warming-induced permafrost degradation will likely increase debris-flow activity and -magnitude on fans in periglacial environments. Geomorphic activity on snow avalanche-dominated colluvial fans will probably increase due to future increases in precipitation, but depends locally on climate-induced changes in dominant wind direction. Abstract Copyright (2015) Elsevier, B.V.
15084829 Séjourné, A. (Université Paris-Sud, Laboratoire Géosciences Paris-Sud, Orsay, France); Costard, F.; Fedorov, A.; Gargani, J.; Skorve, J.; Masse, M. and Mege, D. Evolution of the banks of thermokarst lakes in central Yakutia (central Siberia) due to retrogressive thaw slump activity controlled by insolation: Geomorphology, 241, p. 31-40, illus. incl. 2 tables, sketch maps, 43 ref., July 15, 2015.
As observed in most regions in the Arctic, the thawing of ice-rich permafrost (thermokarst) has been developing in Central Yakutia. However, the relationship between thermokarst development and climate variations is not well understood in this region, in particular the development rate of thaw slumps. The objective of this paper is to understand the current development of thermokarst by studying the evolution of the banks of thermokarst lakes. We studied retrogressive thaw slumps and highly degraded ice-wedge polygons (baydjarakhs), indicative of thermokarst, using high resolution satellite images taken in 2011-2013 and conducting field studies. The retrogressive thaw slump activity results in the formation of thermocirque with a minimum and maximum average headwall retreat of 0.5 and 3.16 m·yr- 1 respectively. The thermocirques and the baydjarakhs are statistically more concentrated on the south- to southwest-facing banks of thermokarst lakes. Moreover, the rate of headwall retreat of the thermocirques is the most important on the south-facing banks of the lakes. These observations indicate a control of the current permafrost thaw on the banks of thermokarst lakes by insolation. In the context of recent air temperature increase in Central Yakutia, the rate of thermocirque development may increase in the future. Abstract Copyright (2015) Elsevier, B.V.
15086812 Baughman, Carson A. (U. S. Geological Survey, Alaska Science Center, Anchorage, AK); Mann, Daniel H.; Verbyla, David L. and Kunz, Michael L. Soil surface organic layers in Arctic Alaska; spatial distribution, rates of formation, and microclimatic effects: Journal of Geophysical Research: Biogeosciences, 120(6), p. 1150-1164, illus. incl. 5 tables, sketch maps, 60 ref., June 2015.
Organic layers of living and dead vegetation cover the ground surface in many permafrost landscapes and play important roles in ecosystem processes. These soil surface organic layers (SSOLs) store large amounts of carbon and buffer the underlying permafrost and its contained carbon from changes in aboveground climate. Understanding the dynamics of SSOLs is a prerequisite for predicting how permafrost and carbon stocks will respond to warming climate. Here we ask three questions about SSOLs in a representative area of the Arctic Foothills region of northern Alaska: (1) What environmental factors control the thickness of SSOLs and the carbon they store? (2) How long do SSOLs take to develop on newly stabilized point bars? (3) How do SSOLs affect temperature in the underlying ground? Results show that SSOL thickness and distribution correlate with elevation, drainage area, vegetation productivity, and incoming solar radiation. A multiple regression model based on these correlations can simulate spatial distribution of SSOLs and estimate the organic carbon stored there. SSOLs develop within a few decades after a new, sandy, geomorphic surface stabilizes but require 500-700 years to reach steady state thickness. Mature SSOLs lower the growing season temperature and mean annual temperature of the underlying mineral soil by 8 and 3°C, respectively. We suggest that the proximate effects of warming climate on permafrost landscapes now covered by SSOLs will occur indirectly via climate's effects on the frequency, extent, and severity of disturbances like fires and landslides that disrupt the SSOLs and interfere with their protection of the underlying permafrost. Abstract Copyright (2015), . American Geophysical Union. All Rights Reserved.
15084228 Jiang, Yueyang (Marine Biological Laboratory, Ecosystems Center, Woods Hole, MA); Rocha, Adrian V.; O'Donnell, Jonathan A.; Drysdale, Jessica A.; Rastetter, Edward B.; Shaver, Gaius R. and Zhuang, Qianlai. Contrasting soil thermal responses to fire in Alaskan tundra and boreal forest: Journal of Geophysical Research: Earth Surface, 120(2), p. 363-378, illus. incl. 3 tables, sketch map, 40 ref., February 2015.
Recent fire activity throughout Alaska has increased the need to understand postfire impacts on soils and permafrost vulnerability. Our study utilized data and modeling from a permafrost and ecosystem gradient to develop a mechanistic understanding of the short- and long-term impacts of tundra and boreal forest fires on soil thermal dynamics. Fires influenced a variety of factors that altered the surface energy budget, soil moisture, and the organic-layer thickness with the overall effect of increasing soil temperatures and thaw depth. The postfire thickness of the soil organic layer and its impact on soil thermal conductivity was the most important factor determining postfire soil temperatures and thaw depth. Boreal and tundra ecosystems underlain by permafrost experienced smaller postfire soil temperature increases than the nonpermafrost boreal forest from the direct and indirect effects of permafrost on drainage, soil moisture, and vegetation flammability. Permafrost decreased the loss of the insulating soil organic layer, decreased soil drying, increased surface water pooling, and created a significant heat sink to buffer postfire soil temperature and thaw depth changes. Ecosystem factors also played a role in determining postfire thaw depth with boreal forests taking several decades longer to recover their soil thermal properties than tundra. These factors resulted in tundra being less sensitive to postfire soil thermal changes than the nonpermafrost boreal forest. These results suggest that permafrost and soil organic carbon will be more vulnerable to fire as climate warms. Abstract Copyright (2015), American Geophysical Union. All Rights Reserved.
15084105 Cheng Yanpei (Chinese Academy of Geological Sciences, Institute of Hydrogeology and Environmental Geology, Shijiazhuang, China); Yue Chen; Zhang Jiankang; Yi Qing; Wen Xueru and Li Yongchao. Influence of fluctuations of frozen soil in north Asia on groundwater and assessment on resources: Journal of Groundwater Science and Engineering, 2(3), p. 71-77, illus. incl. geol. sketch maps, 10 ref., September 2014.
The distribution and fluctuations of frozen soil in North Asia are closely related to the groundwater recharge-runoff-discharge in this area, and play a role in controlling the hydrogeological conditions of North Asia. By using NOAA satellite remote sensing interpretation data of frozen soil distribution in 2009 in conjunction with local hydrogeological conditions, the frozen soil area of North Asia according to the different characteristics of its impact on the groundwater was divided into three great hydrogeologic units, i.e. continuous permafrost, island permafrost, and high-altitude permafrost. By water balance method, the amount of natural renewable resources in North Asia was calculated as 1007.45´109 m3/a, with mineable resource of 705.21´109 m3/a, which indicates that the reduction of frozen soil range due to climate change in recent years gives rise to the richer groundwater resources and greater potential of mineable resources in North Asia, and frozen soil melting poses a relatively significant influence on the groundwater environment and ecological environment in North Asia.
15087363 Anderson, Lesleigh (U. S. Geological Survey, Geosciences and Environmental Change, Denver, CO); Birks, Jean; Rover, Jennifer and Guldager, Nikki. Controls on recent Alaskan lake changes identified from water isotopes and remote sensing: Geophysical Research Letters, 40(13), p. 3413-3418, illus., 40 ref., July 16, 2013.
High-latitude lakes are important for terrestrial carbon dynamics and waterfowl habitat driving a need to better understand controls on lake area changes. To identify the existence and cause of recent lake area changes in the Yukon Flats, a region of discontinuous permafrost in north central Alaska, we evaluate remotely sensed imagery with lake water isotope compositions and hydroclimatic parameters. Isotope compositions indicate that mixtures of precipitation, river water, and groundwater source ~95% of the studied lakes. The remaining minority are more dominantly sourced by snowmelt and/or permafrost thaw. Isotope-based water balance estimates indicate 58% of lakes lose more than half of inflow by evaporation. For 26% of the lakes studied, evaporative losses exceeded supply. Surface area trend analysis indicates that most lakes were near their maximum extent in the early 1980s during a relatively cool and wet period. Subsequent reductions can be explained by moisture deficits and greater evaporation. Abstract Copyright (2013), American Geophysical Union. All Rights Reserved.
15084878 Dempster, Tim (University of Glasgow, School of Geographical and Earth Sciences, Glasgow, United Kingdom) and Jess, Scott A. Ikaite pseudomorphs in Neoproterozoic Dalradian slates record Earth's coldest metamorphism: Journal of the Geological Society of London, 172(4), p. 459-464, illus., 56 ref., July 2015.
Calcite pseudomorphs have replaced euhedral ikaite (CaCO3.6H2O) porphyroblasts in Dalradian calcareous slates and metadolostones of western Scotland, with a volume decrease of at least 47%. Porphyroblast-fabric relationships indicate that the initial growth of ikaite post-dates a penetrative tectonic fabric developed during upright folding. This is the first reported occurrence of metamorphic ikaite porphyroblasts and points towards growth within the slates during an ultra-low-temperature metamorphism with an exceptionally low geothermal gradient. This event is associated with the penetration of long-lived and extreme permafrost deep into subaerially exposed bedrock during Neoproterozoic glaciation. The presence of the well-preserved pseudomorphs within the Easdale slates of the Argyll Group implies that a Neoproterozoic orogenic unconformity exists above the stratigraphic position of these rocks.
15086835 Taylor, Samuel N. (Institut de Physique du Globe de Paris, Paris, France) and Lagroix, France. Magnetic anisotropy reveals the depositional and postdepositional history of a loess-paleosol sequence at Nussloch (Germany): Journal of Geophysical Research: Solid Earth, 120(5), p. 2859-2876, illus. incl. 2 tables, 35 ref., May 2015.
Anisotropy of magnetic susceptibility (AMS) is employed as a tool to unravel the depositional history of the 17 m thick Nussloch P8 Weichselian loess sequence located 10 km south of Heidelberg, Germany. Through an AMS study, the primary aeolian depositional origin of the magnetic fabrics is evaluated, and overprinting due to postdepositional reworking and/or deformation is identified. Primary fabrics along the P8 sequence are defined by near-vertical KMIN axes and horizontal foliations. Eight intervals display secondary fabrics, characterized by either prolate orientation distributions or oblate orientation distributions with dipping foliation planes. These postdepositional fabrics are associated with laminated loess and tundra gley horizons. It is proposed that increased moisture (due to higher precipitation or enhanced snowmelt) and repeated cryogenic processes were able to reorganize and rework the accumulated loess. Primary aeolian fabrics are archived within 6.45 m of cumulated depth or 38% of the profile and dominantly within the Upper Pleniglacial units. Even though maximum susceptibility axes of primary fabrics are statistically well resolved at the specimen (e12 = 10.1° ± 8.6) and population (e12 = 6°) level, any inferred paleowind directions from the magnetic lineation remains speculative given the low concentration of ferrimagnetic minerals (<0.03 wt %). Tundra gley horizons upprofile display primary magnetic fabrics and no major changes in the degree of anisotropy or AMS orientation distributions. This suggests a weakening in gley-induced diagenesis and therefore favorable environmental conditions needed (moisture and presence of permafrost active layer) to initiate their formation in loess deposits. Finally, pedogenesis has not played an important role in modifying the magnetic fabric since paleosols display the same magnetic fabrics observed in primary loess. Abstract Copyright (2015), . American Geophysical Union. All Rights Reserved.
15083429 Wennrich, Volker (University of Cologne, Institute of Geology and Mineralogy, Cologne, Germany); Minyuk, P. S.; Borkhodoev, V.; Francke, A.; Ritter, B.; Nowaczyk, N. R.; Sauerbrey, M. A.; Brigham-Grette, J. and Melles, M. Pliocene to Pleistocene climate and environmental history of Lake El'gygytgyn, Far East Russian Arctic, based on high-resolution inorganic geochemistry data: Climate of the Past, 10(4), p. 1381-1399, illus. incl. sketch map, 1 table, sect., 100 ref., 2014.
The 3.6 Ma sediment record of Lake El'gygytgyn/NE Russia, Far East Russian Arctic, represents the longest continuous climate archive of the terrestrial Arctic. Its elemental composition as determined by X-ray fluorescence scanning exhibits significant changes since the mid-Pliocene caused by climate-driven variations in primary production, postdepositional diagenetic processes, and lake circulation as well as weathering processes in its catchment. During the mid- to late Pliocene, warmer and wetter climatic conditions are reflected by elevated Si / Ti ratios, indicating enhanced diatom production in the lake. Prior to 3.3 Ma, this signal is overprinted by intensified detrital input from the catchment, visible in maxima of clastic-related proxies, such as K. In addition, calcite formation in the early lake history points to enhanced Ca flux into the lake caused by intensified weathering in the catchment. A lack of calcite deposition after ca. 3.3 Ma is linked to the development of permafrost in the region triggered by cooling in the mid-Pliocene. After ca. 3.0 Ma the elemental data suggest a gradual transition to Pleistocene-style glacial-interglacial cyclicity. In the early Pleistocene, the cyclicity was first dominated by variations on the 41 kyr obliquity band but experienced a change to a 100 kyr eccentricity dominance during the middle Pleistocene transition (MPT) at ca. 1.2-0.6 Ma. This clearly demonstrates the sensitivity of the Lake El'gygytgyn record to orbital forcing. A successive decrease of the baseline levels of the redox-sensitive Mn/Fe ratio and magnetic susceptibility between 2.3 and 1.8 Ma reflects an overall change in the bottom-water oxygenation due to an intensified occurrence of pervasive glacial episodes in the early Pleistocene. The coincidence with major changes in the North Pacific and Bering Sea paleoceanography at ca. 1.8 Ma implies that the change in lake hydrology was caused by a regional cooling in the North Pacific and the western Beringian landmass and/or changes in the continentality. Further increases in total organic carbon and total nitrogen content after ca. 1.6 Ma are attributed to reduced organic matter decay in the sediment during prolonged anoxic periods. This points to more extensive periods of perennial ice coverage, and thus, to a progressive shifts towards more intense peak glacial periods. In the course of the Pleistocene glacial-interglacial sequence eight so-called "super-interglacials" occur. Their exceptionally warm conditions are reflected by extreme Si/Ti peaks accompanied by lows in Ti, K, and Fe, thus indicating extraordinary high lake productivity.
15091652 Quinton, William L. (Wilfrid Laurier University, Cold Regions Research Centre, Waterloo, ON, Canada) and Peters, Daniel L., editors. Canadian Geophysical Union; Hydrology Section, 2015: Hydrological Processes, 29(18), p. 3829-4174, illus. incl. tables, geol. sketch map, August 30, 2015. Papers in this special issue were presented in sessions organized by the Hydrology Section of the Canadian Geophysical Union at the annual meetings held in Saskatoon, Saskatchewan, May 26-30, 2013 and in Banff, Alberta, May 4-7, 2014; individual papers within scope are cited separately.
15086485 Wainwright, Haruko M. (Lawrence Berkeley National Laboratory, Earth Sciences Division, Berkeley, CA); Dafflon, Baptiste; Smith, Lydia J.; Hahn, Melanie S.; Curtis, John B.; Wu, Yuxin; Ulrich, Craig; Peterson, John E.; Torn, Margaret S. and Hubbard, Susan S. Identifying multiscale zonation and assessing the relative importance of polygon geomorphology on carbon fluxes in an Arctic tundra ecosystem: Journal of Geophysical Research: Biogeosciences, 120(4), p. 788-808, illus. incl. 4 tables, 61 ref., April 2015.
We develop a multiscale zonation approach to characterize the spatial variability of Arctic polygonal ground geomorphology and to assess the relative controls of these elements on land surface and subsurface properties and carbon fluxes. Working within an ice wedge polygonal region near Barrow, Alaska, we consider two scales of zonation: polygon features (troughs, centers, and rims of polygons) that are nested within different polygon types (high, flat, and low centered). In this study, we first delineated polygons using a digital elevation map and clustered the polygons into four types along two transects, using geophysical and kite-based landscape-imaging data sets. We extrapolated those data-defined polygon types to all the polygons over the study site, using the polygon statistics extracted from the digital elevation map. Based on the point measurements, we characterized the distribution of vegetation, hydrological, thermal, and geochemical properties, as well as carbon fluxes, all as a function of polygon types and polygon features. Results show that nested polygon geomorphic zonation-polygon types and polygon features-can be used to represent distinct distributions of carbon fluxes and associated properties, as well as covariability among those properties. Importantly, the results indicate that polygon types have more power to explain the variations in those properties than polygon features. The approach is expected to be useful for improved system understanding, site characterization, and parameterization of numerical models aimed at predicting ecosystem feedbacks to the climate. Abstract Copyright (2015), . American Geophysical Union. All Rights Reserved.
15091315 Yang Sizhong (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, State Key Laboratory of Frozen Soils Engineering, Lanzhou, China); Cao, Xianyong and Jin Huijun. Validation of ice-wedge isotopes at Yituli'he, northeastern China as climate proxy: Boreas, 44(3), p. 502-510, illus. incl. sect., 1 table, sketch maps, 35 ref., July 2015.
Inactive ice wedges are still present today at Yituli'he in the middle Da Xing'anling (Greater Hinggan) Mountains in northeastern China, which is the southernmost known site (50°37'N) with ice wedges in the Northern Hemisphere. However, it is uncertain whether the ice-wedge isotope composition, characterized by low d18O, dD and low deuterium excess values, is representative of the isotope signature of a broader region. In this paper, the ice-wedge isotope compositions were examined in the context of the stable isotopes of precipitation from the nearby Global Network of Isotopes in Precipitation (GNIP) stations. In addition, the pollen spectra from the host sediments were analysed to provide additional information on local vegetation in order to better understand the climate conditions favouring ice-wedge formation. The pollen spectra suggest that the Yituli'he ice wedges developed during the colder and wetter period after 6000 cal. a BP. The isotopes in the Yituli'he ice wedges are consistent with the isotope background recorded in atmospheric precipitation collected at the nearby GNIP stations. When the snow-melt froze into ice veinlets, the isotope signals did not change substantially because of the strong, cold, continental anticyclones in winter as well as a strong temperature inversion that prevail in the Da Xing'anling Mountains. As the climate pattern did not change substantially, the neoglacial cold period is unlikely to have allowed for strong secondary fractionation of isotope records during ice-wedge formation. Thus, the annual isotope signature can be interpreted as a valid archive of climate data. Abstract Copyright (2010), John Wiley & Sons, Ltd.
15091644 Ekici, A. (Max Planck Institute for Biogeochemistry, Department of Biogeochemical Integration, Jena, Germany); Chadburn, S. E.; Chaudhary, N.; Hajdu, L. H.; Marmy, A.; Peng, S.; Boike, J.; Burke, E. J.; Friend, A. D.; Hauck, C.; Krinner, G.; Langer, M.; Miller, P. A. and Beer, C. Site-level model intercomparison of high latitude and high altitude soil thermal dynamics in tundra and barren landscapes: The Cryosphere (Online), 9(4), p. 1343-1361, illus. incl. 4 tables, sketch map, 95 ref., 2015. Includes appendix.
15083783 Niu Fujun (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Laboratory of Frozen Soil Engineering, Lanzhou, China); Luo Jing; Liu Zhanju; Liu Minhao and Yin Guoan. Morphological characteristics of thermokarst lakes along the Qinghai-Tibet engineering corridor: Arctic, Antarctic, and Alpine Research, 46(4), p. 963-974, illus. incl. 7 tables, sketch map, 48 ref., November 2014.
In order to determine the distribution and morphometric characteristics of thermokarst lakes on the Qinghai-Tibet Plateau, SPOT-5 satellite images were acquired from the Chumaerhe High Plateau to Beiluhe Basin within a 10-km-wide corridor along the Qinghai-Tibet Railway. A total of 2163 water bodies, having a total area of 1.09´107 m2, were identified in the study area using unsupervised classification and image interpretation. Several shape metrics (area, perimeter, circularity index, elongation index, orientation of major axis, and curvature of lake shoreline) were determined for lakes from the imagery, and bathymetric profiles of lake bottoms were derived using ground-penetrating radar. The results highlighted significant morphometric differences between lakes larger than 5000 m2 among three subregions: the Chumaerhe High Plain (CHP), the Hoh Xil Hill region (HXR), and the Beluhe Basin region (BBR). The lakes in CHP usually have a more regular outline and smooth lake bottoms, while the lakes in HXR often have the greatest depths and the most complex shorelines. The most elongated and largest lakes were typically in BBR. Other than a minor NE-SE peak in HXR and BBR, the major axis orientation for lakes in the three subregions is mostly ENE-WSW. The differences in lake morphology between the three subregions are associated with differences in ground-ice content, local relief, and topography. The dominant factors controlling the development of orientated thermokarst lakes in the region are the prevailing summer wind direction and solar insolation.
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15083248 Porter, T. (University of Alberta, Edmonton, AB, Canada); Mahony, M.; Pumple, J.; Calmels, F. and Froese, D. G. 50,000 years of paleoenvironmental change recorded in permafrost water isotopes and coeval paleoecological and cryostratigraphic indicators from the Klondike Goldfields, Yukon, Canada [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract PP41D-06, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Similar to ice cores, permafrost provides a robust archive of meteoric water. Here, we present a stacked record of dD, d18O, and d-excess from ground ice in perennially-frozen loess at eight sites in the Klondike Goldfields spanning the last 50,000 years. The record is constrained by 32 AMS 14C dates, 94 co-isotope measurements, and paleoecological and cryostratigraphic indicators that we use to cross-validate our interpretation of the isotope record. dD and d18O show consistent secular trends and reflect changes seen in ice core records. A negative "cooling" trend (Dd18O = -5.6 ppm) is observed during the MIS 3 to MIS 2 transition, with the most depleted values during the LGM (»24,000 cal. yrs BP). A sharp "warming" trend (Dd18O = +8.3 ppm) from ca. 17,000 to 11,000 cal. yrs BP marks the transition from late glacial conditions to Early Holocene peak warmth. A cooling trend (Dd18O = -1.9 ppm) characterises the remainder of the Holocene. D-excess has no clear trend for most of the record except a +10 ppm anomaly from 28,500 to 22,000 cal. yrs BP. This anomaly was likely caused by a shift in precipitation seasonality with a bias toward winter d-excess values. Cryostratigraphic evidence for this interpretation includes a cessation of large ice wedge growth, possibly from increased snow depths. Moreover, loess deposition increases and plant macrofossils indicate a shift to grasslands during this interval, implying a drier summer climate, which would reinforce the d-excess anomaly. The Klondike permafrost isotopes and coeval paleoenvironmental indicators offer a rich multi-proxy perspective on past hydroclimatic change in eastern Beringia, and firmly establishes the value of developing similar permafrost isotope records in other periglacial regions.
15085807 Saito, K. (Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan); Trombotto, D.; Bigelow, N. H.; Marchenko, S. S.; Romanovsky, V. E.; Walsh, J. E.; Hendricks, A. and Yoshikawa, K. Paleo-permafrost distribution downscaled in South America; examination of the GCM-based maps with the observations [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract PP31C-1878, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
In this paper, we show our attempt to compare the potential regional frozen ground distribution in South America for the present-day, mid-Holocene and the Last Glacial Maximum (LGM), downscaled from the outputs of the sets of global climate model (GCM)s, participating in recent Paleoclimate Model Intercomparison Project (PMIP2 and PMIP3). Due to relatively small portion of the terrestrial areas compared to that of the Northern Hemisphere, the frozen ground distribution in the Southern Hemisphere has not been intensively surveyed and/or mapped, except for the Andes. This scale and recognition gap is one of the reasons why the GCM results have not been widely used in investigations and applications in geography or geomorphology, although field surveys in these disciplines have intensively been conducted in the middle latitude in South America, from the Andes through Patagonia to Tierra del Fuego, to evidence the periglacial processes and to determine the distribution, and their change, in the Quaternary. The PMIP2 downscaled regional maps successfully showed the likely presence of frozen ground, such as permafrost in the Andes for 0 ka, whereas the original coarse-resolution global maps failed. However, it still showed insufficient and/or incorrect classifications, e.g., lowland in Patagonia and Tierra del Fuego that are not underlain by permafrost today but were in 21 ka, failed to produce the LGM permafrost. The mid-latitude mountains with the Pleistocene permafrost evidence, such as Extra-Andean Mountains and Ventania, also failed to be reproduced. This discrepancy in the PMIP2 products is likely due to the regional warm bias in South America, in contrast to the cool bias on hemispheric scales, which has been improved in PMIP3 products.
15089034 Lopez, Robin (Lawrence Berkeley National Laboratory, Hydrogeology Department, Berkeley, CA). Soil texture analysis for the Next Generation Ecosystem Experiment (NGEE) [abstr.]: in Geological Society of America, Cordilleran Section, 111th annual meeting, Abstracts with Programs - Geological Society of America, 47(4), p. 48, May 2015. Meeting: Geological Society of America, Cordilleran Section, 111th annual meeting, May 11-13, 2015, Anchorage, AK.
Research is being conducted in the Arctic region of northern Alaska for the Next Generation Ecosystem Experiment (NGEE). NGEE is a collaborative effort amongst several federal and state research institutions, as they collectively aim to assess and analyze a predictive model of the Arctic ecosystem in response to climate change. The Arctic is abundant with soil that has been frozen for thousands of years, otherwise known as permafrost. Hence, this requires the exploration of permafrost cores to develop a foundation in understanding the soil properties, hydrogeologic features, and ecological and biochemical processes. To gauge these aforementioned processes, one must conduct extensive field and laboratory research to investigate geophysical approaches for the Arctic subsurface. Should our global temperature continue to rise, permafrost is expected to thaw, which in turn could release organic matter that has been stored in the frozen soils, leading to potential high release of greenhouse gases. Thus, the author has engaged in soil texture analysis to develop an understanding of these permafrost cores. From research conducted at the Lawrence Berkeley Lab (LBL), the author and several LBL scientists have extrapolated key data to help determine organic matter and carbon concentrations.
15083262 Niessen, F. (Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Bremerhaven, Germany); Hong, J.; Hegewald, Anne; Matthiessen, J. J.; Stein, R. H.; Kim, H.; Kim, S.; Jensen, L.; Jokat, W.; Nam, S. and Kang, S. Marine ice sheets of Pleistocene age on the East Siberian Continental Margin [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract PP42B-04, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Based on swath bathymetry, sediment echosounding, seismic profiling and sediment coring we present results of the RV "Polarstern" cruise ARK-XIII/3 (2008) and RV "Araon" cruise ARA03B (2012), which investigated an area between the Chukchi Borderland and the East Siberian Sea between 165°W and 170°E. At the southern end of the Mendeleev Ridge, close to the Chukchi and East Siberian shelves, evidence is found for the existence of Pleistocene ice sheets/ice shelves, which have grounded several times in up to 1200 m present water depth. We found mega-scale glacial lineations associated with deposition of glaciogenic wedges and debris-flow deposits indicative of sub-glacial erosion and deposition close to the former grounding lines. Glacially lineated areas are associated with large-scale erosion, accentuated by a conspicuous truncation of pre-glacial strata typically capped with mostly thin layers of diamicton draped by pelagic sediments. Our tentative age model suggests that the youngest and shallowest grounding event of an ice sheet should be within Marine Isotope Stage (MIS) 3. The oldest and deepest event predates MIS 6. According to our results, ice sheets of more than one km in thickness continued onto, and likely centered over, the East Siberian Shelf. They were possibly linked to previously suggested ice sheets on the Chukchi Borderland and the New Siberian Islands. We propose that the ice sheets extended northward as thick ice shelves, which grounded on the Mendeleev Ridge to an area up to 78°N within MIS 5 and/or earlier. These results have important implication for the former distribution of thick ice masses in the Arctic Ocean during the Pleistocene. They are relevant for global sea-level variations, albedo, ocean-atmosphere heat exchange, freshwater export from the Arctic Ocean at glacial terminations and the formation of submarine permafrost. The existence of km-thick Pleistocene ice sheets in the western Arctic Ocean during glacial times predating that of the Last Glacial Maximum (LGM) also implies significantly different atmospheric circulation patterns, in particular availability and distribution of moisture during pre-LGM glaciations.
15085811 Zolitschka, B. (University of Bremen, Bremen, Germany); Ohlendorf, C.; Mayr, C.; Gebhardt, Catalina; Hahn, A.; Hoelzl, S.; Kliem, P. and Oehlerich, M. Impact of Southern Hemispheric westerlies on hydrological variations in southern Patagonia, Argentina [abstr.]: in AGU 2013 fall meeting, American Geophysical Union Fall Meeting, 2013, Abstract PP31C-1882, December 2013. Meeting: American Geophysical Union 2013 fall meeting, Dec. 9-13, 2013, San Francisco, CA.
Semiarid conditions are prevailing at the site of Laguna Potrok Aike (52°S, 70°W; 116 m asl; diameter: 3.5 km, water-depth: 100 m), a currently terminal maar lake in the southern Patagonian steppe of Argentina. Depositional processes of autochthonous sedimentary compounds in this lake are mainly controlled by the evaporation/precipitation ratio (E/P), a direct function of climate. Stratigraphic and chronological correlation of the 106 m composite profile from the deep basin of Laguna Potrok Aike with sediment cores from littoral zones and outcrops in the catchment area allows to reconstruct hydrological fluctuations during the last 51 ka providing evidence for lake-level variations in the range of more than 50 m. During the Late Pleistocene, the sediment facies was influenced by a comparatively high inflow and little evaporation with a responding high lake level. During deglaciation and in particular during the Late Glacial a lake-level lowering (higher E/P) indicates warming, whereas in the early Holocene a higher lake level re-established. Since 9.3 kcal BP intense carbonate precipitation together with salinity-indicating diatoms document prevailing subsaline lacustrine conditions until today with only one distinct interruption for the neoglacial "Little Ice Age" (LIA). For such long-term hydrological variability several factors play important roles. Amongst others these are: 1) changes in runoff due to permafrost sealing of the ground during the last glacial period, 2) variations in precipitation and wind-induced evaporation linked to changes in intensity and position of the Southern Hemispheric Westerlies (SHW) and 3) the Glacial-to-Holocene temperature increase. Based on multiproxy evidence a lake-level record for the last 51 ka was reconstructed and interpreted as the result of the SHW being in a more northerly position during the last Glacial period followed by a southward movement. At 9.3 ka cal. BP the SHW intensified in the study area and caused a pronounced negative water balance with a lake-level lowering of >50 m compared to glacial conditions. Two millennia later SHW intensity or position changed at this latitude (52°S) and the lake level rose in a step-like manner to its Holocene maximum during the LIA. Since the 20th century strengthening of SHW increased the evaporative stress resulting again in a more negative water balance. Comparison of our data with regional records from Patagonia indicates that the core of the SHW shifted southward and established at 52°S around 9.3 kcal. BP. As the late Holocene lake-level high-stand during the LIA is documented for entire Patagonia, it appears to have occurred synchronously over all latitudes and thus seems to be related to a SHW weakening instead of latitudinal shifts of the SHW belt. To improve our understanding of past hydrological variability, new isotopic data will be presented and compared to geochemical and paleobiological evidences.
15090472 Lee, R. F. (North Carolina State University at Raleigh, Raleigh, NC); Abbott, R. E.; Knox, Hunter A. and Pancha, A. Seasonal changes in H/V spectral ratio at high-latitude seismic stations [abstr.]: in AGU 2014 fall meeting, American Geophysical Union Fall Meeting, 2014, Abstract S41A-4438, December 2014. Meeting: American Geophysical Union 2014 fall meeting, Dec. 15-19, 2014, San Francisco, CA.
We present results demonstrating seasonal variations in the Horizontal-to-Vertical Spectral Ratio (HVSR) at high-latitude seismic stations. We analyze data from two sites at Poker Flat Research Range, near Fairbanks, Alaska. From the first site, we analyze 3 stations installed by Sandia National Labs (SNL) in a valley with marshy summer conditions. We also analyze the PASSCAL Instrument Center station PIC2, which is installed on rock approximately 3.2 km from the SNL stations. These stations continuously record data at 125 (SNL) and 200 (PIC2) samples per second. Seasonal changes in HVSR at high frequencies (>20 Hz) appear to be caused by impedance contrasts between frozen and thawed ground. Thawed active layers are known to have slower shear-wave velocities than frozen layers or bedrock. An estimate of active layer thickness at each station is obtained from the quarter-wavelength approximation. We verify the accuracy of this technique by obtaining ground-truth measurements at the sites for both thickness and shear-wave velocity. We use physical probing for the thickness measurements and active-source Refraction-Microtremor (ReMi) surveys for the shear-wave velocities. 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
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