2016056451 Yang Yuzhong (Chinese Academy of Science, Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Wu Qingbai; Yun Hanbo; Jin Huijun and Zhang Zhongqiong. Evaluation of the hydrological contributions of permafrost to the thermokarst lakes on the Qinghai-Tibet Plateau using stable isotopes: Global and Planetary Change, 140, p. 1-8, illus. incl. 3 tables, sketch map, 64 ref., May 2016.

Considering the widespread distribution of thermokarst lakes and their significant influence on the hydrological cycle in permafrost regions on the Qinghai-Tibet Plateau (QTP), it is necessary to study their hydrological regimes, which are responding to ongoing climate-induced permafrost thaw. In this paper, water isotopic tracers were used to assess the temporal and interannual hydrological variations and the hydrological processes of two thermokarst lakes (TL-A and TL-B) associated with thawing permafrost in Beiluhe Basin on the QTP. The isotopic results revealed significant differences between the two thermokarst lakes: the TL-A showed more positive isotopic values and small fluctuations than TL-B did. This can be attributed to the hydrological discrepancies between them. Based on the water isotopic mass balance (IMB) model and estimated evaporation, the contributions of permafrost melt water and precipitation to the thermokarst lakes were determined. In both 2011 and 2012, the contributions of thawing permafrost water to thermokarst lakes were of significance, as high as 61.3%. The modeled isotopic composition of input water (d_I), and the relationships between climatic factors and lake water isotopes were evaluated. Results suggested that the two lakes originated from multiple sources and confirmed the modeling process well. It also indicated that thawing of permafrost significantly affected the development and hydrological regime of thermokarst lakes on the QTP. It is necessary to emphasize the significant impact of thawing permafrost on the thermokarst lakes on the QTP. Findings demonstrate that ongoing permafrost thaw may have major implications for thermokarst landscapes as climate change continues. Abstract Copyright (2016) Elsevier, B.V.

DOI: 10.1016/j.gloplacha.2016.03.006

2016058660 Boike, Julia (Alfred Wegener Institute Helmholtz Center for Polar and Marine Research, Potsdam, Germany); Grau, Thomas; Heim, Birgit; Günther, Frank; Langer, Moritz; Muster, Sina; Gouttevin, Isabelle and Lange, Stephan. Satellite-derived changes in the permafrost landscape of central Yakutia, 2000-2011; wetting, drying, and fires: Global and Planetary Change, 139, p. 116-127, illus. incl. sketch maps, 71 ref., April 2016. Includes appendices.

The focus of this research has been on detecting changes in lake areas, vegetation, land surface temperatures, and the area covered by snow, using data from remote sensing. The study area covers the main (central) part of the Lena River catchment in the Yakutia region of Siberia (Russia), extending from east of Yakutsk to the central Siberian Plateau, and from the southern Lena River to north of the Vilyui River. Approximately 90% of the area is underlain by continuous permafrost. Remote sensing products were used to analyze changes in water bodies, land surface temperature (LST), and leaf area index (LAI), as well as the occurrence and extent of forest fires, and the area and duration of snow cover. The remote sensing analyses (for LST, snow cover, LAI, and fire) were based on MODIS-derived NASA products (250-1000 m) for 2000 to 2011. Changes in water bodies were calculated from two mosaics of (USGS) Landsat (30 m) satellite images from 2002 and 2009. Within the study area's 315,000 km² the total area covered by lakes increased by 17.9% between 2002 and 2009, but this increase varied in different parts of the study area, ranging between 11% and 42%. The land surface temperatures showed a consistent warming trend, with an average increase of about 0.12 °C/year. The average rate of warming during the April-May transition period was 0.17 °C/year and 0.19 °C/year in the September-October period, but ranged up to 0.49 °C/year during September-October. Regional differences in the rates of land surface temperature change, and possible reasons for the temperature changes, are discussed with respect to changes in the land cover. Our analysis of a broad spectrum of variables over the study area suggests that the spring warming trend is very likely to be due to changes in the area covered by snow. The warming trend observed in fall does not, however, appear to be directly related to any changes in the area of snow cover, or to the atmospheric conditions, or to the proportion of the land surface that is covered by water (i.e., to wetting and drying). Supplementary data (original data, digitized version of the maps, metadata) are archived under PANGAEA (URL: http://dx.doi.org/10.1594/PANGAEA.855124). Abstract Copyright (2016) Elsevier, B.V.

DOI: 10.1016/j.gloplacha.2016.01.001

2016054098 Chipman, Melissa L. (University of Illinois, Program in Ecology, Evolution and Conservation Biology, Urbana, IL); Kling, George W.; Lundstrom, Craig C. and Hu, Feng Sheng. Multiple thermo-erosional episodes during the past six millennia; implications for the response of Arctic permafrost to climate change: Geology (Boulder), Pre-Issue Publication, illus. incl. sketch map, 24 ref., April 28, 2016. GSA Data Repository item 2016144.

Anthropogenic warming may promote rapid permafrost thaw in the Arctic and alter the global carbon cycle. Although several studies suggest increased thermo-erosion as a result of recent warming, a long-term context is necessary to assess the linkages of thermokarst processes with climate variability. We analyzed sediment cores from two lakes on the Alaskan North Slope (USA), one with (Lake NE14) and one without (Perch Lake) watershed thermo-erosion. Distinct geochemical and lithological characteristics provide evidence for sedimentary input from carbonate-rich permafrost soils associated with past retrogressive thaw slumping at Lake NE14 but not at Perch Lake. These characteristics include increases in Ca:Sr, Ca:K, carbonate:[feldspar + clay minerals], percent CaCO₃, and d¹³C, and decreases in ⁸⁷Sr:⁸⁶Sr. At least ten episodes of thermo-erosion occurred over the past 6000 yr at Lake NE14. Most of these episodes coincided with periods of elevated summer temperatures, but moisture variation and geomorphic factors likely played a role in driving their occurrence. Our results suggest that positive feedbacks facilitate reactivation of thermo-erosion in ice-rich terrain, adding to the growing body of evidence that these Arctic landscapes are unstable in a changing climate.

DOI: 10.1130/G37693.1

2016053869 Lin Zhanju (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, State Key Laboratory of Frozen Soil Engineering, Lanzhou, China); Luo Jing and Niu Fujun. Development of a thermokarst lake and its thermal effects on permafrost over nearly 10 yr in the Beiluhe Basin, Qinghai-Tibet Plateau: Geosphere (Boulder, CO), 12(2), p. 632-643, illus. incl. sects., 1 table, sketch map, 32 ref., April 2016.

The thermal influence of a thermokarst lake on permafrost in the Beiluhe Basin of the Qinghai-Tibet Plateau was examined over nearly 10 yr (2006-2014), and lake development involved both downward and lateral heat transfers. Downward heat transfer rapidly thawed 8 m of permafrost beneath the lake bottom center, forming a through talik (i.e., year-round unfrozen ground in permafrost that is open to top and unfrozen layers beneath permafrost) by October 2008. Lateral heat transfer resulted in permafrost temperatures and permafrost table depths at the lakeshore that decreased with distance from the lake. In 2014, the maximum differences in the mean annual ground temperature and permafrost table depth within 75 m of the lake were 0.4°C and 0.8 m, respectively. The horizontal extent of the talik has expanded gradually from the lake center to the lakeshore. The development of the thermokarst lake on the Qinghai-Tibet Plateau is discussed in terms of four stages, initiation, development, stabilization, and termination, resulting from changes in the surface energy balance.

DOI: 10.1130/GES01194.1

2016056061 Li Jing (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Sheng Yu; Wu Jichun; Feng Ziliang; Wang Shengting; Cao Yuanbing; Hu Xiaoying; Cao Wei; Wang Jie and Zhang Xiumin. Variations in the ground temperatures of permafrost in the two watersheds of the interior and eastern Qilian Mountains: Environmental Earth Sciences, 75(6), Article 480, illus. incl. 2 tables, sketch map, 34 ref., March 2016.

The Qilian Mountains, which are composed of a series of approximately northwest-southeast-oriented mountains, are one of main alpine permafrost areas in the Qinghai-Tibet Plateau in northwestern China. From east to west, variations in permafrost environments are remarkable. The source areas of the Shule River (SASR) and the Datong River (SADR) are located in the interior and eastern part of the Qilian Mountains. In this study, variations in the ground temperatures of permafrost in the two watersheds represented the characteristics of interior and eastern permafrost environments in the Qilian Mountains. A total of 20 and 30 boreholes, along with ground temperatures measured at 10-15 m depths, were collected in the two areas. The maximum ground temperature in the SASR was 0.7 °C, and the minimum was -3.4 °C. The variations in the ground temperatures can be explained by elevation and local slope facing. The lapse rates of the ground temperatures with elevation were 5.9 °C/km for the south-facing slope, 8.0 °C/km for the gentle flat terrain and approximately 5.7 °C/km for the north-facing slope. It was estimated that the 0 °C ground temperature was located at approximately 3800 m in the flat terrains, at approximately 3880 m on the south-facing slope terrains, and at approximately 3710 m on the north-facing slope terrains. In the SADR, the maximum and minimum ground temperatures were 2.54 and -2.78 °C, respectively. The elevation, vegetation types and soil moisture content can explain most of the variations in the ground temperatures. The lower limits of the permafrost were 3620 m for the wet meadow and 3710 m for the moist meadow. The lapse rates of the ground temperatures with elevation were 3.4 °C/km for wet meadow and 3.0 °C/km for moist meadow. The differences in the ground temperatures of the two areas were primarily caused by regional climatic differences, particularly the varying precipitation and evaporation. However, more areas must be studied to elucidate the regional differentiation of permafrost distribution and the underlying reasons for this differentiation. Copyright 2016 Springer-Verlag Berlin Heidelberg

DOI: 10.1007/s12665-016-5330-1

2016055650 Busby, Jonathan P. (British Geological Survey, Nottingham, United Kingdom); Lee, Jonathan R.; Kender, Sev; Williamson, Paul and Norris, Simon. Regional modelling of permafrost thicknesses over the past 130 ka; implications for permafrost development in Great Britain: Boreas, 45(1), p. 46-60, illus. incl. 2 tables, geol. sketch map, 102 ref., January 2016.

The greatest thicknesses of permafrost in Great Britain most likely occurred during the last glacial-interglacial cycle, as this is when some of the coldest conditions occurred during the last 1 000 000 years. The regional development of permafrost across Great Britain during the last glacial-interglacial cycle was modelled from a ground surface temperature history based on mean annual temperatures and the presence of glacier ice. To quantify the growth and decay of permafrost, modelling was undertaken at six locations across Great Britain that represent upland glaciated, lowland glaciated, upland unglaciated and lowland unglaciated conditions. Maximum predicted permafrost depths derived in this academic study range between several tens of metres to over 100 m depending upon various factors including elevation, glacier ice cover, geothermal heat flux and air temperature. In general, the greatest maximum permafrost thicknesses occur at upland glaciated locations, with minimum thickness at lowland sites. Current direct geological evidence for permafrost is from surface or shallow processes, mainly associated with the active layer. Further research is recommended to identify the imprint of freeze/thaw conditions in permanently frozen porous rocks from beneath the active layer. Abstract Copyright (2010), John Wiley & Sons, Ltd.

DOI: 10.1111/bor.12136

2016055664 Gibson, J. J. (Alberta Innovates Technology Futures, Victoria, BC, Canada); Birks, S. J. and Yi, Y. Higher tritium concentrations measured in permafrost thaw lakes in northern Alberta: Hydrological Processes, 30(2), p. 245-249, illus. incl. 2 tables, sketch map, 10 ref., January 15, 2016.

Tritium concentrations were measured in a survey of 24 lakes, 15 wetlands, and 133 groundwaters in the oil sands region of northeastern Alberta and compared with both recent precipitation and precipitation sampled during the 1960s tritium peak caused by atmospheric thermonuclear weapons testing. Water samples from lakes included a group of 14 thaw lakes that had higher runoff attributed to melting of permafrost in peat plateaus within their watersheds. While tritium in all lakes was found to be intermediate between recent and 1960s concentrations, the thaw lakes were found to be significantly enriched in tritium compared with other lakes, as were unfrozen wetlands characterized by a thick sequence of low-hydraulic conductivity peat. The results provide further evidence of different water sources to the thaw lakes and may indicate that melting of modern permafrost in part formed since the 1950s is occurring in these systems. Copyright Copyright 2015 John Wiley & Sons, Ltd.

DOI: 10.1002/hyp.10599

2016055228 Salvado, Joan A. (Stockholm University, Department of Environmental Science, Stockholm, Sweden); Tesi, Tommaso; Andersson, August; Ingri, Johan; Dudarev, Oleg V.; Semiletov, Igor P. and Gustafsson, Orjan. Organic carbon remobilized from thawing permafrost is resequestered by reactive iron on the Eurasian Arctic Shelf: Geophysical Research Letters, 42(19), p. 8122-8130, illus., 40 ref., October 16, 2015.

Given the potential for permafrost carbon (PF/C)-climate feedbacks in the Siberian-Arctic land-ocean system, there is a need for understanding the fate of thawed-out PF/C. Here we show that the sequestration of OC by reactive iron (OC-Fe) ranges between 0.5 and 22% on the Eurasian Arctic Shelf, with higher values in the Kara Sea (KS) (18 ± 6%) and the Laptev Sea (LS) (14 ± 4%). The D¹⁴C/d¹³C signatures of the OC-Fe are substantially older and more terrestrial than the bulk sediment OC in the LS but younger and more dominated by marine plankton sources in the East Siberian Sea (ESS). Statistical source apportionment modeling reveal that reactive iron phases resequestered 15 ± 5% of thawing PF/C in the LS and 6.4 ± 5% in the ESS, derived from both coastal erosion of ice complex deposit and thawing topsoil. This Fe-associated trap of PF/C constitutes a reduction of the degradation/outgassing and thus also an attenuation of the PF/C-climate feedback. Abstract Copyright (2015), . American Geophysical Union. All Rights Reserved.

DOI: 10.1002/2015GL066058

2016055697 Siewert, Matthias B. (Stockholm University, Department of Physical Geography, Stockholm, Sweden); Hanisch, Jessica; Weiss, Niels; Kuhry, Peter; Maximov, Trofim C. and Hugelius, Gustaf. Comparing carbon storage of Siberian tundra and taiga permafrost ecosystems at very high spatial resolution: Journal of Geophysical Research: Biogeosciences, 120(10), p. 1973-1994, illus. incl. 4 tables, sketch maps, 80 ref., October 2015.

Permafrost-affected ecosystems are important components in the global carbon (C) cycle that, despite being vulnerable to disturbances under climate change, remain poorly understood. This study investigates ecosystem carbon storage in two contrasting continuous permafrost areas of NE and East Siberia. Detailed partitioning of soil organic carbon (SOC) and phytomass carbon (PC) is analyzed for one tundra (Kytalyk) and one taiga (Spasskaya Pad/Neleger) study area. In total, 57 individual field sites (24 and 33 in the respective areas) have been sampled for PC and SOC, including the upper permafrost. Landscape partitioning of ecosystem C storage was derived from thematic upscaling of field observations using a land cover classification from very high resolution (2 ´ 2 m) satellite imagery. Nonmetric multidimensional scaling was used to explore patterns in C distribution. In both environments the ecosystem C is mostly stored in the soil (>&eq;86%). At the landscape scale C stocks are primarily controlled by the presence of thermokarst depressions (alases). In the tundra landscape, site-scale variability of C is controlled by periglacial geomorphological features, while in the taiga, local differences in catenary position, soil texture, and forest successions are more important. Very high resolution remote sensing is highly beneficial to the quantification of C storage. Detailed knowledge of ecosystem C storage and ground ice distribution is needed to predict permafrost landscape vulnerability to projected climatic changes. We argue that vegetation dynamics are unlikely to offset mineralization of thawed permafrost C and that landscape-scale reworking of SOC represents the largest potential changes to C cycling. Abstract Copyright (2015), . American Geophysical Union. All Rights Reserved.

DOI: 10.1002/2015JG002999

2016053122 Frampton, Andrew (Stockholm University, Department of Physical Geography, Stockholm, Sweden) and Destouni, Georgia. Impact of degrading permafrost on subsurface solute transport pathways and travel times: in Fifty years of Water Resources Research; legacy and perspectives for the science of hydrology (Montanari, Alberto, prefacer; et al.), Water Resources Research, 51(9), p. 7680-7701, illus. incl. 1 table, 69 ref., September 2015.

Subsurface solute transport under surface warming and degrading permafrost conditions is studied using a physically based model of coupled cryotic and hydrogeological flow processes combined with a particle tracking method. Changes in the subsurface water and inert solute pathways and travel times are analyzed for different modeled geological configurations. For all simulated cases, the minimum and mean travel times increase nonlinearly with warming irrespective of geological configuration and heterogeneity structure. The timing of the start of increase in travel time depends on heterogeneity structure, combined with the rate of permafrost degradation that also depends on material thermal and hydrogeological properties. The travel time changes depend on combined warming effects of: i) increase in pathway length due to deepening of the active layer, ii) reduced transport velocities due to a shift from horizontal saturated groundwater flow near the surface to vertical water percolation deeper into the subsurface, and iii) pathway length increase and temporary immobilization caused by cryosuction-induced seasonal freeze cycles. Abstract Copyright (2015), . The Authors.

DOI: 10.1002/2014WR016689

2016059797 Li Shuangyang (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, State Key Laboratory of Frozen Soil Engineering, Lanzhou, China); Lai Yuanming; Zhang Mingyi and Yu Wenbing. Seasonal differences in seismic responses of embankment on a sloping ground in permafrost regions: in Recent development of earthquake engineering and soil dynamics for large-scale infrastructure (Ling Xianzhang, editor; et al.), Soil Dynamics and Earthquake Engineering (1984), 76, p. 122-135, illus. incl. 2 tables, geol. sketch maps, 41 ref., September 2015.

Because of its direct influence on the amount of unfrozen water and on the strength of intergranular ice in a frozen soil, temperature has a significant effect on all aspects of the mechanical behavior of the active layer in which temperature fluctuates above and below 0°C. Hence seismic responses of engineering structures such as embankment on a sloping ground in permafrost regions exhibit obvious differences with seasonal alternation. To explore the distinctive seismic characteristics of a railway embankment on the sloping ground in permafrost regions, a coupled water-heat-dynamics model is built based on theories of heat transfer, soil moisture dynamics, frozen soil mechanics, soil dynamics, and so on. A well-monitored railway embankment on a sloping ground in Qinghai-Tibet Plateau is taken as an example to simulate seismic responses in four typical seasons in the 25th service year. The numerical results show that seismic acceleration, velocity and displacement responses are significantly different in four typical seasons, and the responses on October 15 are much higher among the four seasons. When the earthquake is over, there are still permanent differential deformations in the embankment and even severe damages on the left slope on October 15. Therefore, this position should be monitored closely and repaired timely to ensure safe operation. In addition, the numerical model and results may be a reference for maintenance, design and study on other embankments in permafrost regions. Abstract Copyright (2015) Elsevier, B.V.

DOI: 10.1016/j.soildyn.2015.01.005

2016054684 Barnes, Rebecca T. (University of Colorado at Boulder, Department of Geological Sciences, Boulder, CO); Williams, Mark W.; Parman, Jordan N.; Hill, Ken and Caine, Nel. Thawing glacial and permafrost features contribute to nitrogen export from Green Lakes Valley, Colorado Front Range, USA: Biogeochemistry (Dordrecht), 117(2-3), p. 413-430, illus. incl. 1 table, sketch map, 61 ref., March 2014.

Alpine ecosystems are particularly susceptible to disturbance due to their short growing seasons, sparse vegetation and thin soils. Increased nitrogen deposition in wetfall and changes in climate currently affect Green Lakes Valley within the Colorado Front Range. Research conducted within the alpine links chronic nitrogen inputs to a suite of ecological impacts, resulting in increased nitrate export. The atmospheric nitrogen flux decreased by 0.56 kg ha^-1 year^-1 between 2000 and 2009, due to decreased precipitation; however alpine nitrate yields increased by 40 % relative to the previous decade (1990-1999). Long term trends indicate that weathering products such as sulfate, calcium, and silica have also increased over the same period. The geochemical composition of thawing permafrost, as indicated by rock glacial and blockfield meltwater, suggests it is the source of these weathering products. Furthermore, mass balance models indicate the high ammonium loads within glacial meltwater are rapidly nitrified, contributing ~0.5-1.4 kg N ha^-1 to the growing season nitrate flux from the alpine watershed. The sustained export of these solutes during dry, summer months is likely facilitated by thawing cryosphere providing hydraulic connectivity late into the growing season. This mechanism is further supported by the lack of upward weathering or nitrogen solute trends in a neighboring catchment which lacks permafrost and glacial features. These findings suggest that reductions of atmospheric nitrogen deposition alone may not improve water quality, as cryospheric thaw exposes soils to biological and geochemical processes that may affect alpine nitrate concentrations as much as atmospheric deposition trends. Copyright 2014 Springer International Publishing Switzerland and 2013 Springer Science+Business Media Dordrecht

DOI: 10.1007/s10533-013-9886-5

2016056550 Liljedahl, Anna K. (University of Alaska, Water and Environmental Research Centre, Fairbanks, AK); Boike, Julia; Daanen, Ronald P.; Fedorov, Alexander N.; Frost, Gerald V.; Grosse, Guido; Hinzman, Larry D.; Iijma, Yoshihiro; Jorgenson, Janet C.; Matveyeva, Nadya; Necsoiu, Marius; Raynolds, Martha K.; Romanovsky, Vladimir E.; Schulla, Jorg; Tape, Ken D.; Walker, Donald A.; Wilson, Cathy J.; Yabuki, Hironori and Zona, Donatella. Pan-Arctic ice-wedge degradation in warming permafrost and its influence on tundra hydrology: Nature Geoscience, 9(4), p. 312-318, illus. incl. sketch map, 42 ref., April 2016.

DOI: 10.1038/NGEO2674

2016062760 Jackson, Andrew (Texas Tech University, Lubbock, TX); Davila, Alfonso F.; Böhlke, John Karl; Sturchio, Neil C.; Sevanthi, Ritesh; Estrada, Nubia; Brundrett, Maeghan; Lacelle, Denis; McKay, Christopher P.; Poghosyan, Armen; Pollard, Wayne and Zacny, Kris. Deposition, accumulation, and alteration of Cl^-, NO₃^-, ClO₄^- and ClO₃^- salts in a hyper-arid polar environment; mass balance and isotopic constraints: Geochimica et Cosmochimica Acta, 182, p. 197-215, illus. incl. 2 tables, sketch map, 72 ref., June 1, 2016. Includes appendices.

The salt fraction in permafrost soils/sediments of the McMurdo Dry Valleys (MDV) of Antarctica can be used as a proxy for cold desert geochemical processes and paleoclimate reconstruction. Previous analyses of the salt fraction in MDV permafrost soils have largely been conducted in coastal regions where permafrost soils are variably affected by aqueous processes and mixed inputs from marine and stratospheric sources. We expand upon this work by evaluating permafrost soil/sediments in University Valley, located in the ultraxerous zone where both liquid water transport and marine influences are minimal. We determined the abundances of Cl^-, NO₃^-, ClO₄^- and ClO₃^- in dry and ice-cemented soil/sediments, snow and glacier ice, and also characterized Cl^- and NO₃^- isotopically. The data are not consistent with salt deposition in a sublimation till, nor with nuclear weapon testing fall-out, and instead point to a dominantly stratospheric source and to varying degrees of post depositional transformation depending on the substrate, from minimal alteration in bare soils to significant alteration (photodegradation and/or volatilization) in snow and glacier ice. Ionic abundances in the dry permafrost layer indicate limited vertical transport under the current climate conditions, likely due to percolation of snowmelt. Subtle changes in ClO₄^-/NO₃^- ratios and NO₃^- isotopic composition with depth and location may reflect both transport related fractionation and depositional history. Low molar ratios of ClO₃^-/ClO₄^- in surface soils compared to deposition and other arid systems suggest significant post depositional loss of ClO₃^-, possibly due to reduction by iron minerals, which may have important implications for oxy-chlorine species on Mars. Salt accumulation varies with distance along the valley and apparent accumulation times based on multiple methods range from ~10 to 30 kyr near the glacier to 70-200 kyr near the valley mouth. The relatively young age of the salts and relatively low and homogeneous anion concentrations in the ice-cemented sediments point to either a mechanism of recent salt removal, or to relatively modern permafrost soils (<1 million years). Together, our results show that near surface salts in University Valley serve as an end-member of stratospheric sources not subject to biological processes or extensive remobilization. Abstract Copyright (2016) Elsevier, B.V.

DOI: 10.1016/j.gca.2016.03.012

2016060649 Hindshaw, R. S. (University of Saint Andrews, Department of Earth and Environmental Sciences, Saint Andrews, United Kingdom); Lang, S. Q.; Bernasconi, S. M.; Heaton, T. H. E.; Lindsay, M. R. and Boyd, E. S. Origin and temporal variability of unusually low d¹³C-DOC values in two high Arctic catchments: Journal of Geophysical Research: Biogeosciences, 121(4), p. 1073-1085, illus. incl. 1 table, sketch maps, 84 ref., April 2016.

The stable carbon isotopic composition of dissolved organic matter (d¹³C-DOC) reveals information about its source and extent of biological processing. Here we report the lowest d¹³C-DOC values (-43.8 ppm) measured to date in surface waters. The streams were located in the High Arctic, a region currently experiencing rapid changes in climate and carbon cycling. Based on the widespread occurrence of methane cycling in permafrost regions and the detection of the pmoA gene, a proxy for aerobic methanotrophs, we conclude that the low d¹³C-DOC values are due to organic matter partially derived from methanotrophs consuming biologically produced, ¹³C-depleted methane. These findings demonstrate the significant impact that biological activity has on the stream water chemistry exported from permafrost and glaciated environments in the Arctic. Given that the catchments studied here are representative of larger areas of the Arctic, occurrences of low d¹³C-DOC values may be more widespread than previously recognized, with implications for understanding C cycling in these environments. Abstract Copyright (2016), . American Geophysical Union. All Rights Reserved.

DOI: 10.1002/2015JG003303

2016053915 Hodson, Andrew (University of Sheffield, Department of Geography, Sheffield, United Kingdom); Nowak, Aga and Christiansen, Hanne. Glacial and periglacial floodplain sediments regulate hydrologic transfer of reactive iron to a high arctic fjord: Hydrological Processes, 30(8), p. 1219-1229, illus. incl. 2 tables, sketch map, 62 ref., April 15, 2016.

The transport of reactive iron (i.e. colloidal and dissolved) by a glacier-fed stream system draining a high relief periglacial landscape in the high Arctic archipelago of Svalbard is described. A negative, non-linear relationship between discharge and iron concentration is found, indicative of increased iron acquisition along baseflow pathways. Because the glaciers are cold-based and there are no intra- or sub-permafrost groundwater springs, baseflow is principally supplied by the active layer and the colluvial and alluvial sediments in the lower valley. Collectively, these environments increase the flux of iron in the stream by 40% over a floodplain length of just 8 km, resulting in 6 kg Fe km^-2a^-1 of reactive iron export for a 20% glacierized watershed. We show that pyrite oxidation in shallow-groundwater flowpaths of the floodplain is the most important source of reactive iron, although it is far less influential in the upper parts of the catchment where other sources are significant (including ironstone and secondary oxide coatings). Microbial catalysis of the pyrite oxidation occurs in the floodplain, enabling rapid, hyporheic water exchange to enhance the iron fluxes at high discharge and cause the non-linear relationship between discharge and reactive iron concentrations. Furthermore, because the pyrite oxidation is tightly coupled to carbonate and silicate mineral weathering, other nutrients such as base cations and silica are also released to the stream system. Our work therefore shows that high Arctic floodplains should be regarded as critically important regulators of terrestrial nutrient fluxes to coastal ecosystems from glacial and periglacial sources. Copyright Copyright 2015 John Wiley & Sons, Ltd.

DOI: 10.1002/hyp.10701

2016058627 Woronko, Barbara (University of Warsaw, Faculty of Geology, Warsaw, Poland). Frost weathering versus glacial grinding in the micromorphology of quartz sand grains; processes and geological implications: Sedimentary Geology, 335, p. 103-119, illus. incl. sketch map, 124 ref., April 15, 2016.

Micromorphology of quartz sand grains is used to reconstruct processes occurring in the glacial environment and to distinguish the latter from other environments. Two processes dominate in the glacial environment, i.e., crushing and abrasion, or a combination thereof. Their effect is a wide range of microstructures on the surface of quartz grains, e.g., chattermarks, conchoidal fractures and multiple grooves. However, the periglacial environment also effectively modifies the surface of quartz grains. The active layer of permafrost is considered to have a significantly higher contribution to the formation of crushed grains and the number of microstructures resulting from mechanical destruction (e.g., breakage blocks or conchoidal fractures), as compared to deposits which are not affected by freeze-thaw cycles. However, only a few microstructures are found in both environments. At the same time, there are several processes in subglacial environments related to freeze-thaw cycles, e.g., regelation, congelation, basal adfreezing, and glaciohydraulic supercooling. Most likely, therefore, the role of the glacial environment in the destruction of quartz grains has been misinterpreted, and consequently the conclusions regarding environmental processes drawn on the basis of the number of crushed grains and edge-to-edge contacts are erroneous. Abstract Copyright (2016) Elsevier, B.V.

DOI: 10.1016/j.sedgeo.2016.01.021

2016056352 Alfredsson, Hanna (Lund University, Department of Geology, Lund, Sweden); Clymans, W.; Hugelius, Gustaf; Kuhry, P. and Conley, D. J. Estimated storage of amorphous silica in soils of the circum-Arctic tundra region: Global Biogeochemical Cycles, 30(3), p. 479-500, illus. incl. 4 tables, sketch map, 108 ref., March 2016.

We investigated the vertical distribution, storage, landscape partitioning, and spatial variability of soil amorphous silica (ASi) at four different sites underlain by continuous permafrost and representative of mountainous and lowland tundra, in the circum-Arctic region. Based on a larger set of data, we present the first estimate of the ASi soil reservoir (0-1 m depth) in circum-Arctic tundra terrain. At all sites, the vertical distribution of ASi concentrations followed the pattern of either (1) declining concentrations with depth (most common) or (2) increasing/maximum concentrations with depth. Our results suggest that a set of processes, including biological control, solifluction and other slope processes, cryoturbation, and formation of inorganic precipitates influence vertical distributions of ASi in permafrost terrain, with the capacity to retain stored ASi on millennial timescales. At the four study sites, areal ASi storage (0-1 m) is generally higher in graminoid tundra compared to wetlands. Our circum-Arctic upscaling estimates, based on both vegetation and soil classification separately, suggest a storage amounting to 219 ± 28 and 274 ± 33 Tmol Si, respectively, of which at least 30% is stored in permafrost. This estimate would account for about 3% of the global soil ASi storage while occupying an equal portion of the global land area. This result does not support the hypothesis that the circum-Arctic tundra soil ASi reservoir contains relatively higher amounts of ASi than other biomes globally as demonstrated for carbon. Nevertheless, climate warming has the potential to significantly alter ASi storage and terrestrial Si cycling in the Arctic. Abstract Copyright (2016), . The Authors.

DOI: 10.1002/2015GB005344

2016062880 Chen, Albert (Stanford University, Department of Geophysics, Stanford, CA); Parsekian, Andrew D.; Schaefer, Kevin; Jafarov, Elchin; Panda, Santosh; Liu, Lin; Zhang, Tingjun and Zebker, Howard. Ground-penetrating radar-derived measurements of active-layer thickness on the landscape scale with sparse calibration at Toolik and Happy Valley, Alaska: Geophysics, 81(2), p. H9-H19, illus., 39 ref., March 2016.

Active-layer thickness (ALT) is an important parameter for studying surface energy balance, ecosystems, and hydrologic processes in cold regions. We measured ALT along 10 routes with lengths ranging from 0.7 to 6.9 km located on the Alaska North Slope near Toolik Lake and the Happy Valley airstrip (between 68.475° and 69.150°N, and - 149.512° and - 148.769°E). Using a ground-penetrating radar (GPR) system in a common-offset configuration, we measured the two-way traveltimes from the surface to the bottom of the active layer at the end of summer, when the thaw depth was greatest. We used 500 and 800 MHz antennas; the 500 MHz antenna provided suitable vertical resolution, while producing more unambiguous active-layer reflections in the presence of nonideal antenna coupling and active layer inhomogeneity. We derived ALT measurements and their uncertainties from GPR two-way traveltimes, with mechanical probing for velocity calibration. Using an empirical relationship between the wave velocity and soil volumetric water content (VWC), we found that the velocities were consistent with soil VWCs ranging from 0.46 to 0.63. In 31% of traces, the permafrost table horizon was identifiable, resulting in ALT measurements with uncertainties of generally less than 25%. The average ALT was 48.1 cm, with a standard deviation of 16.1 cm. We found distinct patterns of ALT spatial variability at different sites and different length scales. At some sites, the ALT at one point was effectively uncorrelated with ALT at other points separated by lag distances as small as tens of meters; for other sites, there was correlation at lag distances up to approximately 400 m. The ALT statistics were similar to nearby long-term in situ ALT measurements from the Circumpolar Active Layer Monitoring Network, through which yearly ALT measurements have been made since 1990.

DOI: 10.1190/geo2015-0124.1

2016053778 Gao Tanguang (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Zhang Tingjun; Wan Xudong; Kang Shichang; Sillanpaa, Mika; Zheng Yanmei and Cao Lin. Influence of microtopography on active layer thaw depths in Qilian Mountain, northeastern Tibetan Plateau: Environmental Earth Sciences, 75(5), Article 382, illus. incl. 2 tables, sketch map, 52 ref., March 2016.

Climate warming over the Tibetan Plateau has been thickening the active layer, the most significant indicator of the permafrost system. This study evaluates the influence of microtopography on active layer thaw depth in recent years at Eboling basin of the eastern Qilian Mountain, northeastern Tibetan Plateau. Thaw depths were measured at microtopographic levels in 2012, 2013, and 2014, respectively. Watershed-scale sampling was used to estimate the influence of various morphologies on the active layer, while a second sampling scheme to examine the variations in the frost table height along six short transects. A third sampling scheme used spatial autocorrelation analysis in a regular grid at 10 ´ 10 m intervals. The results documented that microtopography (elevation, microrelief, surface configuration, and slope) played a pivotal role on the active layer thickness of mountainous permafrost in the study area. Active layer became thinner in depressions, which was contrary to most of Arctic sites. Spatial autocorrelation analysis elucidated that the dominant topographic factors controlled the changes of active layer thickness. These factors exerted the majority of control over the spatial variations of the active layer. The results can help researchers or engineers to roughly estimate the probable influence of micromorphology on the changes in thickness of the active layer in mountainous permafrost regions in the Tibetan Plateau. Copyright 2016 Springer-Verlag Berlin Heidelberg

DOI: 10.1007/s12665-015-5196-7

2016057124 Monnier, Sébastien (Universidad Católica de Valparaíso, Instituto de Geografía, Valparaiso, Chile) and Kinnard, Christophe. Reconsidering the glacier to rock glacier transformation problem; new insights from the Central Andes of Chile: Geomorphology, 238, p. 47-55, illus. incl. 2 tables, sketch maps, 75 ref., June 1, 2015.

The glacier to rock glacier transformation problem is revisited from a previously unseen angle. A striking case in the Juncal Massif (located in the upper Aconcagua Valley, Chilean central Andes) is documented. There, the Presenteseracae debris-covered glacier has advanced several tens of metres and has developed a rock glacier morphology in its lower part over the last 60 years. The conditions for a theoretically valid glacier to rock glacier transformation are discussed and tested. Permafrost probability in the area of the studied feature is highlighted by regional-scale spatial modelling together with on-site shallow ground temperature records. Two different methods are used to estimate the mean surface temperature during the summer of 2014, and the sub-debris ice ablation rates are calculated as ranging between 0.05 and 0.19 cm d^-1, i.e., 0.04 and 0.17 m over the summer. These low ablation rates are consistent with the development of a coherent surface morphology over the last 60 years. Furthermore, the rates of rock wall retreat required for covering the former glacier at Presenteseracae lie within the common 0.1-2 mm y^-1 range, assuming an average debris thickness and a range of debris-covering time intervals. The integration of the geomorphological observations with the numerical results confirms that the studied debris-covered glacier is evolving into a rock glacier. Abstract Copyright (2015) Elsevier, B.V.

DOI: 10.1016/j.geomorph.2015.02.025

2016061380 Batenipour, Hamid (University of Manitoba, Civil Engineering Department, Winnipeg, MB, Canada); Alfaro, Marolo; Kurz, David and Graham, Jim. Deformations and ground temperatures at a road embankment in northern Canada: Canadian Geotechnical Journal = Revue Canadienne de Géotechnique, 51(3), p. 260-271, illus. incl. 4 tables, 29 ref., March 2014.

The paper examines the behaviour of a highway embankment in an area of discontinuous permafrost about 18 km northwest of Thompson, Manitoba. Frequent maintenance has been required. Research involved site investigation, laboratory testing, installing instruments, data collection, and numerical modeling. The paper reports data from almost 3 years of observation. Measurements of ground temperatures suggest that formerly ice-rich foundation soil has thawed under the toe and side-slope. Approximate values of segregation potential have been back-calculated from observations of settlements and temperatures. Results provide insight into the nature and cause of deformations of the embankment.

DOI: 10.1139/cgj-2012-0425

2016054681 Harms, Tamara K. (University of Alaska Fairbanks, Department of Biology and Wildlife, Fairbanks, AK); Abbott, Benjamin W. and Jones, Jeremy B. Thermo-erosion gullies increase nitrogen available for hydrologic export: Biogeochemistry (Dordrecht), 117(2-3), p. 299-311, illus. incl. 2 tables, sketch map, 57 ref., March 2014.

Formation of thermokarst features, ground subsidence caused by thaw of ice-rich permafrost, can result in increased export of inorganic nitrogen (N) from arctic tundra to downstream ecosystems. We compared physical characteristics, N pools, and rates of N transformations in soils collected from thermo-erosion gullies, intact water tracks (the typical precursor landform to thermo-erosion gullies), and undisturbed tundra to test potential mechanisms contributing to export of inorganic N. Subsidence exposes mineral soils, which tend to contain higher abundance of inorganic ions relative to surface soils, and may bring inorganic N into contact with flowing water. Alternatively, physical mixing may increase aeration and drainage of soils, which could promote N mineralization and nitrification while suppressing denitrification. Finally, some soil types are more prone to formation of thermokarst, and if these soils are relatively N-rich, thermokarst features may export more N than surrounding tundra. Inorganic N pools in thermo-erosion gullies were similar to the mean for all tundra types in this region, as well as to water tracks when integrated across two sampled depths. Thus, soils prone to thermo-erosion are not intrinsically N-rich, and increased N availability in thermokarst features is apparent only at sub-regional spatial scales. However, vertical profiles of N pools and transformation rates were homogenized within thermo-erosion gullies compared to adjacent intact tundra, indicating that physical mixing brings inorganic N to the surface, where it may be subject to hydrologic export. Increased inorganic N availability caused by formation of thermo-erosion gullies may have acute, localized consequences for aquatic ecosystems downstream of positions within drainage networks that are susceptible to thermo-erosion. Copyright 2014 Springer International Publishing Switzerland and 2013 Springer Science+Business Media Dordrecht

DOI: 10.1007/s10533-013-9862-0

2016058707 Armstrong McKay, David I. (University of Southampton, National Oceanography Centre, Southampton, United Kingdom); Tyrrell, Toby and Wilson, Paul A. Global carbon cycle perturbation across the Eocene-Oligocene climate transition: Paleoceanography, 31(2), p. 311-329, illus., 86 ref., February 2016.

The Eocene-Oligocene transition (EOT), ~34 Ma, marks a tipping point in the long-term Cenozoic greenhouse to icehouse climate transition. Paleorecords reveal stepwise rapid cooling and ice growth across the EOT tightly coupled to a transient benthic d¹³C excursion and a major and permanent deepening of the carbonate compensation depth (CCD). Based on biogeochemical box modeling, Merico et al. (2008) suggested that a combination of (1) glacioeustatic sea level fall-induced shelf-basin carbonate burial fractionation and (2) shelf carbonate weathering can account for the carbon cycle perturbation, but this finding has been questioned. Alternative proposed mechanisms include increased ocean ventilation, decreased carbonate burial, increased organic carbon burial, increased silicate weathering, and increased ocean calcium concentration. Here we use an improved version of the biogeochemical box model of Merico et al. (2008) to reevaluate these competing hypotheses and an additional mechanism, the expansion of "carbon capacitors" such as permafrost and peatlands. We find that changes in calcium concentration, silicate weathering, and carbonate or organic carbon burial each yield a response that is fundamentally at odds with the form and/or sign of the paleorecords. Shelf-basin carbonate burial fractionation (CCD change), plus shelf carbonate weathering, sequestration of ¹²C-enriched carbon into carbon capacitors, and possibly increased ocean ventilation (d¹³C excursion), offers the best fit to the paleorecords. Further work is needed to understand why the EOT carbon cycle perturbation is so unique when the forcing mechanisms hypothesized to be responsible (cooling and ice growth) are not peculiar to this event. Abstract Copyright (2016), . The Authors.

DOI: 10.1002/2015PA002818

2016060491 Clow, Gary D. (U. S. Geological Survey, Boulder, CO). A Green's function approach for assessing the thermal disturbance caused by drilling deep boreholes in rock or ice: Geophysical Journal International, 203(3), p. 1877-1895, illus. incl. 2 tables, 20 ref., December 2015.

A knowledge of subsurface temperatures in sedimentary basins, fault zones, volcanic environments and polar ice sheets is of interest for a wide variety of geophysical applications. However, the process of drilling deep boreholes in these environments to provide access for temperature and other measurements invariably disturbs the temperature field around a newly created borehole. Although this disturbance dissipates over time, most temperature measurements are made while the temperature field is still disturbed. Thus, the measurements must be 'corrected' for the drilling-disturbance effect if the undisturbed temperature field is to be determined. This paper provides compact analytical solutions for the thermal drilling disturbance based on 1-D (radial) and 2-D (radial and depth) Green's functions (GFs) in cylindrical coordinates. Solutions are developed for three types of boundary conditions (BCs) at the borehole wall: (1) prescribed temperature, (2) prescribed heat flux and (3) a prescribed convective condition. The BC at the borehole wall is allowed to vary both with depth and time. Inclusion of the depth dimension in the 2-D solution allows vertical heat-transfer effects to be quantified in situations where they are potentially important, that is, near the earth's surface, at the bottom of a well and when considering finite-drilling rates. The 2-D solution also includes a radial- and time-dependent BC at the earth's surface to assess the impact of drilling-related infrastructure (drilling pads, mud pits, permanent shelters) on the subsurface temperature field. Latent-heat effects due to the melting and subsequent refreezing of interstitial ice while drilling a borehole through ice-rich permafrost can be included in the GF solution as a moving-plane heat source (or sink) located at the solid-liquid interface. Synthetic examples are provided illustrating the 1-D and 2-D GF solutions. The flexibility of the approach allows the investigation of thermal drilling effects in rock or ice for a wide variety of drilling technologies. Numerical values for the required radial GFs G_R are available through the Advanced Cooperative Arctic Data and Information Service at doi:10.5065/D64F1NS6.

URL: http://gji.oxfordjournals.org/content/203/3/1877.abstract

2016057215 Sitzia, Luca (Université Bordeaux, Pessac, France); Bertran, Pascal; Bahain, Jean-Jacques; Bateman, Mark D.; Hernandez, Marion; Garon, Henri; de Lafontaine, Guillaume; Mercier, Norbert; Leroyer, Chantal; Queffelec, Alain and Voinchet, Pierre. The Quaternary coversands of southwest France: Quaternary Science Reviews, 124, p. 84-105, illus. incl. 3 tables, sketch map, 167 ref., September 15, 2015.

Detailed stratigraphic analysis and numerical dating (OSL, IRSL, ESR, ¹⁴C) of Pleistocene coversands in southwest France enable the construction of a renewed chronostratigraphic framework for sand deposition. The chronological data obtained from sandsheet units testify to the development of transgressive dunefields since at least the Middle Pleistocene (MIS 10). Three main phases of accumulation occurred during the Last Glacial. The oldest one (64-42 ka) is associated with wet sandsheet facies, histic horizons and zibar-type dune fields, which reflect deposition in a context strongly influenced by the groundwater table. The Late Pleniglacial (24-14 ka) corresponds to the main phase of coversand extension in a drier context. Silty gley horizons suggest, however, local interruptions of sand drifting during GS 2.1. Lateglacial stabilization of the coversands may not have occurred before GI-1c (Allerod), which was typified by the development of cumulic arenosols. These were covered by parabolic dunes during the Younger Dryas. The variations in extent of the emerged continental shelf during the glacial-interglacial cycles may explain the uneven geographical distribution of sand deposition through time. Because of coastline retreat up to 100 km north of 45°N during the LGM lowstand, the coversands were unable to reach the northern part of the basin. Comparison with other European regions highlights stronger affinities of the French record with Portugal than with the Netherlands and Great Britain, probably because of reduced influence of permafrost. Abstract Copyright (2015) Elsevier, B.V.

DOI: 10.1016/j.quascirev.2015.06.019

2016062858 Bergamo, Paolo (Queen's University Belfast, School of Planning, Architecture, Civil Engineering, Belfast, United Kingdom); Dashwood, Ben; Uhlemann, Sebastian; Swift, Russell; Chambers, Jonathan E.; Gunn, David A. and Donohue, Shane. Time-lapse monitoring of climate effects on earthworks using surface waves: Geophysics, 81(2), p. EN1-EN15, illus., 59 ref., March 2016.

The UK's transportation network is supported by critical geotechnical assets (cuttings/embankments/dams) that require sustainable, cost-effective management, while maintaining an appropriate service level to meet social, economic, and environmental needs. Recent effects of extreme weather on these geotechnical assets have highlighted their vulnerability to climate variations. We have assessed the potential of surface wave data to portray the climate-related variations in mechanical properties of a clay-filled railway embankment. Seismic data were acquired bimonthly from July 2013 to November 2014 along the crest of a heritage railway embankment in southwest England. For each acquisition, the collected data were first processed to obtain a set of Rayleigh-wave dispersion and attenuation curves, referenced to the same spatial locations. These data were then analyzed to identify a coherent trend in their spatial and temporal variability. The relevance of the observed temporal variations was also verified with respect to the experimental data uncertainties. Finally, the surface wave dispersion data sets were inverted to reconstruct a time-lapse model of S-wave velocity for the embankment structure, using a least-squares laterally constrained inversion scheme. A key point of the inversion process was constituted by the estimation of a suitable initial model and the selection of adequate levels of spatial regularization. The initial model and the strength of spatial smoothing were then kept constant throughout the processing of all available data sets to ensure homogeneity of the procedure and comparability among the obtained V_S sections. A continuous and coherent temporal pattern of surface wave data, and consequently of the reconstructed V_S models, was identified. This pattern is related to the seasonal distribution of precipitation and soil water content measured on site.

DOI: 10.1190/geo2015-0275.1

2016053719 Jamshidi, Amin (Lorestan University, Department of Geology, Khorramabad, Iran); Nikudel, Mohammad Reza and Khamehchiyan, Mashalah. Evaluation of the durability of Gerdoee travertine after freeze-thaw cycles in fresh water and sodium sulfate solution by decay function models: Engineering Geology, 202, p. 36-43, illus. incl. 4 tables, sketch map, 46 ref., March 4, 2016.

The reduced durability and service life of stones subjected to freeze-thaw action are significant and ongoing problems in stones used for commercial purposes such as building stones. Consequently, evaluating the durability of building stones subjected to freeze-thaw action is important for selecting of an appropriate stone for outdoor applications in cold climatic conditions, which involve excessive freeze-thaw cycles. In this research, the durability of Gerdoee travertine (northwest of Iran), after freeze-thaw cycles in fresh water and sodium sulfate solution (Na₂SO₄), was evaluated using its mechanical properties as well as decay constant (l) and half-time (N_1/2) parameters. For this, freeze-thaw tests in fresh water and sodium sulfate solution were carried out up to 60 cycles, and the uniaxial compressive strength, Brazilian tensile strength, point load strength and ultrasonic wave velocity (quantifying by P-wave velocity) of the travertine were determined after every 10 cycles. Finally, regression models were developed between the measured mechanical properties and various cycles of tests. The models postulate a first order process, and provide meaningful parameters of decay constant (l) and half-time (N_1/2) for the integrity loss of travertine's mechanical properties, and thus its durability, after freeze-thaw action. Using data analysis, the variation in the travertine's mechanical properties and their decay constant (l) and half-time (N_1/2) show that the travertine's durability after the freeze-thaw action in fresh water and sodium sulfate solution was different. Further, it was found that the effect of freeze-thaw action on the travertine's durability was more severe in sodium sulfate solution as compared with fresh water.

DOI: 10.1016/j.enggeo.2016.01.004

2016059710 Friel, Charlotte E. (University of Toronto, Department of Earth Sciences, Toronto, ON, Canada); Finkelstein, Sarah A. and Davis, Anthony M. Relative importance of hydrological and climatic controls on Holocene paleoenvironments inferred using diatom and pollen records from a lake in the central Hudson Bay Lowlands, Canada: Holocene, 24(3), p. 295-306, illus. incl. 2 tables, sketch map, 73 ref., March 1, 2014.

Postglacial paleoenvironmental changes and landscape development in the Hudson Bay Lowlands in subarctic Canada were inferred using sediment properties and diatom and pollen assemblages in the sediments of a lake raised above the surrounding peatlands in an ice-marginal landform. Coarse-grained, inorganic sediments at the base of the Lake AT01 core suggest a high-energy periglacial environment, following isostatic emergence from Hudson Bay around 6840 cal. BP. Initial diatom assemblages dominated by Fragilaria spp., and pollen of Shepherdia canadensis, indicate early successional conditions in a recently deglaciated environment. Around 6200 cal. BP, tychoplanktonic Fragilarioid diatoms are replaced by large benthics. Coincident increases in Equisetum spores, Cyperaceae pollen and sediment organic matter suggest the establishment of a more productive macrophyte-rich shallow lake. While the Holocene Thermal Maximum and subsequent Neoglacial may have contributed to these shifts, pollen and diatom records suggest only subtle responses to Holocene climatic changes. A core chronology inferred from radioisotopes suggests a hiatus in sediment accumulation between 3650 and 200 cal. BP. Peaks in carbonate inferred from loss-on-ignition and increases in bulk density in that section of the core suggest some effect of erosional or thermokarst processes, or the breaching of a sandbar, now a remnant island in the lake, in the drainage of the lake and ensuing hiatus. Sediment accumulation resumed within the past two centuries; diatom assemblages in the uppermost section are characterized initially by benthic diatoms of smaller valve size compared with the pre-hiatus assemblages. More recently, increases in the planktonic diatom Cyclotella stelligera are recorded, signaling significant environmental changes.

DOI: 10.1177/0959683613518587

2016062251 Cheng Xuelei (Tianjin Institute of Urban Construction, Department of Civil Engineering, Tianjin, China); Li Shunqun and Sun Shijuan. Application of principal component analysis in the microstructure of frozen soil: The Electronic Journal of Geotechnical Engineering, 18(Bundle I), p. 1801-1811, illus. incl. 7 tables, 17 ref., 2013. WWW.

The strength of ice and frozen soil interaction is depended on the water content and the temperature of the environment, the principal component analysis is used to analyze the effects of temperature and pressure on the strength of frozen soil through triaxial test simulation and its microstructure parameters. Studies display that the message superposition is clear and severe among micro structural parameters. The first, the second and the third principal components, whose accumulative contribution is 95%, can exhibit almost all messages expressed by 11 original microstructure parameters. The proposed method can be employed to establish the principal components for any kind of soil even it is illustrated by the given clay samples. At a constant temperature, the shear strength of sample increases with the confining pressure; In constant confining pressure, shear strength of frozen soil increases with decreasing temperature. From the analysis of the microstructure of principal components of soil, the decrease of temperature and the increase of confining pressure has little effect on the number of soil particles, but the effect on the other parameters of soil particles.

URL: http://www.ejge.com/2013/Ppr2013.158alr.pdf

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2016058345 Biller, Nicole (Boston College, Chestnut Hill, MA); Shakun, Jeremy D.; McGee, David; Hardt, Benjamin F.; Ford, Derek and Lauriol, Bernard. Pleistocene permafrost thawing history of Alaska, the Yukon, and the Northwest Territories from U-Th dating of cave speleothems [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract PP33A-2276, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

Permafrost, or permanently frozen ground, is widespread in the Arctic and contains twice as much carbon as the atmosphere in the form of frozen organic matter. This carbon may be vulnerable to thaw and release to the atmosphere as methane under a warming climate, making permafrost thaw one of the potentially most significant amplifying feedbacks to anthropogenic warming. Nonetheless, permafrost can be slow to respond to warming, the short instrumental record may not adequately capture long-term trends, and the modest temperature changes of the past few millennia provide poor analogues to understand the possibility of crossing climate thresholds in the next century or beyond. One way to address this problem is to assess the stability of permafrost during previous interglacial periods of varying levels of warmth, which provide natural experiments to examine the Arctic's sensitivity to warming. Cave speleothems in the Arctic are relics of past periods of thaw that enabled meteoric water to seep into caves and deposit calcite. We employed uranium-thorium (U-Th) dating to constrain the chronology and extent of permafrost thaw in the North American Arctic during the past 600,000 years. We sampled caves from a range of permafrost zones and latitudes, including the Fishing Branch Territorial Park, Yukon (66.5°N, continuous permafrost), White Mountains National Recreation Area, Alaska (65°N, discontinuous permafrost), Yukon-Charley Rivers National Preserve, Alaska (64.5°N, discontinuous permafrost), and Nahanni National Park Reserve, Northwest Territories (62°N, discontinuous permafrost). Thirty-five samples from 30 speleothems have been analyzed at this point, with 23 samples lying beyond the U-Th dating range, and finite ages tending to cluster near Marine Isotope Stage 11 (MIS 11) within uncertainty, as well as perhaps MIS 9, 13, and 15. This preliminary dataset, coupled with a similar study in Siberia (Vaks et al., 2013), is thus suggestive of an episode of widespread thaw during the MIS 11 interglacial about 400,000 years ago when global temperature was only ~1°C warmer than pre-industrial temperatures. We anticipate dating more speleothems in the months prior to AGU, and exploring the use of U-Pb for older samples.

2016053346 Bohn, T. J. (Arizona State University, Tempe, AZ). Exploring the impacts of climate change and permafrost thaw on microlandscapes, plant species, and carbon cycling of West Siberian peatlands [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract C21E-04, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

Methane emissions from northern peatlands depend strongly on environmental conditions, wetland plant species assemblages (via root zone oxidation and plant-aided transport), and soil microbial behavior (via metabolic pathways). Potential future changes in high-latitude climate are expected to include permafrost thaw and thermokarst formation, which may change the distribution of microlandscapes such as hummocks and hollows (and plant species therein) within peatlands. While the responses of wetland methane emissions to potential future climate change have been extensively explored, the effects of future changes in plant species and soil microbial metabolism are not as well studied. We ran the Variable Infiltration Capacity (VIC) land surface model over the West Siberian Lowland (WSL), with methane emissions parameters that vary spatially as a function of microlandscape and the dominant plant species therein, and forced with outputs from 32 CMIP5 models for the RCP4.5 scenario. Here we compare the effects of changes in climate, microlandscapes, and vegetation on predicted wetland CH4 emissions for the period 2071-2100, relative to the period 1981-2010, in terms of both total annual emissions and the spatial distribution of emissions. We also explore possible acclimatization of soil microbial communities to these changes. Our work indicates the importance of better constraining the responses of wetland plants and soil microbial communities to changes in climate as they are critical determinants of the region's future methane emissions.

2016060000 Chasmer, Laura (University of Lethbridge, Lethbridge, AB, Canada) and Hopkinson, Chris. Accelerating rates of discontinuous permafrost thaw associated with ground surface morphology and changing vegetation structures determined from multi-temporal lidar data [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B51G-0518, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

Rates of permafrost thaw within the discontinuous permafrost zone are expected to accelerate with permafrost fragmentation. However quantification of drivers of permafrost change remain elusive due to the non-linearity of feedbacks in space and time. Given the extent of permafrost in Canada, there is significant interest in the mechanisms associated with land cover change as climate change and disturbance intensifies.We quantify the variability of rates of thaw associated with structural characteristics of the land surface within a discontinuous permafrost watershed in the NWT, Canada. Results are compared to an isolated permafrost watershed in Alberta, which may exemplify the northern discontinuous landscape in ~350 years. Three airborne Light Detection And Ranging (LiDAR) datasets have been collected in 2008, 2011 and 2015, coincident with digital photogrammetry (2008), thermal infrared (2011) and bathymetry (2015) within both watersheds. Rates of change of land elevation associated with permafrost thaw within plateaus and peatlands are quantified using non-linear spatial regression, and compared with topographic and vegetation derivatives. Results indicate that increasing fragmentation of discontinuous permafrost plateaus results in exponential thaw. Rates of thaw become linear with decreasing complexity. Accelerating thaw is related to substantial Picea mariana mortality (up to 45%), increased gap fraction within 1-2 m of plateau edges, and shrub succession (average growth ~0.2 m yr-1) at the 0-2m boundary within the 7-year period. Thaw rate in parts is also complicated by understory succession within the area of local convexity between the plateau and slope edge and linear thaw pathways. Greatest rates of thaw and vegetation mortality (~30-50%) are found on plateaus with populous tremuloides. In the central boreal watershed, vegetation succession at peatland margins is associated with increased drying and changes to runoff trends over the last 40 years. Increased channelization of runoff along plateau and fen flow pathways combined with growth of short vascular vegetation may increase drying and promote rapid succession. A simple model indicates that the discontinuous permafrost zone could be similar to that of the central boreal forest in less than 300 years.

2016060113 Enders, Sara K. (Oregon State University, Davis, CA); Houlton, B. Z.; Ohkouchi, N.; Wagner, Dirk; Ogawa, N. O.; Chikaraishi, Y. and Suga, H. Reconstructing 40 ky of N cycling from stable isotopes of plant compounds in a Siberian permafrost soil [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract PP41B-2239, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

Terrestrial nitrogen (N) cycling has an important dual role in regulating global climate, as N is both a limiting plant nutrient and a constituent of a potent greenhouse gas. Reconstructing past terrestrial N cycling is a valuable complement to experimental manipulation of complex climate-carbon-N interactions, but has been challenged by shortcomings of available proxies. We here examine 40 y of terrestrial N cycling on the landscape of northeast Siberia as recorded in N-isotopes of chlorophyll degradation products preserved in a permafrost soil core. This dataset gives insight into the response of the N cycle to concurrent changes in climate, plant community, and atmospheric pCO₂ that accompany a cycle of glaciation. This study is the first application to temporal reconstruction of this compound-specific, soil-based proxy for an integrated foliar N isotope signal. We infer ~10 per mil swings in foliar N-isotope values at this site, pointing to the sensitivity of denitrification at high latitudes to changes in environmental conditions. We further observe the effect of increases in N-fixing species on stimulating N cycling as recorded by our proxy. We do not see an effect of progressive N limitation due to pre-anthropogenic increases in pCO₂ accompanying deglaciation.

2016058313 Gaglioti, Benjamin (University of Alaska Fairbanks, Fairbanks, AK); Mann, Daniel H.; Wooller, Matthew J.; Jones, Benjamin M.; Farquharson, Louise Melanie and Pohlman, John. Sensitivity of permafrost carbon release to past climate change in Arctic Alaska [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract PP31D-02, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

Warming may cause arctic permafrost to thaw and release large stores of carbon (C) downstream and into the atmosphere. Documenting how permafrost-C release responded to prehistoric warming events can help determine its sensitivity to future climate change. We did this by first quantifying past climate change in Arctic Alaska over the last 15,000 years using oxygen isotope ratios in ancient wood cellulose, which is a proxy for summer temperatures and moisture sources. We then used radiocarbon (¹⁴C) age-offsets in lake sediment to determine how much permafrost C was being released over this same time period. A ¹⁴C age-offset is the difference between the true age of deposition determined by the ¹⁴C ages of delicate, terrestrial plant remains and the age of bulk sediment from the same stratigraphic layer. This bulk sediment contains ancient C derived from permafrost in the lake's watershed. Shifts in the magnitude of the age-offset over time provide a proxy for changes in the relative amount of permafrost C being released. Today, the age-offset in our study lake is 2,000 calibrated years before present (cal yr BP), which is the lowest it has been over the last 15,000 years. During the warmer-than-present, Bolling-Allerod period (BA; 14,700-12,900 cal yr BP), and the Holocene Thermal Maximum (HTM; 11,700-8,500 cal yr BP), the age offset reached 4,000-6,000 cal yr, indicating large inputs of ancient C to the lake via permafrost thaw. This enhanced input of ancient C was interrupted during the cold and dry Younger Dryas interval (YD; 12,900-11,700 cal yr BP). Interestingly, age-offsets during the YD were similar to today's, suggesting that the insulating peat layer now covering much of the LOP watershed is stabilizing permafrost C in the face of recent warming. However, this buffering capacity has a limit, and judging by the heightened influx of permafrost C during the HTM, this limit may be reached if summer temperatures warm a further 2-3°C. Temperature and effective moisture responses to sea ice loss in the region was a likely mechanism that controlled the sensitivity of ancient carbon release to past climate forcing.

2016053201 Hodgkins, S. B. (Florida State University, Tallahassee, FL); Chanton, J.; Tfaily, M. M.; Wilson, R.; Crill, P. M.; Saleska, S. R.; Rich, V. I. and Cooper, W. T. Changes in peat humification due to permafrost thaw and plant succession [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B11H-0539, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

The potential release of carbon from thawing permafrost peatlands is a major global change uncertainty. In addition to releasing old carbon from permafrost, thaw can also induce changes in hydrology that affect the aboveground plant community, leading to changes in litter quality and organic matter degradability. Stordalen Mire is a peat plateau in northern Sweden where permafrost thaw has led to land subsidence and inundation, causing dry palsas with intact permafrost to be replaced by Sphagnum-dominated bogs followed by sedge-dominated fens. In this study, we examined trends in solid phase peat humification along this permafrost thaw succession using a combination of C/N ratios and Fourier transform infrared (FTIR) spectroscopy. C/N ratios decreased with depth in all sites except fens, likely due to N immobilization during decomposition. In fens, depth trends in C/N ratios were complicated by the presence of Sphagnum-derived peat at depth. However, %N (by weight) at all sites was positively correlated with peat humification indices (HI), which indicate the degree of decomposition and are defined based on FTIR spectra as the ratios of absorbance at wavenumbers 1515, 1630, 2850, and 2920 cm-1 (aromatics and aliphatics) to the absorbance at 1030 cm-1 (polysaccharides). Each of these HI was inversely related to the prevalence of the carboxylic acid peak at 1720 cm-1, and this trend became weaker along the permafrost thaw gradient. This result suggests that decomposition at the early thaw stages is inhibited by organic acids, but this effect becomes less significant as thaw-induced plant succession leads to lower acidity. All of these trends in HI were strongest for the HI defined at 1630 and 1515 cm-1 (representing aromatics), indicating that peat humification at Stordalen is primarily characterized by relative increases in aromatic compounds compared to carbohydrates, with less pronounced relative increases in lipids and other aliphatics (2850 and 2920 cm-1).

2016053340 Kholodov, A. L. (University of Alaska Fairbanks, Fairbanks, AK); Liljedahl, A. K.; Chamberlain, A. J.; Romanovsky, V. E. and Cable, W. Impact of shallow water bodies on the permafrost temperature and estimation of risk of thermokarst development at the Barrow Environmental Observatory area [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract C21C-0755, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

Extension of the thermokarst features such as lakes and ponds had been noticed in many regions of the Arctic affected by the modern climate warming. Thermokarst is a process of permafrost thawing under the water bodies with depths larger than maximal thickness of seasonal ice in the area, i.e. with permanent positive temperature at the bottom. This process is most probable in the areas where massive ice bodies (wedges, lenses, layers etc.) or ice rich deposits exist close to ground surface and even insignificant increasing of thaw depth can lead to its melting and surface subsidence. Local depressions such as low-centered polygonal ponds or interpolygonal troughs can potentially become triggers of thermokarst development. Current research was aimed on determination of warming impact of small water bodies on the permafrost temperature and seasonal thawing and estimation of risk of thermokarst development at Barrow Environmental Observatory area. Comparison of temperature measurements under shallow (10 - 40 cm deep) with relatively dry spots and active layer thickness survey show that warming impact of small water bodies (mean annual temperature at the permafrost table here is up to 2°C higher then under "dry" geomorphological features) is not realized in increasing of the thawing depth. Active layer thickness does not exceed values of 45 cm under polygonal ponds and 35 cm under troughs that is less then thickness of protective layer above ice wedges in the area. For estimation of risk of thermokarst development we used analytical equations developed by V. Kudryavtsev (1974). Results of calculations show that in this area crucial depth of water bodies required for mean annual temperature at the bottom of the pond became higher then freezing point consists of 0.95 cm. Current research was supported by US DOE as a part of research project Next Generation of Ecosystem Experiment (NGEE).

2016053199 O'Donnell, J. A. (National Park Service Fairbanks, Fairbanks, AK); Aiken, G.; Butler, K. D. and Swanson, D. K. Dissolved organic matter composition of Arctic rivers; linking permafrost, parent material, and groundwater to riverine carbon [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B11G-0522, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

Recent warming in the Arctic is modifying the chemical composition of riverine dissolved organic matter (DOM) through changes in growing season length, wildfire, and permafrost thaw. In arctic rivers, DOM composition is an important control on nutrient availability, trace metal mobilization, and greenhouse gas emissions. As a result, shifts in DOM associated with a changing arctic landscape may alter how aquatic ecosystems function in this region. Here, we examined spatial variation in DOM composition in 72 rivers in the Brooks Range and Seward Peninsula of northern Alaska. We characterized DOM using a suite of techniques, including dissolved organic carbon (DOC) concentration, absorbance spectra, fluorescence, and chemical fractionation. Watersheds were classified based on traits that influence subsurface hydrology, including parent material (volcanic deposits, loess, sand, glacial moraine, bedrock) and permafrost extent (continuous vs. discontinuous zone) and state (ice-rich vs. ice-poor). We observed considerable variability in DOM composition across rivers. DOC concentrations were lowest in rivers influenced by glacial deposits (<2 mgC L-1) and highest in rivers draining lowland tundra or extensive wetlands (>10 mgC L-1). Specific ultraviolet absorbance (SUVA254), which serves as an index of DOM aromaticity, was also variable across rivers; spring-fed mountain streams had the lowest SUVA254 values (<1.5 L mgC-1 m-1), whereas tundra and wetland-dominated streams had the highest values (>4 L mgC-1 m-1). While hydrophobic organic acids were the dominant DOM fraction in all rivers, we observed a significant increase in the proportion of hydrophilic compounds during winter flow and in groundwater-fed systems. We also observed variation in DOM composition with permafrost extent and ground ice distribution across the region. Model projections over the next century suggest a heterogeneous response of DOM to thaw, likely mediated by spatial variations in ground ice and parent material.

2016053347 Peterson, R. (University of Alaska Fairbanks, Fairbanks, AK); Garber-Slaght, R. and Daanen, R. P. Effects of a ground source heat pump in discontinuous permafrost [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract C21E-06, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

A ground source heat pump (GSHP) was installed in a discontinuous permafrost region of Fairbanks Alaska in 2013 with the primary aim of determining the effect of different ground cover options on the long-term subterranean temperature regime. Three different surface treatments were applied to separate loops of the GSHP; grass, sand, and gravel, and temperature monitoring was established at several depths above and below the heat sink loops. The GSHP has been actively utilized to supplement the heat in a hydronic heating system of a neighboring 5000 ft2 research facility. The ground immediately surrounding the GSHP was not permafrost when initially installed. Numerical modeling simulations were used to predict the long-term ground temperature regime surrounding the GSHP loops, and results indicate that permafrost would begin to form after the first year. A pseudo-steady state temperature regime would establish in approximately 8 years with a yearly fluctuation of -14°C to -2°C. Simulations also indicate that permafrost could be prevented with a 15 W/m recharge during the summer, such as from a solar thermal system. The ground surface treatments have negligible effect on the ground temperature below 1 meter and therefore have no long-term effect on the active region the GSHP. Data collected from thermistors in the two years since installation indicate that permafrost has not yet been established, although the ground is now becoming seasonally frozen due to the GSHP energy removal. Yearly average temperatures are declining, and extrapolation indicates that permafrost will establish in future years. The GSHP coefficient of performance (COP) was initially 3.6 and is declining with the decreasing ground temperatures. Economic modeling indicates that the system may become uneconomical in future years, although volatile energy costs have a substantial effect of the prediction.

2016060003 Wang Genxu (Chinese Academy of Sciences, IMHE Institute of Mountain Hazards and Environment, Chengdu, China); Mao Tianxu; Zhang Tao and Chen Xiaopeng. Dissolved inorganic and organic carbon yields and fluxes in a permafrost catchment on the Qinghai-Tibet Plateau [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B53G-0645, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

Riverine transport of carbon from terrestrial to the aquatic ecosystems is an important component of the global carbon cycle. A warming climate can inevitably accelerate the microbial breakdown of organic carbon and the release of carbon dioxide especially in frozen soils (permafrost) within Arctic and sub-Arctic regions. In addition, high hydraulic conductivity and low sorption capacity of the shallow soil active layer overlying impermeable permafrost together lead to quick DOM transport to streams. In different regions, the response of dissolved carbon to climate warming is different due to the differences in hydrology, climatic conditions, soil types, vegetation conditions, permafrost distribution, catchment size, flow paths. The Qinghai-Tibet Plateau (QTP), of which a significant portion is underlain by permafrost, is considered to be more sensitive to climatic warming than other regions. However, the knowledge of dissolved inorganic and organic carbon transport in the QTP is very limited. We compared the yields and fluxes of DIC/DOC in a small tropical permafrost catchment. Our results showed that: (1) the concentrations ranged from 7.8 to 30.9 mg L^-1 for the DIC and ranged from 2.3 to 6.4 mg L^-1 for the DOC, the ratio of DIC/DOC concentrations ranged from 2.2 to 5.7 with a mean value of 4.3; (2) the annual export approximately 3.56 t km^-2 year^-1 for the DIC and 0.73 t km^-2 year^-1 for the DOC, indicating that the dissolved carbon transported in majority under the inorganic form; (3) the seasonal variations in DIC/DOC export are strongly regulated by variability in runoff, meanwhile the concentration of DIC/DOC showed significant positive correlation with the thawing depth of the active layer and vegetation coverage. Our results provided an understanding about the characteristics of riverine dissolved carbons transport at a permafrost catchment scale on the QTP.

2016053198 Ward, C. (University of Michigan, Earth & Environmental Sciences, Ann Arbor, MI) and Cory, R. M. Relating the chemical composition of dissolved organic matter draining permafrost soils to its photochemical degradation in Arctic surface waters [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B11G-0521, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

Thawing permafrost soils are expected to shift the chemical composition of DOM exported to and degraded in arctic surface waters. While DOM photo-degradation is an important component of the freshwater C cycle in the Arctic, the molecular controls on DOM photo-degradation remain poorly understood, making it difficult to predict how shifting chemical composition may alter DOM photo-degradation in arctic surface waters. To address this knowledge gap, we quantified the susceptibility of DOM draining the shallow organic mat and the deeper permafrost layer to complete photo-oxidation to CO₂ and partial photo-oxidation to compounds that remain in the DOM pool, and investigated changes in DOM chemical composition following sunlight exposure. DOM leached from the organic mat contained higher molecular weight, more oxidized and unsaturated aromatic species compared to permafrost DOM. Despite significant differences in initial chemical composition, permafrost and organic mat DOM had similar susceptibilities to complete photo-oxidation to CO₂. Concurrent losses of carboxyl moieties and shifts in chemical composition during photo-degradation indicated that carboxyl-rich tannin-like compounds in both DOM sources were likely photo-decarboxylated to CO₂. Permafrost DOM had a higher susceptibility to partial photo-oxidation compared to organic mat DOM, potentially due to a lower abundance of phenolic compounds that act as "antioxidants" and slow the oxidation of DOM. These results demonstrated how chemical composition controls the photo-degradation of DOM in arctic surface waters, and that DOM photo-degradation will likely remain an important component of the freshwater C budget in the Arctic with increased export of permafrost DOM to surface waters.

2016053359 Zubrzycki, S. (University of Hamburg, Hamburg, Germany); Ma, Y. and Zhang, Y. Hillslope-scale variability in seasonal frost depth and soil water content investigated by GPR on the southern margin of the sporadic permafrost zone on the Tibetan Plateau [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract C23A-0767, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

Ground temperature data show that permafrost has recently been absent at a site on the southern edge of the sporadic permafrost zone on the Tibetan Plateau (TP). A detailed survey of seasonal frost depth (SFD) and soil water content (SWC) here is significant for understanding the hydrological response to thawing permafrost. However, little is known about the spatial heterogeneity of SFD and SWC at the hillslope-scale in this vulnerable permafrost region. Thus, high-frequency ground-penetrating radar (GPR) was applied to a field site that varied in terms of topography (slope, aspect and elevation) and surface environments (vegetation cover and stream presence). The GPR data and accompanying field observations of gravimetric water content and frost depth revealed a spatial variation at the hillslope-scale in SFD and SWC, and indicated that topography, vegetation and stream distribution significantly influence the patterns observed. The average SFD was much deeper along the north-facing slope, compared to the south-facing slope in early May and its thickness varied considerably with altitude along each slope. An increase in the extent of vegetation cover correlated with decreasing SFD. The SWC at shallow depth was higher along the south-facing slope than along the north-facing slope in the beginning of the thawing period. For slopes of both aspects, the SWC vertical profiles exhibited a similar variability, with SWC decreasing with depth, but at different rates. This study demonstrates that GPR provides an appropriate method for quantifying soil water content at hillslope scale on the Tibetan Plateau.

2016057739 Merritts, Dorothy J. (Franklin and Marshall College, Department of Earth and Environment, Lancaster, PA); Walter, Robert C.; Grand Pre, Candace A.; Rahnis, Michael; Hilgartner, WIlliam B.; Blair, Aaron; Markey, Erin and Feibel, Samuel. Post-glacial Holocene wetlands developed on permafrost-thaw sediments along valley bottoms in unglaciated Pennsylvania and Maryland [abstr.]: in Geological Society of America, 2015 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 47(7), p. 614, 2015. Meeting: Geological Society of America, 2015 annual meeting & exposition, Nov. 1-4, 2015, Baltimore, MD.

Previous workers (Newell and DeJong, 2011) interpreted the unglaciated, upland New Jersey landscape as a paleo-landscape created by seasonal discharge and mass movement on low slopes underlain by permafrost during Pleistocene cold-climate conditions. Dormant colluvial deposits were viewed as evidence of erosion and transport during active layer thaw, particularly as climate warmed and permafrost degraded. Our research adds to previous work that supports a similar history of landscape development south of Pleistocene full-glacial ice margins in Pennsylvania (PA) and Maryland (MD). Using lidar, orthoimagery, and geomorphic and paleoecological studies, we find the following evidence of past permafrost: 1) extensive networks of thermal contraction polygons; 2) ubiquitous gelifluction sheets and lobes up to 10s of m thick on side slopes and valley bottoms; and 3) retrogressive thaw slumps and other thermokarst features. Gelifluction produced poorly sorted, matrix-supported deposits indicative of mass movement under saturated conditions. These periglacial landforms and associated deposits are less pronounced to the south. A low-relief footslope deposit of fine colluvial material, typically gleyed silt and sand, mantles periglacial rubble and thickens on periglacial tributary fans. We interpret this footslope sediment as the result of downslope transport of fines during permafrost thaw. Our radiocarbon dating at dozens of sites, combined with paleoseed and other macro-fossil analysis, indicates that post-glacial valley bottom wetlands supplied by groundwater became established on periglacial deposits during the early Holocene. Oldest radiocarbon dates from organic-rich wetland soils typically are ≤&eq;11.2 ka, post-dating the Younger Dryas cold period. At one valley bottom location (Great Marsh, PA), calibrated radiocarbon dates of 19.1-19.9 kyrs BP for organic matter in silt immediately below a 12.1-13.2 kyrs BP organic-rich soil indicate a late Pleistocene-Holocene erosional disconformity. Holocene wetland sediments and soils on coarse, wet substrates persisted until European settlement, often preserved beneath historic sediment stored in valley bottoms as a result of upland soil erosion, mill damming, and road building that began circa late 17th to 18th c.

2016053360 Bao, H. (University of Tokyo, Bunkyo-ku, Japan). Development of an enthalpy-based frozen soil model and its validation in a cold region in China [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract C23A-0768, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

A physically-based frozen soil model was developed based on the Water and Energy Budget-based Distributed Hydrological model (WEB-DHM) for the simulation of water and energy transfer in cold regions. In order to simulate the soil freezing/thawing processes stably and efficiently, a two-step algorithm is applied to solve the non-linear energy governing equations: 1) the thermal diffusion equation is used to simulate the heat fluxes between soil layers without considering liquid-ice phase change; 2) a freezing/thawing scheme is used to derive soil temperature, liquid water content and ice content from enthalpy conservation, mass conservation, and freezing point depression equations. In the algorithm, a parameterization set is adopted to update hydraulic and thermal properties by considering the presence of ice and low soil temperatures. The performance of the frozen soil model was validated at point scale in a typical mountainous permafrost region of Binggou Watershed, Heihe Basin, Northwest China. Results show that the model can achieve a convergent solution at a typical time step (hourly) and layer sizes (centimeters) of current land process models. It is able to reproduce the observed soil freezing/thawing processes and hydrological processes. The simulated profiles of soil temperature, liquid water content, ice content and thawing front depth are in good agreement with the observations and the characteristics of permafrost. The freeze-thaw cycle in frozen soil evolution was continuously represented by the contour map of soil temperature and ice content of all soil layers. Therefore, this model can be coupled with hydrological, ecological and climate models to deepen our physical understanding in permafrost regions.

2016053282 Burchwell, A. (Ohio State University, Earth Science Department, Columbus, OH) and Cook, A. Nuclear well log properties of natural gas hydrate reservoirs [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B13B-0627, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

Characterizing gas hydrate in a reservoir typically involves a full suite of geophysical well logs. The most common method involves using resistivity measurements to quantify the decrease in electrically conductive water when replaced with gas hydrate. Compressional velocity measurements are also used because the gas hydrate significantly strengthens the moduli of the sediment. At many gas hydrate sites, nuclear well logs, which include the photoelectric effect, formation sigma, carbon/oxygen ratio and neutron porosity, are also collected but often not used. In fact, the nuclear response of a gas hydrate reservoir is not known. In this research we will focus on the nuclear log response in gas hydrate reservoirs at the Mallik Field at the Mackenzie Delta, Northwest Territories, Canada, and the Gas Hydrate Joint Industry Project Leg 2 sites in the northern Gulf of Mexico. Nuclear logs may add increased robustness to the investigation into the properties of gas hydrates and some types of logs may offer an opportunity to distinguish between gas hydrate and permafrost. For example, a true formation sigma log measures the thermal neutron capture cross section of a formation and pore constituents; it is especially sensitive to hydrogen and chlorine in the pore space. Chlorine has a high absorption potential, and is used to determine the amount of saline water within pore spaces. Gas hydrate offers a difference in elemental composition compared to water-saturated intervals. Thus, in permafrost areas, the carbon/oxygen ratio may vary between gas hydrate and permafrost, due to the increase of carbon in gas hydrate accumulations. At the Mallik site, we observe a hydrate-bearing sand (1085-1107 m) above a water-bearing sand (1107-1140 m), which was confirmed through core samples and mud gas analysis. We observe a decrease in the photoelectric absorption of »0.5 barnes/e-, as well as an increase in the formation sigma readings of »5 capture units in the water-bearing sand as compared to the hydrate sand interval. This is further correlated with the carbon/oxygen ratio showing a decrease of 20% in the water sand compared to the hydrate sand above. In future research, we will quantify the effect of gas hydrate on the nuclear logs at the Mallik well and compare it to wells in the Gulf of Mexico.

2016053237 Deusner, C. (GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany); Gupta, S.; Kossel, E.; Bigalke, N. and Haeckel, M. Hydro-geomechanical behaviour of gas-hydrate bearing soils during gas production through depressurization and CO₂ injection [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B12B-03, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

Results from recent field trials suggest that natural gas could be produced from marine gas hydrate reservoirs at compatible yields and rates. It appears, from a current perspective, that gas production would essentially be based on depressurization and, when facing suitable conditions, be assisted by local thermal stimulation or gas hydrate conversion after injection of CO₂-rich fluids. Both field trials, onshore in the Alaska permafrost and in the Nankai Trough offshore Japan, were accompanied by different technical issues, the most striking problems resulting from unpredicted geomechanical behaviour, sediment destabilization and catastrophic sand production. So far, there is a lack of experimental data which could help to understand relevant mechanisms and triggers for potential soil failure in gas hydrate production, to guide model development for simulation of soil behaviour in large-scale production, and to identify processes which drive or, further, mitigate sand production. We use high-pressure flow-through systems in combination with different online and in situ monitoring tools (e.g. Raman microscopy, MRI) to simulate relevant gas hydrate production scenarios. Key components for soil mechanical studies are triaxial systems with ERT (Electric resistivity tomography) and high-resolution local strain analysis. Sand production control and management is studied in a novel hollow-cylinder-type triaxial setup with a miniaturized borehole which allows fluid and particle transport at different fluid injection and flow conditions. Further, the development of a large-scale high-pressure flow-through triaxial test system equipped with m-CT is ongoing. We will present results from high-pressure flow-through experiments on gas production through depressurization and injection of CO₂-rich fluids. Experimental data are used to develop and parametrize numerical models which can simulate coupled process dynamics during gas-hydrate formation and gas production.

2016053339 Frost, G. V., Jr. (Alaska Biological Research, Fairbanks, AK); Macander, M. J.; Liljedahl, A. K. and Walker, D. A. Regional patterns of ice-wedge degradation across Northern Alaska; what does asynchronous timing of onset tell us regarding triggering mechanisms, thresholds, and impacts? [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract C21C-0750, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

Ice-wedge polygons are conspicuous and widespread in arctic landscapes, creating complex microtopography and strong, meter-scale contrasts in hydrology, soil, vegetation, and ground ice conditions. Thaw of the upper portion of ice-wedges results in ground subsidence (thermokarst), plant mortality and the formation of small, flooded pits along the polygon margins. Secondary impacts, such as changes in flowpaths, spatially-variable flooding and drainage of polygon centers, and thermal erosion of permafrost, extend well beyond the thermokarst pits themselves. We delineated small waterbodies in historical airphotos and modern high-resolution satellite imagery and made ground observations across a network of 45 km² study areas spanning the western and central regions of Alaska's North Slope. The imagery archive covers three epochs: 1948-1955, 1979-1985, and 2009-2012. Our analysis focused on residual upland surfaces dominated by Holocene-aged ice wedges, where surface water is mainly restricted to degraded ice-wedges. Total extent of flooded pits increased at most landscapes since circa 1980 (range -27 - +135%; median +10.6%). An intriguing regional pattern was evident: degradation of Holocene ice-wedges was already well underway by 1950 across much of the western North Slope, but degradation initiated much more recently on eolian sand and silt (yedoma) deposits prevalent to the east. Our results indicate that recent degradation of Holocene ice wedges across northern Alaska cannot be explained by late-20th century warmth alone. Possible mechanisms for earlier onset of degradation on the western North Slope include differences in recent climate history, snow regime, and thermal and physical properties of surficial materials. These findings provide context for interpreting and predicting ice-wedge thermokarst processes, thresholds, and impacts in Alaska and elsewhere in the circumpolar arctic.

2016053345 Hinzman, L. D. (University of Alaska Fairbanks, Fairbanks, AK); Kane, D. L. and Woo, M. K. Frozen ground controls on hydrological processes [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract C21E-02, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

Frozen ground establishes a unique discipline of hydrologic science where the hydrologic regime is intimately coupled with the thermal regime to the extent that one may not be completely understood without correct characterization of the other. In permafrost regions, material properties may change drastically on a scale of centimeters to meters, particularly in the vertical dimension due to distinct changes in soil and thermal characteristics. Properties may vary just as dramatically in the horizontal dimension across the boundary of discontinuous permafrost. Although the spatial extent of permafrost changes on relatively slow time scales in response to disturbance or a changing climate, this too introduces an added level of complexity. Permafrost may nearly eliminate the interactions between near-surface and sub-permafrost aquifers, which in essence defines the hydrologic response of every watershed that is directly influenced by permafrost. Even though the principles governing water movement in permafrost areas are the same as those in more temperate regions, interactions of extremes in climate and the land surface characteristics render permafrost hydrology different from the hydrology of temperate latitudes. Ice-rich permafrost prevents deep percolation of rainfall or snowmelt water, often maintaining a moist to saturated active layer above the permafrost table. Most hydrologic activities are confined above-ground or in the thin active layer, which supplies summer moisture for baseflow and/or plant transpiration. Limited storage capacity of the thawed active layer does not support extended baseflow in a stream, though the proportion of baseflow increases as the percentage of permafrost extent decreases. In areas where permafrost is discontinuous or where it has thawed substantially near the surface, local hydrology may display a markedly different character as there are stronger exchanges between the surface water and the ground water system, or water may drain laterally resulting in drier surface conditions. Understanding the interdependence of frozen ground, hydrology and ecosystems is critically important to enable accurate projections of future conditions in the high latitudes.

2016053335 Hinzman, L. D. (University of Alaska Fairbanks, Fairbanks, AK); Rawlins, M. A.; Serreze, M.; Vorosmarty, C. J. and Walsh, J. E. Will the Arctic land surface become wetter or drier in response to a warming climate [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract C21C-0746, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

There is much concern about a potentially "accelerated" hydrologic cycle, with associated extremes in weather and climate-related phenomena. Whether this translates into wetter or drier conditions across arctic landscapes remains an open question. Arctic ecosystems differ substantially from those in temperate regions, largely due to the interactions of extremes in climate and land surface characteristics. Ice-rich permafrost prevents percolation of rainfall or snowmelt water, often maintaining a moist to saturated active layer where the permafrost table is shallow. Permafrost may also block the lateral movement of groundwater, and act as a confining unit for water in sub- or intra-permafrost aquifers. However, as permafrost degrades, profound changes in interactions between groundwater and surface water occur that affect the partitioning among the water balance components with subsequent impacts to the surface energy balance and essential ecosystem processes. Most simulations of arctic climate project sustained increases in temperature and gradual increases in precipitation over the 21st century. However, most climatic models do not correctly represent the essential controls that permafrost exerts on hydrological, ecological, and climatological processes. If warming continues as projected, we expect large-scale changes in surface hydrology as permafrost degrades. Where groundwater gradients are downward (i.e. surface water will infiltrate to subsurface groundwater), as in most cases, we may expect improved drainage and drier soils, which would result in reduced evaporation and transpiration (ET). In some special cases, where the groundwater gradient is upward (as in many wetlands or springs) surface soils may become wetter or inundated as permafrost degrades. Further, since soil moisture is a primary factor controlling ecosystem processes, interactions between ecosystems, GHG emissions, and high-latitude climate must also be considered highly uncertain. These inter-dependent processes will exert primary controls on several important feedback processes and vary across space and time in some as yet, unknown way.

2016053337 Johansson, E. (SKB Swedish Nuclear Fuel and Waste Management, Stockholm, Sweden); Lindborg, T. and Berglund, S. Modeling present hydrological conditions as a key to predict the future; results from a case study of a periglacial catchment in Greenland [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract C21C-0748, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

The routing of water through periglacial landscapes is closely connected to the presence of permafrost, and freezing and thawing processes. To predict responses in the landscape to climate driven changes, we need to better understand the present day hydrology. The present hydrological processes, and the uncertainties in the data used to describe them, must be investigated and understood before we can develop models describing possible future conditions. In this work we have studied the hydrology of a catchment in the Kangerlussuaq region, Greenland. Johansson et al. (2015) presented a hydrological model of the catchment based on a new hydrological and meteorological data set from the catchment area. The present water balance was quantified, and the spatial and seasonal dynamics of the main hydrological fluxes were presented. It was shown that the model was able to reproduce the measured lake level dynamics and the measured components of the water balance. Based on this work we have used the numerical model to investigate the sensitivity in hydrological responses to different meteorological, geological and geometrical model input data. The aim with this study is to investigate the importance of the use of local data, but also to highlight the importance of present day site understanding when developing and applying the model for predicting responses to a changing climate. The results show that the site specific model is highly sensitive to the meteorological input data. Driving the model with precipitation data from a meteorological station only 30 km away from the catchment instead of local data from the studied catchment, or using local precipitation data not corrected for wind and adhesion losses, resulted in large discrepancies between measured and calculated lake levels. The modelled intra-annual dynamics of the active layer groundwater was shown to be sensitive both to the applied soil temperatures but also to the active layer depth and sediment stratigraphy.

2016058316 Lamoureux, Scott F. (Queen's University, Kingston, ON, Canada) and Normandeau, Alexandre. Connecting process to high resolution paleorecords; long term investigations of linked Arctic climate-hydrology-lacustrine sedimentary processes [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract PP31D-05, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

High resolution lacustrine sedimentary sequences hold substantial potential for paleoenvironmental analyses, particularly in regions where few alternatives are available. Increased attention to quantifying processes that generate sedimentary facies has yielded increasingly detailed environmental interpretations but these efforts have been limited by available field data. The Cape Bounty Arctic Watershed Observatory (CBAWO) was initiated in 2003 to develop a long term site to evaluate the controls over sediment transport and the formation of clastic sedimentary records. This program in the Canadian Arctic has supported 13 years of research in paired watersheds and lakes, both of which contain clastic varves. Results from 2003-14 demonstrate how multiple climatic factors delivery sediment in a complex manner. This comparatively simple hydroclimatic system is dominated by runoff and sediment transport from spring snowmelt, with clear associations between catchment snow water equivalence (or total runoff) and sediment yield, with discharge limited by snow exhaustion as the season progresses. Major rainfall can constitute a dominant contribution to seasonal sediment yield, but antecedent conditions can significantly reduce runoff markedly. Hence, these results indicate two primary competing hydroclimatic factors that control catchment sediment yield, both with independent climatic and hydrological factors. Additionally, the impact of landscape disturbance on downstream sediment yield has been evaluated following a major episode of permafrost thaw in 2007. Results show that localized slope disturbances resulted in enhanced erosion but downstream fluvial storage reduced the magnitude of transport. Sediment from disturbances will be gradually released and may generate decadal-scale sediment delivery changes in the downstream record. Collectively, this research indicates multiple controls over the formation of clastic varves. Advances in high resolution sedimentary structure and composition analysis provide methodological pathways for integrating a fuller set of controls over sediment deposition, and together with sustained process investigations, offer the opportunity for sedimentary records with the highest degree of fidelity.

2016059998 Lara, Mark J. (University of Alaska Fairbanks, Institute of Arctic Biology, Fairbanks, AK); Genet, Helene; McGuire, Anthony David; Euskirchen, Eugenie Susanne; Zhang, Yujin; Brown, Dana Nossov; Jorgenson, Tore; Romanovsky, Vladimir E.; Breen, Amy Lynn and Bolton, William R. Thermokarst rates intensify due to climate change and forest fragmentation in an Alaskan boreal forest lowland [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B51G-0510, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

Lowland boreal forest ecosystems in Alaska are dominated by wetlands comprised of a complex mosaic of fens, collapse scar-bogs, low shrub/scrub, and forests growing on elevated ice rich permafrost soils. Thermokarst has affected the lowlands of the Tanana Flats in central Alaska for centuries, as thawing permafrost collapses forests that transition to wetlands. Located within the discontinuous permafrost zone, this region has significantly warmed over the past half-century, and much of these carbon-rich permafrost soils are now within ~0.5°C of thawing. Increases in the collapse of lowland boreal forests in response to warming may have consequences for the climate system. This study evaluates the trajectories and potential drivers of 60 years of forest change in a landscape subjected to permafrost thaw in unburned dominant forest types (paper birch and black spruce) associated with location on elevated permafrost plateau and across multiple time periods (1949, 1978, 1986, 1998 and 2009) using historical and contemporary aerial and satellite images for change detection. We developed (i) a deterministic statistical model to evaluate the potential climatic controls on forest change using gradient boosting and regression tree analysis, and (ii) a 30´30 m land cover map of the Tanana Flats to estimate the potential landscape-level losses of forest area due to thermokarst from 1949 to 2009. Over the 60-year period, we observed a nonlinear loss of birch forests and a relatively continuous gain of spruce forest associated with thermokarst and forest succession, respectively. Gradient boosting and regression tree models identify precipitation and forest fragmentation as the primary factors controlling birch and spruce forest change, respectively. Between 1950-2009 landscape-level analysis estimates a transition of ~15 km² of birch forest area to wetlands on the Tanana Flats, where the greatest change followed warm periods. This work highlights the vulnerability of lowland ice-rich permafrost ecosystems to recent and ongoing climate change.

2016053338 Liljedahl, A. K. (University of Alaska Fairbanks, Fairbanks, AK); Boike, J.; Daanen, R. P.; Fedorov, A. N.; Frost, G. V., Jr.; Grosse, G.; Hinzman, L. D.; Iijima, Y.; Jorgenson, J.; Matveyeva, N.; Necsoiu, M.; Raynolds, M. K.; Romanovsky, V. E.; Schulla, J.; Tape, K. D.; Walker, D. A.; Wilson, C. J. and Yabuki, H. Ice wedge degradation; why Arctic lowlands are becoming wetter and drier [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract C21C-0749, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

Top melting of ice-wedges and subsequent ground subsidence is now a widespread phenomenon across the Arctic domain. We show field and remote sensing observations that document extensive ice-wedge degradation, which initially has resulted in increased wetness contrast across the landscape (i.e. both a drying and a wetting), a shift in pond type and an overall drying in later stages. The differential ground subsidence at cold continuous permafrost regions appear to be linked to press and pulse climate forcing. Here, the process of crossing the local threshold for ice-wedge stability may be favored by a press occurrence such as long-term, gradual increases in summer air temperature, mean annual air temperature and/or possibly winter precipitation, but our observations suggest it is most likely initiated by pulse atmospheric forcing such as extreme summer warmth and/or winter precipitation. Field measurements of water levels, frost tables and snow accumulation across the main ice-wedge polygon types and their respective features support dramatic shifts in the hydrologic regime with altered topography and a complexity that ultimately affect the larger-scale hydrologic system. For example, our numerical model experiments show that a connected trough-network reduces inundation and increases runoff and that changing patterns of snow distribution due to the differential ground subsidence play a crucial role in altering lowland tundra water balance. These fine-scale (10's cm) geomorphic changes are expected to further expand and amplify in rapidly warming permafrost regions and likely will dramatically modify land-atmosphere and land-ocean fluxes and exchange of carbon, water, and energy.

2016053349 Luo, S., Sr. (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Chen, B.; Lu, S.; Zhang, Y. and Ma, D. Effects of the soil freeze-thaw process on the regional climate of the Tibet Plateau [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract C21E-08, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

Single-point and regional simulation experiments on the Tibet Plateau, both with and without consideration of the soil freeze-thaw process, were set up with CLM3.5 and RegCM4 models. Comparison of the simulated soil temperature and moisture, surface energy flux, and upper-lower atmospheric circulation showed that the regional climate can be influenced by the freeze-thaw process of soil. The results indicate that the freeze-thaw process is a buffer to the seasonal changes in soil and near-surface temperatures and strengthens the energy exchange between the soil and the atmosphere. During the freeze (thaw) process, releasing (absorbing) of phase change energy retards the cooling (heating) effect of air temperature on soil. The soil freeze-thaw process increases (decreases) the surface heat source of the plateau in winter (summer), which increases (decreases) the near-surface temperature in winter (summer). Promoted by atmospheric circulation, the soil freeze-thaw process influences climate at the high and low altitudes of the plateau; this may also contribute to the maintenance of the South Asia High. In the early stages of permafrost degradation, the regional climate effects of freezing and thawing may accelerate the degradation of permafrost.

2016053258 Rudow, Matt (Setaram, Hillsborough, NJ) and Lilova, Kristina. Characterization of gas hydrates formation and dissociation using thermal analysis and calorimetry [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B13B-0603, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

In general, the gas hydrates are formed at low temperature and high pressure which requires a special technique to mimic the natural conditions. The hydrate thermal properties: heat capacity, heat of dissociation, are crucial for evaluating the effects on climate change and for a prediction of the gas production rates from hydrate reservoirs. The effect of the porous materials on the dissociation of synthetic methane hydrates was investigated at 150 - 300 K and atmospheric pressure. Another experiment with methane hydrates, but at high pressure (20 MPa) was performed at near room temperature using a highly sensitive micro-differential scanning calorimeter with a specifically design high pressure vessel (the vessel can withstand a pressure up to 1000 bars). The thermal cycle for measuring the methane hydrate dissociation in water includes cooling down a water solution under a certain methane pressure (30 to 350 bars) to -30 C to allow water crystallization and hydrate formation, then heated up to room temperature. The endothermic peak, following the ice melting is associated to the hydrate dissociation process and gives the enthalpy of the hydrate decomposition. The kinetics of the hydrates formation could also be predicted by a rapid DSC cooling experiment followed by isothermal step and heating. Both dissociation and specific heats of synthetic methane and ethane hydrates were measured under high-pressure condition by using a heat-flow type calorimeter to understand thermodynamic properties of gas hydrates under submarine/sublacustrine environments. The large reserves of natural gas are present as clathrate hydrates in permafrost regions and beneath the oceans have generated interest in the study of their thermophysical properties such as heat capacity and thermal conductivity. The effect of isotopic substitution in both THF and water on the eutectic and hydrate melting temperatures in water-tetrahydrofuran systems studied by DSC will be shown as an example.

2016053235 Ruppel, C. D. (U. S. Geological Survey, Woods Hole, MA); Pohlman, J.; Waite, W. F.; Hunt, A. G.; Stern, L. A. and Casso, M. New methods for gas hydrate energy and climate studies [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B12B-01, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

Over the past few years, the USGS Gas Hydrates Project has focused on advancements designed to enhance both energy resource and climate-hydrate interaction studies. On the energy side, the USGS now manages the Pressure Core Characterization Tools (PCCTs), which includes the Instrumented Pressure Testing Chamber (IPTC) that we have long maintained. These tools, originally built at Georgia Tech, are being used to analyze hydrate-bearing sediments recovered in pressure cores during gas hydrate drilling programs (e.g., Nankai 2012; India 2015). The USGS is now modifying the PCCTs for use on high-hydrate-saturation and sand-rich sediments and hopes to catalyze third-party tool development (e.g., visualization). The IPTC is also being used for experiments on sediments hosting synthetic methane hydrate, and our scanning electron microscope has recently been enhanced with a new cryo-stage for imaging hydrates. To support climate-hydrate interaction studies, the USGS has been re-assessing the amount of methane hydrate in permafrost-associated settings at high northern latitudes and examined the links between methane carbon emissions and gas hydrate dissociation. One approach relies on the noble gas signature of methane emissions. Hydrate dissociation uniquely releases noble gases partitioned by molecular weight, providing a potential fingerprint for hydrate-sourced methane emissions. In addition, we have linked a DOC analyzer with an IRMS at Woods Hole Oceanographic Institution, allowing rapid and precise measurement of DOC and DIC concentrations and carbon isotopic signatures. The USGS has also refined methods to measure real-time sea-air flux of methane and CO₂ using cavity ring-down spectroscopy measurements coupled with other data. Acquiring »8000 km of data on the Western Arctic, US Atlantic, and Svalbard margins, we have tested the Arctic methane catastrophe hypothesis and the link between seafloor methane emissions and sea-air methane flux.

2016053269 Ruprecht, Catherine Marie (Pacific Northwest National Laboratory, Richland, WA); Horner, J. and White, M. D. Experimental and numerical investigation of guest molecule exchange kinetics based on the 2012 Ignik Sikumi gas hydrate field trial [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B13B-0614, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

In 2012 the U.S. DOE/NETL, ConocoPhillips Company, and Japan Oil, Gas and Metals National Corporation jointly sponsored the first field trial of injecting a mixture of N2-CO2 into a CH4-hydrate bearing formation beneath the permafrost on the Alaska North Slope. Known as the Ignik Sikumi #1 Gas Hydrate Field Trial, this experiment involved three stages: 1) the injection of a N2-CO2 mixture into a targeted hydrate-bearing layer, 2) a 4-day pressurized soaking period, and 3) a sustained depressurization and fluid production period. Data collected during the three stages of the field trial were made available after a thorough quality check. The Ignik Sikumi #1 data set is extensive, but contains no direct evidence of the guest-molecule exchange process. This study uses numerical simulation to provide an interpretation of the CH4/CO2/N2 guest molecule exchange process that occurred at Ignik Sikumi #1. Simulations were further informed by experimental observations. The goal of the scoping experiments was to understand kinetic exchange rates and develop parameters for use in Ignik Sikumi history match simulations. The experimental procedure involves two main stages: 1) the formation of CH4 hydrate in a consolidated sand column at 750 psi and 2°C and 2) flow-through of a 77.5/22.5 N2/CO2 molar ratio gas mixture across the column. Experiments were run both above and below the hydrate stability zone in order to observe exchange behavior across varying conditions. The numerical simulator, STOMP-HYDT-KE, was then used to match experimental results, specifically fitting kinetic behavior. Once this behavior is understood, it can be applied to field scale models based on Ignik Sikumi #1.

2016053336 Saito, K. (Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan). What an Arctic terrestrial MIP tells about changes and differences in Arctic subsurface hydrology [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract C21C-0747, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

The spatial and temporal characteristics of Arctic hydrology have been investigated in the GTMIP activity (URL: https://ads.nipr.ac.jp/gtmip/gtmip.html), conducted as a part of GRENE Arctic Climate Change Project in Japan. The activity has two stages, one on local and the other on the circum-Arctic scales. Stage 1 is site simulations for the period of 1980-2013 for four Arctic observation sites, i.e., Fairbanks/AK, Kevo/Finland, Yakutsuk and Tiksi in Siberia, focusing on process evaluations with observation. Stage 2 is pan-arctic simulations for 1850-2100 with 0.5x0.5 degree resolution, targeting at the responses of Arctic terrestrial to global climate change. At both stages multiple terrestrial models have been participating (16+ for Stage 1; 10 for Stage 2), ranging from physically-oriented process models to biogeochemical models to ESM-compatible ecosystem models. The results are delineating a) spatial variations and temporal changes in subsurface thermal and hydrological states, and subsequently the ecosystem in different climatic/ecosystem zones (e.g., Kevo is underlain by seasonally frozen ground while others by permafrost; Tiksi is in tundra whole others in taiga; these two sites are Arctic while the other two sub-Arctic), and b) the differences and similarities in the reproducibility among models with respect to the target of the models (e.g., physical, or biogeochemical) and to the complexity of implemented processes.

2016053362 Strand, S. M. (University Centre in Svalbard, Longyearbyen, Norway) and Christiansen, H. H. Impacts of short-term meteorological fluctuations on near-surface ground temperatures in Spitsbergen, Svalbard [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract C23A-0770, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

The state of permafrost in a given area is dependent on heat balance, which is largely controlled by major trends in climate. However, smaller-scale meteorological events can impact the thermal regime as well, depending on a number of ground surface factors. This project investigates the impact of short-term meteorological fluctuations on near-surface ground temperatures in central Spitsbergen, Svalbard, and identifies the depths at which these changes are perceptible. The Svalbard archipelago is subject to significant air temperature fluctuations due to its maritime climate; this can result in wintertime rain events. Even when snow is present, rain has the potential to notably affect near-surface ground temperatures. A few studies have examined Svalbard ground temperatures during specific wintertime warm periods, but no previous research has utilized the available long-term active layer and permafrost temperature data to compare distinct events. Though summer air temperatures on Svalbard are more stable, particularly warm intervals alter active layer thaw progression. By comparing high-resolution air temperature data with high-resolution ground temperature data, the temporal and spatial impact of short-term meteorological fluctuations is assessed and compared between sites from varying locations and lithology.

2016055299 Chaussé, Christine (INRAP, Madrid, Spain); Blaser, Frédéric; Debenham, Nick; Roque, Céline and Vartanian, Emmanuel. Pléistocène supérieur et paléolithique dans le domaine des sables stampiens (Rupéliens) du sud du bassin de Paris; les données du site de Melun-Montaigu (Seine-et-Marne, France) [Upper Pleistocene and Paleolithic from the Stampian (Rupelian) sand area in the southern Paris Basin; data from the site of Melun-Montaigu (Seine-et-Marne, France)]: in Le Quaternaire; marqueurs, traceurs et chronomètres (Berger, Jean-François, convener; et al.), Quaternaire (Paris), 26(3), p. 245-255 (English sum.), illus. incl. sect., strat. col., 2 tables, geol. sketch maps, 38 ref., September 2015. Meeting: Q9; Le Quaternaire; marquers, traceurs et chronomètres, March 26-28, 2014, Lyons, France.

The site of Melun-Montaigu has yielded several palaeolithic assemblages buried in slope deposits. These accumulated downslope of the hill of Stampian (Rupelian) sand. The morphosedimentary analysis together with OSL and TL dating provide the frame for a chronostratigraphic interpretation of both the sedimentary sequence and the palaeolithic levels. The oldest deposits, accumulated by creeping during a cooling event between the end of the Weichselian Early-Glacial and the Lower Pleniglacial. They overlay a first occupation, level P3, attributed to the beginning of the Weichselian period and which contains reworked lithic artifacts (level Pb). Afterwards, a thermokarstic gully incised the sequence at the beginning of the Middle Pleniglacial. The gully testifies to a phase of permafrost degradation. The infill contains a second reworked Palaeolithic level (Pa). This interstadial interval ended with the formation of a palaeosol which was degraded and cut by a large network ice-wedge pseudomorphoses. This event occurred at the beginning of the Upper Pleniglacial stage, around 30 ka, is contemporaneous of modern human's presence in the immediate vicinity (level P1).

2016052997 Merritts, Dorothy J. (Franklin and Marshall College, Department of Earth and Environment, Lancaster, PA); Walter, Robert C.; Blair, Aaron; Demitroff, Mark; Potter, Noel, Jr.; Alter, Samuel; Markey, Erin; Guillorn, Sally; Gigliotti, Sophia and Studnicky, Caroline. Lidar, orthoimagery, and field analysis of periglacial landforms and their cold climate signature, unglaciated Pennsylvania and Maryland [abstr.]: in Geological Society of America, 2015 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 47(7), p. 831, 2015. Meeting: Geological Society of America, 2015 annual meeting & exposition, Nov. 1-4, 2015, Baltimore, MD.

High-resolution orthoimagery, topographic datasets (e.g., LiDAR), and GPS surveying offer opportunities to map fine-scale landforms, even where forested, over broad areas. Using these technologies, field mapping, backhoe trenching, geophysical techniques, and coring, we are compiling a GIS database of relict periglacial landforms south of Pleistocene full glacial ice margins in Pennsylvania and Maryland. In particular, we search for Pleistocene periglacial landforms diagnostic of the former existence of permafrost (ground that remains at or below freezing >&eq;2 years). Continuous permafrost can occur today in regions with mean annual air temperatures (MAAT) less than -6° to -8° C, and discontinuous permafrost can occur in regions with MAAT less than ~ -0.5° C to -2° C. The boundary of continuous-discontinuous permafrost latitudinally shifted with cold glacial-warm interglacial climate cycles during the Quaternary Period, with the Last Glacial Maximum from ~26.5 to 19 ka. We identify the following evidence of permafrost and/or its thaw: 1) extensive networks of thermal-contraction polygons (TCPs) on crests and side slopes of shale hills; 2) thick, ubiquitous stacks of gelifluction sheets and lobes on quartzite, sandstone, schist, and diabase ridges and side slopes; and 3) potential pingos in synclinal valleys with high relief. We document two other landforms - retrogressive thaw slumps and thermokarst gullies - that are common in regions of permafrost thaw today. All landforms become less pronounced to the south. We only find well-developed TCPs - diagnostic of continuous permafrost - on Paleozoic shale bedrock in Pennsylvania. Roadcut and roadbed exposures reveal vertical to sub-vertical wedge-shaped structures along TCP boundaries (with sand and gravel infill to a depth of ~1.5 m), which often parallel structural joints in bedrock. We only find rimmed circular pingo-like features on valley floors within tightly folded rocks in central Pennsylvania. Paleotemperatures are within the range of the "frost-cracking window", explaining the ubiquitous presence of brecciated bedrock and shattered bedrock fragments on slopes and valley bottoms throughout the region.

2016059877 Winterfeld, Maria (Alfred Wegener Institute for Polar and Marine Research, Bremerhaven, Germany); Goñi, M.; Just, J.; Hefter, J.; Sun, S.; Han, P. and Mollenhauer, Gesine. Sources and age of terrigenous organic matter exported from the Lena River watershed, NE Siberia [abstr.]: in Goldschmidt abstracts 2015, V.M. Goldschmidt Conference - Program and Abstracts, 25, p. 3430, 2015. Meeting: Goldschmidt 2015, Aug. 16-21, 2015, Prague, Czech Republic.

URL: http://goldschmidt.info/2015/uploads/abstracts/finalPDFs/3430.pdf

2016061158 Markussen, T. N. (University of Copenhagen, Copenhagen, Denmark); Andersen, T. J.; Ernstsen, V. B. and Becker, M. Flocculation alters the distribution and flux of melt-water supplied sediments and nutrients in the Arctic; a case from Disko Fjord, West Greenland [abstr.]: in 2014 ocean sciences meeting (Sharp, Jonathan, chairperson; et al.), Ocean Sciences Meeting, 17, Abstract 15954, February 2014. Meeting: 2014 ocean sciences meeting, Feb. 23-28, 2014, Honolulu, HI.

2016061222 Schreiner, Kathryn M. (Northwestern University, Evanston, IL); Bianchi, T. S.; Allison, M. A.; Eglinton, Timothy I. and Wacker, L. Changes to the Alaskan North Slope carbon cycle over the late Holocene; evidence from Colville Delta sediments, Beaufort Sea, Alaska [abstr.]: in 2014 ocean sciences meeting (Sharp, Jonathan, chairperson; et al.), Ocean Sciences Meeting, 17, Abstract 14338, February 2014. Meeting: 2014 ocean sciences meeting, Feb. 23-28, 2014, Honolulu, HI.

2016053297 Agnan, Yannick (Desert Research Institute, Reno, NV); Obrist, D.; Edwards, G. C.; Moore, C.; Hedge, Christine; Helmig, Detlev; Paxton, Dominique and Hueber, Jacques. Spatial and temporal variability of methane mole fractions and exchanges in and between soil, snow, and the atmosphere in a tundra system in Northern Alaska [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B13D-0648, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

An important global source of atmospheric methane (CH₄) is production in tundra soils (an important global source). To place constraints on the potential role that tundra soils play in global CH₄ cycling, we have been continuously measuring mole the air space in soils, snow, and the atmosphere as gradient-based surface-atmosphere fluxes for arctic tundra at Toolik Field Station (68° 38' N) starting in October 2014. We have found that atmospheric CH₄ mole fractions were, on average, relatively constant during the first 9 months of sampling (averaging 1.93 mmol mol^-1), with pronounced diel patterns starting in May and nighttime exceeding daytime mole fractions. However, gradients measured within the soil profile showed high variability in air withdrawn from different locations of these tundra soils (Typic Aquiturbels), with one soil profile indicating a CH₄ sink during fall until January; mole fractions were similar to the atmospheric measurements during winter indicating no source or sink (average 1.89 mmol mol^-1). A second soil profile 5 m away showed production of CH₄ (average 2.48 mmol mol^-1, two-times higher than atmospheric levels), even during mid-winter when soil temperatures were below -10 °C. Measurements of CH₄ in interstitial snowpack air also exhibited a similar combination of sources and sinks. We used micrometeorological gradient surface flux measurements to confirm that the area was a net source of CH₄ in fall, winter, and spring, with emissions averaging 26.6, 25.2, and 16.8 mg m^-2 d^-1, respectively. In the summer months, we saw strong diel flux patterns with deposition during day and emission at night, corresponding with observed diel variability in CH₄ snowpack mole fractions. Our results indicated a high variability of tundra landscape CH₄ fluxes, which locally shift from sources to sinks with high temporal variability. CH₄ oxidation by methanotrophic bacteria probably occurs in tundra soils, confirming observations in one soil, snowpack, and the atmosphere during spring, but oxidation ceased during the coldest months. In close proximity, we suggest a CH₄ production by methanogenic archaea, and surprisingly this production continued throughout winter even during the coldest periods showing little temperature dependence.

2016053305 Hedge, Christine (Desert Research Institute Reno, Reno, NV) and Agnan, Yannick. Soil and plant mercury concentrations and pools in the Arctic tundra of northern Alaska [abstr.]: in AGU 2015 fall meeting, American Geophysical Union Fall Meeting, 2015, Abstract B13I-04, December 2015. Meeting: American Geophysical Union 2015 fall meeting, Dec. 14-18, 2015, San Francisco, CA.

We present vegetation, soil and runoff mercury (Hg) concentrations and pool sizes in vegetation and soils at several arctic tundra sites, an area that represents <7 x 10⁶ km² of land surface globally. The primary measurement location is at Toolik Field Station (TFS, 68° 38' N) in northern Alaska, with additional samples collected along a transect from TFS to the Arctic Ocean, and in Noatak National Preserve to be collected in August 2015. Soil and vegetation samples from all sites will be analyzed for total Hg concentration, pH, soil texture, bulk density, soil moisture content, organic and total carbon (C), nitrogen, along with major and trace elements. Initial results already obtained from TFS (characterized as moist to wet tundra with Typic Aquiturbel soils) show Hg concentrations in tundra vegetation (112±15 mg kg^-1) and organic soil (140±8 mg kg^-1) similar to those found in temperate sites. Calculation of plant-based Hg deposition rates by litterfall of 17.3 mg kg^-1 yr^-1 were surprisingly high, exceeding all other Hg deposition fluxes at this site. Hg concentrations in mineral soils (95±3 mg kg^-1) were 2-3 times higher than those found at temperate sites. Hg concentrations showed weak relationships to organic C concentrations contrasting patterns from temperate soils where concentrations typically decline with depth following lower organic carbon contents. In fact, vertical mass profiles of Hg showed a strong increase with depth, with mineral layers storing over 90% (200-500 g ha^-1) of Hg within these soils. A principle component analysis including major and trace elements indicated that soil Hg was not of lithogenic origin but from atmospheric sources, possibly by long-range transport. Carbon-14 dating results showed over 7,000 years old organic carbon in mineral soils of the active layer where highest concentrations of soil Hg were observed, suggesting long term retention of atmospheric Hg. These patterns suggest vertical translocation of Hg from the surface organic horizons to mineral soils and strong accumulation-possibly over millennia-therein.

2016055350 Watters, Jaclyn (University of Texas, Institute for Geophysics, Austin, TX) and Levy, Joseph. Spatial patterns and drivers of melt and thermokarst erosion in Garwood Valley, McMurdo Dry Valleys, Antarctica [abstr.]: in Geological Society of America, 2015 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 47(7), p. 559, 2015. Meeting: Geological Society of America, 2015 annual meeting & exposition, Nov. 1-4, 2015, Baltimore, MD.

Previous work has shown that thermokarst formation in the Garwood Valley, McMurdo Dry Valleys (MDV), Antarctica, has accelerated to ~10 times the average Holocene rate. A large retrogressive thaw feature known as the Garwood ice cliff is among the thermokarst features representative of this rapid landscape evolution. Along the Garwood ice cliff, gullies are eroding alcoves into the buried ice and overlying sedimentary cap, incising channels in the ice-cored talus cones at the base of the cliff, and are depositing new fans along the Garwood River banks. We used repeat terrestrial laser scanning to measure gully cross-sectional topography through time and tracked the evolution of gully slopes from alcove to channel to apron as the ice cliff recedes. We determined where sediment erosion and redeposition and/or ice subsidence occur across the landscape as a result of gully processes. Measurements of volume loss, scarp apex retreat, and sediment redeposition throughout time are synthesized to form a coherent understanding of hillslope evolution and the effects of gullies on that evolution. Gullies are found to occur on hillslopes with lower slopes, higher relief, faster scarp apex retreat, and lower erosion rates. The lower erosion rates and faster scarp apex retreat indicates that fans deposited beneath gully features are relatively more stable than the ice cliff face. Gully erosion drives the scarp towards a uniform slope, which enhances sediment retention, and which may ultimately preserve underlying ice through re-burial. Understanding gully evolution in Garwood Valley helps connect drivers of landscape change in the MDV to their effect on the landscape. Gullies are associated with lower erosion rates and faster scarp apex retreat, when compared with non-gullied portions of the ice cliff, indicating either that gullies may be drivers of unique erosional patterns or that gullies appear on hillslopes with a specific set of controls. A pattern of decelerating erosion across the ice cliff throughout time indicates the burial of the thermokarst feature as the ice cliff is insulated through redeposition of sediments. Understanding how gullies evolve contributes to the study of buried ice ablation in the Antarctic as climate change begins to influence old landscapes to evolve in new ways.

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