2018090833 Farquharson, L. M. (University of Alaska at Fairbanks, Geophysical Institute, Fairbanks, AK); Mann, D. H.; Swanson, D. K.; Jones, B. M.; Buzard, R. M. and Jordan, J. W. Temporal and spatial variability in coastline response to declining sea-ice in northwest Alaska: Marine Geology, 404, p. 71-83, illus. incl. 4 tables, sketch map, 74 ref., October 1, 2018.
Arctic sea-ice is declining in extent, leaving coastlines exposed to more storm-wave events. There is an urgent need to understand how these changes affect geomorphic processes along Arctic coasts. Here we describe spatial and temporal patterns of shoreline changes along two geomorphologically distinct, storm-wave dominated reaches of the Chukchi Sea coastline over the last 64 years. One study area encompasses the west- to southwest-facing, coarse-clastic shoreline and ice-rich bluffs of Cape Krusenstern (CAKR). The other covers the north-facing, sandy shorelines on barrier islands, ice-rich bluffs, and the Cape Espenberg spit in the Bering Land Bridge National Park (BELA). Both study areas lie within the zone of continuous permafrost, which exists both on and offshore and outcrops as ice-rich bluffs along the BELA coast. We mapped changes in coastal geomorphology over three observation periods: 1950-1980, 1980-2003, and 2003-2014 using aerial and satellite imagery. We then compared these geomorphic changes to changes in sea-ice coverage, which declined ~10 days per decade between 1979 and 2016 in the southern Chukchi Sea. Changes in coastal geomorphology in both BELA and CAKR exhibited high spatial variability over the study period. Between 2003 and 2014, shorelines of barrier islands in BELA exhibited the highest mean rates of change, -1.5 m yr-1, while coarse, clastic barrier beaches in CAKR showed only minimal change. Overall, shorelines in both BELA and CAKR became more dynamic (increasing erosion or increasing accumulation) after ca. 2003, with spatial variability in shoreline changes roughly doubling between the first period of observation (1950-1980) and the last (2003-2014). This increase in coastal dynamism may signal a transitional period leading to new state of geomorphic equilibria along these ice-affected coastlines.
2018094229 Leonard, Ray (Anglo Eurasia, Houston, TX). An Earth scientist's perspective on climate change: AAPG Explorer, 39(10), p. 24-27, illus., October 2018.
2018094189 Matthews, John A. (Swansea University, Department of Geography, Swansea, United Kingdom); Winkler, Stefan; Wilson, Peter; Tomkins, Matt D.; Dortch, Jason M.; Mourne, Richard W.; Hill, Jennifer L.; Owen, Geraint and Vater, Amber E. Small rock-slope failures conditioned by Holocene permafrost degradation; a new approach and conceptual model based on Schmidt-hammer exposure-age dating, Jotunheimen, southern Norway: Boreas, 47(4), p. 1144-1169, illus. incl. 4 tables, sketch map, 223 ref., October 2018.
Rock-slope failures (RSFs) constitute significant natural hazards, but the geophysical processes that control their timing are poorly understood. However, robust chronologies can provide valuable information on the environmental controls on RSF occurrence: information that can inform models of RSF activity in response to climatic forcing. This study uses Schmidt-hammer exposure-age dating (SHD) of boulder deposits to construct a detailed regional Holocene chronology of the frequency and magnitude of small rock-slope failures (SRSFs) in Jotunheimen, Norway. By focusing on the depositional fans of SRSFs (≤&eq;10 m3), rather than on the corresponding features of massive RSFs (~108 m3), 92 single-event RSFs are targeted for chronology building. A weighted SHD age-frequency distribution and probability density function analysis indicated four centennial- to millennial-scale periods of enhanced SRSF frequency, with a dominant mode at ~4.5 ka. Using change detection and discreet Meyer wavelet analysis, in combination with existing permafrost depth models, we propose that enhanced SRSF activity was primarily controlled by permafrost degradation. Long-term relative change in permafrost depth provides a compelling explanation for the high-magnitude departures from the SRSF background rate and accounts for: (i) the timing of peak SRSF frequency; (ii) the significant lag (~2.2 ka) between the Holocene Thermal Maximum and the SRSF frequency peak; and (iii) the marked decline in frequency in the late-Holocene. This interpretation is supported by geomorphological evidence, as the spatial distribution of SRSFs is strongly correlated with the aspect-dependent lower altitudinal limit of mountain permafrost in cliff faces. Results are indicative of a causal relationship between episodes of relatively warm climate, permafrost degradation and the transition to a seasonal-freezing climatic regime. This study highlights permafrost degradation as a conditioning factor for cliff collapse, and hence the importance of paraperiglacial processes; a result with implications for slope instability in glacial and periglacial environments under global warming scenarios. Abstract Copyright (2010), John Wiley & Sons, Ltd.
2018090753 Kula, Damian (University of Silesia, Katowice, Poland); Olszewska, Dorota; Dobinski, Wojciech and Glazer, Michal. Horizontal-to-vertical spectral ratio variability in the presence of permafrost: Geophysical Journal International, 214(1), p. 219-231, illus. incl. geol. sketch maps, 35 ref., July 2018.
Due to fluctuations in the thickness of the permafrost active layer, there exists a seasonal seismic impedance contrast in the permafrost table. The horizontal-to-vertical spectral ratio (HVSR) method is commonly used to estimate the resonant frequency of sedimentary layers on top of bedrock. Results obtained using this method are thought to be stable in time. The aim of the study is to verify whether seasonal variability in the permafrost active layer influences the results of the HVSR method. The research area lies in the direct vicinity of the Polish Polar Station, Hornsund, which is located in Southern Spitsbergen, Svalbard. Velocity models of the subsurface are obtained using the HVSR method, which are juxtaposed with electrical resistivity tomography profiles conducted near the seismic station. Survey results indicate that the active layer of permafrost has a major influence on the high-frequency section of the HVSR results. In addition, the depth of the permafrost table inferred using the HVSR method is comparable to the depth visible in electrical resistivity tomography results. This study proves that, in certain conditions, the HVSR method results vary seasonally, which must be taken into account in their interpretation.
2018086727 Wagner, Anna M. (U. S. Army Cold Regions Research and Engineering Laboratory, Fairbanks, AK); Lindsey, Nathaniel J.; Dou, Shan; Gelvin, Arthur; Saari, Stephanie; Williams, Christopher; Ekblaw, Ian; Ulrich, Craig; Borglin, Sharon; Morales, Alejandro and Ajo-Franklin, Jonathan. Permafrost degradation and subsidence observations during a controlled warming experiment: Scientific Reports, 8(Article 10908), 9 p., illus. incl. sketch map, 44 ref., July 19, 2018.
Global climate change has resulted in a warmer Arctic, with projections indicating accelerated modifications to permafrost in the near future. The thermal, hydrological, and mechanical physics of permafrost thaw have been hypothesized to couple in a complex fashion but data collection efforts to study these feedbacks in the field have been limited. As a result, laboratory and numerical models have largely outpaced field calibration datasets. We present the design, execution, and initial results from the first decameter-scale controlled thawing experiment, targeting coupled thermal/mechanical response, particularly the temporal sequence of surface subsidence relative to permafrost degradation at depth. The warming test was conducted in Fairbanks, AK, and utilized an array of in-ground heaters to induce thaw of a ~11x131x1.5m soil volume over 63 days. The 4-D temperature evolution demonstrated that the depth to permafrost lowered 1m during the experiment. The resulting thaw induced surface deformation was ~10 cm as observed using a combination of measurement techniques. Surface deformation occurred over a smaller spatial domain than the full thawed volume, suggesting that gradients in cryotexture and ice content were significant. Our experiment provides the first large field calibration dataset for multiphysics thaw models.
2018094274 Hollesen, Jorgen (National Museum of Denmark, Department of Conservation and Natural Science, Lyngby, Denmark); Callanan, Martin; Dawson, Tom; Fenger-Nielsen, Rasmus; Friesen, T. Max; Jensen, Anne M.; Markham, Adam; Martens, Vibeke V.; Pitulko, Vladimir V. and Rockman, Marcy. Climate change and the deteriorating archaeological and environmental archives of the Arctic: Antiquity, 92(363), p. 573-586, June 2018.
The cold, wet climate of the Arctic has led to the extraordinary preservation of archaeological sites and materials that offer important contributions to the understanding of our common cultural and ecological history. This potential, however, is quickly disappearing due to climate-related variables, including the intensification of permafrost thaw and coastal erosion, which are damaging and destroying a wide range of cultural and environmental archives around the Arctic. In providing an overview of the most important effects of climate change in this region and on archaeological sites, the authors propose the next generation of research and response strategies, and suggest how to capitalise on existing successful connections among research communities and between researchers and the public.
2018093330 Drake, Travis W. (National High Magnetic Field Laboratory Geochemistry Group, Tallahassee, FL); Guillemette, François; Hemingway, Jordon D.; Chanton, Jeffery P.; Podgorski, David C.; Zimov, Nikita S. and Spencer, Robert G. M. The ephemeral signature of permafrost carbon in an Arctic fluvial network: Journal of Geophysical Research: Biogeosciences, 123(5), p. 1475-1485, illus. incl. 2 tables, sketch map, 54 ref., May 2018.
Arctic fluvial networks process, outgas, and transport significant quantities of terrestrial organic carbon (C), particularly dissolved organic carbon (DOC). The proportion of permafrost C in these fluxes, however, is poorly constrained. A primary obstacle to the quantification of permafrost-derived DOC is that it is rapidly respired without leaving a unique tracer of its presence. In this study, we investigated the production of bacterial respiratory carbon dioxide (CO2; measured as dissolved inorganic carbon; DIC) during maximum late-summer thaw in sites spanning a fluvial network (Kolyma Basin, Siberia) to assess whether the biodegradation of permafrost DOC could be detected by the presence of a persistent aged (14C-depleted) signature on the DIC pool. Using Keeling plot interpretation of DIC produced in bioincubations of river water, we show that bacteria respire varying sources of DOC moving downstream through the fluvial network. Respiration of permafrost (production of aged CO2) was only detected in heavily permafrost thaw influenced sites. In nonpermafrost thaw impacted sites, ambient DIC was modern (14C-enriched), but rather than precluding the respiration of permafrost OC upstream, we suggest that 14C-depleted DIC is overwhelmed by modern DIC. Investigation of dissolved organic matter composition via Fourier transform ion cyclotron resonance mass spectrometry highlighted that elevated levels of aliphatic and nitrogen-containing compounds were associated with the production of aged DIC, providing molecular-level insight as to why permafrost-derived dissolved organic matter is rapidly respired. Overall, results from this study demonstrate the difficulty of tracing inputs of a highly reactive substrate to systems with diverse organic matter sources. Abstract Copyright (2018), . American Geophysical Union. All Rights Reserved.
2018086444 Frauenfelder, Regula (Norwegian Geotechnical Institute, Oslo, Norway); Isaksen, Ketil; Lato, Matthew J. and Noetzli, Jeannette. Ground thermal and geomechanical conditions in a permafrost-affected high-latitude rock avalanche site (Polvartinden, Northern Norway): The Cryosphere (Online), 12(4), p. 1531-1550, illus. incl. 2 tables, sketch map, 119 ref., April 2018.
On 26 June 2008, a rock avalanche detached in the northeast facing slope of Polvartinden, a high-alpine mountain in Signaldalen, northern Norway. Here, we report on the observed and modelled past and present near-surface temperature regime close to the failure zone, as well as on a subsequent simulation of the subsurface temperature regime, and on initial geomechanical mapping based on laser scanning. The volume of the rock avalanche was estimated to be approximately 500 000 m3. The depth to the actual failure surface was found to range from 40 m at the back of the failure zone to 0 m at its toe. Visible in situ ice was observed in the failure zone just after the rock avalanche. Between September 2009 and August 2013, ground surface temperatures were measured with miniature temperature data loggers at 14 different localities, close to the original failure zone along the northern ridge of Polvartinden and on the valley floor. The results from these measurements and from a basic three-dimensional heat conduction model suggest that the lower altitudinal limit of permafrost at present is at 600-650 m a.s.l., which corresponds to the upper limit of the failure zone. A coupling of our in situ data with regional climate data since 1958 suggests a general gradual warming and that the period with highest mean near surface temperatures on record ended four months before the Signaldalen rock avalanche detached. A comparison with a transient permafrost model run at 10 m depth, representative for areas where snow accumulates, strengthen these findings, which are also in congruence with measurements in nearby permafrost boreholes. It is likely that permafrost in and near the failure zone is presently subject to degradation. This degradation, in combination with the extreme warm year antecedent to the rock failure, is seen to have played an important role in the detaching of the Signaldalen rock avalanche.
2018086387 Cable, Stefanie (University of Copenhagen, Department of Geosciences and Natural Resource Management, Copenhagen, Denmark); Christiansen, Hanne H.; Westergaard-Nielsen, Andreas; Kroon, Aart and Elberling, Bo. Geomorphological and cryostratigraphical analyses of the Zackenberg Valley, NE Greenland and significance of Holocene alluvial fans: Geomorphology, 303, p. 504-523, illus. incl. 3 tables, geol. sketch map, 117 ref., February 15, 2018. Includes appendices.
In High Arctic northern Greenland, future responses to climatic changes are poorly understood on a landscape scale. Here, we present a study of the geomorphology and cryostratigraphy in the Zackenberg Valley in NE Greenland (74°N) containing a geomorphological map and a simplified geocryological map, combined with analyses of 13 permafrost cores and two exposures. Cores from a solifluction sheet, alluvial fans, and an emerged delta were studied with regards to cryostructures, ice and total carbon contents, grain size distribution, and pore water electrical conductivity; and the samples were AMS 14C dated. The near-surface permafrost on slopes and alluvial fans is ice rich, as opposed to the ice-poor epigenetic permafrost in the emerged delta. Ground ice and carbon distribution are closely linked to sediment transport processes, which largely depend on lithology and topography. Holocene alluvial fans on the lowermost hillslopes, covering 12% of the study area, represent paleoenvironmental archives. During the contrasting climates of the Holocene, the alluvial fans continued to aggrade--through the warmer early Holocene Optimum, the colder late Holocene, and the following climate warming--and by 0.45 mm a-1, on average. This is caused by three factors: sedimentation, ground ice aggradation, and vegetation growth and is reflected by AMS 14C dating and continuously alternating cryostructures. Highly variable sedimentation rates in space and time at the alluvial fans have been detected. This is also reflected by alternating lenticular and microlenticular cryostructures indicating syngenetic permafrost aggradation during sedimentation with suspended and organic-matrix cryostructures indicating quasi-syngenetic permafrost aggradation in response to vegetation growth in periods with reduced or no sedimentation. Over time, this causes organic matter to become buried, indicating that alluvial fans represent effective carbon sinks that have previously been overlooked.
2018096315 Dobinski, Wojciech (University of Silesia, Faculty of Earth Sciences, Sosnowiec, Poland) and Glazer, Michal. Probable two-layered permafrost formation, as a result of climatic evolution in mountainous environment of Storglaciaren Forefield, Tarfala, northern Scandinavia: Polish Polar Research, 39(2), p. 177-209, illus. incl. sects., 1 table, sketch map, 82 ref., 2018.
The analysis of climate changes in of the Tarfala valley and Kebnekaise Mts area, and changes within the range of the Scandinavian Glaciation shows that even in the warmest period of Holocene there were favourable environmental conditions for permafrost of the Pleistocene origin to be preserved in this area. The results of electrical resistivity surveys together with analysis of available publications indicate that two layers of permafrost can be distinguished in the Storglaciaren forefield. The shallower, discontinuous, with thickness ca. 2-6 meters is connected to the current climate, The second, deeper located layer of permafrost, separated with talik, is older. Its thickness can reach dozens of metres and is probably the result of permafrost formation during Pleistocene. The occurrence of two-layered permafrost in the Tarfala valley in Kebnekaise area shows the evolution of mountain permafrost may be seen as analogous to that in Western Siberia. This means that the effect of climate changes gives a similar effect in permafrost formation and evolution in both altitudinal and latitudinal extent. The occurrence of two-layered permafrost in Scandes and Western Siberia plain indicates possible analogy in climatic evolution, and gives opportunity to understand them in uniform way.
2018096764 Jongejans, Loeka L. (Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research, Potsdam, Germany); Strauss, Jens; Lenz, Josefine; Peterse, Francien; Mangelsdorf, Kai; Fuchs, Matthias and Grosse, Guido. Organic matter characteristics in yedoma and thermokarst deposits on Baldwin Peninsula, west Alaska: Biogeosciences, 15(20), p. 6033-6048, illus. incl. 3 tables, geol. sketch maps, 85 ref., 2018.
As Arctic warming continues and permafrost thaws, more soil and sedimentary organic matter (OM) will be decomposed in northern high latitudes. Still, uncertainties remain in the quality of the OM and the size of the organic carbon (OC) pools stored in different deposit types of permafrost landscapes. This study presents OM data from deep permafrost and lake deposits on the Baldwin Peninsula which is located in the southern portion of the continuous permafrost zone in west Alaska. Sediment samples from yedoma and drained thermokarst lake basin (DTLB) deposits as well as thermokarst lake sediments were analyzed for cryostratigraphical and biogeochemical parameters and their lipid biomarker composition to identify the belowground OC pool size and OM quality of ice-rich permafrost on the Baldwin Peninsula. We provide the first detailed characterization of yedoma deposits on Baldwin Peninsula. We show that three-quarters of soil OC in the frozen deposits of the study region (total of 68 Mt) is stored in DTLB deposits (52 Mt) and one-quarter in the frozen yedoma deposits (16 Mt). The lake sediments contain a relatively small OC pool (4 Mt), but have the highest volumetric OC content (93 kg m-3) compared to the DTLB (35 kg m-3) and yedoma deposits (8 kg m-3), largely due to differences in the ground ice content. The biomarker analysis indicates that the OM in both yedoma and DTLB deposits is mainly of terrestrial origin. Nevertheless, the relatively high carbon preference index of plant leaf waxes in combination with a lack of a degradation trend with depth in the yedoma deposits indicates that OM stored in yedoma is less degraded than that stored in DTLB deposits. This suggests that OM in yedoma has a higher potential for decomposition upon thaw, despite the relatively small size of this pool. These findings show that the use of lipid biomarker analysis is valuable in the assessment of the potential future greenhouse gas emissions from thawing permafrost, especially because this area, close to the discontinuous permafrost boundary, is projected to thaw substantially within the 21st century.
2018096687 Kroisleitner, Christine (Zentralanstalt für Meteorologie und Geodynamik, Vienna, Austria); Bartsch, Annett and Bergstedt, Helena. Circumpolar patterns of potential mean annual ground temperature based on surface state obtained from microwave satellite data: The Cryosphere (Online), 12(7), p. 2349-2370, illus. incl. 5 tables, sketch maps, 59 ref., 2018.
Gap filling is required for temporally and spatially consistent records of land surface temperature from satellite data due to clouds or snow cover. Land surface state, frozen versus unfrozen conditions, can be, however, captured globally with satellite data obtained by microwave sensors. The number of frozen days per year has been previously proposed to be used for permafrost extent determination. This suggests an underlying relationship between number of frozen days and mean annual ground temperature (MAGT). We tested this hypothesis for the Northern Hemisphere north of 50° N using coarse-spatial-resolution microwave satellite data (Metop Advanced SCATterometer - ASCAT - and Special Sensor Microwave Imager - SSM/I; 12.5 and 25 km nominal resolution; 2007-2012), which provide the necessary temporal sampling. The MAGT from GTN-P (Global Terrestrial Network for Permafrost) borehole records at the coldest sensor depth was tested for validity in order to build a comprehensive in situ data set for calibration and validation and was eventually applied. Results are discussed with respect to snow water equivalent, soil properties, land cover and permafrost type. The obtained temperature maps were classified for permafrost extent and compared to alternative approaches. An R2 of 0.99 was found for correlation between and MAGT at zero annual amplitude provided in GTN-P metadata and MAGT at the coldest sensor depth. The latter could be obtained with an RMSE of 2.2 °C from ASCAT and 2.5 °C from SSM/I surface state records using a linear model. The average deviation within the validation period is less than 1 °C at locations without glaciers and coastlines within the resolution cell in the case of ASCAT. The exclusion of snow melt days (available for ASCAT) led to better results. This suggests that soil warming under wet snow cover needs to be accounted for in this context. Specifically Scandinavia and western Russia are affected. In addition, MAGT at the coldest sensor depth was overestimated in areas with a certain amount of organic material and in areas of cold permafrost. The derived permafrost extent differed between the used data sets and methods. Deviations are high in central Siberia, for example. We show that microwave-satellite-derived surface state records can provide an estimation of not only permafrost extent but also MAGT without the need for gap filling. This applies specifically to ASCAT. The deviations among the tested data sets, their spatial patterns as well as in relation to environmental conditions, revealed areas which need special attention for modelling of MAGT.
2018096786 Mamot, Philipp (Technical University of Munich, Department of Landslide Research, Munich, Germany); Weber, Samuel; Schröder, Tanja and Krautblatter, Michael. A temperature- and stress-controlled failure criterion for ice-filled permafrost rock joints: The Cryosphere (Online), 12(10), p. 3333-3353, illus. incl. 1 table, sketch maps, 77 ref., 2018.
Instability and failure of high mountain rock slopes have significantly increased since the 1990s coincident with climatic warming and are expected to rise further. Most of the observed failures in permafrost-affected rock walls are likely triggered by the mechanical destabilisation of warming bedrock permafrost including ice-filled joints. The failure of ice-filled rock joints has only been observed in a small number of experiments, often using concrete as a rock analogue. Here, we present a systematic study of the brittle shear failure of ice and rock-ice interfaces, simulating the accelerating phase of rock slope failure. For this, we performed 141 shearing experiments with rock-ice-rock sandwich' samples at constant strain rates (10-3 s-1) provoking ice fracturing, under normal stress conditions ranging from 100 to 800 kPa, representing 4-30 m of rock overburden, and at temperatures from -10 to -0.5 °C, typical for recent observed rock slope failures in alpine permafrost. To create close to natural but reproducible conditions, limestone sample surfaces were ground to international rock mechanical standard roughness. Acoustic emission (AE) was successfully applied to describe the fracturing behaviour, anticipating rock-ice failure as all failures are predated by an AE hit increase with peaks immediately prior to failure. We demonstrate that both the warming and unloading (i.e. reduced overburden) of ice-filled rock joints lead to a significant drop in shear resistance. With a temperature increase from -10 to -0.5 °C, the shear stress at failure reduces by 64%-78% for normal stresses of 100-400 kPa. At a given temperature, the shear resistance of rock-ice interfaces decreases with decreasing normal stress. This can lead to a self-enforced rock slope failure propagation: as soon as a first slab has detached, further slabs become unstable through progressive thermal propagation and possibly even faster by unloading. Here, we introduce a new Mohr-Coulomb failure criterion for ice-filled rock joints that is valid for joint surfaces, which we assume similar for all rock types, and which applies to temperatures from -8 to -0.5 °C and normal stresses from 100 to 400 kPa. It contains temperature-dependent friction and cohesion, which decrease by 12% °C-1 and 10% °C-1 respectively due to warming and it applies to temperature and stress conditions of more than 90% of the recently documented accelerating failure phases in permafrost rock walls.
2018096685 Ran Zeze (Peking University, College of Urban and Environmental Sciences, Beijing, China) and Liu Gengnian. Rock glaciers in Daxue Shan, south-eastern Tibetan Plateau; an inventory, their distribution, and their environmental controls: The Cryosphere (Online), 12(7), p. 2327-2340, illus. incl. 2 tables, geol. sketch maps, 70 ref., 2018.
Rock glaciers are typical periglacial landforms. They can indicate the existence of permafrost, and can also shed light on the regional geomorphological and climatic conditions under which they may have developed. This article provides the first rock glacier inventory of Daxue Shan, south-eastern Tibetan Plateau. The inventory is based on analyses of Google Earth imagery. In total, 295 rock glaciers were identified in Daxue Shan, covering a total area of 55.70 km2 between the altitudes of 4300 and 4600 m above sea level. Supported by ArcGIS and SPSS software programmes, we extracted and calculated morphometric parameters of these rock glaciers, and analysed the characteristics of their spatial distribution within Daxue Shan. Our inventory suggests that the lower altitudinal boundary for permafrost across the eight aspects of observed slopes differs significantly and that the lower altitudinal permafrost boundary is ~ 104 m higher on western than eastern-facing slopes. Moraine-type and talus-derived rock glaciers exhibit mean gradients that are all concentrated within the 22-35° range. However, lobate rock glaciers (27-45°) have a higher mean gradient than tongue-shaped rock glaciers (22-35°). Shady (i.e. N, NE, and E) slopes appear related to the presence of moraine-type rock glaciers, whereas sunny (i.e. W, SW, and S) slopes appear related to the presence of talus-derived rock glaciers. Rock glaciers in Daxue Shan are more concentrated within tertiary monzonitic granite, which is more sensitive than other lithological components to the freeze-thaw process. Continuous weathering of this substrate provides the ideal raw material for the rock glacier development. These results show that environmental controls (i.e. topographical, climatic, lithological factors) greatly affect the formation and development of rock glaciers. This study provides important data for exploring the relation between maritime periglacial environments and the development of rock glaciers on the south-eastern Tibetan Plateau (TP). It may also highlight the characteristics typical of rock glaciers found in a maritime setting.
2018096784 Sparkes, Robert B. (Manchester Metropolitan University, School of Science and the Environment, Manchester, United Kingdom); Maher, Melissa; Blewett, Jerome; Selver, Ayca Dogrul; Gustafsson, Orjan; Semiletov, Igor P. and van Dongen, Bart E. Carbonaceous material export from Siberian permafrost tracked across the Arctic Shelf using Raman spectroscopy: The Cryosphere (Online), 12(10), p. 3293-3309, illus. incl. 2 tables, sketch maps, 69 ref., 2018.
Warming-induced erosion of permafrost from Eastern Siberia mobilises large amounts of organic carbon and delivers it to the East Siberian Arctic Shelf (ESAS). In this study Raman spectroscopy of carbonaceous material (CM) was used to characterise, identify and track the most recalcitrant fraction of the organic load: 1463 spectra were obtained from surface sediments collected across the ESAS and automatically analysed for their Raman peaks. Spectra were classified by their peak areas and widths into disordered, intermediate, mildly graphitised and highly graphitised groups and the distribution of these classes was investigated across the shelf. Disordered CM was most prevalent in a permafrost core from Kurungnakh Island and from areas known to have high rates of coastal erosion. Sediments from outflows of the Indigirka and Kolyma rivers were generally enriched in intermediate CM. These different sediment sources were identified and distinguished along an E-W transect using their Raman spectra, showing that sediment is not homogenised on the ESAS. Distal samples, from the ESAS slope, contained greater amounts of highly graphitised CM compared to the rest of the shelf, attributable to degradation or, more likely, winnowing processes offshore. The presence of all four spectral classes in distal sediments demonstrates that CM degrades much more slowly than lipid biomarkers and other traditional tracers of terrestrial organic matter and shows that alongside degradation of the more labile organic matter component there is also conservative transport of carbon across the shelf toward the deep ocean. Thus, carbon cycle calculations must consider the nature as well as the amount of carbon liberated from thawing permafrost and other erosional settings.
2018096761 Walz, Josefine (Universität Hamburg, Institute of Soil Science, Hamburg, Germany); Knoblauch, Christian; Tigges, Ronja; Opel, Thomas; Schirrmeister, Lutz and Pfeiffer, Eva-Maria. Greenhouse gas production in degrading ice-rich permafrost deposits in northeastern Siberia: Biogeosciences, 15(17), p. 5423-5436, illus. incl. 2 tables, sketch map, 74 ref., 2018.
Permafrost deposits have been a sink for atmospheric carbon for millennia. Thaw-erosional processes, however, can lead to rapid degradation of ice-rich permafrost and the release of substantial amounts of organic carbon (OC). The amount of the OC stored in these deposits and their potential to be microbially decomposed to the greenhouse gases carbon dioxide (CO2) and methane (CH4) depends on climatic and environmental conditions during deposition and the decomposition history before incorporation into the permafrost. Here, we examine potential greenhouse gas production as a result of degrading ice-rich permafrost deposits from three locations in the northeastern Siberian Laptev Sea region. The deposits span a period of about 55 kyr from the last glacial period and Holocene interglacial. Samples from all three locations were incubated under aerobic and anaerobic conditions for 134 days at 4 °C. Greenhouse gas production was generally higher in deposits from glacial periods, where 0.2%-6.1% of the initially available OC was decomposed to CO2. In contrast, only 0.1%-4.0% of initial OC was decomposed in permafrost deposits from the Holocene and the late glacial transition. Within the deposits from the Kargin interstadial period (Marine Isotope Stage 3), local depositional environments, especially soil moisture, also affected the preservation of OC. Sediments deposited under wet conditions contained more labile OC and thus produced more greenhouse gases than sediments deposited under drier conditions. To assess the greenhouse gas production potentials over longer periods, deposits from two locations were incubated for a total of 785 days. However, more than 50% of total CO2 production over 785 days occurred within the first 134 days under aerobic conditions, while 80% were produced over the same period under anaerobic conditions, which emphasizes the nonlinearity of the OC decomposition processes. Methanogenesis was generally observed in active layer samples but only sporadically in permafrost samples and was several orders of magnitude smaller than CO2 production.
2018096778 Yi Shuhua (Nantong University, School of Geographic Sciences, Nantong, China); He Yujie; Guo, Xinlei; Chen Jianjun; Wu Qingbai; Qin Yu and Ding Yongjian. The physical properties of coarse-fragment soils and their effects on permafrost dynamics; a case study on the central Qinghai-Tibetan Plateau: The Cryosphere (Online), 12(9), p. 3067-3083, illus. incl. 6 tables, sketch map, 67 ref., 2018.
Soils on the Qinghai-Tibetan Plateau (QTP) have distinct physical properties from agricultural soils due to weak weathering and strong erosion. These properties might affect permafrost dynamics. However, few studies have investigated both quantitatively. In this study, we selected a permafrost site on the central region of the QTP and excavated soil samples down to 200 cm. We measured soil porosity, thermal conductivity, saturated hydraulic conductivity, and matric potential in the laboratory. Finally, we ran a simulation model replacing default sand or loam parameters with different combinations of these measured parameters. Our results showed that the mass of coarse fragments in the soil samples (diameter > 2 mm) was ~ 55 % on average, soil porosity was less than 0.3 m3 m-3, saturated hydraulic conductivity ranged from 0.004 to 0.03 mm s-1, and saturated matric potential ranged from -14 to -604 mm. When default sand or loam parameters in the model were substituted with these measured values, the errors of soil temperature, soil liquid water content, active layer depth, and permafrost lower boundary depth were reduced (e.g., the root mean square errors of active layer depths simulated using measured parameters versus the default sand or loam parameters were about 0.28, 1.06, and 1.83 m). Among the measured parameters, porosity played a dominant role in reducing model errors and was typically much smaller than for soil textures used in land surface models. We also demonstrated that soil water dynamic processes should be considered, rather than using static properties under frozen and unfrozen soil states as in most permafrost models. We conclude that it is necessary to consider the distinct physical properties of coarse-fragment soils and water dynamics when simulating permafrost dynamics of the QTP. Thus it is important to develop methods for systematic measurement of physical properties of coarse-fragment soils and to develop a related spatial data set for porosity.
2018087914 Yang Yuzhong (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, State Key Laboratory of Frozen Soil Engineering, Lanzhou, China); Wu Qingbai; Zhang Peng and Jiang Guanli. Stable isotopic evolutions of ground ice in permafrost of the Hoh Xil regions on the Qinghai-Tibet Plateau: in Third pole; the last 20,000 years; Part 2 (Kotlia, Bahadur, editor; et al.), Quaternary International, 444(Part A), p. 182-190, illus. incl. 3 tables, sketch maps, 38 ref., July 15, 2017.
Climatic warming-induced permafrost (ground ice) thaw is expected to considerably alter hydro-geomorphology and the water cycle on the Qinghai-Tibet Plateau (QTP). A unique feature of permafrost is the substantial enrichment of ground ice, which can be used to directly indicate the past climate and hydrological cycle. However, essential characteristics of ground ice on the QTP are not yet understood. The stable isotope technique was used to investigate the formation processes and initial source of water in the ground ice in a borehole of Zhuonaihu (ZNH) lake at the Hoh Xil permafrost regions in the hinterland of the QTP. Variability in water migration, replenishment of water, and climatic conditions (freezing rate) have created a complex isotopic stratigraphy and ice growth history. The dD-d18O relationship of ground ice samples showed similar characteristics to a local meteoric water line of regional precipitation on QTP, and the D-excess-dD relations of ground ice reveal different features from those of precipitation and freezing condition. The near-surface ground ice (0-3 m) was enriched in d18O and dD which was formed from freezing of active layer water suffering evaporation, and deep layer ground ice (>3 m) was depleted in these isotopes. Stable isotope results were indicative of past-precipitation origin of ground ice between 2.5 and 5.5 m. Ground ice between depths of 5.5 and 10 m was formed under unstable freezing conditions. However, ice from 10 to 16 m was formed by freezing segregation of liquid water. Comparison of the results with other five boreholes indicates that differences in lithology, source water, and climatic conditions were responsible for the significant deviations in ground ice isotopes. This research provides an insight into the fundamental formation processes related to ground ice in the QTP, which will provide important guidance for future studies of permafrost hydrology.
2018087910 Zhu Xiaofan (Chinese Academy of Sciences, Cold and Arid Regions Environmental and Engineering Research Institute, Cryosphere Research Station on the Qinghai-Tibet Plateau, State Key Laboratory of Cryospheric Sciences, Lanzhou, China); Wu Tonghua; Li Ren; Wang Shengjie; Hu Guojie; Wang Weihua; Qin Yanhui and Yang Shuhua. Characteristics of the ratios of snow, rain and sleet to precipitation on the Qinghai-Tibet Plateau during 1961-2014: in Third pole; the last 20,000 years; Part 2 (Kotlia, Bahadur, editor; et al.), Quaternary International, 444(Part A), p. 137-150, illus. incl. 4 tables, sketch maps, 68 ref., July 15, 2017.
Precipitation in different types has great influence not only on water resources and distribution of annual precipitation in cold regions, but also on the thermal regimes of frozen ground. The long-term variations of the ratios of snow, rain and sleet to precipitation were analyzed in this study. The 44 meteorological stations were selected, which are located on the Qinghai-Tibet Plateau (QTP) including permafrost and seasonal frozen ground regions. The results indicate that the monthly snow/precipitation ratio in permafrost regions is far higher than that in seasonal frozen ground regions, but the monthly rain/precipitation ratio in permafrost regions is lower than that in seasonal frozen ground regions, and the monthly variation of sleet/precipitation ratio is indistinctive. The annual ratios of snow and sleet to precipitation show decreasing trends in both regions, and annual rain/precipitation ratio shows an increasing tendency. The dropping magnitude of annual snow/precipitation ratio in seasonal frozen ground regions is larger than that in permafrost regions. The maximum and minimum annual snow/precipitation ratios in both regions occur in winter and summer, respectively, and the second is in spring, instead, the maximum and minimum annual rain/precipitation ratios appear in summer and winter, respectively. The spatial features of the ratios of snow and rain to precipitation are largely opposite, that is, the low snow/precipitation ratio stations are usually associated with the high rain/precipitation ratio, and prominent seasonal diversities of three ratios can be found from their spatial patterns. In addition, the decreasing (increasing) tendency of snow (rain)/precipitation ratio in spring and autumn is more significant than that in winter and summer, and these stations of snow/precipitation ratio with downward trends are mainly located at the edge of the QTP. The ratios of snow and sleet to precipitation will gradually decrease (increase), and the rain/precipitation ratio will increase (decrease) with the air temperature (altitude) rises, respectively, while there are significant seasonal discrepancies. Moreover, the altitude zone showing remarkable variations of the ratios of snow and rain to precipitation ranges from 3000 to 4000 m a.s.l, especially in spring and summer.
2018086726 Lu Qing (Chinese Academy of Sciences, Institute of Geographic Sciences and Natural Resources Research, Beijing, China); Zhao Dongsheng and Wu Shaohong. Simulated responses of permafrost distribution to climate change on the Qinghai-Tibet Plateau: Scientific Reports, 7(Article 3845), 13 p., illus. incl. 1 table, sketch map, 79 ref., June 19, 2017.
Climate warming causes changes in permafrost distribution, which affects the surface energy balance, hydrologic cycle and carbon flux in cold regions. In this study, the Surface Frost Number model was applied to examine permafrost distribution on the Qinghai-Tibet Plateau (QTP) under the four RCPs (RCP2.6, RCP4.5, RCP6.0, and RCP8.5). The Kappa statistic was used to evaluate model results by comparing simulations of baseline permafrost distribution (1981-2010) with the existing frozen soil maps. The comparison shows that the Surface Frost Number model is suitable for simulating the general characteristics of permafrost distribution on the QTP. Simulated results suggest that areas of permafrost degradation would be the smallest in the near-term (2011-2040) with the rates of 17.17%, 18.07%, 12.95% and 15.66% under RCP2.6, RCP4.5, RCP6.0 and RCP8.5, respectively. The rate of permafrost degradation would be faster in the mid-term (2041-2070), especially under the RCP8.5 scenario (about 41.42%). Areas of permafrost degradation would be the largest in the long-term (2071-2099) relative to baseline conditions, with a modelled 64.31% decrease in permafrost distribution using the RCP8.5 scenario. Our results would help the decision-making for engineering construction program on the QTP, and support local units in their efforts to adapt climate change.
2018089661 Beka, Thomas I. (Arctic University of Norway, Faculty of Science and Technology, Tromso, Norway); Senger, Kim; Autio, Uula A.; Smirnov, Maxim and Birkelund, Yngve. Integrated electromagnetic data investigation of a Mesozoic CO2 storage target reservoir-cap-rock succession, Svalbard: Journal of Applied Geophysics, 136, p. 417-430, illus. incl. sects., strat. col., geol. sketch map, 69 ref., January 2017.
Recently acquired time-domain electromagnetic (TEM) and magnetotelluric (MT) data sets are utilized in the first electromagnetic (EM) characterization of a geological CO2 storage target site in Adventdalen, Arctic Norway. Combining the two EM data sets enabled to resolve the electrical resistivity structure of the target site better than either of the methods alone. 2D inverting the MT data in the audio period interval (0.003-1 s) with supporting input derived from the TEM data (0.01-10 ms) provided a geologically meaningful resistivity model that included information not previously evident from existing seismic and borehole data. The ca. 1.8 ´ 1 km 2D resistivity model displays a laterally constrained highly conductive anomaly (ca. 10 W m) at about 400-500 m depth, where reflectors of a parallel seismic section are concealed and core samples indicate a highly fractured décollement zone formed during Paleogene compression. The base of the permafrost is imaged at ca. 200 m depth. Synthetic inversion tests, however, suggest that this may be exaggerated by tens of meters, due to a thin conductive layer present approximately between 10 and 25 m depth. The resistivity model does not give indication for a fluid pathway we can connect to leakage, in line with water injection and leak-off tests in the reservoir and cap-rock, both of which indicate a sealing shale-dominated cap-rock separating an over-pressured compartment above the sealing shale from a severely under-pressured reservoir interval. The results we present indicate the advantage of integrating EM exploration techniques in a CO2 reservoir-cap-rock study to obtain a more complete picture.
2018085304 Romankevich, E. A. (Russian Academy of Sciences, Shirshov Institute of Oceanology, Moscow, Russian Federation); Vetrov, A. A.; Belyaev, N. A.; Sergienko, V. I.; Semiletov, I. P.; Sukhoverkhov, S. V.; Bratskaya, S. Yu.; Prokuda, N. A. and Ulyantsev, A. S. Alkanes in Quaternary deposits of the Laptev Sea: Doklady Earth Sciences, 472(1), p. 36-39, illus., 10 ref., January 2017.
The distribution and genesis of n-alkanes in sediments from the 38-m sequence obtained during core boring in the Ivashkina lagoon were studied. Sediments were formed in the Holocene as a result of thermokarst and penetration of seawater. The sequence mostly includes permafrost rocks partially molten in the upper horizons and covered by Quaternary deposits, which are mostly the products of thermoabrasion. Copyright 2017 Pleiades Publishing, Ltd.
2018095315 Kaiser, Sonja (Max Planck Institute for Biogeochemistry, Jena, Germany); Göckede, Mathias; Castro-Morales, Karel; Knoblauch, Christian; Ekici, Altug; Kleinen, Thomas; Zubrzycki, Sebastian; Sachs, Torsten; Wille, Christian and Beer, Christian. Process-based modelling of the methane balance in periglacial landscapes (JSBACH-methane): Geoscientific Model Development (GMD), 10(1), p. 333-358, illus. incl. 5 tables, 73 ref., 2017. Includes appendices.
A detailed process-based methane module for a global land surface scheme has been developed which is general enough to be applied in permafrost regions as well as wetlands outside permafrost areas. Methane production, oxidation and transport by ebullition, diffusion and plants are represented. In this model, oxygen has been explicitly incorporated into diffusion, transport by plants and two oxidation processes, of which one uses soil oxygen, while the other uses oxygen that is available via roots. Permafrost and wetland soils show special behaviour, such as variable soil pore space due to freezing and thawing or water table depths due to changing soil water content. This has been integrated directly into the methane-related processes. A detailed application at the Samoylov polygonal tundra site, Lena River Delta, Russia, is used for evaluation purposes. The application at Samoylov also shows differences in the importance of the several transport processes and in the methane dynamics under varying soil moisture, ice and temperature conditions during different seasons and on different microsites. These microsites are the elevated moist polygonal rim and the depressed wet polygonal centre. The evaluation shows sufficiently good agreement with field observations despite the fact that the module has not been specifically calibrated to these data. This methane module is designed such that the advanced land surface scheme is able to model recent and future methane fluxes from periglacial landscapes across scales. In addition, the methane contribution to carbon cycle-climate feedback mechanisms can be quantified when running coupled to an atmospheric model.
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2018092334 Weissl, M. (University Vienna, Department of Geodynamics and Sedimentology, Vienna, Austria); Hintersberger, E.; Lomax, J.; Lüthgens, C. and Decker, K. Active tectonics and geomorphology of the Gaenserndorf Terrace in the central Vienna Basin (Austria): in Quaternary earthquakes; geology and palaeoseismology for seismic hazard assessment (Blumetti, Anna Maria, editor; et al.), Quaternary International, 451, p. 209-222, illus. incl. sects., 1 table, geol. sketch maps, 55 ref., September 7, 2017. Meeting: 6th International Union for Quaternary Research workshop on Palaeoseismology, active tectonics and archaeoseismology, April 19-24, 2015, Pescina, Italy.
In the central Vienna Basin, the area north of the River Danube is dominated by large river terraces consisting mainly of coarse sandy gravels and sand deposited by the Danube and the Morava River. IRSL dating for the terrace body yielded minimum ages from about 200 to 300 ka. The terrace deposits are locally covered with loess and aeolian sand of the last glacial period revealing OSL/IRSL ages of about 15 ka.The terraces are dissected by a system of normal faults. One of these faults, the Aderklaa-Bockfliess Fault, was investigated in 2014 by paleoseismological trenching. Eventually, the exact fault location and its vertical offset of 10 m were defined by combining electrical resistivity measurements and the analysis of remote sensing data.In addition, at the northern part of this so-called Gaenserndorf terrace, high-resolution digital terrain models based on LIDAR measurements show landforms comparable with relief features resulting from permafrost degradation. Large elongated and clam-shaped depressions are interpreted as basins of former thermokarst lakes. Current dry valleys are interpreted as the Pleistocene drainages of the terrace surface. The cryogenic morphology is preserved only in the elevated parts of the terrace and therefore in the footwall of the bounding normal faults. In contrast, Quaternary basins of the hanging wall are filled with up to 40 m thick Pleistocene and Holocene growth strata. Therefore, most characteristics of the recent geomorphology can be interpreted as a result of overlapping neotectonic processes and permafrost degeneration during the Pleistocene.
2018093076 Fouché, Julien (Queen's University, Department of Geography and Planning, Kingston, ON, Canada); Christiansen, C. T.; Lafrenière, M. J.; Grogan, P. and Lamoureux, S. F. A Pan-Canadian study of optical properties of dissolved organic matter in the active layer and permafrost [abstr.]: in Goldschmidt abstracts 2017, V.M. Goldschmidt Conference - Program and Abstracts, 27, 2 ref., 2017. Meeting: Goldschmidt 2017, Aug. 13-18, 2017, Paris, France.
2018092894 Geertsema, Marten (Ministry of Forests, Lands and Natural Resource Operations, Prince George, BC, Canada). Cryospheric conditioning of landslides in Western Canada and Alaska [abstr.]: in Geological Society of America, 2017 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 49(6), Abstract no. 216-11, 2017. Meeting: Geological Society of America, 2017 annual meeting & exposition, Oct. 22-25, 2017, Seattle, WA.
Cryospheric changes may be contributing to landslide size and magnitude in western Canada and Alaska. Placing large rock slide initiation zones in recently deglaciated areas is relatively simple. Glacier changes are very recognizable on coarse satellite imagery. Establishing linkages between slope instability and mountain permafrost degradation is much more difficult. Permafrost is a thermal state, its presence or absence much less obvious that of a glacier. Nonetheless advances in permafrost distribution mapping, rock temperature data, and frozen rock mechanics suggest landslides may be increasing due to permafrost thaw. On larger scales, the repositioning of landscape elements may be giving cryospheric landslides a much greater impact zone. For example, the retreat of valley glaciers may bring glacial lakes and fjords closer to steep slopes, increasing the likelihood of landslide tsunamis or rock slide - debris flows. Here I give an overview of some recent cryospheric landslides and their consequences.
2018095865 in 't Zandt, Michiel (Utrecht University, Utrecht, Netherlands); de Jong, Anniek; Rasigraf, Olivia; Meisel, Ove; Dean, Joshua; Dolman, Han; Jetten, Mike and Welte, Cornelia. Methane microbiology of Arctic thermokarst lake sediments in response to warming [abstr.]: in Goldschmidt abstracts 2017, V.M. Goldschmidt Conference - Program and Abstracts, 27, 2017. WWW. Meeting: Goldschmidt 2017, Aug. 13-18, 2017, Paris, France.
2018093082 Macalady, J. L. (Pennsylvania State University, Department of Geosciences, State College, PA); Mankoff, K.; Lutz, S. and Benning, Liane G. Novel microbial communities in subglacial (dark) permafrost [abstr.]: in Goldschmidt abstracts 2017, V.M. Goldschmidt Conference - Program and Abstracts, 27, 2017. Meeting: Goldschmidt 2017, Aug. 13-18, 2017, Paris, France.
2018086081 Pawley, Steven (Alberta Geological Survey, Edmonton, AB, Canada) and Utting, Daniel. Regional-scale probabilistic permafrost mapping of northern Alberta, Canada, using GRASS GIS and scikit-learn [abstr.]: in Geological Society of America, 2017 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 49(6), Abstract no. 327-8, 2017. Meeting: Geological Society of America, 2017 annual meeting & exposition, Oct. 22-25, 2017, Seattle, WA.
Approximately 210,000 km2 of Northern Alberta exists within the zone of sporadic permafrost, with 26% of the peatlands estimated to contain components of perennially frozen ground. Understanding the distribution of sporadic permafrost is important because ongoing thawing affects ground stability, ecology and surface hydrology. Further, the sensitivity of permafrost to disturbance by infrastructure development makes it an important consideration for land use and reclamation planning. However, to date there has been limited mapping of sporadic permafrost in Alberta at a scale sufficient for these purposes, with previous airphoto-based interpretations providing only a small-scale delineation of the forest-covered permafrost terrain. This presentation will focus on the development of a methodology that integrates Landsat best pixel mosaics, climatic data, and terrain information from a regional 15 m LiDAR DEM to classify permafrost terrain consisting of forest-covered palsa bogs and larger peat plateaus using a suite of machine learning techniques. The software r.learn.ml, which is freely available as a GRASS GIS add on, was developed for the purpose of providing a linkage between popular open-source GIS with the Python machine learning library, scikit-learn. Evaluation of the modelled results revealed high classification accuracies when compared to ground-truth data (>85%). These results also demonstrate that near-surface permafrost is significantly more extensive than previously identified in northern Alberta, even at relatively low latitudes (»56.5°).
2018086061 Terry, Neil (U. S. Geological Survey, Storrs, CT); Grunewald, Elliot; Briggs, Martin A.; Kass, Andrew M.; Huryn, Alexander; Gooseff, Michael; Hendrickson, Patrick J. and Lane, John W. A conceptual model for seasonal thaw dynamics of an aufeis feature inferred from surface geophysical methods [abstr.]: in Geological Society of America, 2017 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 49(6), Abstract no. 325-10, 2017. Meeting: Geological Society of America, 2017 annual meeting & exposition, Oct. 22-25, 2017, Seattle, WA.
Aufeis are layered accumulations of ice, up to several meters thick, formed from groundwater discharge during freezing conditions. In winter, these features are thought to act as ecological oases by supplying water and heat in an otherwise frozen environment. In summer, the melting ice provides a stable supply of water downstream. The Kuparuk Aufeis (Northslope, AK) is a large (» 5 km2) aufeis feature that forms in the cobble bed of the Kuparuk river. Ground penetrating radar (GPR) data were collected along transects corresponding to fifty piezometer locations within the Kuparuk Aufeis during a summer (little surface ice) and late winter (maximum predicted surface ice thickness) campaign to gain insight into the freeze-thaw dynamics of below the aufeis feature. Surface nuclear magnetic resonance (NMR) data were also collected in late winter at select piezometer locations to constrain interpretations. Results provide evidence for a revised conceptual model for aufeis hydrology that assumes a "wet base" of the surface ice pack. Our data indicate a several meter thick seasonally frozen cobble layer forms between the surface ice and the flowing groundwater below, except in areas of focused discharge to regions below the surface ice (providing a "wet base" to the ice in these areas) and to the surface. These interpretations are drawn from the presence of two strong subhorizontal reflectors observed in the GPR data that are punctuated by sudden rises in the lower reflector, and are supported by NMR profiles of unfrozen water content. The NMR and GPR data further suggest that regions of groundwater upwelling have a deep permafrost boundary (possibly in excess of 20 m in winter) in relatively close horizontal proximity to completely frozen areas that show a permafrost boundary on the order of a few meters during summer time.
2018093071 Vonk, J. E. (Vrije Universiteit Amsterdam, Amsterdam, Netherlands). Geochemical insights into a changing Arctic carbon cycle [abstr.]: in Goldschmidt abstracts 2017, V.M. Goldschmidt Conference - Program and Abstracts, 27, 2017. Meeting: Goldschmidt 2017, Aug. 13-18, 2017, Paris, France.
2018093074 Ziolkowski, Lori A. (University of South Carolina, School of Earth, Ocean, and the Environment, Columbia, SC); Czimczik, C. I.; Onstott, T. C. and Slater, G. F. Arctic soil carbon; does permafrost carbon matter for future climate feedbacks? [abstr.]: in Goldschmidt abstracts 2017, V.M. Goldschmidt Conference - Program and Abstracts, 27, 2017. Meeting: Goldschmidt 2017, Aug. 13-18, 2017, Paris, France.
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