2020086126 Skierszkan, Elliott K. (University of British Columbia, Department of Earth, Ocean and Atmospheric Sciences, Vancouver, BC, Canada); Dockrey, John W.; Mayer, K. Ulrich and Beckie, Roger D. Release of geogenic uranium and arsenic results in water-quality impacts in a subarctic permafrost region of granitic and metamorphic geology: Journal of Geochemical Exploration, 217, Paper no. 106607, illus. incl. 2 tables, geol. sketch maps, 83 ref., October 2020.
This study investigates geogenic U and As mobilization in relation to bedrock geology, groundwater geochemistry, and the presence of mineral deposits in the Dawson Range, Yukon, Canada, a remote subarctic region that has drawn recent interest from mining industry. For this study we compiled and interpreted a geochemical dataset from the region that includes 1075 rock samples, 365 sediment samples, 3189 surface water samples, and 384 groundwater samples. Elevated concentrations of U and As occur through natural weathering processes. Median U concentrations exceed the Canadian guideline for the protection of aquatic life of 15 mg/L (long-term exposure) at 8% of 547 surface-water monitoring locations and the maximum observed concentration is 337 mg/L. 39% of monitoring wells have median groundwater U concentrations above this guideline and the maximum observed concentration is 589 mg/L. Uranium mobilization is driven by weathering of granitic and metamorphic bedrock that has contents near or slightly above the average upper crustal abundance of 2.7 mg/g and by formation of soluble calcium-carbonato-uranyl complexes in groundwater. Arsenic is more heterogeneously distributed in rock than U, with localized enrichment occurring near sulfide-mineral bearing ore deposits. While >2000 mg/L As is observed present in chemically reduced groundwater, As attenuation is also observed through sorption onto Fe-(oxyhydr)oxides. Despite the occurrence of As-rich groundwater, surface-water As concentrations are consistently low (<1 mg/L), likely due to As attenuation in groundwater discharge zones. This work provides understanding of processes controlling U and As at a regional scale and presents baseline against which possible water-quality changes induced by climate change or industrial activity can be evaluated.
2020083936 Bertran, Pascal (Institut National de Recherches Archéologiques Préventives, Préhistoire à l'Actuel: Culture, Environnement et Anthropologie (PACEA), Pessac, France); Manchuel, Kevin and Sicilia, Deborah. Palaeoseismic structures in Quaternary sediments, related to an assumed fault zone north of the Permian Peissen-Gnutz salt structure (NW Germany); neotectonic activity and earthquakes from the Saalian to the Holocene (Grube, 2019); discussion: Geomorphology, 365, Paper no. 106704, illus. incl. sects., block diag., 69 ref., September 15, 2020. For reference to original see Grube, A., Geomorphology, Vol. 328, p. 15-27, 2019.
We discuss the significance of deformation structures in Quaternary sediments observed by Grube (2019) in the Peissen quarries (NW Germany) in light of the geological context. Evidence for polygonal patterns visible in aerial images in the study area shows that the wedge structures interpreted by Grube (2019) as earthquake-induced sand blows may rather correspond to thermal contraction cracks filled with aeolian sand in a permafrost environment. In the study sites, brittle deformations caused by (i) the rise of a salt diapir, (ii) salt dissolution, (iii) the development of Pleistocene permafrost and (iv) possibly, water circulation under pressure in the Scandinavian ice sheet margin may have coexisted. We support the idea that, while the morphology of deformation generally makes it possible to determine the stress state to which the sediments have been subjected and the quantity of water available in the system at the time of deformation, the nature of the factors causing the stresses remains difficult to identify. In the end, we highlight other useful criteria that should be privileged for palaeoseismic research in such complex geological settings.
2020083947 Fey, Christine (University of Natural Resources and Life Sciences, Department of Civil Engineering and Natural Hazards, Institute of Applied Geology, Vienna, Austria) and Krainer, Karl. Analyses of UAV and GNSS based flow velocity variations of the rock glacier Lazaun (Otztal Alps, south Tyrol, Italy): Geomorphology, 365, Paper no. 107261, illus. incl. strat. col., 3 tables, sketch map, 86 ref., September 15, 2020.
Flow velocities were measured on the active rock glacier Lazaun by eleven GNNS (2006-2018) and six UAV campaigns (2016-2018) to better understand the flow pattern and its possible causes. This medium-sized, active rock glacier is located W of Kurzras/Maso Corto in the Schnals/Senales Valley in the southern Otztal Alps (South Tyrol, northern Italy). The UAV data were used to generate displacement maps by image correlation techniques, to analyse surface lowering and accumulation processes, and to interpret the geomorphology base on shaded relief images. The spatial information from UAV contributes much more to the understanding of the rock glacier flow patterns as the point based GNSS measurements even when the UAV based horizontal displacement analyses are less precise. The level of detection (LoD) for the absolute horizontal displacements derived by image correlation from UAV data ranges between 0.05 and 0.15 m. A comparison of the displacement lengths shows that the UAV derived displacement vectors deviate in average about ±0.05 m from the GNSS measured displacement lengths. The deviation in the displacement directions is smaller when the absolute displacement is higher and ranges in zones with an absolute displacement higher than 0.3 m in dependence to the data quality between 0 and 4°. Consequently, when planning a UAV based rock glacier monitoring, the achievable data accuracy, rock glacier flow velocity and the time span must be considered. Analyses of the rock glacier velocities from GNSS and UVA data show that the calculated horizontal mean velocity increased significantly from 2 mm/day in 2006 up to 6 mm/day in the period 2012 to 2016 and then decreased to values of 3-4 mm/day until 2018. We assume that internal structures and hydrogeology are essential parameters that control the flow mechanism of rock glacier Lazaun, particularly the shear horizon composed of debris and banded ice that is present at the base of the permafrost body, and the unfrozen, groundwater-bearing sediment layer between the shear horizon and the bedrock. We conclude that climate warming caused increased infiltration of meltwater into the shear horizon and that this is the main driving force for the movement of the rock glacier. Increased meltwater infiltration as result of climate warming caused an increase of flow velocity until 2016. The observed thickness loss near the front of the rock glacier indicates increased melting of permafrost ice resulting in a significant loss of permafrost ice during the last years. This process that particularly occurs in the lower part of the rock glacier is believed to be responsible for the decrease in flow velocity since 2017.
2020084099 Li Zhiqing (Chinese Academy of Sciences, Institute of Geology and Geophysics, Key Laboratory of Shale Gas and Geoengineering, Beijing, China); Hu Feng; Qi Shengwen and Hu Ruilin. Strain-softening failure mode after the post-peak as a unique mechanism of ruptures in a frozen soil-rock mixture: Engineering Geology, 274, Article 105725, illus. incl. 3 tables, 6 plates, 43 ref., September 5, 2020.
A large number of traffic systems in China pass through a large area of frozen soil, most of which contains frozen soil-rock mixtures (FSRMs). For a profound understanding of the mechanical behaviours and damage mechanisms of geotechnical and geoenvironmental projects, it is necessary to understand the stress-strain characteristics and failure modes of FSRMs. This study focuses on the uniaxial compression strength (UCS), Young's modulus, and complete stress-strain curve under loading, considering the post-peak behaviour. More than 250 FSRM specimens were tested for UCS evaluations, while considering the effects of different freezing temperatures (-5, -10, -20, -30, and -40°C), initial water contents (15.0, 25.0, and 30.0%), and volumetric block proportions (0, 30, 40, 50, and 100%). The stress-strain curve of the FSRM was characterised by six distinct stress levels and deformation stages, different from those of rock or soil in the normal state. Particularly, the turning point from volume compression to expansion was observed after the post-peak, at which superficial cracks were initiated. Ice crystals provided ductility of the FSRM and maximised its load capacity to prevent premature cracks on the FSRM surface. The block stone hindered the linear propagation of cracks. The failure patterns of the FSRM for the UCS evaluation could be classified into four types. The UCS was influenced by mainly the strength of the mixture composed of ice crystals and soil particles and friction and occlusal strength between blocks. Notably, the gradual thawing of the FSRM might cause the largest deformation at the bottom of the active layer in summer and autumn, according to the experimental results. Thus, it is very important to understand the strength characteristics, deformation stages, and failure patterns associated with the geomechanical behaviour of the FSRM for engineering design and applications in a permafrost region.
2020083943 Villarroel, Cristian Daniel (National University of San Juan, Geosphere and Biosphere Research Centre (CIGEOBIO-CONICET), San Juan, Argentina); Forte, Ana Paula; Ortiz, Diana Agostina; Beliveau, Guillermo Tamburini and Güell, Arturo. Active layer and permafrost thickness in rock glaciers derived from geophysical methods in the semiarid Andes of Argentina: Geomorphology, 365, Paper no. 107249, illus. incl. sect., 1 table, sketch map, 47 ref., September 15, 2020.
The Argentinean Central Andes region (31°S to 35°S) exhibits one of the largest densities of rock glaciers on Earth. However, few studies have focused on the knowledge of the internal structure of these landforms. In the present paper, a characterization of the internal structure of two rock glaciers has been achieved by using Seismic Refraction Tomography and Vertical Electrical Sounding. In one of the rock glaciers, the thickness of the active layer is quite homogeneous, while in the other said thickness diminishes towards the front. In both rock glaciers, near the top of the active layer, the P-wave velocity values vary between 350 and 600 m/s, while in the bottom of the layer the P-values range from 800 to 1700 m/s. As regards the permafrost layer, it shows an irregular thickness with values varying between 4 and 27 m approximately. In addition, P-wave values ranging from 1600 to 3300 m/s and a few kWm values of electrical resistivity have been recorded. The increase of geophysical surveys in rock glaciers in the Andes region is expected to give a better understanding of the characteristics, distribution and origin of the ice present in these landforms. It should also allow researchers to estimate with certainty their ice content as solid-state reserves.
2020086388 Dzhurik, V. I. (Russian Academy of Sciences, Institute of the Earth's Crust, Irkutsk, Russian Federation); Bryzhak, E. V.; Serebrennikov, S. P. and Eskin, A. Yu. The spectral behavior of ground coseismic motion in the Baikal region; effect of seasonal thawing-freezing cycles: Russian Geology and Geophysics, 61(8), p. 929-936, illus. incl. 1 table, sketch map, 18 ref., August 2020.
Reliable solution of theoretical and applied seismological problems requires the knowledge of natural factors that influence ground motion induced by earthquakes. The effect of seasonal freezing and thawing on the behavior of coseismic ground motion in the Baikal region has been studied using data on local geology, earthquake source parameters, seismogeology, and seismic risk zoning for East Siberia. East Siberia, including the highly seismic Baikal region, is located in a temperate and cold, sharply continental climate, with the mean annual air temperature locally falling below -10°C. In this respect, the knowledge of seasonal variations in the ground motion spectra in different seismic-climatic zones of the region is of special importance. We study the dynamic parameters of seismic signals and their variations caused by seasonal thawing and freezing of the ground, using calculated spectra of selected earthquakes that were recorded by 0.5-20 Hz digital seismic stations at a sampling interval (D) of 0.01 s. Spectral analysis was applied to three-component records of more than two hundred M=2.8 (K=9-14) earthquakes that occurred in the region for the past twenty years at distances from 32 to 280 km from the stations. The influence of seasonal temperature variations on the frequency responses of coseismic ground motion is discussed for the case of two seismic stations in zones of continuous and sporadic permafrost. The results are complemented by generalized data from other seismic stations located in different permafrost conditions within the Baikal region. The effect of seasonal freezing and thawing turns out to be the most prominent at frequencies above 5-6 Hz and depend on the properties and thermal state of soils beneath the stations. At the same time, they are more prominent in thawing than in freezing curves for any soil, including relatively solid bedrock. The spectral behavior of earthquake-induced ground motion is associated with variations in wave amplitudes, which correlate with seasonal temperature variations. The reported results have implications for geophysical prospecting, seismic-risk zoning, and prediction of shaking intensity of large earthquakes, which require due regard for local permafrost conditions.
2021003455 Jong, Dirk (Vrije Universiteit Amsterdam, Department of Earth Sciences, Amsterdam, Netherlands); Bröder, Lisa; Tanski, George; Fritz, Michael; Lantuit, Hugues; Tesi, Tommaso; Haghipour, Negar; Eglinton, Timothy I. and Vonk, Jorien E. Nearshore zone dynamics determine pathway of organic carbon from eroding permafrost coasts: Geophysical Research Letters, 47(15), Paper no. e2020GL088561, illus. incl. sketch maps, 60 ref., August 16, 2020.
Collapse of permafrost coasts delivers large quantities of particulate organic carbon (POC) to Arctic coastal areas. With rapidly changing environmental conditions, sediment and organic carbon (OC) mobilization and transport pathways are also changing. Here, we assess the sources and sinks of POC in the highly dynamic nearshore zone of Herschel Island-Qikiqtaruk (Yukon, Canada). Our results show that POC concentrations sharply decrease, from 15.9 to 0.3 mg L-1, within the first 100-300 m offshore. Simultaneously, radiocarbon ages of POC drop from 16,400 to 3,600 14C years, indicating rapid settling of old permafrost POC to underlying sediments. This suggests that permafrost OC is, apart from a very narrow resuspension zone (<5 m water depth), predominantly deposited in nearshore sediments. While long-term storage of permafrost OC in marine sediments potentially limits biodegradation and its subsequent release as greenhouse gas, resuspension of fine-grained, OC-rich sediments in the nearshore zone potentially enhances OC turnover. Abstract Copyright (2020). The Authors.
2020081958 Melaku, Nigus Demelash (Athabasca University, Faculty of Science and Technology, Athabasca, AB, Canada); Wang, Junye and Meshesha, Tesfa Worku. Improving hydrologic model to predict the effect of snowpack and soil temperature on carbon dioxide emission in the cold region peatlands: Journal of Hydrology, 587, Paper no. 124939, illus. incl. 1 table, geol. sketch map, 58 ref., August 2020.
Peatlands cover only about 3% of the Earth's surface and store 15-30% of the Global soil carbon as a peat. However, human intervention and climate change threatens the stability of peatlands, owing to deforest, wildfire, mining, drainage, glacial retreat, and permafrost. In our study, we modified the SWAT model to couple snow, soil temperature and carbon dioxide emission. Then the modified SWAT was used for predicting snow depth, soil temperature at different depths and carbon dioxide emission from peatlands and other land uses at Athabasca river basin, Canada. The results of the study indicated that SWAT model estimated the daily snow depth with R2, NSE, RMSE and PBIAS values of 0.83, 0.76, 0.52 and -2.3 in the calibration period (2006-2007) and 0.79, 0.71, 0.97 and -3.6 for the validation period (2008-2009), respectively. The SWAT model also predicted soil temperature very well at three depths (5 cm, 10 cm and 30 cm). The simulation model results also confirmed that the modified SWAT model estimates the CO2 emission at Athabasca river basin with good model fit during calibration (R2=0.71, NSE=0.67, RMSE=2.6 and PBIAS=3.2) and during validation (R2=0.63, NSE=0.58, RMSE=3.1 and PBIAS=9.3). Overall, our result confirmed that SWAT model performed well in representing the dynamics of snow depth, soil temperature and CO2 emissions in the peatlands at the Athabasca river basin.
2021003491 Rey, David M. (U. S. Geological Survey, Lakewood, CO); Walvoord, Michelle A.; Minsley, Burke J.; Ebel, Brian A.; Voss, Clifford I. and Singha, Kamini. Wildfire-initiated talik development exceeds current thaw projections; observations and models from Alaska's continuous permafrost zone: Geophysical Research Letters, 47(15), Paper no. e2020GL087565, illus. incl. sects., sketch map, 69 ref., August 16, 2020.
As the Arctic warms and wildfire occurrence increases, talik formation in permafrost regions is projected to expand and affect the cycling of water and carbon. Yet, few unified field and modeling studies have examined this process in detail, particularly in areas of continuous permafrost. We address this gap by presenting multimethod, multiseasonal geophysical measurements of permafrost and liquid-water content that reveal substantial talik development in response to recent wildfire in continuous permafrost of boreal Alaska. Results from observation-based cryohydrogeologic model simulations suggest that predisturbance subsurface conditions are key factors influencing thaw response to fire disturbance and air temperature warming. Our high-resolution integrated study illustrates enhanced vulnerability of boreal continuous permafrost, with observed talik formation that exceeds coarse-scale model projections by ~100 years even under the most extreme future emissions scenario. Results raise important scaling questions for representing extreme permafrost thaw phenomena of growing widespread importance in large-scale predictive models. Abstract Copyright (2020). The Authors.
2020085945 Steinemann, Olivia (Swiss Federal Institute of Technology in Zurich, Laboratory of Ion Beam Physics, Zurich, Switzerland); Reitner, Jürgen M.; Ivy-Ochs, Susan; Christl, Marcus and Synal, Hans-Arno. Tracking rockglacier evolution in the Eastern Alps from the lateglacial to the early Holocene: Quaternary Science Reviews, 241, Paper no. 106424, illus. incl. 2 tables, geol. sketch maps, 133 ref., August 2020.
Relict rockglaciers are distinctive indicators of past permafrost occurrence. Their lower limit is attributed to a former mean annual air temperature (MAAT) of below -2 °C. This study provides a comprehensive dataset of 34 10Be exposure ages from boulders along two complex series of relict rockglaciers, called Tandl rockglaciers and Norbert rockglaciers (Carinthia, Austria). The lowest Tandl rockglacier complex stabilised around 14 ka at an elevation of 1350 m a.s.l., the lowest Norbert rockglaciers (1580 and 1730 m a.s.l.) stabilised around 15.7 ka. Additionally, in both study sites the low elevation relict rockglaciers interacted with glacial deposits of the local pre-Bolling glaciers (Gschnitz stadial glacier). Temperature lowering based on our data of the Gschnitz rockglaciers ranges between 6.3 and 4.5 °C compared to modern MAAT. The cross-cutting relationships of the rockglaciers and the glacial deposits together with the exposure ages of the rockglaciers, indicate that these rockglaciers, and therewith also permafrost, developed shortly after or even simultaneously with retreat of the Gschnitz stadial glaciers. This is the first permafrost formation in the Alpine areas after the retreat of the (warm-based) Last Glacial Maximum glaciers. The Tandl and Norbert rockglacier lobes located at higher elevations, up to about 2300 m a.s.l., finally stabilised in the early Holocene; ages of several dated lobes lie between 12-10 ka. At this time, which corresponds to the Egesen stadial (Younger Dryas) cold phase, rockglaciers and glaciers co-existed. From the lowest position of the Egesen rockglacier lobe at the Tandl site (1700 m a.s.l.), a temperature lowering for the Egesen stadial of -4.6 °C was calculated. This study highlights the potential of relict rockglacier deposits as an independent paleoclimate archive and their usefulness for reconstruction of past permafrost development and distribution in high mountain areas when they can be placed in a temporal framework.
2020081971 Xiao Xiong (Chinese Academy of Sciences, Institute of Tibetan Plateau Research, Laboratory of Tibetan Environment Changes and Land Surface Processes, Beijing, China); Zhang Fan; Che Tao; Shi Xiaonan; Zeng Chen and Wang Guanxing. Changes in plot-scale runoff generation processes from the spring-summer transition period to the summer months in a permafrost-dominated catchment: Journal of Hydrology, 587, Paper no. 124966, illus. incl. sects., sketch map, 74 ref., August 2020.
The hydrological regimes in permafrost-dominated catchments have unique characteristics. However, studies based on plot-scale experiments of runoff generation processes and the factors influencing these processes are limited on the Tibetan Plateau, which is experiencing rapid warming and permafrost degradation. Runoff generation processes were studied on a standard runoff plot (5´20 m) in a permafrost-dominated catchment on the Tibetan Plateau with an alpine meadow cover to analyze these processes during the spring-summer transition period (from mid-May to early June) and in the summer months of June and July. The discharge, including surface and subsurface runoff, the soil hydrothermal and moisture conditions, and the meteorological conditions were monitored from May 2018 to May 2019. Partial Least-Squares Path Modeling was used to identify the influencing factors in the two time periods. The lateral subsurface flow at 30-60 cm depth accounted for the majority of the discharge from the runoff plot (>99%) and showed a sharp increase when the soil water contents of the thawed soil layers exceeded a threshold value that varied from 0.41 to 0.52. During the spring-summer transition period, the lateral subsurface flow at 30-60 cm depth was promoted by both event precipitation and the antecedent precipitation with an average runoff ratio of 1.7, indicating that the antecedent moisture condition maintained by the underlying permafrost drives runoff generation via meltwater from snow and frozen soil. In the summer months, the lateral subsurface flow at 30-60 cm depth was directly promoted by event precipitation, especially the moderate precipitation that occurred in this period, with a reduced runoff ratio of 0.5 as a result of deepening of the thawed soil layer from 30 to >60 cm, enhanced evapotranspiration and an increased soil water storage capacity caused by an increase of air temperature and the soil temperature. Prediction models obtained via Multiple Linear Regressions of the identified influencing factors were able to accurately estimate the discharge. This study shows the important role of lateral subsurface flow in runoff generation processes in this permafrost area and the most important influencing factors in different seasons.
2021001950 Douglas, Thomas A. (U. S. Army Cold Regions Research and Engineering Laboratory, Fort Wainwright, AK); Turetsky, Merritt R. and Koven, Charles D. Increased rainfall stimulates permafrost thaw across a variety of interior Alaskan boreal ecosystems: npj Climate and Atmospheric Science, 3(28), 7 p., illus., 50 ref., July 24, 2020.
Earth's high latitudes are projected to experience warmer and wetter summers in the future but ramifications for soil thermal processes and permafrost thaw are poorly understood. Here we present 2750 end of summer thaw depths representing a range of vegetation characteristics in Interior Alaska measured over a 5 year period. This included the top and third wettest summers in the 91-year record and three summers with precipitation close to mean historical values. Increased rainfall led to deeper thaw across all sites with an increase of 0.7 ± 0.1 cm of thaw per cm of additional rain. Disturbed and wetland sites were the most vulnerable to rain-induced thaw with »1 cm of surface thaw per additional 1 cm of rain. Permafrost in tussock tundra, mixed forest, and conifer forest was less sensitive to rain-induced thaw. A simple energy budget model yields seasonal thaw values smaller than the linear regression of our measurements but provides a first-order estimate of the role of rain-driven sensible heat fluxes in high-latitude terrestrial permafrost. This study demonstrates substantial permafrost thaw from the projected increasing summer precipitation across most of the Arctic region.
2020082008 Yanagiya, Kazuki (Hokkaido University, Department of Natural History Sciences, Graduate School of Science, Sapporo, Japan) and Furuya, Masato. Post-wildfire surface deformation near Batagay, eastern Siberia, detected by L-band and C-band InSAR: Journal of Geophysical Research: Earth Surface, 125(7), Article 2019JF005473, illus. incl. 2 tables, sketch maps, 70 ref., July 2020.
Thawing of ice-rich permafrost and subsequent ground subsidence can form characteristic landforms, and the resulting topography they create is collectively called "thermokarst." The impact of wildfire on thermokarst development remains uncertain. Here, we report on the post-wildfire ground deformation associated with the 2014 wildfire near Batagay, Eastern Siberia. We used Interferometric Synthetic Aperture Radar (InSAR) to generate both long-term (1-4 years) and short-term (subseasonal to seasonal) deformation maps. Based on two independent satellite-based microwave sensors, we could validate the dominance of vertical displacements and their heterogeneous distributions without relying on in situ data. The inferred time series based on L-band ALOS2 InSAR data indicated that the cumulative subsidence at the area of greatest magnitude was greater than 30 cm from October 2015 to June 2019 and that the rate of subsidence slowed in 2018. The burn severity was rather homogeneous, but the cumulative subsidence magnitude was larger on the east-facing slopes where the gullies were also predominantly developed. The correlation suggests that the active layer on the east-facing slopes might have been thinner before the fire. Meanwhile, C-band Sentinel-1 InSAR data with higher temporal resolution showed that the temporal evolution included episodic changes in terms of deformation rate. Moreover, we could unambiguously detect frost heave signals that were enhanced within the burned area during the early freezing season but were absent in the mid-winter. We could reasonably interpret the frost heave signals within a framework of premelting theory instead of assuming a simple freezing and subsequent volume expansion of preexisting pore water. Abstract Copyright (2020). The Authors.
2021003391 Li Zongjie (Lanzhou University, Laboratory of Western China's Environmental Systems, Lanzhou, China); Ma Jinzhu; Song Lingling; Gui Juan; Xue Jian; Zhang Baijuan; Gao Wende and Li Zongxing. Investigation of soil water hydrological process in the permafrost active layer using stable isotopes: Hydrological Processes, 34(12), p. 2810-2822, illus., 33 ref., June 15, 2020.
Here, we studied the isotope characteristics and source contributions of soil water in the permafrost active layer by collecting soil samples in July 2018 in Yangtze River basin. Soil moisture and temperature showed decreasing trends from 0-80 cm, and an increasing trend from 80-100 cm. The value of d18O and dD first increased and then decreased in the soil profile of 0-100 cm; however, d-excess increased from 0-100 cm. d18O values became gradually positive from the southwest to northeast of the study area, while d-excess gradually increased from southeast to northwest. The evaporation water line (EL) was dD=7.56 d18O+1.50 (R2=0.90, p<0.01, n=96). Due to intense solar radiation and evaporation on the Tibetan Plateau, the elevation did not impact the surface soil. The altitude effect of the soil depths of 0-20 cm was not obvious, but the other soil layers had a significant altitude effect. Soil moisture and temperature were closely related to the stable isotopic composition of soil water. The contribution of precipitation to soil water on the sunny slope was 86%, while the contribution of the shady slope was 84%. However, the contribution of ground ice to soil water on sunny slope was 14% and the shady slope was 16%. The contribution of ground ice to soil water increased with increasing altitude on the sunny slope, but the contribution of ground ice to soil water had no obvious trend on the shady slope. Abstract Copyright (2020), John Wiley & Sons, Ltd.
2021003387 Evans, Sarah G. (Appalachian State University, Department of Geological and Environmental Sciences, Boone, NC); Yokeley, Brandon; Stephens, Connor and Brewer, Benjamin. Potential mechanistic causes of increased baseflow across northern Eurasia catchments underlain by permafrost: Hydrological Processes, 34(11), p. 2676-2690, illus. incl. 1 table, sketch map, 75 ref., May 30, 2020.
Warming in the Arctic is occurring at twice the rate of the global average, resulting in permafrost thaw and a restructuring of the Arctic hydrologic cycle as indicated by increased stream discharge during low-flow periods. In these cold regions, permafrost thaw is postulated to increase low-flow discharge, or baseflow, through either: (a) localized increases in groundwater storage and discharge to streams due to increased aquifer transmissivity from thickening of the freeze-thaw layer above permafrost known as the active layer or (b) long-term increases in regional groundwater circulation via enhancement of groundwater-surface water interactions due to extensive permafrost loss over decades. While increasing baseflow has been observed throughout northern Eurasia, the precise mechanistic causes remain elusive. In this study, we differentiate between where these two subsurface physical mechanisms of baseflow increase are occurring by performing a baseflow recession analysis using daily streamflow records from 1913 to 2003 for 139 stations in northern Eurasia underlain by varying permafrost areal extents. Results indicate that from 1913 to 2003, the majority of catchments underlain by continuous permafrost have an increasing trend in their recession flow intercepts, a proxy for increasing active layer thickness. Alternatively, the majority of catchments underlain by permafrost types that are less spatially extensive (e.g., discontinuous, sporadic, isolated, or no permafrost) have decreasing trends in their recession flow intercepts, indicating that a potential increase in active layer thickness is not the driving factor of baseflow variations in these catchments. This may indicate that in catchments underlain by continuous permafrost, active layer thickening correlates with increases in baseflow, whereas, in other catchments with less extensive permafrost, increases in baseflow may be caused by wholesale permafrost loss and vertical talik expansion that enhances regional groundwater circulation. The results of this work may inform our understanding of the subsurface mechanisms responsible for the changing Arctic hydrologic cycle. Abstract Copyright (2020), John Wiley & Sons, Ltd.
2021003367 Heffernan, Liam (University of Alberta, Department of Renewable Resources, Edmonton, AB, Canada); Estop-Aragonés, Cristian; Knorr, Klaus-Holger; Talbot, Julie and Olefeldt, David. Long-term impacts of permafrost thaw on carbon storage in peatlands; deep losses offset by surficial accumulation: Journal of Geophysical Research: Biogeosciences, 125(3), illus. incl. 2 tables, sketch map, 48 ref., March 2020.
Peatlands in northern permafrost regions store a significant proportion of global soil carbon. Recent warming is accelerating peatland permafrost thaw and thermokarst collapse, exposing previously frozen peat to microbial decomposition and potential mineralization into greenhouse gases. Here, we show from a site in the sporadic-discontinuous permafrost zone of western Canada that thermokarst collapse leads to neither large losses nor gains following thaw, as deep carbon losses are offset by surficial accumulation. We collected peat cores along two thaw chronosequences, from peat plateau, through young (~30 years since thaw), intermediate (~70 years), and mature (~200 years) thermokarst bog locations. Macrofossil and 14C analysis showed synchronicity of peatland development until recent thaw, with wetland initiation ~8,500 cal yr BP followed by succession through peatland stages prior to permafrost aggradation ~1,800 cal yr BP. Analysis and modeling of soil carbon stocks indicated 8.7±12.4 kg C m-2 of carbon accumulated prior to thaw was lost in ~200 years post-thaw. Despite these losses, there was no observed increase in peat humification as assessed by Fourier transform infrared and C:N ratios. Rapid peat accumulation post-thaw (9.8±1.6 kg C m-2 over 200 years) offset deeper losses. Our approach constrains the net carbon balance to be between uptake of 27.3 g C m-2 yr-1 and loss of 106.6 g C m-2 yr-1 over 200 years post-thaw. While our approach cannot determine whether thermokarst bogs in the sporadic-discontinuous permafrost zone act as long-term carbon sinks or sources post-thaw, our study better constrains post-thaw C losses and gains. Abstract Copyright (2020). American Geophysical Union. All Rights Reserved.
2021003369 Pastor, Ada (Aarhus University, Department of Biology, Aarhus, Denmark); Wu, N.; Skovsholt, L. J. and Riis, T. Biofilm growth in two streams draining mountainous permafrost catchments in NE Greenland: Journal of Geophysical Research: Biogeosciences, 125(3), illus. incl. 2 tables, sketch map, 34 ref., March 2020.
The objective of this study was to evaluate how stream water nutrient concentrations influence biofilm accrual in streams draining mountainous permafrost headwaters. We selected six stream locations in the Zackenberg area (NE Greenland, 74°N) subjected to a gradient in the areal contribution of different geomorphological units in the watersheds and channel stability. We used nutrient diffusing substrates to evaluate biofilm growth (autotrophic and total biomass). We found elevated stream nitrate concentrations in samples from upstream reaches draining larger areas of solifluction sheets and bare rock and with higher channel instability. Nitrate had the highest standardized effect on autotrophic biofilm growth on control disks. However, stream biofilm growth was not nutrient limited as shown by the absence of an increase in biofilm biomass as a response to the experimental nutrient additions. The response to nutrient additions via diffusing substrates depended on the altitude gradient. Overall, our results showed stream nitrogen availability to be one of the main drivers of algal biofilm accrual in high-Arctic streams, suggesting that the predicted changes in nutrient exports induced by climate change will have strong impacts on the biogeochemistry and ecological functioning of high-Arctic streams. Abstract Copyright (2020). American Geophysical Union. All Rights Reserved.
2021003370 Perryman, Clarice R. (University of New Hampshire, Department of Earth Sciences, Durham, NH); McCalley, Carmody K.; Malhotra, Avni; Fahnestock, M. Florencia; Kashi, Natalie N.; Bryce, Julia G.; Giesler, Reiner and Varner, Ruth K. Thaw transitions and redox conditions drive methane oxidation in a permafrost peatland: Journal of Geophysical Research: Biogeosciences, 125(3), illus. incl. 2 tables, 35 ref., March 2020.
Permafrost peatlands are a significant source of methane (CH4) emissions to the atmosphere and could emit more CH4 with continued permafrost thaw. Aerobic methane-oxidizing bacteria may attenuate a substantial fraction of CH4 emissions in thawing permafrost peatlands; however, the impact of permafrost thaw on CH4 oxidation is uncertain. We measured potential CH4 oxidation rates (hereafter, CH4 oxidation) and their predictors using laboratory incubations and in situ porewater redox chemistry across a permafrost thaw gradient of eight thaw stages at Stordalen Mire, a permafrost peatland complex in northernmost Sweden. Methane oxidation rates increased across a gradient of permafrost thaw and differed in transitional thaw stages relative to end-member stages. Oxidation was consistently higher in submerged fens than in bogs or palsas across a range of CH4 concentrations. We also observed that CH4 oxidation increased with decreasing in situ redox potential and was highest in sites with lower redox potential (Eh <10 mV) and high water table. Our results suggest that redox potential can be used as an important predictor of CH4 oxidation, especially in thawed permafrost peatlands. Our results also highlight the importance of considering transitional thaw stages when characterizing landscape-scale CH4 dynamics, because these transitional areas have different rates and controls of CH4 oxidation relative to intact or completely thawed permafrost areas. As permafrost thaw increases the total area of semiwet and wet thaw stages in permafrost peatlands, CH4 oxidation represents an important control on CH4 emissions to the atmosphere. Abstract Copyright (2020). American Geophysical Union. All Rights Reserved.
2021003433 Bouchard, Frédéric (Université Paris-Saclay, Géosciences Paris Sud, Orsay, France); Fortier, Daniel; Paquette, Michel; Boucher, Vincent; Pienitz, Reinhard and Laurion, Isabelle. Thermokarst lake inception and development in syngenetic ice-wedge polygon terrain during a cooling climatic trend, Bylot Island (Nunavut), eastern Canadian Arctic: The Cryosphere (Online), 14(8), p. 2607-2627, illus. incl. 1 table, 114 ref., 2020.
Thermokarst lakes are widespread and diverse across permafrost regions, and they are considered significant contributors to global greenhouse gas emissions. Paleoenvironmental reconstructions documenting the inception and development of these ecologically important water bodies are generally limited to Pleistocene-age permafrost deposits of Siberia, Alaska, and the western Canadian Arctic. Here we present the gradual transition from syngenetic ice-wedge polygon terrain to a thermokarst lake in Holocene sediments of the eastern Canadian Arctic. We combine geomorphological surveys with paleolimnological reconstructions from sediment cores in an effort to characterize local landscape evolution from a terrestrial to freshwater environment. Located on an ice- and organic-rich polygonal terrace, the studied lake is now evolving through active thermokarst, as revealed by subsiding and eroding shores, and was likely created by water pooling within a pre-existing topographic depression. Organic sedimentation in the valley started during the mid-Holocene, as documented by the oldest organic debris found at the base of one sediment core and dated at 4.8 kyr BP. Local sedimentation dynamics were initially controlled by fluctuations in wind activity, local moisture, and vegetation growth and accumulation, as shown by alternating loess (silt) and peat layers. Fossil diatom assemblages were likewise influenced by local hydro-climatic conditions and reflect a broad range of substrates available in the past (both terrestrial and aquatic). Such conditions likely prevailed until ~2000 BP, when peat accumulation stopped as water ponded the surface of degrading ice-wedge polygons, and the basin progressively developed into a thermokarst lake. Interestingly, this happened in the middle of the Neoglacial cooling period, likely under colder-than-present but wetter-than-average conditions. Thereafter, the lake continued to develop as evidenced by the dominance of aquatic (both benthic and planktonic) diatom taxa in organic-rich lacustrine muds. Based on these interpretations, we present a four-stage conceptual model of thermokarst lake development during the late Holocene, including some potential future trajectories. Such a model could be applied to other formerly glaciated syngenetic permafrost landscapes.
2021002150 Brady, Michael B. (Rutgers, University, Department of Geography, Piscataway, NJ) and Leichenko, Robin. The impacts of coastal erosion on Alaska's North Slope communities; a co-production assessment of land use damages and risks: Polar Geography (1995), 43(4), p. 259-279, illus. incl. , 99 ref., 2020. Based on Publisher-supplied data.
ABSTRACT The impacts of coastal erosion on municipal infrastructure and property have been widely documented within coastal Alaska. Less is known, however, about erosion-related impacts on natural resource-based land uses that contribute to the well-being of Alaska's Native residents. This study explores erosion impacts on resource-based land uses on Alaska's North Slope. The study utilized a collaborative mapping workshop approach, in which research participants defined major categories of land use impacts, identified locations most at risk, and described key local and regional effects of erosion. The study findings highlight three critical types of land use impacts associated with coastal erosion. These include: (1) disruption of subsistence hunting; (2) losses associated with damaged military radar assets (DEW-Line); and, (3) constrained hydrocarbon related development opportunities on land controlled by Native corporations. Through specification of locally relevant land use impacts, the study findings contribute to a better understanding of how climate change is undermining cryosphere-related ecosystem services, particularly buffering cultural and economic activity from coastal storms. The study results reinforce the utility and value of co-production approaches for Arctic climate impact assessments. Through integration of local perspectives on erosion risks, the study contributes to collective regional knowledge about climate change risks to Arctic communities.
2021003432 Cao Bin (Chinese Academy of Sciences, Institute of Tibetan Plateau Research, Beijing, China); Gruber, Stephan; Zheng Donghai and Li Xin. The ERA5-Land soil temperature bias in permafrost regions: The Cryosphere (Online), 14(8), p. 2581-2595, illus. incl. 3 tables, 72 ref., 2020. Includes 2 appendices.
ERA5-Land (ERA5L) is a reanalysis product derived by running the land component of ERA5 at increased resolution. This study evaluates ERA5L soil temperature in permafrost regions based on observations and published permafrost products. We find that ERA5L overestimates soil temperature in northern Canada and Alaska but underestimates it in mid-low latitudes, leading to an average bias of -0.08°C. The warm bias of ERA5L soil is stronger in winter than in other seasons. As calculated from its soil temperature, ERA5L overestimates active-layer thickness and underestimates near-surface (<1.89 m) permafrost area. This is thought to be due in part to the shallow soil column and coarse vertical discretization of the land surface model and to warmer simulated soil. The soil temperature bias in permafrost regions correlates well with the bias in air temperature and with maximum snow height. A review of the ERA5L snow parameterization and a simulation example both point to a low bias in ERA5L snow density as a possible cause for the warm bias in soil temperature. The apparent disagreement of station-based and areal evaluation techniques highlights challenges in our ability to test permafrost simulation models. While global reanalyses are important drivers for permafrost simulation, we conclude that ERA5L soil data are not well suited for informing permafrost research and decision making directly. To address this, future soil temperature products in reanalyses will require permafrost-specific alterations to their land surface models.
2021002146 Liljedahl, Anna K. (University of Alaska Fairbanks, Institute of Northern Engineering, Fairbanks, AK); Timling, Ina; Frost, Gerald V. and Daanen, Ronald P. Arctic riparian shrub expansion indicates a shift from streams gaining water to those that lose flow: Communications Earth & Environment, 1(1), Article 50, illus. incl. sketch map, 86 ref., 2020.
Shrub expansion has been observed across the Arctic in recent decades along with warming air temperatures, but tundra shrub expansion has been most pronounced in protected landscape positions such as floodplains, streambanks, water tracks, and gullies. Here we show through field measurements and laboratory analyses how stream hydrology, permafrost, and soil microbial communities differed between streams in late summer with and without tall shrubs. Our goal was to assess the causes and consequences of tall shrub expansion in Arctic riparian ecosystems. Our results from Toolik Alaska, show greater canopy height and density, and distinctive plant and soil microbial communities along stream sections that lose water into unfrozen ground (talik) compared to gaining sections underlain by shallow permafrost. Leaf Area Index is linearly related to the change in streamflow per unit stream length, with the densest canopies coinciding with increasingly losing stream sections. Considering climate change and the circumpolar scale of riparian shrub expansion, we suggest that permafrost thaw and the resulting talik formation and shift in streamflow regime are occurring across the Low Arctic.
2020082231 Kashirtsev, V. A. (Russian Academy of Sciences, A. Trofimuk Institute of Petroleum Geology and Geophysics, Novosibirsk, Russian Federation); Parfenova, T. M.; Moiseev, S. A.; Chernykh, A. V.; Novikov, D. A.; Burshtein, L. M.; Dolzhenko, K. V.; Rogov, V. I.; Mel'nik, D. S.; Zueva, I. N. and Chalaya, O. N. The Sukhana sedimentary basin, Siberian Platform; source rock characterization and direct evidence of oil and gas presence: Russian Geology and Geophysics, 60(10), p. 1175-1187, illus. incl. sects., strat. col., sketch map, 45 ref., October 2019.
Despite the known large natural bitumen accumulations and oil seeps in several kimberlite pipes along the periphery of the Sukhana sedimentary basin, interpreted as direct evidence of petroleum potential, the basin still remains one of the least studied (by geological and geophysical methods) regions of the Siberian Platform. The platform cover of the basin is composed by Riphean, Vendian, and Cambrian clastic (terrigenous) and carbonate deposits reaching 5.5-6 km in thickness in the central part of the basin. The hydrogeological specifics of the basin is largely governed by its location within the northern geocryological zone (Olenek cryoartesian basin) and is expressed as a continuous distribution of permafrost aggraded into the permafrost zone of unique thickness. Direct indicators of ore and gas presence are the East Anabar, Central Olenek, and Siligir-Markha fields of natural bitumen and oil shows in kimberlite pipes of the Daldyn-Alakit region (Udachnaya pipe). The bituminous-carbonate sediments of the Khatyspyt Formation (Vendian, Ediacaran) and the highly carbonaceous carbonate-siliceous-shaly sediments of the Kuonamka Formation (lower-middle Cambrian) are the Sukhana source rock complexes. The geochemically substantiated genetic relationship between the natural bitumen deposits of the East Anabar field and the organic matter of the Vendian Khatyspyt Formation makes it possible to estimate the area of the spread of the latter far to the west, beyond the axial part of the basin. Gammacerane, inherited from the organic matter of the Khatyspyt Formation and ranking as well-preserved and most characteristic biomarker of these bitumens, provides a compelling evidence of their consanguinity. The bitumen and oil of kimberlite pipes in the south of the basin, in the area of reefs of the Siligir-Markha bar, are similar in all geochemical criteria to oils of the Nepa-Botuobiya anteclise. In particular, in primary geochemical characteristics (12- and 13-monomethylalkanes, unique secosteranes, identical carbon isotope composition, etc.) the oils of the Udachnaya pipe are identical to the Irelyakh oils (oil field in the Mirnyi arch). No accumulations of oil or natural bitumen genetically related to the highly carbonaceous Kuonamka Formation have been found within the basin. At the same time, "intraformational" shows of viscous oil, solid bitumen, and allochthonous bitumen (bitumen extracted with chloroform) were documented directly in the sections of the formation, which makes the sedimentary basin a very attractive target for "shale oil" exploration. As for the regional assessment of the petroleum potential of the entire basin, its axial part (Sukhana depression) complicated by local uplifts is of the greatest interest. Both the Khatyspyt and Kuonamka Formations are widespread there, with the thermal maturity of their organic matter corresponding to the oil window. In addition, the regional reservoirs at the Vendian-Cambrian boundary have good petrophysical properties on both the western and the eastern flanks of the basin.
2020084334 Khazin, L. B. (Russian Academy of Sciences, A. Trofimuk Institute of Petroleum Geology and Geophysics, Novosibirsk, Russian Federation); Khazina, I. V.; Kuzmina, O. B.; Ayunov, D. E.; Golikov, N. A. and Tsibizov, L. V. A borehole record of late Quaternary permafrost on Kurungnakh Island (Lena Delta, northeastern Siberia); reconstruction of deposition environments: Russian Geology and Geophysics, 60(7), p. 768-780, illus. incl. sketch map, 29 ref., July 2019.
Paleoenvironmenal reconstructions have been made from a multidisciplinary study of a borehole permafrost record on Kurungnakh Island (Lena delta). According to data on palynomorphs and ostracods, the clay silt units from the 10.58 to 13.54 m and 1.58 to 10.3 m core depth intervals were deposited in the Late Pleistocene (during the Karginian interstadial) and Early-Middle Holocene, respectively. The sediments were studied in terms of moisture contents, grain size distribution, mineralogy, and magnetic susceptibility, and the results were compared with published evidence from nearby natural outcrops. Quite a cold oligotrophic lake existed in the area during the Karginian period, and the deposition was interrupted by a gap recorded at a core depth of about 11 m. In the Early and Middle Holocene, the area was covered with shrub tundra vegetation.
2021002217 Khazin, L. B. (Rossiyskaya Akademiya Nauk, Sibirskoye Otdeleniye, Institut Neftegazonoy Geologii i Geofiziki, Novosibirsk, Russian Federation); Khazina, I. V.; Kuz'mina, O. B.; Ayunov, D. E.; Golikov, N. A. and Tsibizov, L. V. Rekonstruktsiya usloviy obrazovaniya pozdnechetvertichnykh otlozheniy, vskrytykh skvazhinoy na o. Kurungnakh (del'ta Leny, severo-vostok Sibiri) [A borehole record of the late Quaternary permafrost on Kurungnakh Island, Lena River delta, northeastern Siberia; reconstruction of deposition environments]: Geologiya i Geofizika, 60(7), p. 973-987 (English sum.), illus. incl. 1 table, 29 ref., July 2019.
Paleoenvironmental reconstructions have been made from a multidisciplinary study of a borehole permafrost record on Kurungnakh Island (Lena delta). According to data on polymorphs and ostracods, the clay silt units from the 10.58 to 13.54 m and 1.58 to 10.3 m core depth intervals were deposited in the late Pleistocene (during the Karginian interstadial) and early-middle Holocene, respectively. The sediments were studied in terms of moisture contents, grain size distribution, mineralogy, and magnetic susceptibility, and the results were compared with published evidence from nearly natural outcrops. Quite a cold oligotrophic lake existed in the area during the Karginian period, and the deposition was interrupted by a gap recorded at a core depth of about 11 km. In the early and middle Holocene, the area was covered with shrub tundra vegetation.
2021002219 Sudakova, M. S. (Rossiyskaya Akademiya Nauk, Sibirskoye Otdeleniye, Tyumenskiy Nauchnyy Tsentr, Institut Kriosfery Zemli, Tyumen, Russian Federation); Sadurtdinov, M. R.; Tsarev, A. M.; Skvortsov, A. G. and Malkova, G. V. Vozmozhnosti georadiolokatsii dlya issledovaniya zabolochennykh torfyanikov v kriolitozone [Ground-penetrating radar for investigation of peatlands in permafrost]: Geologiya i Geofizika, 60(7), p. 1004-1013 (English sum.), illus. incl. sketch map, 24 ref., July 2019.
Ground-penetrating radar (GPR) profiling is applicable to study peatlands and swampy areas in permafrost but have some limitations in summer time. Theoretical calculations and field experiments show that estimating attenuation of electromagnetic waves is required for planning GPR survey. Radar images acquired with a 300 MHz antenna fail to resolve reflections from below the permafrost if the thaw/permafrost boundary is deeper than 1.5 m and the attenuation coefficient is 0.7, as in water-saturated peat. GPR data allow high-resolution lithological division of permafrost and provide reliable constraints on the depth to interfaces and physical properties of the ground. Thus, GPR can fully or partly substitute for the time- and labor-consuming direct measurements. The inferences have been confirmed by field results.
2020084336 Sudakova, M. S. (Russian Academy of Sciences, Earth's Cryosphere Institute, Tyumen, Russian Federation); Sadurtdinov, M. R.; Tsarev, A. M.; Skvortsov, A. G. and Malkova, G. V. Ground-penetrating radar for studies of peatlands in permafrost: Russian Geology and Geophysics, 60(7), p. 793-800, illus. incl. sketch map, 23 ref., July 2019.
Ground-penetrating radar (GPR) profiling is applicable to study peatlands and swampy areas in permafrost but have some limitations in summer time. Theoretical calculations and field experiments show that estimating attenuation of electromagnetic waves is required for planning GPR survey. GPR data acquired with a 300 MHz antenna fail to resolve reflections from below the permafrost if the thaw/permafrost boundary is deeper than 1.5 m and the attenuation coefficient is 0.7, as in water-saturated peat. GPR data allow high-resolution lithological division of permafrost and provide reliable constraints on the depths to interfaces and physical properties of the ground. Thus, GPR can fully or partly substitute for the time- and labor-consuming direct measurements. The inferences have been confirmed by field results.
2020083340 Ruiz-Fernández, Jesús (University of Oviedo, Department of Geography, Spain); Oliva, Marc; Nyvlt, Daniel; Cannone, Nicoletta; Garcia-Hernández, Cristina; Guglielmin, Mauro; Hrbacek, Filip; Roman, Matej; Fernández, Susana; López-Martinez, Jerónimo and Antoniades, Dermot. Patterns of spatio-temporal paraglacial response in the Antarctic Peninsula region and associated ecological implications: Earth-Science Reviews, 192, p. 379-402, illus. incl. sketch maps, 4 tables, sect., 233 ref., May 2019.
The Antarctic Peninsula (AP) constitutes the warmest region of Antarctica, although 98% of the surface is still covered by glaciers. The region shows contrasting geographic and climatic properties, which have conditioned past and present glacial activity. This paper constitutes a review of the spatial and temporal patterns of paraglacial activity across the AP bridging the geomorphological and ecological perspectives. The number and extent of ice-free environments has increased since the Last Glacial Maximum, particularly during the Early Holocene and the 20th century. Following deglaciation, the redefinition of coastlines and the uplift of landmasses proceeded differently in the three sectors of AP, with maximum uplift in the western sector (40 m a.s.l.), the minimum on the north (20.4 m a.s.l.), and intermediate in the eastern sector (30 m). There are also differences in the levels of raised beaches, with the highest complexity in the northern AP (5-7 levels) and the lowest in the eastern AP (3 levels). The transition from glacial to periglacial conditions (paraglacial stage) also differed greatly between the three sectors, with the absence of rock glaciers in the western sector, the development almost exclusively of glacier-derived rock glaciers in the eastern AP, and the majority of talus-derived rock glaciers in the northern AP. The development of protalus lobes, block streams and other periglacial features was highly dependent on the cold/warm based character of individual glaciers; this characteristic determines the existence or absence of permafrost following deglaciation which, in turn, conditions the type and intensity of geomorphic processes in newly exposed ice-free areas. More recently, following the post-1950s regional warming, there have still been important differences between the three sectors in the development of paraglacial environments. Permafrost degradation has occurred in newly exposed areas, accelerating mass wasting and sediment redistribution and changing hydrological processes, especially in the northern and western AP, while sudden glacial outburst flooding has occurred in the eastern AP. The most apparent major ecological response to this recent warming is greening due to vegetation expansion, which is more evident where paraglacial and periglacial processes are less intense. The accurate characterization of the different paraglacial responses existing in the AP enables a better understanding of future environmental responses in this climatically sensitive region, where climate models forecast significant environmental change for during forthcoming decades.
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