2021011685 Kong, Xiangbing (Laval University, Department of Civil and Water Engineering, Quebec City, QC, Canada); Doré, Guy; Calmels, Fabrice and Lemieux, Chantal. Modeling the thermal response of air convection embankment in permafrost regions: Cold Regions Science and Technology, 182, Article no. 103169, illus. incl. 3 tables, sketch map, February 2021. Based on Publisher-supplied data.
Permafrost degradation under transportation infrastructure often results in thaw settlement due to thawing of the ice-rich subgrade. Climate change is associated with permafrost-related engineering problems. Air convection embankments (ACE) have been proven to be an effective method to prevent permafrost thawing, in response to climate change. Poorly-graded aggregates are used to facilitate the air flow in an ACE, especially during winter when the air density gradient is unstable. A large-scale ACE test section was constructed along the Alaska Highway in 2008 at Beaver Creek, Yukon, Canada, to investigate the heat extraction capacity of ACEs. Boreholes under the toe, the side slope and the centerline were drilled and instrumented. Temperature data collected at this site were used to investigate the thermal performance of the ACE and to calibrate a 2D thermal model that was developed based on the Beaver Creek experimental site. Specific site characteristics, such as air temperature, foundation soil properties and embankment dimensions, were measured and used as input parameters to improve the accuracy of the 2D model developed. A relatively new approach based on heat balance at the embankment-soil interface has been proposed to investigate the heat extraction capacity of ACEs. After satisfactory calibration of the model at the Beaver Creek site, an engineering design chart has been developed and is proposed to assess the heat balance at the embankment-soil interface for different embankment thicknesses and site conditions.
2021011689 Oldenborger, Greg A. (Natural Resources Canada, Geological Survey of Canada, Ottawa, ON, Canada). Subzero temperature dependence of electrical conductivity for permafrost geophysics: Cold Regions Science and Technology, 182, Article no. 103214, illus. incl. 2 tables, February 2021. Based on Publisher-supplied data.
Temperature dependence of the electrical conductivity of natural waters due to viscosity-based reduction in ionic mobility is well-established for unfrozen conditions. For cold regions, a model for the temperature dependence of electrolyte conductivity at subzero temperatures is required for geophysical studies of permafrost terrain, for which salinity and tension forces may result in freezing-point depression. Extension of the linear temperature model for unfrozen conditions has been applied to geophysical studies of permafrost, but has not been experimentally validated. The temperature dependence of electrical conductivity is measured at subzero temperatures, but above the depressed freezing point for NaCl solutions at a range of concentrations from seawater to brine. Measurements show near-linear dependence of electrical conductivity on temperature down to the lowest experimental temperature of -9 °C with no distinct change in behavior observed for subzero temperatures. Given the observed temperature dependence, the linear temperature-conductivity compensation equation is extended to -9 °C with a temperature compensation coefficient of 0.019 °C-1 for a reference temperature of 20 °C with subzero prediction errors of 1-6%. This equation can be used to compensate for temperature dependence of electrical conductivity with reasonable accuracy for geophysical experiments in permafrost terrain. Subzero accuracy is improved by adopting a quadratic temperature compensation equation that accounts for an observed increase in nonlinear behavior at lower temperatures distant from the reference.
2021011688 Yu Wenbing (Chongqing Jiaotong University, State Key Laboratory of Mountain Bridge and Tunnel Engineering, Chongqing, China); Yi Xin; Han Fenglei; Pei Wansheng and Chen Lin. Study on the geometric parameters of elbow ventiduct embankment in permafrost regions along the Qinghai-Tibet engineering corridor: Cold Regions Science and Technology, 182, Article no. 103209, illus. incl. 4 tables, February 2021. Based on Publisher-supplied data.
Using cold air to cool down infrastructures in permafrost regions is a common technique, but the horizontal ventiduct method has defects. This paper presents the elbow-shaped ventiduct and focuses on its designing parameters, considering the regional climate along the Qinghai-Tibet Engineering Corridor. Based on the natural convection principle, a program for calculating the parameters of the elbow ventiduct of embankment is compiled. By using this program and according to the climatic conditions, the required freezing radius of elbow ventiduct is calculated, and the specific thermal parameters of elbow ventiduct in different climatic regions are calculated. Results show that the lower the average temperature is, the smaller the required freezing radius is. The required freezing radius at Anduo, Kaixinling, Liangdaogou, and the Buqu Valley are 2.45 m, 1.7 m, 1.13 m, and 0.54 m, respectively, and the corresponding longest horizontal pipes that can be used are 32 m, 101 m, 228 m and 799 m, respectively. The regions where the elbow-shaped ventiduct are not suitable or not necessary are figured out. Results also show that the bigger the pipe diameter, the longer the maximum allowable length of horizontal pipe; the higher the vertical pipe length, the longer maximum allowable length of horizontal pipe.
2021006775 Baral, Prashant (NIIT University, Computer Science and Engineering, Neemrana, India) and Haq, M. Anul. Spatial prediction of permafrost occurrence in Sikkim Himalayas using logistic regression, random forests, support vector machines and neural networks: Geomorphology, 371, Article no. 107331, illus. incl. 5 tables, sketch maps, December 15, 2020. Based on Publisher-supplied data.
We have generated permafrost probability distribution maps (10 m resolution) for the north-eastern Himalayan region in Sikkim using remote sensing measurements and machine learning algorithms. Four machine learning algorithms, logistic regression, random forests, support vector machines and neural networks, and two different sets of input data set, were used to generate a total of 8 machine learning models and hence 8 permafrost probability distribution maps. The first set of input data set included surface reflectance from atmospherically corrected Sentinel-2A spectral bands, elevation and slope parameters while the second set of input data set included mean annul air temperature (MAAT) and potential incoming solar radiation (PISR). Permafrost probability distribution maps obtained from the 8 models show reasonable agreement in the total spatial extent of permafrost occurrence but dissimilarities in the pattern of probability distribution. Accuracy assessment results are more optimistic towards models developed using spectral reflectance, elevation and slope parameters as input data set. Nevertheless, 5 out of 8 models agree that around 60% of total area under observation is highly likely to contain permafrost. This congruence in outputs, despite the use of different machine learning algorithms and separate sets of input data set, establishes reliability in the application of machine learning models for the preliminary estimation of permafrost distribution for remote and data-scarce Himalayan region.
2021011495 Xie Meizhen (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, State Key Laboratory of Cryospheric Science, Lanzhou, China); Zhao Lin; Wu Xiaodong; Tian Liming; Yue Guangyang; Zhou Huayun and Wu, Zhenming. Seasonal variations of nitrogen in permafrost-affected soils of the Qinghai-Tibetan Plateau: Catena (Giessen), 195, Article no. 104793, illus. incl. 5 tables, sketch map, 74 ref., December 2020.
The largest permafrost area in China is on the Qinghai-Tibetan Plateau (QTP), and the nitrogen biogeochemical cycles in this area have received significant attention. However, there is insufficient knowledge of the available soil nitrogen and microbial biomass nitrogen (MBN) dynamics in this region, which hinders our understanding of the changes in the ecosystem and the effects of climate change on the nitrogen dynamics in the future. In this study, we determined the monthly changes in ammonium nitrogen, nitrate nitrogen, dissolved organic nitrogen (DON), and MBN contents of the topsoil (at depths of 0-20 cm) from April 2016 to March 2017 in the permafrost region on the QTP. The results show that soil NH4+-N and DON contents decreased during the growing season, while soil NO3--N content increased during the growing season and in the middle of the winter. The soil MBN contents increased at the beginning of the growing season and decreased during peak growth period, despite significant variations among the different sites. The soil temperature was positively correlated with soil NO3--N content but it was negatively correlated with the NH4+-N and DON contents. The soil moisture was positively correlated with the soil NO3--N, DON, and MBN contents. The primary factor affecting the seasonal patterns in soil NO3--N and DON contents was soil moisture. Soil moisture and plant growth also affected soil MBN via nutrient competition. The nutrient uptake by plants overwhelmed effect of temperature on the MBN in growing season. These findings improve our understanding of the nitrogen biochemical cycles and their response to future climate change.
2021006736 Patton, A. I. (Colorado State University, Department of Geosciences, Fort Collins, CO); Rathburn, S. R.; Capps, D.; Brown, R. A. and Singleton, J. S. Lithologic, geomorphic, and permafrost controls on recent landsliding in the Alaska Range: Geosphere (Boulder, CO), 16(6), p. 1479-1494, illus. incl. 3 tables, sketch maps, 85 ref., November 2, 2020.
Because landslide regimes are likely to change in response to climate change in upcoming decades, the need for mechanistic understanding of landslide initiation and up-to-date landslide inventory data is greater than ever. We conducted surficial geologic mapping and compiled a comprehensive landslide inventory of the Denali National Park road corridor to identify geologic and geomorphic controls on landslide initiation in the Alaska Range. The supplemental geologic map refines and improves the resolution of mapping in the study area and adds emphasis on surficial units, distinguishing multiple glacial deposits, hillslope deposits, landslides, and alluvial units that were previously grouped. Results indicate that slope angle, lithology, and thawing ice-rich permafrost exert first-order controls on landslide occurrence. The majority (84%) of inventoried landslides are <0.01 km2 in area and occur most frequently on slopes with a bimodal distribution of slope angles with peaks at 18° and 28°. Of the 85 mapped landslides, a disproportionate number occurred in unconsolidated sediments and in felsic volcanic rocks. Weathering of feldspar within volcanic rocks and subsequent interactions with groundwater produced clay minerals that promote landslide initiation by impeding subsurface conductivity and reducing shear strength. Landslides also preferentially initiated within permafrost, where modeled mean decadal ground temperature is -0.2±0.04°C on average, and active layer thickness is ~1 m. Landslides that initiated within permafrost occurred on slope angles ~7° lower than landslides on seasonally thawed hillslopes. The bimodal distribution of slope angles indicates that there are two primary drivers of landslide failure within discontinuous permafrost zones: (1) atmospheric events (snowmelt or rainfall) that saturate the subsurface, as is commonly observed in temperate settings, and (2) shallow-angle landslides (<20° slopes) in permafrost demonstrate that permafrost and ice thaw are also important triggering mechanisms in the study region. Melting permafrost reduces substrate shear strength by lowering cohesion and friction along ice boundaries. Increased permafrost degradation associated with climate change brings heightened focus to low-angle slopes regionally as well as in high-latitude areas worldwide. Areas normally considered of low landslide potential will be more susceptible to shallow-angle landslides in the future. Our landslide inventory and analyses also suggest that landslides throughout the Alaska Range and similar climatic zones are most likely to occur where low-cohesion unconsolidated material is available or where alteration of volcanic rocks produces sufficient clay content to reduce rock and/or sediment strength. Permafrost thaw is likely to exacerbate slope instability in these materials and expand areas impacted by landslides.
2021006486 Wilson, Peter (Ulster University, School of Geography and Environmental Sciences, Londonderry, United Kingdom); Matthews, John A.; Mourne, Richard W.; Linge, Henriette and Olsen, Jesper. Interpretation, age and significance of a relict paraglacial and periglacial boulder-dominated landform assemblage in Alnesdalen, Romsdalsalpane, Southern Norway: Geomorphology, 369, Article 107362, illus. incl. 6 tables, sketch maps, 112 ref., November 15, 2020.
A boulder-dominated landform assemblage in an alpine setting in Norway is described, interpreted and dated using a combination of Schmidt-hammer exposure-age dating (SHD) and cosmogenic 10Be surface-exposure dating. The origin and formation of these features is determined from their morphology, topographic setting and age. Three main components of the assemblage are recognized. First a ~300 m long and ~160 m wide, tongue-shaped rock-slope failure with a SHD age of 11.49±0.82-12.96±0.86 ka is identified on the basis of its planform, thickness, 'runout distance' and association with a fractured backing scarp. This is interpreted as a relict paraglacial landform triggered by deglaciation. Second, a 400-m long unequivocal pronival (protalus) rampart with an SHD age of 6.95±0.97-8.35±1.21 ka is identified on the basis of its narrow ridge form aligned close to the foot of an extensive talus slope. Although formation of the rampart probably commenced with deglaciation, the younger SHD ages indicate formation at a diminishing rate through the Holocene. Third, a ~550 m by ~150 m lobate component with transverse ridges, longitudinal and transverse depressions and enclosed pits, previously identified as a rock glacier, is dated to 11.33±0.83-13.33±0.90 ka with the Schmidt hammer and between 13.3±2.0-14.7±2.0 ka with 10Be. This third component may also be a product of rock-slope failure but attribution to rock-glacier creep associated with either interstitial ice (permafrost) or buried glacier ice during the Allerod Interstadial - Younger Dryas Stadial, and to which one or more rock-slope failures contributed debris, cannot be rejected. The advantages and limitations of compiling such evidence for identifying, differentiating and classifying apparently similar boulder-dominated colluvial landforms are exemplified.
2021011574 Bao Tao (Chinese Academy of Sciences, Institute of Atmospheric Physics, Beijing, China); Xu Xiyan; Jia Gensuo; Billesbach, David P. and Sullivan, Ryan C. Much stronger tundra methane emissions during autumn-freeze than spring-thaw: Global Change Biology, Pre-Issue Publication, p. 376-387, illus. incl. 1 table, 35 ref., October 28, 2020.
Warming in the Arctic has been more apparent in the non-growing season than in the typical growing season. In this context, methane (CH4) emissions in the non-growing season, particularly in the shoulder seasons, account for a substantial proportion of the annual budget. However, CH4 emissions in spring and autumn shoulders are often underestimated by land models and measurements due to limited data availability and unknown mechanisms. This study investigates CH4 emissions during spring thaw and autumn freeze using eddy covariance CH4 measurements from three Arctic sites with multi-year observations. We find that the shoulder seasons contribute to about a quarter (25.6±2.3%, mean ± standard deviation) of annual total CH4 emissions. Our study highlights the three to four times higher contribution of autumn freeze CH4 emission to total annual emission than that of spring thaw. Autumn freeze exhibits significantly higher CH4 flux (0.88±0.03 mg m-2 h-1) than spring thaw (0.48±0.04 mg m-2 h-1). The mean duration of autumn freeze (58.94±26.39 days) is significantly longer than that of spring thaw (20.94±7.79 days), which predominates the much higher cumulative CH4 emission during autumn freeze (1212.31±280.39 mg m-2 yr-1) than that during spring thaw (307.39±46.11 mg m-2 yr-1). Near-surface soil temperatures cannot completely reflect the freeze-thaw processes in deeper soil layers and appears to have a hysteresis effect on CH4 emissions from early spring thaw to late autumn freeze. Therefore, it is necessary to consider commonalities and differences in CH4 emissions during spring thaw versus autumn freeze to accurately estimate CH4 source from tundra ecosystems for evaluating carbon-climate feedback in Arctic.
2021004872 Lin Zhanju (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, State Key Laboratory of Frozen Soil Engineering, Lanzhou, China); Gao Zeyong; Fan Xingwen; Niu Fujun; Luo Jing; Yin Guoan and Liu Minghao. Factors controlling near surface ground-ice characteristics in a region of warm permafrost, Beiluhe Basin, Qinghai-Tibet Plateau: Geoderma, 376, 114540, illus. incl. 3 tables, geol. sketch map, 83 ref., October 15, 2020.
Ground ice is a key component of permafrost, and its melt induced by climate change and anthropogenic disturbance has been causing increased ground surface subsidence, thermal erosion, and engineering problems. However, the distribution and quantity of ground ice in permafrost have yet to be investigated in detail on the Qinghai-Tibet Plateau (QTP), and consequently, an assessment of the nature of impacts associated with permafrost degradation is challenging. In this study, variation in near-surface ground ice content of the upper 2-3 m of the permafrost layer was examined by drilling 72 boreholes at eight sites in Beiluhe Basin, QTP, an area with relatively warm (near 0°C) permafrost. High ground ice contents occur at most sites, but visible ice was absent at one site, where the vegetation cover has transitioned from a meadow to a sparsely-covered grassland. The moisture content within the active layer (surface to 2 m depth) increases with depth at most sites, and the higher moisture contents were associated with greater near-surface ground ice contents. The gravimetric moisture content (Mg) in permafrost typically ranged from 8% to 500%, and »76% of samples were classified as ice rich (Mg >&eq; 20%). The mean excess-ice content in near-surface permafrost was »19% for all boreholes. At six flat sites, the minimum mean excess-ice content was about zero, and the mean maximum was »22% at an alpine grassland site. The mean excess-ice content at a sunny sloping site was much higher (»27%) than at a north-facing shady site (10%) and the ice was distributed differently with depth. The mean subsidence ratio at the eight sites was from 0.05 to 0.44. The volumetric ice content varied from 1% to 70% in samples from the different sites, with an average value of »16%. Topographically controlled moisture availability, slope direction, and fine-particle content are important controls on ground ice content in Beiluhe Basin. This study provides fundamental information about the spatial distribution of ground ice on QTP, which is important for future assessments of thermal erosion potential and infrastructure instability in the region.
2021004891 Luo Dongliang (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, State Key Laboratory of Frozen Soil Engineering, Lanzhou, China); Jin Huijun; Bense, Victor F.; Jin Xiaoying and Li Xiaoying. Hydrothermal processes of near-surface warm permafrost in response to strong precipitation events in the headwater area of the Yellow River, Tibetan Plateau: Geoderma, 376, Article no. 114531, illus. incl. 4 tables, geol. sketch map, 59 ref., October 15, 2020.
Permafrost is mostly warm and thermally unstable on the Tibetan Plateau (TP), particularly in some marginal areas, thereby being susceptible to degrade or even disappear under climate warming. The degradation of permafrost consequently leads to changes in hydrological cycles associated with seasonal freeze-thaw processes. In this study, we investigated seasonal hydrothermal processes of near-surface permafrost layers and their responses to rain events at two warm permafrost sites in the Headwater Area of the Yellow River, northeastern TP. Results demonstrated that water content in shallow active layers changed with infiltration of rainwater, whereas kept stable in the perennially frozen layer, which serves as an aquitard due to low hydraulic conductivity or even imperviousness. Accordingly, the supra-permafrost water acts as a seasonal aquifer in the thawing period and as a seasonal aquitard in the freezing period. Seasonal freeze-thaw processes in association with rain events correlate well with the recharge and discharge of the supra-permafrost water. Super-heavy precipitation (44 mm occurred on 2 July 2015) caused a sharp increase in soil water content and dramatic rises in soil temperatures by 0.3-0.5 °C at shallow depths and advancement thawing of the active layer by half a month. However, more summer precipitation amount tends to reduce the seasonal amplitude of soil temperatures, decrease mean annual soil temperatures and thawing indices and thin active layers. High salinity results in the long remaining of a large amount of unfrozen water around the bottom of the active layer. We conclude that extremely warm permafrost with TZAA (the temperature at the depth of zero annual amplitude) >-0.5 °C is likely percolated under heavy and super-heavy precipitation events, while hydrothermal processes around the permafrost table likely present three stages concerning TZAA of <-0.5 °C, -0.5-0 °C, and >0 °C.
2021011529 Pang Hongxi (Nanjing University, School of Geography and Ocean Science, Laboratory of Coast and Island Development, Nanjing, China); Hou Shugui; Zhang Wangbin; Wu, Shuangye; Jenk, Theo M.; Schwikowski, Margit and Jouzel, Jean. Temperature trends in the northwestern Tibetan Plateau constrained by ice core water isotopes over the past 7,000 years: Journal of Geophysical Research: Atmospheres, 125(19), Article e2020JD032560, illus. incl. 1 table, sketch maps, 85 ref., October 16, 2020.
The reasons for the Holocene temperature conundrum, known as the inconsistency between the reconstructed cooling and the inferred warming simulations during the Holocene, remain unclear. Temperature reconstructions from the Tibetan Plateau (TP) provide important insights for understanding the Holocene temperature conundrum due to enhanced sensitivity to climate at high altitudes. Given the significant positive correlation between air temperature and d18O in precipitation over the northern TP, the stable isotopic records of ice cores recovered from this area are widely used for paleotemperature reconstruction. Here we present a new high-resolution d18O record from the Chongce ice cores to bedrock, dated back to 7 ka BP by the accelerator mass spectrometry (AMS) 14C dating technique. Our reconstructed temperature record shows a long-term warming trend until ~2 ka BP, followed by an abrupt change to a relatively cool period until the start of the industrial-era warming. This record challenges the widely recognized Holocene reconstruction from the neighboring Guliya ice core. It is also different from many previous temperature reconstructions, most of which have summer biases and show a long-term cooling trend over the past two millennia. In addition, our record shows that temperatures during the recent decades are almost the highest during the past 7 ka BP, highlighting the unusual warming forced by anthropogenic greenhouse gases. Abstract Copyright (2020). American Geophysical Union. All Rights Reserved.
2021011684 Pedrazas, Micaela N. (University of Texas Austin, Department of Geological Sciences, Austin, TX); Cardenas, M. Bayani; Demir, Cansu; Watson, Jeffery A.; Connolly, Craig T. and McClelland, James W. Absence of ice-bonded permafrost beneath an Arctic lagoon revealed by electrical geophysics: Science Advances, 6(43), Article no. eabb5083, illus. incl. sketch map, 35 ref., October 2020.
Relict permafrost is ubiquitous throughout the Arctic coastal shelf, but little is known about it near shore. The presence and thawing of subsea permafrost are vital information because permafrost stores an atmosphere's worth of carbon and protects against coastal erosion. Through electrical resistivity imaging across a lagoon on the Alaska Beaufort Sea coast in summer, we found that the subsurface is not ice-bonded down to »20 m continually from within the lagoon, across the beach, and underneath an ice-wedge polygon on the tundra. This contrasts with the broadly held idea of a gently sloping ice-bonded permafrost table extending from land to offshore. The extensive unfrozen zone is a marine talik connected to on-land cryopeg. This zone is a potential source and conduit for water and dissolved organic matter, is vulnerable to physical degradation, and is liable to changes in biogeochemical processes that affect carbon cycling and climate feedbacks.
2021006943 Solotchin, P. A. (Russian Academy of Sciences, V. Sobolev Institute of Geology and Mineralogy, Novosibirsk, Russian Federation); Solotchina, E. P.; Bezrukova, E. V. and Zhdanova, A. N. Climate signals in the late Quaternary bottom sediments of Lake Baunt (northern Transbaikalia): Russian Geology and Geophysics, 61(10), p. 1146-1155, illus. incl. 3 tables, sketch map, 49 ref., October 2020.
The bottom sediments of lakes with different mineralization located in the basins of inland areas are high-resolution archives of climate and environmental changes. We present results of study of the Late Pleistocene-Holocene sediments of freshwater Lake Baunt, one of the lakes of the Baunt (Tsipa) depression in the permafrost zone in northern Buryatia. The sediments were studied by XRD, IR spectroscopy, laser granulometry, elemental analysis, AMS dating, etc. Mineral analysis of the bottom sediments with an age of ~18 ka has revealed predominant phyllosilicates, quartz, and feldspars. Mathematical modeling of complex XRD spectra made it possible to identify chlorite, muscovite, illite, mixed-layer illite-smectite and chlorite-smectite, and kaolinite among the phyllosilicates. We have determined their structural and crystal-chemical features and quantitative proportions in the section (800 cm long core), which vary in accordance with the climate cycles and lake level fluctuations. The results obtained helped to reconstruct the evolution of the Lake Baunt Basin controlled by the regional climate throughout the late Pleistocene-Holocene. This paper continues a series of our publications concerned with the reconstruction of the late Pleistocene-Holocene climate in East Siberia by comprehensive studies of the mineral composition of sedimentary sections of small lakes.
2021009542 Zhu Xiaofan (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, Cryosphere Research Station on the Qinghai-Tibet Plateau, State Key Laboratory of Cryospheric Science, Lanzhou, China); Wu Tonghua; Hu Guojie; Wang Shengjie; Wu Xiaodong; Li Ren; Wang Weiguo; Wen Amin; Ni Jie; Li Xiangfei and Hao Junming. Long-distance atmospheric moisture dominates water budget in permafrost regions of the central Qinghai-Tibet Plateau: Hydrological Processes, 34(22), p. 4280-4294, illus. incl. 5 tables, geol. sketch map, 96 ref., October 30, 2020.
Precipitation plays an important role in permafrost hydrology; it can alter the hydrothermal condition of the active layer and even influence the permafrost aggradation or degradation. Moisture recycling from evaporation and transpiration can greatly contribute to local precipitation in some regions. This study selected four monitoring sites and used an isotope mixing model to investigate local moisture recycling in permafrost regions of the central Qinghai-Tibet Plateau (QTP). The results showed that the local water vapour flux in the summer and autumn were dominantly influenced by westerlies and the Indian monsoon. Moistures for precipitation in Wudaoliang (WDL) and Fenghuoshan (FHS) mainly came from the western QTP, eastern Tianshan Mountains, western Qilian Mountains, and the surrounding regions. In comparison, more than half of precipitation at Tanggula (TGL) was mostly sourced from the Indian monsoon. Local moisture recycling ratios at the four sites ranged from 14%±3.8% to 31.6%±4.8%, and depended on the soil moisture and relative humidity. In particular, the higher soil moisture and relative humidity promoted local moisture recycling, but frozen ground might be a potential influencing factor as well. The moisture recycling ratios of the study area were consistent with the results from both the Qinghai Lake Basin and the Nam Co Basin, but differed from those of the northwestern QTP. This difference may indirectly confirm the great spatial variability in precipitation on the QTP. Moreover, the rising air temperature and ground temperature, increasing precipitation, higher soil moisture, higher vegetation cover, and expanding lakes in the study area may be conductive to enhancing future local moisture recycling by altering ground surface conditions and facilitating the land surface evaporation and plant transpiration. Abstract Copyright (2020), John Wiley & Sons, Ltd.
2021006527 Estop-Aragonés, Cristian (University of Alberta, Department of Renewable Resources, Edmonton, AB, Canada); Olefeldt, David; Abbott, Benjamin W.; Chanton, Jeffrey P.; Czimczik, Claudia I.; Dean, Joshua F.; Egan, Jocelyn E.; Gandois, Laure; Garnett, Mark H.; Hartley, Iain P.; Hoyt, Alison; Lupascu, Massimo; Natali, Susan M.; O'Donnell, Jonathan A.; Raymond, Peter A.; Tanentzap, Andrew J.; Tank, Suzanne E.; Schuur, Edward A. G.; Turetsky, Merritt and Anthony, Katey Walter. Assessing the potential for mobilization of old soil carbon after permafrost thaw; a synthesis of 14C measurements from the northern permafrost region: Global Biogeochemical Cycles, 34(9), Article 2020GB006672, illus. incl. 2 tables, sketch map, 130 ref., September 2020.
The magnitude of future emissions of greenhouse gases from the northern permafrost region depends crucially on the mineralization of soil organic carbon (SOC) that has accumulated over millennia in these perennially frozen soils. Many recent studies have used radiocarbon (14C) to quantify the release of this "old" SOC as CO2 or CH4 to the atmosphere or as dissolved and particulate organic carbon (DOC and POC) to surface waters. We compiled ~1,900 14C measurements from 51 sites in the northern permafrost region to assess the vulnerability of thawing SOC in tundra, forest, peatland, lake, and river ecosystems. We found that growing season soil 14C-CO2 emissions generally had a modern (post-1950s) signature, but that well-drained, oxic soils had increased CO2 emissions derived from older sources following recent thaw. The age of CO2 and CH4 emitted from lakes depended primarily on the age and quantity of SOC in sediments and on the mode of emission, and indicated substantial losses of previously frozen SOC from actively expanding thermokarst lakes. Increased fluvial export of aged DOC and POC occurred from sites where permafrost thaw caused soil thermal erosion. There was limited evidence supporting release of previously frozen SOC as CO2, CH4, and DOC from thawing peatlands with anoxic soils. This synthesis thus suggests widespread but not universal release of permafrost SOC following thaw. We show that different definitions of "old" sources among studies hamper the comparison of vulnerability of permafrost SOC across ecosystems and disturbances. We also highlight opportunities for future 14C studies in the permafrost region. Abstract Copyright (2020). American Geophysical Union. All Rights Reserved.
2021009562 Okkonen, Jarkko (University of Oulu, Oulu Mining School, Oulu, Finland); Neupauer, Roseanna M.; Kozlovskaya, Elena; Afonin, Nikita; Moisio, K.; Taewook, K. and Muurinen, E. Frost quakes; crack formation by thermal stress: Journal of Geophysical Research: Earth Surface, 125(9), Paper no.e2020JF005616, illus. incl. 3 tables, sketch map, 38 ref., September 2020.
Fractures in frozen soils (frost quakes) can cause damage to buildings and other infrastructure, but their formation mechanisms remain poorly understood. A methodology was developed to assess thermal stress on soil due to changes in climate and weather conditions and to investigate the connection between thermal stress and frost quakes in central Finland due to brittle fracturing in uppermost soils. A hydrological model was used to simulate snow accumulation and melt, and a soil temperature model was used to simulate soil temperature at different depths beneath the snow pack. The results of modeling, together with measurements of air temperature, snow cover thickness, and soil temperature, were used to calculate temporal variations in thermal stress in soil. We show that frost quakes occur when thermal stress caused by a rapid decrease in temperature exceeds fracture toughness and strength of the soil-ice mixture. We compared calculated thermal stress on soil, critical stress intensity factor, and a seismogram recorded in a suburban region in central Finland. Our results suggest that this methodology can be used to predict thermal stresses on soil and identify stress values that may lead to fractures of frozen soils, that is, frost quakes. Abstract Copyright (2020). American Geophysical Union. All Rights Reserved.
2021011470 Schaefer, Kevin (National Snow and Ice Data Center, Boulder, CO); Elshorbany, Yasin; Jafarov, Elchin; Schuster, Paul F.; Striegl, Robert G.; Wickland, Kimberly P. and Sunderland, Elsie M. Potential impacts of mercury released from thawing permafrost: Nature Communications, 11(Article 4650), Article 4650, illus., 38 ref., September 16, 2020.
Mercury (Hg) is a naturally occurring element that bonds with organic matter and, when converted to methylmercury, is a potent neurotoxicant. Here we estimate potential future releases of Hg from thawing permafrost for low and high greenhouse gas emissions scenarios using a mechanistic model. By 2200, the high emissions scenario shows annual permafrost Hg emissions to the atmosphere comparable to current global anthropogenic emissions. By 2100, simulated Hg concentrations in the Yukon River increase by 14% for the low emissions scenario, but double for the high emissions scenario. Fish Hg concentrations do not exceed United States Environmental Protection Agency guidelines for the low emissions scenario by 2300, but for the high emissions scenario, fish in the Yukon River exceed EPA guidelines by 2050. Our results indicate minimal impacts to Hg concentrations in water and fish for the low emissions scenario and high impacts for the high emissions scenario.
2021005101 Song Lei (Chinese Academy of Sciences, Institute of Tibetan Plateau Research, Laboratory of Tibetan Environment Changes and Land Surface Processes, Beijing, China); Wang Lei; Li Xiuping; Zhou Jing; Luo Dongliang; Jin Huijun; Qi Jia; Zeng Tian and Yin Yuanyuan. Improving permafrost physics in a distributed cryosphere-hydrology model and its evaluations at the upper Yellow River basin: Journal of Geophysical Research: Atmospheres, 125(18), Article e2020JD032916, illus. incl. 3 tables, sketch maps, 110 ref., September 27, 2020.
Frozen soil undergoing freeze-thaw cycles has effects on local hydrology, ecosystems, and engineering infrastructure by global warming. It is important to clarify the hydrological processes of frozen soil, especially permafrost. In this study, the performance of a distributed cryosphere-hydrology model (WEB-DHM, Water and Energy Budget-based Distributed Hydrological Model) was significantly improved by the addition of enthalpy-based permafrost physics. First, we formulated the water phase change in the unconfined aquifer and its exchanges of water and heat with the upper soil layers, with enthalpy adopted as a prognostic variable instead of soil temperature in the energy balance equation to avoid instability when calculating water phase changes. Second, more reasonable initial conditions for the bottom soil layer (overlying the unconfined aquifer) were considered. The improved model (hereinafter WEB-DHM-pf) was carefully evaluated at three sites with seasonally frozen ground and one permafrost site over the Qinghai-Tibetan Plateau ("the Third Pole"), to demonstrate the capability of predicting the internal processes of frozen soil at the point scale, particularly the "zero-curtain" phenomenon in permafrost. Four different experiments were conducted to assess the impacts of augmentation of single model improvement on simulating soil water/ice and temperature dynamics in frozen soil. Finally, the WEB-DHM-pf was demonstrated to be capable of accurately reproducing the zero curtain, detecting long-term changes in frozen soil at the point scale, and discriminating basin-wide permafrost from seasonally frozen ground in a basin at the headwaters of the Yellow River. Abstract Copyright (2020). American Geophysical Union. All Rights Reserved.
2021008053 Keuper, Frida (Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement, BioEcoAgro Joint Research Unit, Barenton-Bugny, France); Wild, Birgit; Kummu, Matti; Beer, Christian; Blume-Werry, Gesche; Fontaine, Sébastien; Gavazov, Konstantin; Gentsch, Norman; Guggenberger, Georg; Hugelius, Gustaf; Jalava, Mika; Koven, Charles; Krab, Eveline J.; Kuhry, Peter; Monteux, Sylvain; Richter, Andreas; Shahzad, Tanvir; Weedon, James T. and Dorrepaal, Ellen. Carbon loss from northern circumpolar permafrost soils amplified by rhizosphere priming: Nature Geoscience, 13(8), p. 560-565, illus. incl. 1 table, sketch map, 52 ref., August 2020.
2021008052 Shi, Zheng (University of California at Irvine, Depratment of Ecology and Evolutionary Biology, Irvine, CA); Allison, Steven D.; He, Yujie; Levine, Paul A.; Hoyt, Alison M.; Beem-Miller, Jeffrey; Zhu, Qing; Wieder, William R.; Trumbore, Susan and Randerson, James T. The age distribution of global soil carbon inferred from radiocarbon measurements: Nature Geoscience, 13(8), p. 555-559, illus. incl. 1 table, geol. sketch maps, 36 ref., August 2020.
2021004806 Rodenhizer, Heidi (Northern Arizona University, Center for Ecosystem Science and Society, Flagstaff, AZ); Ledman, Justin; Mauritz, Marguerite; Natali, Susan M.; Pegoraro, Elaine; Plaza, César; Romano, Emily; Schädel, Christina; Taylor, Meghan and Schuur, Edward. Carbon thaw rate doubles when accounting for subsidence in a permafrost warming experiment: Journal of Geophysical Research: Biogeosciences, 125(6), Article e2019JG005528, illus., 94 ref., June 2020.
Permafrost thaw is typically measured with active layer thickness, or the maximum seasonal thaw measured from the ground surface. However, previous work has shown that this measurement alone fails to account for ground subsidence and therefore underestimates permafrost thaw. To determine the impact of subsidence on observed permafrost thaw and thawed soil carbon stocks, we quantified subsidence using high-accuracy GPS and identified its environmental drivers in a permafrost warming experiment near the southern limit of permafrost in Alaska. With permafrost temperatures near 0°C, 10.8 cm of subsidence was observed in control plots over 9 years. Experimental air and soil warming increased subsidence by five times and created inundated microsites. Across treatments, ice and soil loss drove 85-91% and 9-15% of subsidence, respectively. Accounting for subsidence, permafrost thawed between 19% (control) and 49% (warming) deeper than active layer thickness indicated, and the amount of newly thawed carbon within the active layer was between 37% (control) and 113% (warming) greater. As additional carbon thaws as the active layer deepens, carbon fluxes to the atmosphere and lateral transport of carbon in groundwater could increase. The magnitude of this impact is uncertain at the landscape scale, though, due to limited subsidence measurements. Therefore, to determine the full extent of permafrost thaw across the circumpolar region and its feedback on the carbon cycle, it is necessary to quantify subsidence more broadly across the circumpolar region. Abstract Copyright (2020), American Geophysical Union. All Rights Reserved.
2021011244 Kinder, Malgorzata (University of Gdansk, Faculty of Oceanography and Geography, Environmental Change Reconstruction Laboratory, Gdansk, Poland); Tylmann, Wojciech; Rzeszewski, Michal and Zolitschka, Bernd. Varves and mass-movement deposits record distinctly different sedimentation dynamics since the late glacial (Lake Szurpily, northeastern Poland): Quaternary Research, 93, p. 299-313, illus. incl. strat. col., sketch maps, 97 ref., January 2020.
The sedimentological and geochemical characteristics of sediments from Lake Szurpily (northeastern Poland) can be used as a record of mass movement and climate dynamics since the Allerod. Late-glacial sediments suggest enhanced runoff conditions in the catchment after the retreat of the Scandinavian Ice Sheet, while Holocene varved sediments are interrupted by mass-movement deposits (MMDs). We identified 85 thin (<10 cm) MMDs (type 1) that consist of autochthonous material and frequently occur during the Atlantic period. Mobilization of littoral zone and slope sediments caused redeposition in the deepest part of the lake and was likely related to climatic conditions. In contrasting, one sedimentary unit (>1-m-thick MMD type 2) consists of auto- and allochthonous material and represents multistage processes, including erosion and deformation of underlying varved sediments, rapid deposition of clastic material, and redeposition of previously eroded varved sediments. Seismic activity or permafrost degradation was responsible for the deposition of MMD type 2. Furthermore, varve-thickness variability suggests Gleissberg and Suess solar cycles before 850 BC, when human impact was limited. Additionally, 22 and 11 yr sunspot cycles are recognized in light/dark laminae-thickness ratios and reflect influences of solar irradiance on lacustrine productivity.
2021004787 Peng Xiaoqing (Lanzhou University, College of Earth and Environmental Sciences, Key Laboratory of Western China's Environmental Systems (Ministry of Education), Lanzhou, China); Zhang Tingjun; Frauenfeld, Oliver W.; Wang Shijin; Qiao Lina; Du Ran and Mu Cuicui. Northern Hemisphere greening in association with warming permafrost: Journal of Geophysical Research: Biogeosciences, 125(1), Article e2019JG005086, illus. incl. 4 tables, 77 ref., January 2020.
Vegetation is closely tied to climate change, hydrological processes, the carbon cycle, and the energy balance. However, in cold regions, both climate and vegetation changes are also closely coupled to permafrost. The association between amplified warming and greening in Northern Hemisphere permafrost regions is not clearly understood. We therefore produce an extended 1982-2015 normalized difference vegetation index record based on concatenated Global Inventory Modeling and Mapping Studies and Moderate-Resolution Imaging Spectroradiometer data to quantify the spatiotemporal patterns of vegetation variability. We also establish spatiotemporal permafrost warming patterns based on a thawing index, active layer thickness, soil temperature, the first thaw date, and thawing days. Next, we establish the association between vegetation and warming permafrost. We find that normalized difference vegetation index increases in approximately 70% of Northern Hemisphere permafrost regions during the growing season (April-October) and in 72% of the region during autumn. Warming permafrost shows a positive relationship with greening. A higher thawing index, greater active layer thickness, higher soil temperature, and also increased precipitation are linked with the observed greening. An earlier first thaw date and an increased number of thawing days also correlate with vegetation greening. These findings underscore the sensitivity of vegetation to warming permafrost. Continued permafrost warming will result in further greening of Northern Hemisphere cold regions (and vice versa), with important implications for the permafrost soil-vegetation-atmosphere carbon cycles, and the water, nutrient, and energy budgets. Abstract Copyright (2019), American Geophysical Union. All Rights Reserved.
2021011572 Alexander, Andreas (University of Oslo, Department of Geosciences, Oslo, Norway); Obu, Jaroslav; Schuler, Thomas V.; Kääb, Andreas and Christiansen, Hanne H. Subglacial permafrost dynamics and erosion inside subglacial channels driven by surface events in Svalbard: The Cryosphere (Online), 14(11), p. 4217-4231, illus. incl. 1 table, sketch map, 54 ref., 2020.
Cold glacier beds, i.e., where the ice is frozen to its base, are widespread in polar regions. Common theories state that stable permafrost should exist under glacier beds on shorter timescales, varying from years to decades. Presently, only a few direct measurements of both subglacial permafrost and the processes influencing its thermal regime exist. Here, we present subglacial permafrost and active layer measurements obtained from within the basal drainage systems of two cold-based glaciers on Svalbard during the summer melt season. Temperature observations were obtained from subglacial sediment that was accessed through the drainage systems of the two glaciers in the previous winters. The temperature records cover the periods from spring to autumn in 2016 and 2019 at the glaciers Larsbreen and Tellbreen in central Svalbard. The ground temperature below Larsbreen indicates colder ground conditions, whereas the temperatures of the Tellbreen drainage system show considerably warmer conditions, close to the freezing point. We suggest the latter is due to the presence of liquid water all year round inside the Tellbreen drainage system. Both drainage systems investigated show an increase in subglacial sediment temperatures after the disappearance of snow bridges and the subsequent connection to surface meltwater supply at the start of the summer melt season. Temperature records show influence of sudden summer water supply events, when heavy melt and rain left their signatures on the thermal regime and the erosion of the glacier bed. Observed vertical erosion can reach up to 0.9 m d-1 at the base of basal drainage channels during summer. We also show that the thermal regime under the subglacial drainage systems is not stable during summer but experiences several freeze-thaw cycles driven by weather events. Our results show the direct importance of heavy melt events and rain on the thermal regime of subglacial permafrost and the erosion of the glacier bed in the vicinity of subglacial drainage channels. Increased precipitation and surface melt, as expected for future climate, will therefore likely lead to increased degradation of subglacial permafrost, as well as higher subglacial erosion of available sediment around the preferential hydrological paths. This in turn might have significant impacts on proglacial and fjord ecosystems due to increased sediment and nutrient input.
2021011571 Chesnokova, Anna (École de Technologie Supérieure, Hydrology, Climate and Climate Change Laboratory, Montreal, QC, Canada); Baraër, Michel and Bouchard, Émilie. Proglacial icings as records of winter hydrological processes: The Cryosphere (Online), 14(11), p. 4145-4164, illus. incl. 2 tables, sketch map, 96 ref., 2020.
The ongoing warming of cold regions is affecting hydrological processes, causing deep changes, such as a ubiquitous increase in river winter discharges. The drivers of this increase are not yet fully identified mainly due to the lack of observations and field measurements in cold and remote environments. In order to provide new insights into the sources generating winter runoff, the present study explores the possibility of extracting information from icings that form over the winter and are often still present early in the summer. Primary sources detection was performed using time-lapse camera images of icings found in both proglacial fields and upper alpine meadows in June 2016 in two subarctic glacierized catchments in the upper part of the Duke watershed in the St. Elias Mountains, Yukon. As images alone are not sufficient to entirely cover a large and hydrologically complex area, we explore the possibility of compensating for that limit by using four supplementary methods based on natural tracers: (a) stable water isotopes, (b) water ionic content, (c) dissolved organic carbon, and (d) cryogenic precipitates. The interpretation of the combined results shows a complex hydrological system where multiple sources contribute to icing growth over the studied winter. Glaciers of all sizes, directly or through the aquifer, represent the major parent water source for icing formation in the studied proglacial areas. Groundwater-fed hillslope tributaries, possibly connected to suprapermafrost layers, make up the other detectable sources in icing remnants. If similar results are confirmed in other cold regions, they would together support a multi-causal hypothesis for a general increase in winter discharge in glacierized catchments. More generally, this study shows the potential of using icing formations as a new, barely explored source of information on cold region winter hydrological processes that can contribute to overcoming the paucity of observations in these regions.
2021011561 Hodson, Andrew J. (University Centre in Svalbard, Department of Arctic Geology, Longyearbyen, Svalbard and Jan Mayen Islands); Nowak, Aga; Hornum, Mikkel T.; Senger, Kim; Redeker, Kelly; Christiansen, Hanne H.; Jessen, Soren; Betlem, Peter; Thornton, Steve F.; Turchyn, Alexandra V.; Olaussen, Snorre and Marca, Alina. Sub-permafrost methane seepage from open-system pingos in Svalbard: The Cryosphere (Online), 14(11), p. 3829-3842, illus. incl. 2 tables, sketch map, 46 ref., 2020.
Methane release from beneath lowland permafrost represents an important uncertainty in the Arctic greenhouse gas budget. Our current knowledge is arguably best developed in settings where permafrost is being inundated by rising sea level, which means much of the methane is oxidised in the water column before it reaches the atmosphere. Here we provide a different process perspective that is appropriate for Arctic fjord valleys where local deglaciation causes isostatic uplift to out pace rising sea level. We describe how the uplift induces permafrost aggradation in former marine sediments, whose pressurisation results in methane escape directly to the atmosphere via groundwater springs. In Adventdalen, central Spitsbergen, we show how the springs are historic features responsible for the formation of open-system pingos and capable of discharging brackish waters enriched with high concentrations of mostly biogenic methane (average 18 mg L-1). Thermodynamic calculations show that the methane concentrations sometimes marginally exceed the solubility limit for methane in water at 0 °C (41 mg L-1). Year-round emissions from the pingos are described. During winter, rapid methane loss to the atmosphere occurs following outburst events from beneath an ice blister. During summer, highly variable emissions occur due to complex surface processes at the seepage point and its inundation by surface runoff. In spite of this complexity, our observations confirm that sub-permafrost methane migration deserves more attention for the improved forecasting of Arctic greenhouse gas emissions.
2021011565 Ji Mukan (Chinese Academy of Sciences, Institute of Tibetan Plateau Research, Beijing, China); Kong Weidong; Liang Chao; Zhou Tianqi; Jia Hongzeng and Dong Xiaobin. Permafrost thawing exhibits a greater influence on bacterial richness and community structure than permafrost age in Arctic permafrost soils: The Cryosphere (Online), 14(11), p. 3907-3916, illus., 52 ref., 2020.
Global warming accelerates permafrost thawing and changes its microbial community structure, but little is known about how microorganisms in permafrost with different ages respond to thawing. Herein, we disentangled the relative importance of permafrost age (young, medium-aged, old, and ancient, spanning from 50 to 5000 years) and thawing status (active, transitional, and permanently frozen) in shaping bacterial community structure using HiSeq sequencing of the 16S rRNA gene. Our results revealed significant influences of both permafrost thawing and age on bacterial richness. The bacterial richness was significantly higher in the young and thawed permafrost, and the richness increase was mainly observed in Firmicutes, Actinobacteria, Chloroflexi, Deltaproteobacteria, and Alphaproteobacteria. Permafrost thawing led to a gradual change in bacterial community structure and increased contribution of determinism. Permutational analysis of variance demonstrated that thawing significantly changed bacterial community structure at all soil ages, but the community convergence due to permafrost thawing was not observed. Structural equation modeling revealed that permafrost thawing exhibited a greater influence on both bacterial richness and community structure than permafrost age. Our results indicate that microorganisms in permafrost with different ages respond differently to thawing, which eventually leads to distinct bacterial community compositions and different organic carbon decomposition processes in Arctic permafrost.
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