|
2019003276 Weber, Samuel (University of Zurich, Department of Geography, Zurich, Switzerland); Fäh, D.; Beutel, J.; Faillettaz, J.; Gruber, S. and Vieli, A. Ambient seismic vibrations in steep bedrock permafrost used to infer variations of ice-fill in fractures: Earth and Planetary Science Letters, 501, p. 119-127, illus., 49 ref., November 1, 2018. Includes appendix.
The behavior of ice in frozen rock masses is an important control on rock slope stability but the knowledge of the formation, extent and evolution of ice-filled fractures in steep bedrock permafrost is limited. Therefore, this study aims at characterizing the site specific ambient seismic vibration recorded at the Matterhorn Hornligrat fieldsite over the course of more than three years. The observed normal mode resonance frequencies vary seasonally with four distinct phases: persistent decrease during summer (phase I), rapid increase during freezing (phase II), trough-shaped pattern in winter (phase III) and a sharp peak with a rapid decay during the melting/thawing season (phase IV). The relation between resonance frequency and rock temperature exhibits an annually repeated pattern with hysteretic behavior. The link between resonance frequency, fracture width and rock temperature indicates that irreversible fracture displacement is dominant in summer periods with low resonance frequency. These findings suggest that the temporal variations in resonance frequencies are linked to the formation and melt of ice-fill in bedrock fractures.
DOI: 10.1016/j.epsl.2018.08.042
2019003191 Peng Xu (Peking University, College of Urban and Environmental Sciences, Beijing, China); Chen Yixin; Liu Beibei; Liu Gengnian; Liu Qi and Liu Junnan. Timing and features of a late MIS 2 rock avalanche in the eastern Himalayas, constrained by 10Be exposure dating: Geomorphology, 318, p. 58-68, illus. incl. 2 tables, sketch maps, 94 ref., October 2018. Includes appendices.
We investigate a previously unrecorded rock avalanche deposit (Yadong rock avalanche) that resulted from a major mountain slope failure on the northwest slopes of Mt. Chomo Lhari in the Eastern Himalayas. We provide detailed mapping of the Yadong rock avalanche, and date the rock avalanche using 10Be surface exposure dating. The 10Be exposure ages of six samples suggest that the Yadong rock avalanche occurred between 14.2 ± 1.3-13.1 ± 1.3 ka during the Bolling-Allerod (BA) period. The climate was semi-arid during the BA period as it is today, which suggests that precipitation was unlikely the trigger for this rock avalanche. The relatively small paleo glaciers make glacial debuttressing trigger unlikely. Since the rock scar is situated above the lower permafrost limit, degradation of permafrost associated with deglaciation was also unlikely to be the trigger. Given the rock avalanche is located near the Yadong fault which is part of the active Yadong-Gulu rift, and the Yadong-Gulu rift has experienced great earthquakes on centennial to millennial timescales, we suggest that the most probable trigger for this rock avalanche was a seismic event associated with the Yadong fault. The result provides evidence for identifying a paleo seismic event occurred during 14.2 ± 1.3-13.1 ± 1.3 ka. These findings have important implications for understanding the mechanisms for driving rock avalanches and associated landscape evolution across the Himalayas, as well as for extending the limited scientifically documented records of major mass movements in the Eastern Himalayan region.
DOI: 10.1016/j.geomorph.2018.05.022
2019003494 Ravanel, Ludovic (University of Lausanne, IDYST, Lausanne, Switzerland); Duvillard, Pierre-Allain; Jaboyedoff, Michel and Lambiel, Christophe. Recent evolution of an ice-cored moraine at the Gentianes Pass, Valais Alps, Switzerland: Land Degradation & Development, 29(10), p. 3693-3708, illus. incl. 2 tables, sketch map, 103 ref., October 2018. Part of a special issue on Paraglacial processes.
Lateral moraines located in permafrost environments often preserve large amounts of both glacier and periglacial ice. To understand how ice-cored moraines located in high alpine environments evolve in a context of both glacier retreat and permafrost degradation, we performed 11 terrestrial laser-scanning measurement campaigns between 2007 and 2014 on a highly anthropogenic overprinted moraine prone to instability. Resulting comparison of the subsequent 3D models allowed to qualitatively and quantitatively analyze the morphological evolution of the moraine. The comparisons indicate a very high geomorphic activity of the moraine including large areas affected by downslope movements of blocks and 10 landslides with a volume between 24 ± 1 and 1,138 ± 47 m3. Data also indicated a very strong ice melt with a loss of ice thickness locally reaching 17.7 m at the foot of the moraine. These results, compared with resistivity and thermal measurements of the ground, suggest the combined role of ice loss at the foot of the moraine and the permafrost activity/warming in triggering these processes. Abstract Copyright (2018), John Wiley & Sons, Ltd.
DOI: 10.1002/ldr.3088
2018101636 Harrington, Jordan S. (University of Calgary, Department of Geoscience, Calgary, AB, Canada); Mozil, Alexandra; Hayashi, Masaki and Bentley, Laurence R. Groundwater flow and storage processes in an inactive rock glacier: Hydrological Processes, 32(20), p. 3070-3088, illus. incl. 2 tables, sketch map, 110 ref., September 30, 2018.
Groundwater flow through coarse blocky landforms contributes to streamflow in mountain watersheds, yet its role in the alpine hydrologic cycle has received relatively little attention. This study examines the internal structure and hydrogeological characteristics of an inactive rock glacier in the Canadian Rockies using geophysical imaging techniques, analysis of the discharge hydrograph of the spring draining the rock glacier, and chemical and stable isotopic compositions of source waters. The results show that the coarse blocky sediments forming the rock glacier allow the rapid infiltration of snowmelt and rain water to an unconfined aquifer above the bedrock surface. The water flowing through the aquifer is eventually routed via an internal channel parallel to the front of the rock glacier to a spring, which provides baseflow to a headwater stream designated as a critical habitat for an at-risk cold-water fish species. Discharge from the rock glacier spring contributes up to 50% of basin streamflow during summer baseflow periods and up to 100% of basin streamflow over winter, despite draining less than 20% of the watershed area. The rock glacier contains patches of ground ice even though it may have been inactive for thousands of years, suggesting the resiliency of the ground thermal regime under a warming climate. Abstract Copyright (2018), John Wiley & Sons, Ltd.
DOI: 10.1002/hyp.13248
2018101659 Luo, D. L. (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, Lanzhou, China); Jin, H. J.; He, R. X.; Wang, X. F.; Muskett, R. R.; Marchenko, S. S. and Romanovsky, V. E. Characteristics of water-heat exchanges and inconsistent surface temperature changes at an elevational permafrost site on the Qinghai-Tibet Plateau: Journal of Geophysical Research: Atmospheres, 123(18), p. 10,057-10,075, illus. incl. 4 tables, sketch map, 55 ref., September 27, 2018.
Increase of surface temperatures has long been recognized as an unequivocal response to radiative forcing and one of the most important implications for global warming. However, it remains unclear whether the variation of ground surface temperature (GST) and soil temperatures is consistent with simultaneous changes of the near-surface air and land (or skin) surface temperatures (Ta and LST). In this study, a seven-year continuous observation of GST, Ta, and surface water and heat exchange was carried out at an elevational permafrost site at Chalaping, northeastern Qinghai-Tibet Plateau. Results showed a distinct retarding of warming on the ground surface and subsurface under the presence of dense vegetation and moist peat substrates. Mean annual Ta and LST increased at noteworthy rates of 0.22 and 0.32 °C/a, respectively, while mean annual GST increased only at a rate of 0.057 °C/a. No obvious trends were detected for the four radiation budgets except the soil heat flux (G), which significantly increased at a rate of 0.29 W · m-2 · a-1, presumably inducing the melting of ground ice and resulted in much higher moisture content through the summers of 2015 and 2016 than preceding years and subsequent 2017 at the depths between 80 and 120 cm. However, no noticeable immediate variations of soil temperatures occurred owing to the large latent heat effect (thermal inertia) and the extending zero-curtain period. We suggest that a better protected eco-environment, particularly the surface vegetation, helps preserving the underlying permafrost, and thus to mitigates the potential degradation of elevational permafrost on the Qinghai-Tibet Plateau. Abstract Copyright (2018), . American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018JD028298
2019003516 Sherman, D. (University of California at San Diego, Scripps Institution of Oceanography, San Diego, CA) and Constable, S. C. Permafrost extent on the Alaskan Beaufort shelf from surface-towed controlled-source electromagnetic surveys: Journal of Geophysical Research: Solid Earth, 123(9), p. 7253-7265, illus. incl. sects., sketch maps, 31 ref., September 2018.
We have developed a surface-towed electric dipole-dipole system capable of operating in shallow water and deployable from small vessels. Our system uses electromagnetic energy from a modulated manmade source to interrogate the underlying resistivity structure of the seafloor. We used this system in the summers of 2014 and 2015 to map subsea ice-bearing permafrost on the Beaufort shelf along 200 km of coastline, from Tigvariak Island to Harrison Bay. Permafrost is resistive and was found to be anisotropic, likely due to interbedded layers of frozen and unfrozen sediment. Maps of depth to permafrost and its thickness were produced from electrical resistivity inversions and results compared to borehole logs in the area. We observed elevated resistivity values offshore the Sagavanirktok River outflow, supporting the idea that fresh groundwater flow has a preserving effect on submerged permafrost. This system provides a cost effective method that could be used to further quantify permafrost extent, provide a baseline for measurements of future degradation, and provide observational constraints to aid in permafrost modeling studies. Abstract Copyright (2018), . American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018JB015859
2019003505 Taylor, Meghan A. (Northern Arizona University, Center for Ecosystem Society and Science, Flagstaff, AZ); Celis, G.; Ledman, J. D.; Bracho, R. and Schuur, E. A. G. Methane efflux measured by eddy covariance in Alaskan upland tundra undergoing permafrost degradation: Journal of Geophysical Research: Biogeosciences, 123(9), p. 2695-2710, illus. incl. 6 tables, 65 ref., September 2018.
Greenhouse gas emissions from thawing permafrost in arctic ecosystems may amplify global warming, yet estimates of the rate of carbon release, and the proportion of carbon released as methane (CH4) or carbon dioxide (CO2), have a high degree of uncertainty. There are many areas where no measurements exist, and few year-round or long-term records. Existing year-round eddy covariance measurements of arctic CH4 fluxes suggest that nongrowing season emissions make up a significant proportion of tundra systems emissions on an annual basis. Here we present continuous CH4 flux measurements made at Eight Mile Lake, an upland tundra ecosystem undergoing permafrost degradation in Interior Alaska. We found net CH4 emissions throughout the year (1.2 ± 0.011 g C-CH4 m2/yr) that made up 61% of total radiative forcing from annual C emissions (CO2 and CH4; 32.3 g C m2/yr) when taking into account the greenhouse warming potential of CH4 relative to CO2. Nongrowing season emissions accounted for 50% of the annual CH4 budget, characterized by large pulse emissions. These were related to abrupt increases in air and shallow soil temperatures rather than consistent emissions during the zero curtain-a period of the fall/early winter season when subsurface soil temperatures remain near the 0 °C freezing point. Weekly growing season CH4 emissions in 2016 and 2017 were significantly related with thaw depth, and the magnitude of CH4 emissions between these seasons was proportional to the rate of active layer thaw throughout the season. Abstract Copyright (2018), . American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018JG004444
2019000231 Wu Daoyong (Guizhou University, College of Resource and Environmental Engineering, Guiyang, China); Zhou Xiangyang and Jiang Xingyuan. Water and salt migration with phase change in saline soil during freezing and thawing processes: Ground Water, 56(5), p. 742-752, illus. incl. 5 tables, 26 ref., September 2018.
Water and salt transfer coupled with phase change may cause serious damage to engineering structures in saline soil regions. In this study, the migration of water and salt in silty clay collected from the Qinghai-Tibet Plateau is explored experimentally and numerically during freezing and thawing processes. The results revealed that there are significant differences in the variations of liquid water content and solution concentration for different initial salt contents, due to salt crystallization and dissolution. The temperature-induced water migration is determined by the soil properties, which can be well explained by the thermodynamics of mass transfer. The amount of salt migrated upward during cooling is slightly larger than that transported downward in the warming period, implying that salt may be accumulated in the surface soil after a large number of circulations and finally result in soil salinization. Abstract Copyright (2017), National Ground Water Association.
DOI: 10.1111/gwat.12605
2019001904 Zolkos, Scott (University of Alberta, Department of Biological Sciences, Edmonton, AB, Canada); Tank, Suzanne E. and Kokelj, Steven V. Mineral weathering and the permafrost carbon-climate feedback: Geophysical Research Letters, 45(18), p. 9623-9632, illus. incl. sketch maps, 80 ref., September 28, 2018.
Permafrost thaw in the Arctic enables the biogeochemical transformation of vast stores of organic carbon into carbon dioxide (CO2). This CO2 release has significant implications for climate feedbacks, yet the potential counterbalance from CO2 fixation via chemical weathering of minerals exposed by thawing permafrost is entirely unstudied. We show that thermokarst in the western Canadian Arctic can enable rapid weathering of carbonate tills, driven by sulfuric acid from sulfide oxidation. Unlike carbonic acid-driven weathering, this caused significant and previously undocumented CO2 production and outgassing in headwater streams. Increasing riverine solute fluxes correspond with long-term intensification of thermokarst and reflect the regional predominance of sulfuric acid-driven carbonate weathering. We conclude that thermokarst-enhanced mineral weathering has potential to profoundly disrupt Arctic freshwater carbon cycling. While thermokarst and sulfuric acid-driven carbonate weathering in the western Canadian Arctic amplify CO2 release, regional variation in sulfide oxidation will moderate the effects on the permafrost carbon-climate feedback. Abstract Copyright (2018), . American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018GL078748
2018101649 Cao Bin (Lanzhou University, College of Earth and Environmental Sciences, Lanzhou, China); Zhang Tingjun; Peng Xiaoqing; Mu Cuicui; Wang Qingfeng; Zheng Lei; Wang, Kang and Zhong Xinyue. Thermal characteristics and recent changes of permafrost in the upper reaches of the Heihe River basin, western China: Journal of Geophysical Research: Atmospheres, 123(15), p. 7935-7949, illus. incl. 3 tables, sketch map, 76 ref., August 16, 2018.
To investigate the thermal characteristics and dynamics of permafrost as well as seasonally frozen ground over the upper reaches of the Heihe River Basin (URHR), an observation network with 14 boreholes was established during 2011-2014. The in situ measurements indicated mean annual air temperature that ranged from -5.2 to -2.3°C at the monitored elevation range of ~3,600-4,150 m, and mean annual ground surface temperature that ranged from -1.3 to 1.7°C during 2013-2017. The mean annual ground temperature at 16- to 18-m depth ranged from -1.71°C on the high (>4,000 m above sea level) north facing slope to about 0-C around areas near the lower limit of permafrost. Active layer thickness at the monitored sites varied significantly with the range of 0.77-4.90 m during 2011-2017, and maximum frozen depth in seasonally frozen ground was about 5 m. Permafrost thickness was between ~136 m and less than 10 m. Both permafrost and seasonally frozen ground were found to be subject to serious warming during the measured period in the URHR. This study provides new quantitative insights for permafrost and seasonally frozen ground in the URHR. Abstract Copyright (2018), . American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018JD028442
2018099060 Eckerstorfer, Markus (Norut Northern Research Institute, Tromso, Norway); Eriksen, Harald Overli; Rouyet, Line; Christiansen, Hanne H.; Lauknes, Tom Rune and Blikra, Lars Harald. Comparison of geomorphological field mapping and 2D-InSAR mapping of periglacial landscape activity at Nordnesfjellet, northern Norway: Earth Surface Processes and Landforms, 43(10), p. 2147-2156, illus. incl. geol. sketch maps, 30 ref., August 2018.
The ability to continuously monitor the dynamic response of periglacial landforms in a climate change context is of increasing scientific interest. Satellite radar interferometry provides information on surface displacement that can be related to periglacial processes. Here we present a comparison of two-dimensional (2D) surface displacement rates and geomorphological mapping at periglacial landform and sediment scale from the mountain Nordnesfjellet in northern Norway. Hence, 2D Interferometric Synthetic Aperture Radar (InSAR) results stem from a 2009-2014 TerraSAR-X dataset from ascending and descending orbits, decomposed into horizontal displacement vectors along an east-west plane, vertical displacement vectors and combined displacement velocity. Geomorphological mapping was carried out on aerial imagery and validated in the field. This detailed landform and sediment type mapping revealed an altitudinal distribution dominated by, weathered bedrock blockfields, surrounded primarily by slightly, to non-vegetated solifluction landforms at the mountain tops. Below, an active rockslide and associated rockfall deposits are located on the steep east-facing side of the study area, whereas glacial sediments dominate on the gentler western side. We show that 2D InSAR correctly depicts displacement rates that can be associated with typical deformation patterns for flat-lying or inclined landforms, within and below the regional permafrost limit, for both wet and dry areas. A net lowering of the entire landscape caused by general denudation of the periglacial landforms and sediments is here quantified for the first time using radar remote sensing. Copyright Copyright 2018 John Wiley & Sons, Ltd.
DOI: 10.1002/esp.4380
2019001921 Koch, J. C. (U. S. Geological Survey, Alaska Science Center, Anchorage, Ak); Jorgenson, M. T.; Wickland, K. P.; Kanevskiy, M. and Striegl, R. Ice wedge degradation and stabilization impact water budgets and nutrient cycling in arctic trough ponds: Journal of Geophysical Research: Biogeosciences, 123(8), p. 2604-2616, illus. incl. 3 tables, 65 ref., August 2018.
Trough ponds are ubiquitous features of Arctic landscapes and an important component of freshwater aquatic ecosystems. Permafrost thaw causes ground subsidence, creating depressions that gather water, creating ponds. Permafrost thaw also releases solutes and nutrients, which may fertilize these newly formed ponds. We measured water budget elements and chloride, ammonium, and dissolved organic nitrogen (DON) across a chronosequence of trough ponds representing different stages of ice wedge degradation and stabilization. We developed a coupled hydrologic and biogeochemical model to explore how ice wedge degradation affects hydrology and nutrient availability in trough ponds in the advanced degradation stages (DAs), which are characterized by deep troughs with warmer temperatures relative to the other stages. DAs experienced greater evaporation than the other stages, and subsurface inflows entered the DAs from a wide area. Chloride accumulated in the ponds with time since thaw, implying that subsurface fluxes are delivering solutes from the thawing permafrost. Ammonium accumulated at high rates in the initial degradation stage and was seasonally depleted over the summer in all degradation stages. Ammonium trends in the DAs were consistent with high concentration inflows and in-pond assimilation at rates between 0.37 and 2.0 mg N m-2 day-1. Seasonal DON trends indicated that the accumulation of recalcitrant organic matter may eventually limit aquatic ecosystem production and foster pond infilling. These results provide direct evidence of nutrient release from thawing permafrost and the utilization of these nutrients by Arctic trough pond ecosystems and highlight infilling as a mechanism by which Arctic surface waters may be lost. Abstract Copyright (2018), . American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018JG004528
2018099192 Liu, Lu (University of Washington at Seattle, Department of Earth and Space Sciences, Seattle, WA); Sletten, Ronald S.; Hallet, Bernard and Waddington, Edwin D. Thermal regime and properties of soils and ice-rich permafrost in Beacon Valley, Antarctica: Journal of Geophysical Research: Earth Surface, 123(8), p. 1797-1810, illus. incl. 2 tables, geol. sketch map, 45 ref., August 2018.
Subsurface temperatures in polar environments control geomorphic, hydrologic, and biologic processes and ground ice stability. Most studies of the thermal regime in permafrost areas have been developed for the Arctic where interest and concern focus on permafrost thawing. In contrast, this study focuses on soils in the McMurdo Dry Valleys of Antarctica where conditions are much colder and drier, and long-term persistence of ground ice is of interest including as an analog site for Mars. The soil temperature in Beacon Valley, one of the McMurdo Dry Valleys, has been modeled using the surface temperature, measured heat capacity, and temperature-dependent thermal conductivity and compared to continuous, high-resolution measurements of temperatures for a decade down to 19.6-m depth. For the temperature range of -47.9 to 7.5 °C at our study site, the heat capacity of the dry soil ranges from 580 to 690 J · kg-1 · K-1, thermal conductivity from 0.22 to 0.27 W · m-1 · K-1, and the calculated thermal diffusivity from 0.23 to 0.25 mm2/s. Both the finite difference method and the finite volume method are used to solve the 1-D heat diffusion equation; the finite volume method-modeled temperature most closely approximates the measured temperature at all depths with average differences ranging from 0.01 to 0.03 °C. The latent heat contribution of documented episodic snowmelt events and of modeled changes in ice content due to condensation or sublimation is negligible. This study can be applied readily to thermal regimes of similar systems where subsurface temperature measurements are not available such as on Mars. Abstract Copyright (2018), . American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2017JF004535
2018099190 Nicolsky, D. J. (University of Alaska at Fairbanks, Geophysical Institute, Fairbanks, AL) and Romanovsky, V. E. Modeling long-term permafrost degradation: Journal of Geophysical Research: Earth Surface, 123(8), p. 1756-1771, illus. incl. 3 tables, geol. sketch map, 35 ref., August 2018.
Permafrost, as an important part of the Cryosphere, has been strongly affected by climate warming, and a wide spread of permafrost responses to the warming is currently observed. In particular, at some locations rather slow rates of permafrost degradations are noticed. We related this behavior to the presence of unfrozen water in frozen fine-grained earth material. In this paper, we examine not-very-commonly-discussed heat flux from the ground surface into the permafrost and consequently discuss implications of the presence of unfrozen liquid water on long-term thawing of permafrost. We conducted a series of numerical experiments and demonstrated that the presence of fine-grained material with substantial unfrozen liquid water content at below 0°C temperature can significantly slow down the thawing rate and hence can increase resilience of permafrost to the warming events. This effect is highly nonlinear, and a difference between the rates of thawing in fine- and coarse-grained materials is more drastic for lower values of heat flux incoming into permafrost. For high heat flux, the difference between these rates almost disappears. As near-surface permafrost temperature increases towards 0°C and the changes in the ground temperature become less evident, the future observation networks should try to incorporate measurements of unfrozen liquid water content in the near-surface permafrost and heat flux into permafrost in addition to the existing temperature observations. Abstract Copyright (2018), . American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018JF004655
2019001918 Salmon, Verity G. (Oak Ridge National Laboratory, Environmental Sciences Division and Climate Change Science Institute, Oak Ridge, TN); Schädel, Christina; Bracho, Rosvel; Pegoraro, Elaine; Celis, Gerardo; Mauritz, Marguerite; Mack, Michelle C. and Schuur, Edward A. G. Adding depth to our understanding of nitrogen dynamics in permafrost soils: Journal of Geophysical Research: Biogeosciences, 123(8), p. 2497-2512, illus. incl. 4 tables, 65 ref., August 2018.
Losses of C from decomposing permafrost may be offset by increased productivity of tundra plants, but nitrogen availability partially limits plant growth in tundra ecosystems. In this soil incubation experiment carbon (C) and nitrogen (N) cycling dynamics were examined from the soil surface down through upper permafrost. We found that losses of CO2 were negatively correlated to net N mineralization because C-rich surface soils mineralized little N, while deep soils had low rates of C respiration but high rates of net N mineralization. Permafrost soils released a large flush of inorganic N when initially thawed. Depth-specific rates of N mineralization from the incubation were combined with thaw depths and soil temperatures from a nearby manipulative warming experiment to simulate the potential magnitude, timing, and depth of inorganic N release during the process of permafrost thaw. Our calculations show that inorganic N released from newly thawed permafrost may be similar in magnitude to the increase in N mineralized by warmed soils in the middle of the profile. The total release of inorganic N from the soil profile during the simulated thaw process was twice the size of the observed increase in the foliar N pool observed at the manipulative experiment. Our findings suggest that increases in N availability are likely to outpace the N demand of tundra plants during the first 5 years of permafrost thaw and may increase C losses from surface soils as well as induce denitrification and leaching of N from these ecosystems. Abstract Copyright (2018), . American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2018JG004518
2019001915 Wik, Martin (Stockholm University, Department of Geological Sciences and Bolin Centre for Climate Research, Stockholm, Sweden); Johnson, Joel E.; Crill, Patrick M.; DeStasio, Joel P.; Erickson, Lance; Halloran, Madison J.; Fahnestock, M. Florencia; Crawford, Maurice K.; Phillips, Stephen C. and Varner, Ruth K. Sediment characteristics and methane ebullition in three subarctic lakes: Journal of Geophysical Research: Biogeosciences, 123(8), p. 2399-2411, illus. incl. 2 tables, sketch maps, 70 ref., August 2018.
Ebullition (bubbling) from climate-sensitive northern lakes remains an unconstrained source of atmospheric methane (CH4). Although the focus of many recent studies, ebullition is rarely linked to the physical characteristics of lakes. In this study we analyze the sediments of subarctic postglacial lakes and investigate how sediment properties relate to the large spatial variation in CH4 bubble flux, quantified over multiple years using bubble traps. The results show that the sediments from our lakes are rich in total organic carbon, containing 37 kg/m3 on average. This number is roughly 40% higher than the average for yedoma deposits, which have been identified as high CH4 emitters. However, the quantity of total organic carbon is not a useful indicator of high emissions from the study lakes. Neither is the amount of CH4 in the sediment a reliable measure of ebullition potential. Instead, our data point to coarse detritus, partly from buried submerged aquatic vegetation and redeposited peat as spatial controls on fluxes, often in combination with previously established effects of incoming solar radiation and water depth. The results once again highlight the climate sensitivity of northern lakes, indicating that biological responses to warmer waters and increased energy input and heating of organic sediments during longer ice-free seasons can substantially alter future CH4 emissions. Abstract Copyright (2018), . American Geophysical Union. All Rights Reserved.
DOI: 10.1029/2017JG004298
2019000736 de Guzman, Earl Marvin B. (University of Manitoba, Department of Civil Engineering, Winnipeg, MB, Canada); Stafford, Dylan; Alfaro, Marolo C.; Doré, Guy and Arenson, Lukas U. Large-scale direct shear testing of compacted frozen soil under freezing and thawing conditions: Cold Regions Science and Technology, 151, p. 138-147, illus. incl. 4 tables, July 2018. Based on Publisher-supplied data.
Embankments in the Arctic are often constructed during winter conditions to preserve the underlying permafrost and minimize environmental impacts. However, there is a limited understanding as to how frozen soils, compacted during sub-freezing conditions behave, and how this impacts the overall performance of the embankment, especially during the first thawing season following winter construction. Fills are very difficult to compact at sub-zero temperatures with ground ice present in them. They are strong and stiff when frozen but they become softer and more compressible upon thawing. This reduction in shear strength due to thawing can lead to slope instability and embankment failure. This paper describes part of a larger study on the structural stability of embankments constructed in the winter along the new Inuvik-Tuktoyaktuk Highway in the Northwest Territories, Canada. A series of large-scale direct shear tests was conducted on laboratory-compacted frozen fill to determine its shear strength. Frozen soil chunks were compacted at -10°C. Normal stresses of 25, 50, and 100 kPa were selected corresponding to the range of applied vertical stresses expected in the field. Horizontal and vertical displacements, applied normal stresses, and horizontal loads were recorded throughout testing. The tests were conducted in an environmental chamber under frozen, thawed, and cyclic freeze-thaw conditions. The frozen soil samples showed high shear strength when frozen, but upon thaw and following freeze-thaw conditions the shear strength was reduced by as much as 50%. The most critical condition, based on the tests conducted, occurs during the onset of the first thawing when the ice bonding in the soil matrix melts. Numerical models were developed using a finite difference program and calibrated with the results from the large-scale direct shear tests. It was demonstrated that restrained dilatancy affects the results of the simulations but the soil maintains the critical state friction angle for increased normal stresses.
DOI: 10.1016/j.coldregions.2018.03.011
2019000737 Kutasov, I. M. (BYG Consulting, Boston) and Eppelbaum, L. V. The effect of thermal properties changing (at ice-water transition) on the radius of permafrost thawing: Cold Regions Science and Technology, 151, p. 156-158, illus. incl. 3 tables, July 2018. Based on Publisher-supplied data.
Earlier we developed an approximate method of calculating the radius of permafrost thawing by a cylindrical source with a constant temperature. In this study, we show that the effect of thermal properties changing at the ice-water transition on the radius of thawing in many cases can be neglected. Two typical examples are presented.
DOI: 10.1016/j.coldregions.2018.03.018
2019000741 Li Shuangyang (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, State Key Laboratory of Frozen Soil Engineering, Lanzhou, China); Zhang Mingyi; Pei Wansheng; Lai Yuanming and Yu Wenbing. Thermo-seismic characteristics of a crushed-rock interlayer embankment on a permafrost slope: Cold Regions Science and Technology, 151, p. 249-259, illus. incl. 3 tables, sketch maps, July 2018. Based on Publisher-supplied data.
Crushed rock is a highly porous medium widely used to cool embankments in permafrost regions. The thermal transfer of a crushed-rock embankment (CRE) was fully investigated by experimental and numerical methods. However, the CRE's mechanical process, especially under dynamic loading, is a key factor for its safe operation but has been ignored. To study the dynamic characteristics of the CRE, we proposed a thermo-dynamic coupled model for the CRE, selected a crushed-rock interlayer embankment (CRIE) on a permafrost slope, and conducted a series of numerical computations over four seasons in its 20th service year. The CRIE temperature changed seasonally, causing seasonal differences in mechanical behaviors and seismic responses. By comparing the acceleration, velocity, displacement and pore water pressure responses of the CRIE, the seismic damage mechanism of the CRIE is analyzed and the time at which the earthquake-induced damage of the CRIE is the heaviest among these four seasons is identified. The numerical model and results in the study can provide theoretical support to the construction and maintenance of the CRIE as well as a reference for further study of the CRE in permafrost regions.
DOI: 10.1016/j.coldregions.2018.03.019
2019000743 Shen Yupeng (Beijing Jiaotong University, School of Civil Engineering, Beijing, China); Zuo Ruifang; Liu Jiankun; Tian Yahu and Wang Qing. Characterization and evaluation of permafrost thawing using GPR attributes in the Qinghai-Tibet Plateau: Cold Regions Science and Technology, 151, p. 302-313, illus. incl. 1 table, sketch map, July 2018. Based on Publisher-supplied data.
Recognizing the status of permafrost thawing and providing information for permafrost treatment in the Tibetan Plateau is a key problem. In this paper, a GPR experiment is designed to explore effective geophysical attributes for characterizing and evaluating the impact of key factors on permafrost thawing. A new algorithm for the assessment of rapid relative water content is also presented. After processing the GPR data, the weighted average frequency attribute, sweetness attribute and relative wave impedance attribute, which better characterize the effect of different factors on permafrost thawing, are selected. The weighted average frequency attribute can distinguish the thawing front and evaluate the extent of thawing in addition to the completely thawed fringe; the sweetness attribute can help to characterize thawing in water ice mixed with permafrost and evaluate the impact of free water on permafrost below the thawing front. The relative wave impedance attribute highlights the completely thawed fringe and other smaller internal stratifications in the permafrost thawing zone. Using the rapid relative water content assessment algorithm, it is easy to evaluate the extent of thawing using only GPR data. In addition, a thermokarst lake strengthens the degree of permafrost thawing. Permafrost thawing accelerates on sunny slopes. This study shows that roadbeds inhibit permafrost thawing and that a thermosyphon significantly inhibits permafrost thawing.
DOI: 10.1016/j.coldregions.2018.03.028
2019000735 Zhang Xuefu (Chongqing Jiaotong University, College of Civil Engineering, State Key Laboratory Breeding Base of Mountain Bridge and Tunnel Engineering, Chongqing, China); Zhou Zihan; Li Junqi; Zhou Yuanfu and Han Fenglei. A physical model experiment for investigating into temperature redistribution in surrounding rock of permafrost tunnel: Cold Regions Science and Technology, 151, p. 47-52, illus., July 2018. Based on Publisher-supplied data.
The temperature distribution is one of the most important issues which should be considered in permafrost tunnel design. In order to investigate the influence of temperature disturbance caused by construction and boundary temperature on temperature distribution of surrounding rock in permafrost tunnel, a physical model experiment had been completed. A heater was working for half an hour to simulate the heat which was from construction. Both the inner face of tunnel and model top were exposed to air of test box. The results showed that the boundary conditions were successfully set up. The non-uniform force would act on support structure of tunnel because there were not uniform temperature distributions near the tunnel. The temperature distributions near the tunnel also would be affected by the temperature of ground surface if there is an enough small buried depth. In addition, the heat should be prevented to store in surrounding rock. Speeding up construction and installing reasonable insulation layer may be the effective methods. The results would contribute to understand frost damages mechanism and provide help for permafrost tunnel researches and design.
DOI: 10.1016/j.coldregions.2018.03.007
2019003581 Anderson, Lesleigh (U. S. Geological Survey, Geosciences and Environmental Change Science Center, Denver, CO); Finney, Bruce P. and Shapley, Mark D. Lake levels in a discontinuous permafrost landscape; late Holocene variations inferred from sediment oxygen isotopes Yukon Flats, Alaska: Arctic, Antarctic, and Alpine Research, 50, e1496565, illus. incl. 6 tables, sketch map, 40 ref., 2018.
During recent decades, lake levels in the Yukon Flats region of interior Alaska have fluctuated dramatically. However, prior to recorded observations, no data are available to indicate if similar or more extreme variations occurred during past centuries and millennia. This study explores the history of Yukon Flats lake origins and lake levels for the past approximately 5,500 years from sediment analyses guided by previous work on permafrost extent, thermokarst, and modern isotope hydrology. Sediments dated by 210Pb and AMS radiocarbon indicate stable chronologies following initial lake initiation. Subsequent lithology is autochthonous, and oxygen isotope ratios of endogenic carbonate reflect lake level change at multiple time scales. Sediment results indicate high lake levels between approximately 4000 and 1850 cal yr BP, which is interpreted to reflect wetter-than-modern conditions. Lower lake levels with short-lived high stands during the past approximately 800 years reflect generally arid conditions with brief wet intervals similar to the region's moisture regime today. The millennial trend is one of increasing aridity and corresponds closely with fire reconstructions and regional paleoclimatic trends. We conclude that high-magnitude lake-level fluctuations and decadal scale trends occurred before the observational period and are persistent hydroclimatic features of the Yukon Flats region.
DOI: 10.1080/15230430.2018.1496565
2019003579 Charbonneau, Ansley A. (University of Victoria, Department of Geology, Victoria, BC, Canada) and Smith, Dan J. An inventory of rock glaciers in the central British Columbia Coast Mountains, Canada, from high resolution Google Earth imagery: Arctic, Antarctic, and Alpine Research, 50, e1489026, illus. incl. 8 tables, sketch map, 42 ref., 2018.
Little is known about the presence, distribution, age, or activity of rock glaciers in the British Columbia Coast Mountains of western Canada. Reflecting debris accumulation and mass wasting under a periglacial climate, these rock glaciers describe a geomorphic response to permafrost regimes that may or may not presently exist. An inventory of rock glacier landforms in the eastern front ranges of the Coast Mountains, using high-resolution Google Earth imagery, documented 165 rock glaciers between lat. 50°10' and 52°08' N. The majority of these rock glaciers occur at sites positioned between 1,900 and 2,300 m above sea level, where rain shadow effects and continental air masses result in persistent dry, cold conditions. Morphology and field observation suggest that these features contain intact ice. The rock glaciers occupy predominately northwest to northeast-facing slopes, with talus-derived rock glaciers largely restricted to north-facing slopes. Glacier-derived features outnumber talus-derived features by a ratio of 5:1. Several of the inventoried rock glaciers were located up valley from presumed Younger Dryas terminal moraines, indicating that they formed after 9390 BP. Dendrogeomorphological investigations at one rock glacier record contemporary activity that resulted in 1.3 cm/yr of frontal advance since AD 1674. This inventory is the first to document the presence of rock glaciers in the Coast Mountains and supports preliminary understandings of permafrost distribution in the southwestern Canadian Cordillera.
DOI: 10.1080/15230430.2018.1489026
2019003576 Jiang Huiru (Sichuan University, Laboratory of Hydraulics and Mountain River, Chengdu, China); Zhang Wenjiang; Yi, Yonghong; Yang Kun; Li Guicai and Wang Gengxu. The impacts of soil freeze/thaw dynamics on soil water transfer and spring phenology in the Tibetan Plateau: Arctic, Antarctic, and Alpine Research, 50, e1439155, illus. incl. 2 tables, 44 ref., 2018.
Climate warming has induced significant changes in permafrost and seasonally frozen ground (SFG) in the Tibetan Plateau, which have complex influences on local environments. A better understanding of the impacts of soil freeze/thaw (F/T) dynamics on soil water transfer and vegetation growth is important to explore related eco-hydrological influences. We investigated soil F/T dynamics and their impacts with in-situ and satellite-based observations. Our results showed the contrasting F/T dynamics between SFG and permafrost areas. In permafrost areas, soil froze downward from the ground surface and upward from the active layer bottom with a distinct freezing zero-curtain, and minimum soil moisture occurred in the intermediate layer, but the thawing process was unidirectional. However, the vertical F/T directions were contrary in SFG areas, where soil moisture generally increased with depth and the thawing zero-curtain was distinct. The spring onset showed a positive correlation with thaw onset in permafrost areas, but such a correlation was variable in SFG areas likely depending on soil-moisture level. Our results implied that the different soil-moisture patterns and the varying vegetation response might be related to the spatially contrasting F/T dynamics, which may have different impacts on soil water transfer, and further affect the zero-curtain and vegetation phenology.
DOI: 10.1080/15230430.2018.1439155
2019003250 Kurchatova, A. N. (Russian Academy of Sciences, Siberian Division, Institute of the Cryosphere, Tyumen, Russian Federation) and Rogov, V. V. Formirovaniye geokhimicheskikh anomaliy pri migratsii uglevodorodov v kriolitozone Zapadnoy Sibiri [Geochemical anomalies caused by hydrocarbon migration in the permafrost of West Siberia]: Led i Sneg = Ice and Snow, 58(2), p. 199-212 (English sum.), illus. incl. sketch map, 38 ref., 2018.
Climate warming can be caused by global changes due to emissions of the greenhouse gases, which are mainly carbon dioxide and methane. Although vertical migration of hydrocarbons (seepages) to the surface from oil and gas fields has been known for many years, this important environmental factor has not yet received due attention in the study of the Arctic and Subarctic regions. The major hydrocarbon-induced chemical and mineralogical changes within the permafrost stratum were investigated in the south of the Taz Peninsula in Western Siberia. The samples of frozen core from the deep (35 m) hole, which had been drilled from the top of hydrolaccolite, were examined to analyze the cryogenic texture of the frozen rock mass, to estimate the gas content in rock and ice, and to determine the authigenous mineral association using SEM and EDX spectroscopy analysis. It is shown that the migration of hydrocarbon gases through the permafrost stratum is caused by shear deformations with the formation of cryogenic crack-type textures on the sliding surfaces, which are characterized by the presence of gas-saturated ice crystallites and high jointing of quartz. It has been established that the migration of hydrocarbons, primarily methane, frozen in sedimentary strata causes significant changes of the pH/Eh parameters: local anaerobic conditions may be changed by micro-aerophilic ones through the formation of oxygen during crystallization of the water in the slide area; mainly neutral and weakly acidic conditions can locally be changed by the alkaline ones due to the cryogenic concentration of chlorides during freezing. It was found that the impulse character of hydrocarbon migration in permeation zones of frozen strata causes mosaic distribution of sulfate and iron reduction processes, which control the neogenesis (including as a result of microbiological processes) of various forms of iron compounds: sulfides-carbonates-oxides.
2019003252 Malakhova, V. V. (Russian Academy of Sciences, Siberian Division, Institute of Computational Mathematics and Mathematical Geophysics, Novosibirsk, Russian Federation) and Yeliseyev, A. V. Vliyaniye riftovykh zon i termokarstovykh ozer na formirovaniye subakval'noy merzloty i zony stabil'nosti metanogidratov shel'fa morya Laptevykh v Pleystotsene [Influence of rift zones and thermokarst lakes on formation of the permafrost and stability of methane hydrates on the Laptev Sea continental shelf during the Pleistocene]: Led i Sneg = Ice and Snow, 58(2), p. 231-242 (English sum.), illus. incl. 1 table, 7 ref., 2018.
This paper presents results of the analysis of the influence of talik zones associated with thermokarst lakes and processes in rift zones on the dynamics of subaqueous permafrost and zones of stability of methane hydrates for conditions of the Laptev Sea shelf. The model of thermophysical processes in the bottom sediments together with the scenario of climate change on the Arctic shelf for the last 400 thousand years (kyr) were used. Typical value of geothermal heat flux for the most part of the shelf and for the shallow shelf (with the present-day depth of ≤&eq;50 m) is estimated as 60 mW/m2. It is shown that with this value the duration of the interglacials and the corresponding ocean transgression periods is not sufficient for the complete degradation of permafrost and destruction of the gas hydrates. For a deeper shelf, however, the complete disappearance of the stability zone of the methane hydrates is possible during the interglacial periods. In the areas of oceanic faults (rifts), higher values of the deep heat flux increase rates of degradation of the underwater permafrost rocks in the interglacial periods as compared with the condition when the heat flux is 60 mW/m2. Intensification of degradation of the subsea permafrost is manifested in areas where thermokarst lakes arise, but here it is associated with the temperature rise at the upper boundary of the bottom sediments. The presence of the rift zones and/or the thermokarst lakes promotes decreasing of the present-day thickness of the permafrost, and simultaneous impact of these two factors can lead to a through thawing of the shelf in the interglacials (including Holocene).
DOI: 10.15356/2076-6734-2018-2-231-242
2019003574 Malhotra, Avni (McGill University, Department of Geography, Montreal, QC, Canada); Moore, Tim R.; Limpens, Juul and Roulet, Nigel T. Post-thaw variability in litter decomposition best explained by microtopography at an ice-rich permafrost peatland: Arctic, Antarctic, and Alpine Research, 50, e1415622, illus. incl. 2 tables, 45 ref., 2018.
Litter decomposition, a key process by which recently fixed carbon is lost from ecosystems, is a function of environmental conditions and plant community characteristics. In ice-rich peatlands, permafrost thaw introduces high variability in both abiotic and biotic factors, both of which may affect litter decomposition rates in different ways. Can the existing conceptual frameworks of litter decomposition and its controls be applied across a structurally heterogeneous thaw gradient? We investigated the variability in litter decomposition and its predictors at the Stordalen subarctic peatland in northern Sweden. We measured in situ decomposition of representative litter and environments using litter bags throughout two years. We found highly variable litter decomposition rates with turnover times ranging from five months to four years. Surface elevation was a strong correlate of litter decomposition across the landscape, likely as it integrates multiple environmental and plant community changes brought about by thaw. There was faster decomposition but also more mass remaining after two years in thawed areas relative to permafrost areas, suggesting faster initial loss of carbon but more storage into the slow-decomposing carbon pool. Our results highlight mechanisms and predictors of carbon cycle changes in ice-rich peatlands following permafrost thaw.
DOI: 10.1080/15230430.2017.1415622
2018098732 Palmtag, Juri (Stockholm University, Department of Physical Geography, Stockholm, Sweden); Cable, Stefanie; Christiansen, Hanne H.; Hugelius, Gustaf and Kuhry, Peter. Landform partitioning and estimates of deep storage of soil organic matter in Zackenberg, Greenland: The Cryosphere (Online), 12(5), p. 1735-1744, illus. incl. 2 tables, geol. sketch maps, 30 ref., 2018.
Soils in the northern high latitudes are a key component in the global carbon cycle, with potential feedback on climate. This study aims to improve the previous soil organic carbon (SOC) and total nitrogen (TN) storage estimates for the Zackenberg area (NE Greenland) that were based on a land cover classification (LCC) approach, by using geomorphological upscaling. In addition, novel organic carbon (OC) estimates for deeper alluvial and deltaic deposits (down to 300 cm depth) are presented. We hypothesise that landforms will better represent the long-term slope and depositional processes that result in deep SOC burial in this type of mountain permafrost environments. The updated mean SOC storage for the 0-100 cm soil depth is 4.8 kg C m-2, which is 42% lower than the previous estimate of 8.3 kg C m-2 based on land cover upscaling. Similarly, the mean soil TN storage in the 0-100 cm depth decreased with 44% from 0.50 kg (±0.1 CI) to 0.28 (±0.1 CI) kg TN m-2. We ascribe the differences to a previous areal overestimate of SOC- and TN-rich vegetated land cover classes. The landform-based approach more correctly constrains the depositional areas in alluvial fans and deltas with high SOC and TN storage. These are also areas of deep carbon storage with an additional 2.4 kg C m-2 in the 100-300 cm depth interval. This research emphasises the need to consider geomorphology when assessing SOC pools in mountain permafrost landscapes.
DOI: 10.5194/tc-12-1735-2018
2018099119 Way, Robert G. (Queen's University, Department of Geography and Planning, Kingston, ON, Canada); Lewkowicz, Antoni G. and Zhang, Yu. Characteristics and fate of isolated permafrost patches in coastal Labrador, Canada: The Cryosphere (Online), 12(8), p. 2667-2688, illus. incl. 3 tables, sketch maps, 83 ref., 2018.
Bodies of peatland permafrost were examined at five sites along a 300 km transect spanning the isolated patches permafrost zone in the coastal barrens of southeastern Labrador. Mean annual air temperatures ranged from +1°C in the south (latitude 51.4°N) to -1.1°C in the north (53.7°N) while mean ground temperatures at the top of the permafrost varied respectively from -0.7 to -2.3°C with shallow active layers (40-60 cm) throughout. Small surface offsets due to wind scouring of snow from the crests of palsas and peat plateaux, and large thermal offsets due to thick peat are critical to permafrost, which is absent in wetland and forested and forest-tundra areas inland, notwithstanding average air temperatures much lower than near the coast. Most permafrost peatland bodies are less than 5 m thick, with a maximum of 10 m, with steep geothermal gradients. One-dimensional thermal modelling for two sites showed that they are in equilibrium with the current climate, but the permafrost mounds are generally relict and could not form today without the low snow depths that result from a heaved peat surface. Despite the warm permafrost, model predictions using downscaled global warming scenarios (RCP2.6, RCP4.5, and RCP8.5) indicate that perennially frozen ground will thaw from the base up and may persist at the southern site until the middle of the 21st century. At the northern site, permafrost is more resilient, persisting to the 2060s under RCP8.5, the 2090s under RCP4.5, or beyond the 21st century under RCP2.6. Despite evidence of peatland permafrost degradation in the study region, the local-scale modelling suggests that the southern boundary of permafrost may not move north as quickly as previously hypothesized.
DOI: 10.5194/tc-12-2667-2018
2018097933 Eckerstorfer, Markus (Northern Research Institute (NORUT), Earth Observation, Tromso, Norway); Malnes, E. and Christiansen, H. H. Freeze/thaw conditions at periglacial landforms in Kapp Linne, Svalbard, investigated using field observations, in situ, and radar satellite monitoring: in Permafrost and periglacial research from coasts to mountains (Schrott, Lothar, editor; et al.), Geomorphology, 293(PART B), p. 433-447, illus. incl. 3 tables, geol. sketch map, 54 ref., September 15, 2017.
In periglacial landscapes, snow dynamics and microtopography have profound implications of freeze-thaw conditions and thermal regime of the ground. We mapped periglacial landforms at Kapp Linne, central Svalbard, where we chose six widespread landforms (solifluction sheet, nivation hollow, palsa and peat in beach ridge depressions, raised marine beach ridge, and exposed bedrock ridge) as study sites. At these six landforms, we studied ground thermal conditions, freeze-thaw cycles, and snow dynamics using a combination of in situ monitoring and C-band radar satellite data in the period 2005-2012. Based on these physical parameters, the six studied landforms can be classified into raised, dry landforms with minor ground ice content and a thin, discontinuous snow cover and into wet landforms with high ice content located in the topographical depressions in-between with medium to thick snow cover. This results in a differential snow-melting period inferred from the C-band radar satellite data, causing the interseasonal and interlandform variability in the onset of ground surface thawing once the ground becomes snow free. Therefore, variability also exists in the period of thawed ground surface conditions. However, the length of the season with thawed ground surface conditions does not determine the mean annual ground surface temperature, it only correlates well with the active layer depths. From the C-band radar satellite data series, measured relative backscatter trends hint toward a decrease in snow cover through time and a more frequent presence of ice layers from mid-winter rain on snow events at Kapp Linne, Svalbard.
DOI: 10.1016/j.geomorph.2017.02.010
2018097931 Haeberli, Wilfried (University of Zurich, Geography Department, Zurich, Switzerland); Schaub, Yvonne and Huggel, Christian. Increasing risks related to landslides from degrading permafrost into new lakes in deglaciating mountain ranges: in Permafrost and periglacial research from coasts to mountains (Schrott, Lothar, editor; et al.), Geomorphology, 293(PART B), p. 405-417, illus. incl. sketch maps, 97 ref., September 15, 2017.
While glacier volumes in most cold mountain ranges rapidly decrease due to continued global warming, degradation of permafrost at altitudes above and below glaciers is much slower. As a consequence, many still existing glacier and permafrost landscapes probably transform within decades into new landscapes of bare bedrock, loose debris, sparse vegetation, numerous new lakes and steep slopes with slowly degrading permafrost. These new landscapes are likely to persist for centuries if not millennia to come.During variable but mostly extended future time periods, such new landscapes will be characterized by pronounced disequilibria within their geo- and ecosystems. This especially involves long-term stability reduction of steep/icy mountain slopes as a slow and delayed reaction to stress redistribution following de-buttressing by vanishing glaciers and to changes in mechanical strength and hydraulic permeability caused by permafrost degradation. Thereby, the probability of far-reaching flood waves from large mass movements into lakes systematically increases with the formation of many new lakes and systems of lakes in close neighborhood to, or even directly at the foot of, so-affected slopes. Results of recent studies in the Swiss Alps are reviewed and complemented with examples from the Cordillera Blanca in Peru and the Mount Everest region in Nepal.Hot spots of future hazards from potential flood waves caused by large rock falls into new lakes can already now be recognized. To this end, integrated spatial information on glacier/permafrost evolution and lake formation can be used together with scenario-based models for rapid mass movements, impact waves and flood propagation. The resulting information must then be combined with exposure and vulnerability considerations related to settlements and infrastructure. This enables timely planning of risk reduction options. Such risk reduction options consist of two components: Mitigation of hazards, which in the present context are due to effects from climate change, and reduction in consequences, which result from societal conditions and changes. Hazard mitigation may include artificial lake drainage or lake-level lowering and flood retention, optimally in connection with multipurpose structures for hydropower production and/or irrigation. Reduction in damage potential (exposure, vulnerability) can be accomplished by installing early-warning systems, adapting spatial planning and/or by improving preparedness of local people and institutions.
DOI: 10.1016/j.geomorph.2016.02.009
2018097927 Hinkel, K. M. (University of Cincinnati, Department of Geography, Cincinnati, OH); Eisner, Wendy R. and Kim, C. J. Detection of tundra trail damage near Barrow, Alaska using remote imagery: in Permafrost and periglacial research from coasts to mountains (Schrott, Lothar, editor; et al.), Geomorphology, 293(PART B), p. 360-367, illus. incl. 1 table, sketch map, 23 ref., September 15, 2017.
In the past several decades, the use of all-terrain vehicles (ATVs) has proliferated in many Arctic communities in North America. One example is the village of Barrow, Alaska. This coastal community has only local roads, so all access to the interior utilizes off-road machines. These 4-wheel vehicles are the primary means of tundra traverse and transport in summer by hunters and berry-pickers, and by village residents accessing summer camps. Traveling cross-country is difficult due to the large number of thermokarst lakes, wetlands, and streams, and tundra trails tend to follow dryer higher ground while avoiding areas of high microrelief such as high-centered ice-wedge polygons. Thus, modern ATV trails tend to follow the margins of drained or partially drained thermokarst lake basins where it is flat and relatively dry, and these trails are heavily used. The deeply-ribbed tires of the heavy and powerful ATVs cause damage by destroying the vegetation and disturbing the underlying organic soil. Exposure of the dark soil enhances summer thaw and leads to local thermokarst of the ice-rich upper permafrost. The damage increases over time as vehicles continue to follow the same track, and sections eventually become unusable; this is especially true where the trail crosses ice-wedge troughs. Deep subsidence in the ponded troughs results in ATV users veering to avoid the wettest area, which leads to a widening of the damaged area. Helicopter surveys, site visits, and collection of ground penetrating radar data were combined with time series analysis of high-resolution aerial and satellite imagery for the period 1955-2014. The analysis reveals that there are 507 km of off-road trails on the Barrow Peninsula. About 50% of the total trail length was developed before 1955 in association with resource extraction, and an additional 40% were formed between 1979 and 2005 by ATVs. Segments of the more modern trail are up to 100 m wide. Damage to the tundra is especially pronounced in wet areas, such as ice-wedge troughs. Knowledgeable indigenous people are aware of the problem. Some remediation has been attempted by using heavy-duty PVC matting in areas of greatest damage, but this approach is prohibitively expensive on a large scale.
DOI: 10.1016/j.geomorph.2016.09.013
2018097926 Kasprzak, Marek (University of Wroclaw, Institute of Geography and Regional Development, Wroclaw, Poland); Strzelecki, Mateusz Czeslaw; Traczyk, Andrzej; Kondracka, Marta; Lim, Michael and Migala, Krzysztof. On the potential for a bottom active layer below coastal permafrost; the impact of sea water on permafrost degradation imaged by electrical resistivity tomography (Hornsund, SW Spitsbergen): in Permafrost and periglacial research from coasts to mountains (Schrott, Lothar, editor; et al.), Geomorphology, 293(PART B), p. 347-359, illus. incl. 1 table, sketch map, 101 ref., September 15, 2017.
This paper presents the results of two-dimensional electrical resistivity tomography (ERT) of permafrost developed in coastal zone of Hornsund, SW Spitsbergen. The measurements were made using the Wenner-Schlumberger electrode array with an electrode spacing 5 m for overview and 1.5 or 1 m spacing for detailed imaging. Using the ERT inversion results, we studied the 'sea influence' on deeper parts of the frozen ground. During the investigations we tested hypotheses that the operation of seawater on shoreface may cause changes in the shape of the coastal permafrost base, and that the impact of seawater on more inland permafrost depends on the shape of the shoreline (differently in the embayment, and differently in a headland exposed to the open sea). Our study was inspired by previous ground temperature measurements conducted in several boreholes located in study area which captured the propagation of ground heat waves from the base of permafrost. Our resistivity models indicate a major differentiation in terms of resistivity of permafrost in the coastal zone. The resistivity measures obtained in deeper layers of ground were so low (<100 W·m) that in the 'warm permafrost' conditions they exclude a possibility of freezing the coastal sediments and bedrock from the side of the sea. Low values continue further inland, going down under the surface layer of permafrost with higher resistivity. We interpret this situation as an influence of seawater's temperature and salinity on deeper parts of permafrost. Based on the measurements conducted within two years, we stated a change in the distribution of resistivity, both in the active layer, and in coastal front of permafrost in deeper parts of the ground. As observed in the inverse models, the geometric arrangement between the fields of extreme resistivity indicates the existence of a bottom active layer by the permafrost base, depending on thermal and chemical characteristics of seawater. The measurements conducted in the embayment, as well as on the headland exposed to the operation of storm waves, proved strong differences in the scale of the impact of seawater on permafrost.
DOI: 10.1016/j.geomorph.2016.06.013
2018097925 Obu, Jaroslav (Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Potsdam, Germany); Lantuit, Hugues; Grosse, Guido; Günther, Frank; Sachs, Torsten; Helm, Veit and Fritz, Michael. Coastal erosion and mass wasting along the Canadian Beaufort Sea based on annual airborne lidar elevation data: in Permafrost and periglacial research from coasts to mountains (Schrott, Lothar, editor; et al.), Geomorphology, 293(PART B), p. 331-346, illus. incl. 6 tables, sketch map, 44 ref., September 15, 2017.
Erosion of permafrost coasts has received increasing scientific attention since 1990s because of rapid land loss and the mobilisation potential of old organic carbon. The majority of permafrost coastal erosion studies are limited to time periods from a few years to decades. Most of these studies emphasize the spatial variability of coastal erosion, but the intensity of inter-annual variations, including intermediate coastal aggradation, remains poorly documented. We used repeat airborne Light Detection And Ranging (LiDAR) elevation data from 2012 and 2013 with 1 m horizontal resolution to study coastal erosion and accompanying mass-wasting processes in the hinterland. Study sites were selected to include different morphologies along the coast of the Yukon Coastal Plain and on Herschel Island. We studied elevation and volume changes and coastline movement and compared the results between geomorphic units. Results showed simple uniform coastal erosion from low coasts (up to 10 m height) and a highly diverse erosion pattern along coasts with higher backshore elevation. This variability was particularly pronounced in the case of active retrogressive thaw slumps, which can decrease coastal erosion or even cause temporary progradation by sediment release. Most of the extremes were recorded in study sites with active slumping (e.g. 22 m of coastline retreat and 42 m of coastline progradation). Coastline progradation also resulted from the accumulation of slope collapse material. These occasional events can significantly affect the coastline position on a specific date and can affect coastal retreat rates as estimated in long term by coastline digitalisation from air photos and satellite imagery. These deficiencies can be overcome by short-term airborne LiDAR measurements, which provide detailed and high-resolution information about quickly changing elevations in coastal areas.
DOI: 10.1016/j.geomorph.2016.02.014
2018097928 Oliva, Marc (Universidade de Lisboa, Instituto de Geografia e Ordenamento do Territorio (IGOT), Lisbon, Portugal) and Ruiz Fernández, Jesús. Geomorphological processes and frozen ground conditions in Elephant Point (Livingston Island, South Shetland Islands, Antarctica): in Permafrost and periglacial research from coasts to mountains (Schrott, Lothar, editor; et al.), Geomorphology, 293(PART B), p. 368-379, illus. incl. 3 tables, geol. sketch map, 67 ref., September 15, 2017.
Elephant Point is an ice-free area in the SW corner of Livingston Island (Maritime Antarctica). The retreat of Rotch Dome glacier during the Holocene has exposed a land area of 1.16 km2. Up to 17.3% of this surface has become ice-free between 1956 and 2010. A detailed geomorphological mapping of this ice-free environment was conducted in late January 2014. A wide range of active periglacial landforms show that periglacial processes are widespread. From the glacier to the coast four different geomorphological areas are identified: proglacial environment, moraine complex, bedrock plateaus and marine terraces. In situ measurements of the thawed soil depth show evidence of the widespread frozen ground conditions in the area. Field observations of permafrost exposures suggest that these frost conditions may be related to a soil permafrost regime, almost down to sea level. The activity of penguin colonies and elephant seals has created minor geomorphological features in the raised marine terraces. Here, several archaeological sites related to early human colonization of Antarctica were also found in natural shelters.
DOI: 10.1016/j.geomorph.2016.01.020
2018097930 Onaca, Alexandru (West University of Timisoara, Timis, Romania); Ardelean, Florina; Urdea, Petru and Magori, Brigitte. Southern Carpathian rock glaciers; inventory, distribution and environmental controlling factors: in Permafrost and periglacial research from coasts to mountains (Schrott, Lothar, editor; et al.), Geomorphology, 293(PART B), p. 391-404, illus. incl. 3 tables, sketch maps, 91 ref., September 15, 2017.
Rock glaciers are valuable diagnostic landforms indicating permafrost creeping during their genesis and activity. Based on the analysis of high quality air-orthophoto and field work, a first polygon-based inventory of rock glaciers from the Southern Carpathians has been elaborated. In total, 306 rock glaciers were included in the inventory comprising 79 debris and 227 talus rock glaciers. Most of these landforms were classified as relict (258), while only 48, covering 2.81 km2, were considered intact. The size of rock glaciers, considered as a proxy for past environmental conditions, and the relationships with the predictor variables (lithology, aspect, contributing area, geographic coordinates, elevation and slope range) were analysed using bivariate statistics, analysis of variance (ANOVA) and various post hoc tests. The statistical analysis revealed that the rock glaciers occurring in the highest mountain ranges in areas composed of granites and granodiorites are considerably larger than the others, because their duration of activity is greater. Strong dependences between rock glacier size and other topographic attributes (contributing area, aspect and slope range) were also confirmed. The rock glacier distribution in the Southern Carpathians is clearly controlled by topography, lithology and debris availability. The abundance of rock glaciers increases with altitude, but their size decreases slightly. In mountain units where granites and granodiorites predominate (Retezat and Parang Mountains), the density of rock glaciers and the mean specific area covered by these spectacular landforms are considerably higher than in other areas. The higher continentality effects of the Southern Carpathians enabled the formation of rock glaciers at substantially lower elevations than in the Alps. The mean altitude of intact rock glaciers front, which could be used as a morphological indicator of discontinuous permafrost, is located at 2088 m.
DOI: 10.1016/j.geomorph.2016.03.032
2018097929 Stan, Dominika (University of Silesia, Faculty of Earth Sciences, Sosnowiec, Poland); Stan-Kleczek, Iwona and Kania, Maciej. Geophysical approach to the study of a periglacial blockfield in a mountain area (Ztracene kameny, eastern Sudetes, Czech Republic): in Permafrost and periglacial research from coasts to mountains (Schrott, Lothar, editor; et al.), Geomorphology, 293(PART B), p. 380-390, illus. incl. 1 table, sketch maps, 59 ref., September 15, 2017.
Fluctuation of climatic events in Central Europe with oceanic and continental influences intensified during the Pleistocene, especially above the timberline, enabled the analysis of this record on the ridge and slopes of the Ztracene kameny massif (1245 m a.s.l.), Czech Republic. Seismic refraction tomography (SRT) and electrical resistivity tomography (ERT) are geophysical methods that, that allow the comprehensive recognition of shallow geological structures in a strongly folded area of the High Jesenik Mountains. Geophysical surveys were performed to determine structure and thickness of the quartzite blockfield and its boundary with consolidated rock. The measured resistivity values were compared with the seismic wave velocities. The resistivity values of the block cover show significant differences according to its morphology, slope orientation and altitude. The data analysis indicates an occurrence of remnants of Pleistocene permafrost. The subnival traces within the blockfield demonstrate the intensity of past slope processes and the role of frost weathering even during the Holocene.
DOI: 10.1016/j.geomorph.2016.12.004
2018097954 Sun Zhe (Lanzhou University, College of Earth and Environment Sciences, Lanzhou, China); Wang Yibo; Sun Yan; Niu Fujun; Li Guoyu and Gao Zeyong. Creep characteristics and process analyses of a thaw slump in the permafrost region of the Qinghai-Tibet Plateau, China: Geomorphology, 293(PART A), p. 1-10, illus. incl. 4 tables, sketch map, 31 ref., September 15, 2017.
A thaw slump in the permafrost region of the Qinghai-Tibet Plateau was monitored to investigate typical characteristics of creep positions and processes in combination with soil property analyses. The results show that the thaw settlement exhibits a contraction effect in the horizontal direction because of uneven thaw settlement. Slope displacement of creep occurs only in the top 50 cm of the soil. The gravimetric water content, soil porosity, and soil temperature are higher near the thaw slump in thaw seasons compared with the undisturbed soil; however, the shear strength is lower. Melting ground ice releases thaw water that converges along the slope and forms an overland flow at the front part of the gentle slope area and a ponding depression at the slope bottom. The analyses of slope stability using the infinite slope model shows that the headwall of the slope is inevitably unstable and slides under saturated conditions, whereas the gentle slope area and slope bottom with slight creep displacement are relatively stable. The small retrogressive thaw slump is in an early development stage. With increasing degree of thaw settlement and rate of erosion, the headwall will become steeper and a thermokarst lake will form at the slope bottom.
DOI: 10.1016/j.geomorph.2017.04.045
2018100061 Senderak, Krzysztof (University of Silesia, Faculty of Earth Sciences, Sosnowiec, Poland); Kondracka, Marta and Gadek, Bogdan. Talus slope evolution under the influence of glaciers with the example of slopes near the Hans Glacier, SW Spitsbergen, Norway: Geomorphology, 285, p. 225-234, illus. incl. 2 tables, sketch map, 79 ref., May 15, 2017.
On Spitsbergen, which is 60% glaciated, talus slopes have frequently developed in interaction with glaciers, which had an influence on the evolution of the internal structure of slopes. This paper presents the results of geophysical surveys (electrical resistivity tomography - ERT and ground-penetrating radar - GPR) of the talus slopes near the Hans Glacier (SW Spitsbergen). The aim of investigations was to compare the talus slopes under the influence of glaciers in two different parts of the area in order to reveal differences in their internal structure. We assumed that different locations of talus slopes can have an influence on the slope structure, showing different stages of evolution of the talus slopes. The maximum thickness of studied slopes ranges from 20 m in a marginal zone of the glacier, to up to 35 m without contact with the glacier. Permafrost begins at a depth of 2-3 m and can develop until bedrock is reached. The internal structure of these talus slopes contains glacial ice, which is covered by a layer of slope material with a thickness from a few to up to 10 m. The buried glacial ice is slowly melting simultaneously with the deglaciation of the area but can remain in the structure of the talus slopes for much longer. Morphogenetic processes, such as avalanches, rockfalls, and debris flows are most visible until the glacial ice is completely melted within the internal structure of the slope. Based on the geophysical and geomorphological data, general models were proposed for the early stages of evolution of talus slopes in valleys under deglaciation.
DOI: 10.1016/j.geomorph.2017.02.023
2018100059 Sudman, Zachary (850 Baum Street, Unit D, Fort Collins, CO); Gooseff, Michael N.; Fountain, Andrew G.; Levy, Joseph S.; Obryk, Maciej K. and Van Horn, David. Impacts of permafrost degradation on a stream in Taylor Valley, Antarctica: Geomorphology, 285, p. 205-213, illus. incl. 1 table, sketch maps, 21 ref., May 15, 2017.
The McMurdo Dry Valleys (MDV) of Antarctica are an ice-free landscape that supports a complex, microbially dominated ecosystem despite a severely arid, cold environment (< 5 cm water equivalent/y, - 18 °C mean annual air temperature). Recent observations of permafrost degradation in the coastal zones of the MDV suggest that this region is nearing a threshold of rapid landscape change. In 2012, substantial thermokarst development was observed along several kilometers of the west branch of Crescent Stream in Taylor Valley mostly in the form of bank failures, whereas the adjacent east branch was unaffected. The objective of this study was to quantify the changes to the stream banks of the west branch of Crescent Stream and to determine the impacts on the composition of the stream bed material. Three annually repeated terrestrial LiDAR scans were compared to determine the rates of ground surface change caused by thermokarst formation on the stream bank. The areal extent of the thermokarst was shown to be decreasing; however, the average vertical rate of retreat remained constant. Field measurements of bed materials indicated that the west branch and the reach downstream of the confluence (of east and west branches) consistently contained more fines than the unaffected east branch. This suggests that the finer bed material is a result of the thermokarst development on the west branch. These finer bed material compositions are likely to increase the mobility of the bed material, which will have implications for stream morphology, stream algal mat communities, and downstream aquatic ecosystems.
DOI: 10.1016/j.geomorph.2017.02.009
2018099937 Lin, Z. J. (Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Niu, F. J.; Fang, J. H.; Luo, J. and Yin, G. A. Interannual variations in the hydrothermal regime around a thermokarst lake in Beiluhe, Qinghai-Tibet Plateau: Geomorphology, 276, p. 16-26, illus. incl. 2 tables, sketch maps, 40 ref., January 2017.
Thermokarst is a term associated with the thaw of ice-rich permafrost and the resulting formation of irregular depressions in the landscape from thaw settlement. Thermokarst lakes may subsequently develop from ponds formed in depressions. These lakes commonly have collapsing shorelines, and the development of thermokarst terrain and associated thermal erosion may significantly influence the stability of infrastructure and the hydrothermal conditions of the surrounding permafrost. In this study, we examined interannual variations in the hydrothermal regime of a thermokarst lake in Beiluhe Basin based on field data measured in 2006-2013. The timing and nature of lake ice growth and melt were recorded. We observed considerable seasonal differences in lake water level (~ 0.5 m) and differences in water level between the lake and the water table in the surrounding ground (over 1.0 m). The nearly-saturated ground at the lakeshore (~ 35% in maximum volumetric water content) highlights the seepage effect from the lake to the surrounding ground. The vertical temperature profile from + 2 m (air) to - 2 m (lake bottom) and to 60 m depth in the ground was measured. The annual mean air temperature, lake-surface temperature, and annual mean lake-bottom temperature in 2010-2011 were approximately - 3.6, 0.4, and > 5°C, respectively. The thermal offsets between the air and the lake surface and between the lake surface and lake bottom were 3 and 7°C, respectively. The annual mean lake-bottom temperatures ranged from 2.3 to 6.9°C at water depths from 1.2 to 2.1 m. The asymmetry of the bathymetry has resulted in distinct thermal regimes beneath the lake bottom in different locations. A through-talik was present at the deepest side of the lake, but some permafrost extended laterally beneath the lake bottom at the shallower side, forming an hourglass shape in cross section at one end. Lateral thermal erosion along the lakeshore was linked to the lake-bottom temperature and lake depth. Variation in permafrost table depth from the lake center to the lakeshore was greater on the east side near deeper water (>&eq; 2 m) than at the west side where water was shallower (≤&eq; 70 cm). The results from this study have highlighted the hydrothermal relations between thermokarst lake development and permafrost conditions.
DOI: 10.1016/j.geomorph.2016.09.035
2018097256 Cassidy, Alison E. (University of British Columbia, Department of Geography, Vancouver, BC, Canada); Christen, Andreas and Henry, Gregory H. R. The effect of a permafrost disturbance on growing-season carbon-dioxide fluxes in a high Arctic tundra ecosystem: Biogeosciences, 13(8), p. 2291-2303, illus. incl. 2 tables, 66 ref., 2016.
Soil carbon stored in high-latitude permafrost landscapes is threatened by warming and could contribute significant amounts of carbon to the atmosphere and hydrosphere as permafrost thaws. Thermokarst and permafrost disturbances, especially active layer detachments and retrogressive thaw slumps, are present across the Fosheim Peninsula, Ellesmere Island, Canada. To determine the effects of retrogressive thaw slumps on net ecosystem exchange (NEE) of CO2 in high Arctic tundra, we used two eddy covariance (EC) tower systems to simultaneously and continuously measure CO2 fluxes from a disturbed site and the surrounding undisturbed tundra. During the 32-day measurement period in the 2014 growing season, the undisturbed tundra was a small net sink (NEE = -0.1 g C m-2 d-1); however, the disturbed terrain of the retrogressive thaw slump was a net source (NEE = +0.4 g C m-2 d-1). Over the measurement period, the undisturbed tundra sequestered 3.8 g C m-2, while the disturbed tundra released 12.5 g C m-2. Before full leaf-out in early July, the undisturbed tundra was a small source of CO2 but shifted to a sink for the remainder of the sampling season (July), whereas the disturbed tundra remained a source of CO2 throughout the season. A static chamber system was also used to measure daytime fluxes in the footprints of the two towers, in both disturbed and undisturbed tundra, and fluxes were partitioned into ecosystem respiration (Re) and gross primary production (GPP). Average GPP and Re found in disturbed tundra were smaller (+0.40 mmol m-2 s-1 and +0.55 mmol m-2 s-1, respectively) than those found in undisturbed tundra (+1.19 mmol m-2 s-1 and +1.04 mmol m-2 s-1, respectively). Our measurements indicated clearly that the permafrost disturbance changed the high Arctic tundra system from a sink to a source for CO2 during the majority of the growing season (late June and July).
DOI: 10.5194/bg-13-2291-2016
2019002522 Marushchak, M. E. (University of Eastern Finland, Department of Environmental and Biological Sciences, Kuopio, Finland); Friborg, T.; Biasi, C.; Herbst, M.; Johansson, T.; Kiepe, I.; Liimatainen, M.; Lind, S. E.; Martikainen, P. J.; Virtanen, T.; Soegaard, H. and Shurpali, Narasinha J. Methane dynamics in the subarctic tundra; combining stable isotope analyses, plot- and ecosystem-scale flux measurements: Biogeosciences, 13(2), p. 597-608, illus. incl. 3 tables, 50 ref., 2016.
Methane (CH4) fluxes were investigated in a subarctic Russian tundra site in a multi-approach study combining plot-scale data, ecosystem-scale eddy covariance (EC) measurements, and a fine-resolution land cover classification scheme for regional upscaling. The flux data as measured by the two independent techniques resulted in a seasonal (May-October 2008) cumulative CH4 emission of 2.4 (EC) and 3.7 g CH4 m-2 (manual chambers) for the source area representative of the footprint of the EC instruments. Upon upscaling for the entire study region of 98.6 km2, the chamber measured flux data yielded a regional flux estimate of 6.7 g CH4 m-2 yr-1. Our upscaling efforts accounted for the large spatial variability in the distribution of the various land cover types (LCTs) predominant at our study site. Wetlands with emissions ranging from 34 to 53 g CH2 m-2 yr-1 were the most dominant CH4-emitting surfaces. Emissions from thermokarst lakes were an order of magnitude lower, while the rest of the landscape (mineral tundra) was a weak sink for atmospheric methane. Vascular plant cover was a key factor in explaining the spatial variability of CH4 emissions among wetland types, as indicated by the positive correlation of emissions with the leaf area index (LAI). As elucidated through a stable isotope analysis, the dominant CH4 release pathway from wetlands to the atmosphere was plant-mediated diffusion through aerenchyma, a process that discriminates against 13C-CH4. The CH4 released to the atmosphere was lighter than that in the surface porewater, and d13C in the emitted CH4 correlated negatively with the vascular plant cover (LAI). The mean value of d13C obtained here for the emitted CH4, -68.2±2.0 ppm, is within the range of values from other wetlands, thus reinforcing the use of inverse modelling tools to better constrain the CH4 budget. Based on the IPCC A1B emission scenario, a temperature increase of 6.1°C relative to the present day has been predicted for the European Russian tundra by the end of the 21st Century. A regional warming of this magnitude will have profound effects on the permafrost distribution leading to considerable changes in the regional landscape with a potential for an increase in the areal extent of CH4-emitting wet surfaces.
DOI: 10.5194/bg-13-597-2016
2019002545 Perreault, Naim (Université du Québec à Trois-Rivières, Département des sciences de l'environnement, Trois-Rivieres, Canada); Lévesque, Esther; Fortier, Daniel and Lamarque, Laurent J. Thermo-erosion gullies boost the transition from wet to mesic tundra vegetation: Biogeosciences, 13(4), p. 1237-1253, illus. incl. 6 tables, sketch map, 113 ref., 2016. Includes appendices.
Continuous permafrost zones with well-developed polygonal ice-wedge networks are particularly vulnerable to climate change. Thermo-mechanical erosion can initiate the development of gullies that lead to substantial drainage of adjacent wet habitats. How vegetation responds to this particular disturbance is currently unknown but has the potential to significantly disrupt function and structure of Arctic ecosystems. Focusing on three major gullies of Bylot Island, Nunavut, we estimated the impacts of thermo-erosion processes on plant community changes. We explored over 2 years the influence of environmental factors on plant species richness, abundance and biomass in 62 low-centered wet polygons, 87 low-centered disturbed polygons and 48 mesic environment sites. Gullying decreased soil moisture by 40% and thaw-front depth by 10 cm in the center of breached polygons within less than 5 years after the inception of ice wedge degradation, entailing a gradual yet marked vegetation shift from wet to mesic plant communities within 5 to 10 years. This transition was accompanied by a five times decrease in graminoid above-ground biomass. Soil moisture and thaw-front depth changed almost immediately following gullying initiation as they were of similar magnitude between older (>5 years) and recently (<5 years) disturbed polygons. In contrast, there was a lag-time in vegetation response to the altered physical environment with plant species richness and biomass differing between the two types of disturbed polygons. To date (10 years after disturbance), the stable state of the mesic environment cover has not been fully reached yet. Our results illustrate that wetlands are highly vulnerable to thermo-erosion processes, which drive landscape transformation on a relative short period of time for High Arctic perennial plant communities (5 to 10 years). Such succession towards mesic plant communities can have substantial consequences on the food availability for herbivores and carbon emissions of Arctic ecosystems.
DOI: 10.5194/bg-13-1237-2016
Back to the Top
|
