2017025965 Kokelj, Steven V. (Northwest Territories Geological Survey, Yellowknife, NT, Canada); Lantz, Trevor C.; Tunnicliffe, Jon; Segal, Rebecca and Lacelle, Denis. Climate-driven thaw of permafrost preserved glacial landscapes, northwestern Canada: Geology (Boulder), 45(4), p. 371-374, illus. incl. geol. sketch map, 27 ref., April 2017. GSA Data Repository item 2017106.
Ice-marginal glaciated landscapes demarcate former boundaries of the continental ice sheets. Throughout circumpolar regions, permafrost has preserved relict ground ice and glacigenic sediments, delaying the sequence of postglacial landscape change that transformed temperate environments millennia earlier. Here we show that within 7 ´ 106 km2 of glaciated permafrost terrain, extensive landscapes remain poised for major climate-driven change. Across northwestern Canada, 60-100-km-wide concentric swaths of thaw slump-affected terrain delineate the maximum and recessional positions of the Laurentide Ice Sheet. These landscapes comprise ~17% of continuous permafrost terrain in a 1.27 ´ 106 km2 study area, indicating widespread preservation of late Pleistocene ground ice. These thaw slump, relict ground ice, and glacigenic terrain associations are also evident at the circumpolar scale. Recent intensification of thaw slumping across northwestern Canada has mobilized primary glacial sediments, triggering a cascade of fluvial, lacustrine, and coastal effects. These geologically significant processes, highlighted by the spatial distribution of thaw slumps and patterns of fluvial sediment mobilization, signal the climate-driven renewal of deglaciation and postglacial permafrost landscape evolution.
2017030492 Phillips, Marcia (Eidgenössische Forschungsanstalt für Wald, Schnee und Landschaft, Davos Dorf, Switzerland); Wolter, Andrea; Lüthi, Rachel; Amann, Florian; Kenner, Robert and Bühler, Yves. Rock slope failure in a recently deglaciated permafrost rock wall at Piz Kesch (Eastern Swiss Alps), February 2014: Earth Surface Processes and Landforms, 42(3), p. 426-438, illus. incl. 1 table, sketch map, 62 ref., March 15, 2017.
In February 2014, a rock pillar with a volume of around 150 000 m3 collapsed at Piz Kesch in the Eastern Swiss Alps. A reconstruction of the conditions prior to the event and of the event itself is presented on the basis of different sources of data. The methods applied include photogrammetry, terrestrial laser scanning, structural geological analysis, examination of meteorological data, carbon-14 (14C) dating of organic material in permafrost ice from a tension crack and numerical modelling of likely modes of failure. Despite a complete lack of in situ measurements in the rock wall prior to the event and of direct observations during the event, the available data allow the determination of the approximate timing of the event as well as the structural predisposition, the probable mode of failure and the timescale of several millennia involved in the triggering of the failure of the rock pillar. The interdisciplinary analysis of this event contributes towards understanding the complex interaction of processes involved in large rock slope failures currently occurring in warming mountain permafrost regions. Copyright Copyright 2016 John Wiley & Sons, Ltd.
2017027623 Wilson, R. M. (Florida State University, Department of Earth Ocean and Atmospheric Sciences, Tallahassee, FL); Fitzhugh, L.; Whiting, G. J.; Frolking, S.; Harrison, M. D.; Dimova, N.; Burnett, W. C. and Chanton, J. P. Greenhouse gas balance over thaw-freeze cycles in discontinuous zone permafrost: Journal of Geophysical Research: Biogeosciences, 122(2), p. 387-404, illus. incl. 1 table, sketch map, 67 ref., February 2017.
Peat in the discontinuous permafrost zone contains a globally significant reservoir of carbon that has undergone multiple permafrost-thaw cycles since the end of the mid-Holocene (~3700 years before present). Periods of thaw increase C decomposition rates which leads to the release of CO2 and CH4 to the atmosphere creating potential climate feedback. To determine the magnitude and direction of such feedback, we measured CO2 and CH4 emissions and modeled C accumulation rates and radiative fluxes from measurements of two radioactive tracers with differing lifetimes to describe the C balance of the peatland over multiple permafrost-thaw cycles since the initiation of permafrost at the site. At thaw features, the balance between increased primary production and higher CH4 emission stimulated by warmer temperatures and wetter conditions favors C sequestration and enhanced peat accumulation. Flux measurements suggest that frozen plateaus may intermittently (order of years to decades) act as CO2 sources depending on temperature and net ecosystem respiration rates, but modeling results suggest that-despite brief periods of net C loss to the atmosphere at the initiation of thaw-integrated over millennia, these sites have acted as net C sinks via peat accumulation. In greenhouse gas terms, the transition from frozen permafrost to thawed wetland is accompanied by increasing CO2 uptake that is partially offset by increasing CH4 emissions. In the short-term (decadal time scale) the net effect of this transition is likely enhanced warming via increased radiative C emissions, while in the long-term (centuries) net C deposition provides a negative feedback to climate warming. Abstract Copyright (2017), . American Geophysical Union. All Rights Reserved.
2017027625 Xia Jianyang (East China Normal University, Research Center for Global Change and Ecological Forecasting and Tiantong National Field Observation Station for Forest Ecosystem, Shanghai, China); McGuire, A. David; Lawrence, David; Burke, Eleanor; Chen, Guangsheng; Chen, Xiaodong; Delire, Christine; Koven, Charles; MacDougall, Andrew; Peng, Shushi; Rinke, Annette; Saito, Kazuyuki; Zhang, Wenxin; Alkama, Ramdane; Bohn, Theodore J.; Ciais, Philippe; Decharme, Bertrand; Gouttevin, Isabelle; Hajima, Tomohiro; Hayes, Daniel J.; Huang Kun; Ji Duoying; Krinner, Gerhard; Lettenmaier, Dennis P.; Miller, Paul A.; Moore, John C.; Smith, Benjamin; Sueyoshi, Tetsuo; Shi, Zheng; Yan Liming; Liang, Junyi; Jiang, Lifen; Zhang Qian and Luo, Yiqi. Terrestrial ecosystem model performance in simulating productivity and its vulnerability to climate change in the northern permafrost region: Journal of Geophysical Research: Biogeosciences, 122(2), p. 430-446, illus. incl. 2 tables, 129 ref., February 2017.
Realistic projection of future climate-carbon (C) cycle feedbacks requires better understanding and an improved representation of the C cycle in permafrost regions in the current generation of Earth system models. Here we evaluated 10 terrestrial ecosystem models for their estimates of net primary productivity (NPP) and responses to historical climate change in permafrost regions in the Northern Hemisphere. In comparison with the satellite estimate from the Moderate Resolution Imaging Spectroradiometer (MODIS; 246 ± 6 g C m-2 yr-1), most models produced higher NPP (309 ± 12 g C m-2 yr-1) over the permafrost region during 2000-2009. By comparing the simulated gross primary productivity (GPP) with a flux tower-based database, we found that although mean GPP among the models was only overestimated by 10% over 1982-2009, there was a twofold discrepancy among models (380 to 800 g C m-2 yr-1), which mainly resulted from differences in simulated maximum monthly GPP (GPPmax). Most models overestimated C use efficiency (CUE) as compared to observations at both regional and site levels. Further analysis shows that model variability of GPP and CUE are nonlinearly correlated to variability in specific leaf area and the maximum rate of carboxylation by the enzyme Rubisco at 25°C (Vcmax_25), respectively. The models also varied in their sensitivities of NPP, GPP, and CUE to historical changes in climate and atmospheric CO2 concentration. These results indicate that model predictive ability of the C cycle in permafrost regions can be improved by better representation of the processes controlling CUE and GPPmax as well as their sensitivity to climate change. Abstract Copyright (2017), . American Geophysical Union. All Rights Reserved.
2017027493 Morison, Matthew Q. (University of Waterloo, Department of Geography and Environmental Management, Waterloo, ON, Canada); Macrae, Merrin L.; Petrone, Richard M. and Fishback, LeeAnn. Seasonal dynamics in shallow freshwater pond-peatland hydrochemical interactions in a subarctic permafrost environment: Hydrological Processes, 31(2), p. 462-475, illus. incl. 1 table, sketch map, 80 ref., January 15, 2017.
Terrestrial and aquatic ecological productivity are often nutrient limited in subarctic permafrost environments. High latitude regions are experiencing significant climatic change, including rapid warming and changing precipitation patterns, which may result in changes in nutrient dynamics within terrestrial and aquatic systems and hydrochemical transport between them. The objective of this research was to characterize changes in runoff quantity and quality within, and between peatlands and ponds throughout the snow-free summer season. Two ponds and their catchments were monitored over the snow-free season to measure changes in hydrologic storage, and to determine how water chemistry changed with the evolution of the frost table depth. Thresholds in hydrologic storage combined with frost table position (which inhibited infiltration and storage) produced nonlinear responses for runoff generation through highly conductive shallow peat layers while deeper, less conductive layers retarded flow. Greater inputs were required to exceed hydrologic storage (fill and spill) as a deepening frost table increased the hydrologically active portion of the soil, leading to seasonal variability in runoff pathways between peatlands and ponds. Runoff contributions to ponds were an integral component of the snow-free water balance during the study period, contributing up to 60% of all snow-free inputs. Groundwater chemistry (and pond chemistry following runoff events when ponds were connected with peatlands) reflected the different depths of peat and mineral soil accessed throughout the season. This work has improved scientific understanding of the combined controls of hydrologic inputs and ground frost on runoff and nutrient transport between peatlands and ponds, and sheds insight into how nutrient dynamics in cold regions may evolve under a changing climate. Abstract Copyright (2010), John Wiley & Sons, Ltd.
2017027640 Nicolsky, D. J. (University of Alaska at Fairbanks, Geophysical Institute, Fairbanks, AK); Romanovsky, V. E.; Panda, S. K.; Marchenko, S. S. and Muskett, R. R. Applicability of the ecosystem type approach to model permafrost dynamics across the Alaska North Slope: Journal of Geophysical Research: Earth Surface, 122(1), p. 50-75, illus. incl. 3 tables, sketch maps, 101 ref., January 2017.
Thawing and freezing of Arctic soils is affected by many factors, with air temperature, vegetation, snow accumulation, and soil physical properties and soil moisture among the most important. We enhance the Geophysical Institute Permafrost Laboratory model and develop several high spatial resolution scenarios of changes in permafrost characteristics in the Alaskan Arctic in response to observed and projected climate change. The ground thermal properties of surface vegetation and soil column are upscaled using the Ecosystems of Northern Alaska map and temperature data assimilation from the shallow boreholes across the Alaska North Slope. Soil temperature dynamics are simulated by solving the 1-D nonlinear heat equation with phase change, while the snow temperature and thickness are simulated by considering the snow accumulation, compaction, and melting processes. The model is verified by comparing with available active layer thickness at the Circumpolar Active Layer Monitoring sites, permafrost temperature, and snow depth records from existing permafrost observatories in the North Slope region. Abstract Copyright (2016), . American Geophysical Union. All Rights Reserved.
2017029921 Gulbrandsen, Mats Lundh (University of Copenhagen, Niels Bohr Institute, Copenhagen, Denmark); Minsley, Burke J.; Ball, Lyndsay B. and Hansen, Thomas Mejer. Semiautomatic mapping of permafrost in the Yukon Flats, Alaska: Geophysical Research Letters, 43(23), p. 12,131-12,137, illus. incl. sketch map, 34 ref., December 16, 2016.
Thawing of permafrost due to global warming can have major impacts on hydrogeological processes, climate feedback, arctic ecology, and local environments. To understand these effects and processes, it is crucial to know the distribution of permafrost. In this study we exploit the fact that airborne electromagnetic (AEM) data are sensitive to the distribution of permafrost and demonstrate how the distribution of permafrost in the Yukon Flats, Alaska, is mapped in an efficient (semiautomatic) way, using a combination of supervised and unsupervised (machine) learning algorithms, i.e., Smart Interpretation and K-means clustering. Clustering is used to sort unfrozen and frozen regions, and Smart Interpretation is used to predict the depth of permafrost based on expert interpretations. This workflow allows, for the first time, a quantitative and objective approach to efficiently map permafrost based on large amounts of AEM data. Abstract Copyright (2016), . American Geophysical Union. All Rights Reserved.
2017029920 Toohey, R. C. (Alaska Climate Science Center, Anchorage, AK); Herman-Mercer, N. M.; Schuster, P. F.; Mutter, E. A. and Koch, J. C. Multidecadal increases in the Yukon River basin of chemical fluxes as indicators of changing flowpaths, groundwater, and permafrost: Geophysical Research Letters, 43(23), p. 12,120-12,130, illus., 82 ref., December 16, 2016.
The Yukon River Basin, underlain by discontinuous permafrost, has experienced a warming climate over the last century that has altered air temperature, precipitation, and permafrost. We investigated a water chemistry database from 1982 to 2014 for the Yukon River and its major tributary, the Tanana River. Significant increases of Ca, Mg, and Na annual flux were found in both rivers. Additionally, SO4 and P annual flux increased in the Yukon River. No annual trends were observed for dissolved organic carbon (DOC) from 2001 to 2014. In the Yukon River, Mg and SO4 flux increased throughout the year, while some of the most positive trends for Ca, Mg, Na, SO4, and P flux occurred during the fall and winter months. Both rivers exhibited positive monthly DOC flux trends for summer (Yukon River) and winter (Tanana River). These trends suggest increased active layer expansion, weathering, and sulfide oxidation due to permafrost degradation throughout the Yukon River Basin. Abstract Copyright Published 2016. This article has been contributed to by US Government employees and their work is in the public domain in the USA.
2017025471 Wang Xiaoyun (Lanzhou University, College of Earth and Environmental Sciences, Lanzhou, China); Yi Shuhua; Wu Qingbai; Yang Kun and Ding Yongjian. The role of permafrost and soil water in distribution of alpine grassland and its NDVI dynamics on the Qinghai-Tibetan Plateau: Global and Planetary Change, 147, p. 40-53, illus. incl. 2 tables, sketch maps, 76 ref., December 2016.
Soil temperature and soil water are two important factors controlling vegetation growth. Climate warming and associated permafrost degradation might change these soil conditions and affect alpine grassland on the Qinghai-Tibetan Plateau. However, our current understanding of the role of soil temperature and water at the plateau scale is inadequate. In this study, we used plateau scale soil water content, frozen soil type, vegetation index and land surface temperature datasets to investigate the spatial distribution, limiting factors of vegetation growth and normalized difference vegetation index (NDVI) changing trends in two major alpine grasslands, alpine meadow and alpine steppe, in relation to soil temperature and soil water conditions. Our results showed that: 1) alpine meadow is mainly distributed in seasonal frozen soil areas (55.90% of alpine meadow) with a soil water content between 0.15 and 0.25 m3/m3 and alpine steppe is mainly found in seasonal frozen and sub-stable permafrost areas (69.38% of alpine steppe) with a soil water content between 0.05 and 0.20 m3/m3; 2) at the plateau scale, there were 35.6% (more in colder regions) of alpine meadow pixels and 33.6% (more in wetter regions) of alpine steppe pixels having increase NDVI changing trends during 1982-2012, respectively; and the values having decrease NDVI changing trends are 7.3% and 9.7%, respectively; and 3) the vegetation growth of alpine meadow is mainly limited by soil temperature, while that of alpine steppe is limited by both soil temperature and soil water. We also find the limiting factors of temperature or water can only explain < 50% variation of vegetation growth trends in alpine grasslands. Our findings warrant the use of process-based ecosystem models to consider other factors, such as grazing, erosion and soil texture, among others, in addition to soil temperature and water to make proper projections when simulating the responses of vegetation growth to climate warming in alpine grasslands with different hydro-thermal conditions.
2017025598 Ruppel, Carolyn D. (U. S. Geological Survey, Woods Hole, MA); Herman, Bruce M.; Brothers, Laura L. and Hart, Patrick E. Subsea ice-bearing permafrost on the U.S. Beaufort margin; 2, Borehole constraints: Geochemistry, Geophysics, Geosystems - G3, 17(11), p. 4333-4353, illus. incl. 2 tables, sketch map, 50 ref., November 2016.
Borehole logging data from legacy wells directly constrain the contemporary distribution of subsea permafrost in the sedimentary section at discrete locations on the U.S. Beaufort Margin and complement recent regional analyses of exploration seismic data to delineate the permafrost's offshore extent. Most usable borehole data were acquired on a ~500 km stretch of the margin and within 30 km of the contemporary coastline from north of Lake Teshekpuk to nearly the U.S.-Canada border. Relying primarily on deep resistivity logs that should be largely unaffected by drilling fluids and hole conditions, the analysis reveals the persistence of several hundred vertical meters of ice-bonded permafrost in nearshore wells near Prudhoe Bay and Foggy Island Bay, with less permafrost detected to the east and west. Permafrost is inferred beneath many barrier islands and in some nearshore and lagoonal (back-barrier) wells. The analysis of borehole logs confirms the offshore pattern of ice-bearing subsea permafrost distribution determined based on regional seismic analyses and reveals that ice content generally diminishes with distance from the coastline. Lacking better well distribution, it is not possible to determine the absolute seaward extent of ice-bearing permafrost, nor the distribution of permafrost beneath the present-day continental shelf at the end of the Pleistocene. However, the recovery of gas hydrate from an outer shelf well (Belcher) and previous delineation of a log signature possibly indicating gas hydrate in an inner shelf well (Hammerhead 2) imply that permafrost may once have extended across much of the shelf offshore Camden Bay. Abstract Copyright (2016), . American Geophysical Union. All Rights Reserved.
2017023163 Yu Fan (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, Lanzhou, China); Qi Jilin; Lai Yuanming; Sivasithamparam, Nallathamby; Yao Xiaoliang; Zhang Mingyi; Liu Yongzhi and Wu Guilong. Typical embankment settlement/heave patterns of the Qinghai-Tibet Highway in permafrost regions; formation and evolution: Engineering Geology, 214, p. 147-156, illus. incl. 2 tables, sketch map, 43 ref., November 30, 2016.
The Qinghai-Tibet Highway (QTH) in China has been experiencing a serious embankment settlement/heave for more than half a century. The settlement/heave is resulted from several mechanical processes taking place in different soil layers. In this paper, four typical settlement/heave patterns of road embankments in permafrost regions, namely "steady-low rate", "fluctuate", "down step" and "steady-high rate" are proposed based on 3-year monitored data of embankment settlement/heave and ground temperature at four road sections as well as previous published data of the QTH. Their formation mechanisms and evolution trend in the process of permafrost degradation are discussed from the viewpoints of engineering geology and mechanical process, based on the clarification of the deformation characteristics of different soil layers of a typical road embankment. The results show that the four patterns are caused by the negligible settlement/heave, freeze-thaw cycling in an open condition, consolidation of the thawed permafrost layers, and creep of warm permafrost layers respectively. The pattern will change from one to another during the process of permafrost degradation, which will become very complex with the occurrence of frost heave. The results can help revealing the deformation mechanism of road embankments in permafrost regions, and can benefit road construction and maintenance in the future.
2017028700 Kurchatova, A. N. (Russian Academy of Sciences, Institute of the Earth's Cryosphere, Tyumen, Russian Federation); Melnikov, V. P.; Rogov, V. V. and Slagoda, E. A. Authigenic mineral formation in fluid permeability zones in the West Siberia permafrost: Doklady Earth Sciences, 468(2), p. 571-573, illus., 11 ref., June 2016.
Basic chemical and mineralogical anomalies in permafrost caused by hydrocarbon migration are considered. Direct evidence for bacterial oxidation of light hydrocarbons, primarily methane, were first obtained in fluid permeability zones in the permafrost as a stepwise formation of authigenic minerals such as iron sulfides and oxides, carbonates, silicates, and gypsum. Copyright 2016 Pleiades Publishing, Ltd.
2017022637 Cable, William L. (University of Alaska at Fairbanks, Geophysical Institute, Fairbanks, AK); Romanovsky, Vladimir E. and Jorgenson, M. Torre. Scaling-up permafrost thermal measurements in western Alaska using an ecotype approach: The Cryosphere (Online), 10(5), p. 2517-2532, illus. incl. 4 tables, sketch maps, 41 ref., 2016.
Permafrost temperatures are increasing in Alaska due to climate change and in some cases permafrost is thawing and degrading. In areas where degradation has already occurred the effects can be dramatic, resulting in changing ecosystems, carbon release, and damage to infrastructure. However, in many areas we lack baseline data, such as subsurface temperatures, needed to assess future changes and potential risk areas. Besides climate, the physical properties of the vegetation cover and subsurface material have a major influence on the thermal state of permafrost. These properties are often directly related to the type of ecosystem overlaying permafrost. In this paper we demonstrate that classifying the landscape into general ecotypes is an effective way to scale up permafrost thermal data collected from field monitoring sites. Additionally, we find that within some ecotypes the absence of a moss layer is indicative of the absence of near-surface permafrost. As a proof of concept, we used the ground temperature data collected from the field sites to recode an ecotype land cover map into a map of mean annual ground temperature ranges at 1 m depth based on analysis and clustering of observed thermal regimes. The map should be useful for decision making with respect to land use and understanding how the landscape might change under future climate scenarios.
2017022221 Overduin, Pier Paul (Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research, Potsdam, Germany); Wetterich, Sebastian; Günther, Frank; Grigoriev, Mikhail N.; Grosse, Guido; Schirrmeister, Lutz; Hubberten, Hans-Wolfgang and Makarov, Aleksandr. Coastal dynamics and submarine permafrost in shallow water of the central Laptev Sea, east Siberia: The Cryosphere (Online), 10(4), p. 1449-1462, illus. incl. sects., 1 table, sketch map, 48 ref., 2016.
Coastal erosion and flooding transform terrestrial landscapes into marine environments. In the Arctic, these processes inundate terrestrial permafrost with seawater and create submarine permafrost. Permafrost begins to warm under marine conditions, which can destabilize the sea floor and may release greenhouse gases. We report on the transition of terrestrial to submarine permafrost at a site where the timing of inundation can be inferred from the rate of coastline retreat. On Muostakh Island in the central Laptev Sea, East Siberia, changes in annual coastline position have been measured for decades and vary highly spatially. We hypothesize that these rates are inversely related to the inclination of the upper surface of submarine ice-bonded permafrost (IBP) based on the consequent duration of inundation with increasing distance from the shoreline. We compared rapidly eroding and stable coastal sections of Muostakh Island and find permafrost-table inclinations, determined using direct current resistivity, of 1 and 5 %, respectively. Determinations of submarine IBP depth from a drilling transect in the early 1980s were compared to resistivity profiles from 2011. Based on borehole observations, the thickness of unfrozen sediment overlying the IBP increased from 0 to 14 m below sea level with increasing distance from the shoreline. The geoelectrical profiles showed thickening of the unfrozen sediment overlying ice-bonded permafrost over the 28 years since drilling took place. We use geoelectrical estimates of IBP depth to estimate permafrost degradation rates since inundation. Degradation rates decreased from over 0.4 m a-1 following inundation to around 0.1 m a-1 at the latest after 60 to 110 years and remained constant at this level as the duration of inundation increased to 250 years. We suggest that long-term rates are lower than these values, as the depth to the IBP increases and thermal and porewater solute concentration gradients over depth decrease. For the study region, recent increases in coastal erosion rate and changes in benthic temperature and salinity regimes are expected to affect the depth to submarine permafrost, leading to coastal regions with shallower IBP.
2017022223 Pan, Xicai (University of Saskatchewan, Global Institute for Water Security, Saskatoon, SK, Canada); Li, Yanping; Yu Qihao; Shi, Xiaogang; Yang, Daqing and Roth, Kurt. Effects of stratified active layers on high-altitude permafrost warming; a case study on the Qinghai-Tibet Plateau: The Cryosphere (Online), 10(4), p. 1591-1603, illus. incl. 3 tables, sketch map, 45 ref., 2016.
Seasonally variable thermal conductivity in active layers is one important factor that controls the thermal state of permafrost. The common assumption is that this conductivity is considerably lower in the thawed than in the frozen state, lt/lf < 1. Using a 9-year dataset from the Qinghai-Tibet Plateau (QTP) in conjunction with the GEOtop model, we demonstrate that the ratio lt/lf may approach or even exceed 1. This can happen in thick (> 1.5 m) active layers with strong seasonal total water content changes in the regions with summer-monsoon-dominated precipitation pattern. The conductivity ratio can be further increased by typical soil architectures that may lead to a dry interlayer. The unique pattern of soil hydraulic and thermal dynamics in the active layer can be one important contributor for the rapid permafrost warming at the study site. These findings suggest that, given the increase in air temperature and precipitation, soil hydraulic properties, particularly soil architecture in those thick active layers must be properly taken into account in permafrost models.
2017022633 Porada, Philipp (Stockholm University, Department of Environmental Science and Analytical Chemistry, Stockholm, Sweden); Ekici, Altug and Beer, Christian. Effects of bryophyte and lichen cover on permafrost soil temperature at large scale: The Cryosphere (Online), 10(5), p. 2291-2315, illus. incl. 4 tables, 83 ref., 2016. Includes appendices.
Bryophyte and lichen cover on the forest floor at high latitudes exerts an insulating effect on the ground. In this way, the cover decreases mean annual soil temperature and can protect permafrost soil. Climate change, however, may change bryophyte and lichen cover, with effects on the permafrost state and related carbon balance. It is, therefore, crucial to predict how the bryophyte and lichen cover will react to environmental change at the global scale. To date, current global land surface models contain only empirical representations of the bryophyte and lichen cover, which makes it impractical to predict the future state and function of bryophytes and lichens. For this reason, we integrate a process-based model of bryophyte and lichen growth into the global land surface model JSBACH (Jena Scheme for Biosphere-Atmosphere Coupling in Hamburg). The model simulates bryophyte and lichen cover on upland sites. Wetlands are not included. We take into account the dynamic nature of the thermal properties of the bryophyte and lichen cover and their relation to environmental factors. Subsequently, we compare simulations with and without bryophyte and lichen cover to quantify the insulating effect of the organisms on the soil. We find an average cooling effect of the bryophyte and lichen cover of 2.7 K on temperature in the topsoil for the region north of 50° N under the current climate. Locally, a cooling of up to 5.7 K may be reached. Moreover, we show that using a simple, empirical representation of the bryophyte and lichen cover without dynamic properties only results in an average cooling of around 0.5 K. This suggests that (a) bryophytes and lichens have a significant impact on soil temperature in high-latitude ecosystems and (b) a process-based description of their thermal properties is necessary for a realistic representation of the cooling effect. The advanced land surface scheme, including a dynamic bryophyte and lichen model, will be the basis for an improved future projection of land-atmosphere heat and carbon exchange.
2017022226 Wang Wenli (Beijing Normal University, College of Global Change and Earth System Science, Beijing, China); Rinke, Annette; Moore, John C.; Ji Duoying; Cui Xuefeng; Peng, Shushi; Lawrence, David M.; McGuire, A. David; Burke, Eleanor J.; Chen, Xiaodong; Decharme, Bertrand; Koven, Charles; MacDougall, Andrew; Saito, Kazuyuki; Zhang, Wenxin; Alkama, Ramdane; Bohn, Theodore J.; Ciais, Philippe; Delire, Christine; Gouttevin, Isabelle; Hajima, Tomohiro; Krinner, Gerhard; Lettenmaier, Dennis P.; Miller, Paul A.; Smith, Benjamin; Sueyoshi, Tetsuo and Sherstiukov, Artem B. Evaluation of air-soil temperature relationships simulated by land surface models during winter across the permafrost region: The Cryosphere (Online), 10(4), p. 1721-1737, illus. incl. 4 tables, 71 ref., 2016.
A realistic simulation of snow cover and its thermal properties are important for accurate modelling of permafrost. We analyse simulated relationships between air and near-surface (20 cm) soil temperatures in the Northern Hemisphere permafrost region during winter, with a particular focus on snow insulation effects in nine land surface models, and compare them with observations from 268 Russian stations. There are large cross-model differences in the simulated differences between near-surface soil and air temperatures (DT; 3 to 14 °C), in the sensitivity of soil-to-air temperature (0.13 to 0.96 °C °C-1), and in the relationship between DT and snow depth. The observed relationship between DT and snow depth can be used as a metric to evaluate the effects of each model's representation of snow insulation, hence guide improvements to the model's conceptual structure and process parameterisations. Models with better performance apply multilayer snow schemes and consider complex snow processes. Some models show poor performance in representing snow insulation due to underestimation of snow depth and/or overestimation of snow conductivity. Generally, models identified as most acceptable with respect to snow insulation simulate reasonable areas of near-surface permafrost (13.19 to 15.77 million km2). However, there is not a simple relationship between the sophistication of the snow insulation in the acceptable models and the simulated area of Northern Hemisphere near-surface permafrost, because several other factors, such as soil depth used in the models, the treatment of soil organic matter content, hydrology and vegetation cover, also affect the simulated permafrost distribution.
2017022225 Wu Qingbai (Chinese Academy of Science, Cold and Arid Regions Environmental and Engineering Research Institute, Lanzhou, China); Zhang Zhongqiong; Gao Siru and Ma Wei. Thermal impacts of engineering activities and vegetation layer on permafrost in different alpine ecosystems of the Qinghai-Tibet Plateau, China: The Cryosphere (Online), 10(4), p. 1695-1706, illus. incl. 4 tables, sketch maps, 57 ref., 2016.
Climate warming and engineering activities have various impacts on the thermal regime of permafrost in alpine ecosystems of the Qinghai-Tibet Plateau. Using recent observations of permafrost thermal regimes along the Qinghai-Tibet highway and railway, the changes of such regimes beneath embankments constructed in alpine meadows and steppes are studied. The results show that alpine meadows on the Qinghai-Tibet Plateau can have a controlling role among engineering construction effects on permafrost beneath embankments. As before railway construction, the artificial permafrost table (APT) beneath embankments is not only affected by climate change and engineering activities but is also controlled by alpine ecosystems. However, the change rate of APT is not dependent on ecosystem type, which is predominantly affected by climate change and engineering activities. Instead, the rate is mainly related to cooling effects of railway ballast and heat absorption effects of asphalt pavement. No large difference between alpine and steppe can be identified regarding the variation of soil temperature beneath embankments, but this difference is readily identified in the variation of mean annual soil temperature with depth. The vegetation layer in alpine meadows has an insulation role among engineering activity effects on permafrost beneath embankments, but this insulation gradually disappears because the layer decays and compresses over time. On the whole, this layer is advantageous for alleviating permafrost temperature rise in the short term, but its effect gradually weakens in the long term.
2017025599 Brothers, Laura L. (U. S. Geological Survey, Woods Hole, MA); Herman, Bruce M.; Hart, Patrick E. and Ruppel, Carolyn D. Subsea ice-bearing permafrost on the U.S. Beaufort margin; 1, Minimum seaward extent defined from multichannel seismic reflection data: Geochemistry, Geophysics, Geosystems - G3, 17(11), p. 4354-4365, illus. incl. sketch map, 71 ref., November 2016.
2017030115 Narancic, Biljana (Université Laval, Département de Géographie, Ville de Quebec, QC, Canada); Wolfe, Brent B.; Pienitz, Reinhard; Meyer, Hanno and Lamhonwah, Daniel. Landscape gradient assessment of thermokarst lake hydrology using water isotope tracers: Journal of Hydrology, 545, p. 327-338, illus. incl. 5 tables, sketch map, 46 ref., February 2017. Includes appendices.
Thermokarst lakes are widespread in arctic and subarctic regions. In subarctic Quebec (Nunavik), they have grown in number and size since the mid-20th century. Recent studies have identified that these lakes are important sources of greenhouse gases. This is mainly due to the supply of catchment-derived dissolved organic carbon that generates anoxic conditions leading to methane production. To assess the potential role of climate-driven changes in hydrological processes to influence greenhouse-gas emissions, we utilized water isotope tracers to characterize the water balance of thermokarst lakes in Nunavik during three consecutive mid- to late summer sampling campaigns (2012-2014). Lake distribution stretches from shrub-tundra overlying discontinuous permafrost in the north to spruce-lichen woodland with sporadic permafrost in the south. Calculation of lake-specific input water isotope compositions (dI) and lake-specific evaporation-to-inflow (E/I) ratios based on an isotope-mass balance model reveal a narrow hydrological gradient regardless of diversity in regional landscape characteristics. Nearly all lakes sampled were predominantly fed by rainfall and/or permafrost meltwater, which suppressed the effects of evaporative loss. Only a few lakes in one of the southern sampling locations, which overly highly degraded sporadic permafrost terrain, appear to be susceptible to evaporative lake-level drawdown. We attribute this lake hydrological resiliency to the strong maritime climate in coastal regions of Nunavik. Predicted climate-driven increases in precipitation and permafrost degradation will likely contribute to persistence and expansion of thermokarst lakes throughout the region. If coupled with an increase in terrestrial carbon inputs to thermokarst lakes from surface runoff, conditions favorable for mineralization and emission of methane, these water bodies may become even more important sources of greenhouse gases.
2017030144 Drake, Henrik (Linnaeus University, Department of Biology and Environmental Science, Kalmar, Sweden); Suksi, Juhani; Tullborg, Eva-Lena and Lahaye, Yann. Quaternary redox transitions in deep crystalline rock fractures at the western margin of the Greenland ice sheet: Applied Geochemistry, 76, p. 196-209, illus. incl. sketch map, 72 ref., January 2017. Includes appendices.
When planning for long term deep geological repositories for spent nuclear fuel knowledge of processes that will influence and change the sub-surface environment is crucial. For repositories in northern Europe and similar areas, influence from advancing and retreating continental ice sheets must be planned for. Rapid transport of meltwater into the bedrock may introduce oxic conditions at great depth, which may affect the copper canisters planned to encapsulate the spent fuel. The lack of direct observations has led to simplified modelling assumptions not reflecting the complexity of natural systems. As part of a unique field and modelling study, The Greenland Analogue Project, of a continental ice sheet and related sub-surface conditions, we here present mineralogical and U-series data unravelling the Quaternary redox history in the deep bedrock fracture system close to the margin of the Greenland ice sheet. The aim was to increase the understanding of circulation of potentially oxygenated glacial meltwater from the surface down to 650 m depth. Secondary mineral coatings were sampled from open fractures in cored boreholes down to 650 m, within and below the current permafrost. Despite continental ice sheet coverage and/or prevailing permafrost during large parts of the last 1 Ma, measured disequilibrium in the 238U-234U-230Th system shows that water has circulated in the bedrock fracture system at various occasions during this time span. In fractures of the upper 60 m, infiltration of oxygenated surface water has resulted in a prominent near-surface "oxidised zone" with abundant FeOOH precipitation. However, this zone must be relict because it is currently within permafrost and the U-series disequilibrium signatures of most fracture coatings show evidence of deposition of U prior to the Holocene and even prior to the last glaciation maximum which occurred less than 100 ka ago. This U deposition is found both within and below the near surface "oxidised zone" indicating temporal redox variation within this zone during the last 1 Ma. Potential Holocene leaching of U is indicated by 230Th/238U much greater than 1 and close to secular equilibrium for 234U/238U in some of the near surface fractures and also in a couple of deeper fractures. Indicated U-leaching in the talik within the last 200 ka is proposed to be the result of talik-related discharge of water with a capability of keeping U in solution. Circulation of oxidative water in the deep system beneath the permafrost is indicated only in a few fractures and solely by U-series disequilibrium (230Th/238U activity ratios up to 2.97 at 431 m depth), probably due to restricted, perhaps sporadic infiltration of oxidative water, potentially during the Holocene. In these fractures, the conditions have in general been more reducing than in the near surface system where oxidising conditions have prevailed and penetration of oxygenated waters may have been continuous.
2017029319 Ma Jianmin (Lanzhou University, Department of Environmental Science and Engineering, Lanzhou, China); Hung, Hayley and Macdonald, Robie W. The influence of global climate change on the environmental fate of persistent organic pollutants; a review with emphasis on the Northern Hemisphere and the Arctic as a receptor: Global and Planetary Change, 146, p. 89-108, illus. incl. 1 table, 257 ref., November 2016.
Following worldwide bans and restrictions on the use of many persistent organic pollutants (POPs) from the late 1970s, their regional and global distributions have become governed increasingly by phase partitioning between environmental reservoirs, such as air, water, soil, vegetation and ice, where POPs accumulated during the original applications. Presently, further transport occurs within the atmospheric and aquatic reservoirs. Increasing temperatures provide thermodynamic forcing to drive these chemicals out of reservoirs, like soil, vegetation, water and ice, and into the atmosphere where they can be transported rapidly by winds and then recycled among environmental media to reach locations where lower temperatures prevail (e.g., polar regions and high elevations). Global climate change, widely considered as global warming, is also manifested by changes in hydrological systems and in the cryosphere; with the latter now exhibiting widespread loss of ice cover on the Arctic Ocean and thawing of permafrost. All of these changes alter the cycling and fate of POPs. There is abundant evidence from observations and modeling showing that climate variation has an effect on POPs levels in biotic and abiotic environments. This article reviews recent progress in research on the effects of climate change on POPs with the intention of promoting awareness of the importance of interactions between climate and POPs in the geophysical and ecological systems.
2017028710 Arzhanov, M. M. (Russian Academy of Sciences, Obukhov Institute of Atmospheric Physics, Moscow, Russian Federation); Mokhov, I. I. and Denisov, S. N. Impact of regional climatic change on the stability of relic gas hydrates: Doklady Earth Sciences, 468(2), p. 616-618, illus., 15 ref., June 2016.
This paper considers the impact of current climatic change on the permafrost strength and stability of relic gas hydrates in the Yamal Peninsula based on the results of permafrost thermal regime simulations and model estimates of climate change within last 100 ka. Copyright 2016 Pleiades Publishing, Ltd.
2017028682 Drozdova, A. N. (Russian Academy of Sciences, Shirshov Institute of Oceanology, Moscow, Russian Federation); Vetrov, A. A.; Romankevich, E. A.; Prokuda, N. A.; Sukhoverkhov, S. V.; Bratskaya, S. Yu.; Sergienko, V. I.; Semiletov, I. P. and Ulyantsev, A. S. Polycyclic aromatic hydrocarbons in Holocene-Pleistocene sediments of the Laptev Sea: Doklady Earth Sciences, 468(1), p. 496-499, illus., 9 ref., May 2016.
The distribution and genesis of polycyclic aromatic hydrocarbons (PAHs) were studied in a 40-m core from a lagoon of the Laptev Sea that appeared during the Holocene resulting from the flooding of seawater into a freshwater lake in the area of the Buor-Khaya Gulf. The bulk of the core is constituted of permafrost rocks, thawed partially in their upper layers and covered with recent sediments (mainly by the products of intense thermoabrasion). The ratio of petrogenic and pyrogenic PAHs was evaluated. Copyright 2016 Pleiades Publishing, Ltd.
2017022632 Kumar, Jitendra (Oak Ridge National Laboratory, Environmental Sciences Division, Oak Ridge, TN); Collier, Nathan; Bisht, Gautam; Mills, Richard T.; Thornton, Peter E.; Iversen, Colleen M. and Romanovsky, Vladimir E. Modeling the spatiotemporal variability in subsurface thermal regimes across a low-relief polygonal tundra landscape: The Cryosphere (Online), 10(5), p. 2241-2274, illus. incl. 11 tables, 41 ref., 2016. Includes appendices.
Vast carbon stocks stored in permafrost soils of Arctic tundra are under risk of release to the atmosphere under warming climate scenarios. Ice-wedge polygons in the low-gradient polygonal tundra create a complex mosaic of microtopographic features. This microtopography plays a critical role in regulating the fine-scale variability in thermal and hydrological regimes in the polygonal tundra landscape underlain by continuous permafrost. Modeling of thermal regimes of this sensitive ecosystem is essential for understanding the landscape behavior under the current as well as changing climate. We present here an end-to-end effort for high-resolution numerical modeling of thermal hydrology at real-world field sites, utilizing the best available data to characterize and parameterize the models. We develop approaches to model the thermal hydrology of polygonal tundra and apply them at four study sites near Barrow, Alaska, spanning across low to transitional to high-centered polygons, representing a broad polygonal tundra landscape. A multiphase subsurface thermal hydrology model (PFLOTRAN) was developed and applied to study the thermal regimes at four sites. Using a high-resolution lidar digital elevation model (DEM), microtopographic features of the landscape were characterized and represented in the high-resolution model mesh. The best available soil data from field observations and literature were utilized to represent the complex heterogeneous subsurface in the numerical model. Simulation results demonstrate the ability of the developed modeling approach to capture - without recourse to model calibration - several aspects of the complex thermal regimes across the sites, and provide insights into the critical role of polygonal tundra microtopography in regulating the thermal dynamics of the carbon-rich permafrost soils. Areas of significant disagreement between model results and observations highlight the importance of field-based observations of soil thermal and hydraulic properties for modeling-based studies of permafrost thermal dynamics, and provide motivation and guidance for future observations that will help address model and data gaps affecting our current understanding of the system.
2017026873 Pickler, Carolyne (Université du Québec à Montréal, Centre de Recherche en Géochimie et en Géodynamique, Montreal, QC, Canada); Beltrami, Hugo and Mareschal, Jean-Claude. Climate trends in northern Ontario and Quebec from borehole temperature profiles: Climate of the Past, 12(12), p. 2215-2227, illus. incl. 4 tables, sketch map, 73 ref., 2016. Includes appendices.
The ground surface temperature histories of the past 500 years were reconstructed at 10 sites containing 18 boreholes in northeastern Canada. The boreholes, between 400 and 800 m deep, are located north of 51° N and west and east of James Bay in northern Ontario and Quebec. We find that both sides of James Bay have experienced similar ground surface temperature histories with a warming of 1.51 ± 0.76 K during the period of 1850 to 2000, similar to borehole reconstructions for the southern portion of the Superior Province and in agreement with available proxy data. A cooling period corresponding to the Little Ice Age was found at only one site. Despite permafrost maps locating the sites in a region of discontinuous permafrost, the ground surface temperature histories suggest that the potential for permafrost was minimal to absent over the past 500 years. This could be the result of air surface temperature interpolation used in permafrost models being unsuitable to account for the spatial variability of ground temperatures along with an offset between ground and air surface temperatures due to the snow cover.
2017022635 Sparkes, Robert B. (University of Manchester, School of Earth and Environmental Sciences and Williamson Research Centre for Molecular Environmental Science, Manchester, United Kingdom); Selver, Ayca Dogrul; Gustafsson, Orjan; Semiletov, Igor P.; Haghipour, Negar; Wacker, Lukas; Eglinton, Timothy I.; Talbot, Helen M. and van Dongen, Bart E. Macromolecular composition of terrestrial and marine organic matter in sediments across the East Siberian Arctic shelf: The Cryosphere (Online), 10(5), p. 2485-2500, illus. incl. 1 table, sketch map, 68 ref., 2016.
Mobilisation of terrestrial organic carbon (terrOC) from permafrost environments in eastern Siberia has the potential to deliver significant amounts of carbon to the Arctic Ocean, via both fluvial and coastal erosion. Eroded terrOC can be degraded during offshore transport or deposited across the wide East Siberian Arctic Shelf (ESAS). Most studies of terrOC on the ESAS have concentrated on solvent-extractable organic matter, but this represents only a small proportion of the total terrOC load. In this study we have used pyrolysis-gas chromatography-mass spectrometry (py-GCMS) to study all major groups of macromolecular components of the terrOC; this is the first time that this technique has been applied to the ESAS. This has shown that there is a strong offshore trend from terrestrial phenols, aromatics and cyclopentenones to marine pyridines. There is good agreement between proportion phenols measured using py-GCMS and independent quantification of lignin phenol concentrations (r2 = 0.67, p < 0.01, n = 24). Furfurals, thought to represent carbohydrates, show no offshore trend and are likely found in both marine and terrestrial organic matter. We have also collected new radiocarbon data for bulk OC (14COC) which, when coupled with previous measurements, allows us to produce the most comprehensive 14COC map of the ESAS to date. Combining the 14COC and py-GCMS data suggests that the aromatics group of compounds is likely sourced from old, aged terrOC, in contrast to the phenols group, which is likely sourced from modern woody material. We propose that an index of the relative proportions of phenols and pyridines can be used as a novel terrestrial vs. marine proxy measurement for macromolecular organic matter. Principal component analysis found that various terrestrial vs. marine proxies show different patterns across the ESAS, and it shows that multiple river-ocean transects of surface sediments transition from river-dominated to coastal-erosion-dominated to marine-dominated signatures.
2017030129 Langman, Jeff B. (University of Idaho, Department of Geological Sciences, Moscow, ID); Blowes, David W.; Amos, Richard T.; Atherton, Colleen; Wilson, David; Smith, Leslie; Sego, David C. and Sinclair, Sean A. Influence of a tundra freeze-thaw cycle on sulfide oxidation and metal leaching in a low sulfur, granitic waste rock: Applied Geochemistry, 76, p. 9-21, illus. incl. 2 tables, sketch map, 52 ref., January 2017.
Drill cuttings were collected at 1 m depths from an instrumented, low sulfur, experimental waste rock pile containing a 4C-pyrrhotite that had been exposed to the extreme freeze-thaw cycle of a tundra climate. Boreholes were drilled from the top to base in the center of the pile and near the core-batter transition. Waste rock samples were analyzed for carbon, sulfur, and metal concentrations; sulfur oxidation states; and variation in iron and nickel forms due to oxidative dissolution of pyrrhotite. Results from X-ray absorption spectroscopy and aqueous extraction experiments were used to relatively compare samples from various depths in the boreholes, which indicate sulfide weathering fronts that decrease in intensity from the top to core to base at the center of the pile and from the core-batter transition to the center of the pile. The tundra climate and waste pile configuration produce a permafrost base, a seasonally frozen core, and an atmospheric-like zone near the surface. The fluctuation of the freeze-thaw cycle caused the greatest sulfide weathering near the surface and lesser weathering in the core and base of the pile. Metal- and sulfur-rich leachate from the higher weathering zone likely is collecting on a variable and seasonal frozen surface beneath the surface layer that causes metals and S to precipitate and (or) sorb during a portion of the year. The accumulation of sulfur and metals with the flux of this frozen surface produces a nickel and possibly an iron and sulfur enrichment zone beneath the surface layer in the center of the pile. The weathering front from the top to core to base of the pile and from core-batter transition to the core corresponds to a previously formulated leachate model, but the enrichment zone below the surface zone is unique to this conceptual waste-rock weathering model for this tundra climate.
2017030489 Imaizumi, Fumitoshi (Shizuoka University, Faculty of Agriculture, Shizuoka-shi, Japan); Suzuki, Osamu and Togari-Ohta, Asako. Seasonal changes in the sediment flux on steep hillslopes in a humid diurnal frost environment: Earth Surface Processes and Landforms, 42(3), p. 389-398 (Italian sum.), illus. incl. 4 tables, 56 ref., March 15, 2017.
2017022630 Geilfus, Nicolas-Xavier (University of Manitoba, Centre for Earth Observation Science, Winnipeg, MB, Canada); Galley, Ryan J.; Else, Brent G. T.; Campbell, Karley; Papakyriakou, Tim; Crabeck, Odile; Lemes, Marcos; Delille, Bruno and Rysgaard, Soren. Estimates of ikaite export from sea ice to the underlying seawater in a sea ice-seawater mesocosm: The Cryosphere (Online), 10(5), p. 2173-2189, illus. incl. 2 tables, 58 ref., 2016.
The precipitation of ikaite and its fate within sea ice is still poorly understood. We quantify temporal inorganic carbon dynamics in sea ice from initial formation to its melt in a sea ice-seawater mesocosm pool from 11 to 29 January 2013. Based on measurements of total alkalinity (TA) and total dissolved inorganic carbon (TCO2), the main processes affecting inorganic carbon dynamics within sea ice were ikaite precipitation and CO2 exchange with the atmosphere. In the underlying seawater, the dissolution of ikaite was the main process affecting inorganic carbon dynamics. Sea ice acted as an active layer, releasing CO2 to the atmosphere during the growth phase, taking up CO2 as it melted and exporting both ikaite and TCO2 into the underlying seawater during the whole experiment. Ikaite precipitation of up to 167 mmol kg-1 within sea ice was estimated, while its export and dissolution into the underlying seawater was responsible for a TA increase of 64-66 mmol kg-1 in the water column. The export of TCO2 from sea ice to the water column increased the underlying seawater TCO2 by 43.5 mmol kg-1, suggesting that almost all of the TCO2 that left the sea ice was exported to the underlying seawater. The export of ikaite from the ice to the underlying seawater was associated with brine rejection during sea ice growth, increased vertical connectivity in sea ice due to the upward percolation of seawater and meltwater flushing during sea ice melt. Based on the change in TA in the water column around the onset of sea ice melt, more than half of the total ikaite precipitated in the ice during sea ice growth was still contained in the ice when the sea ice began to melt. Ikaite crystal dissolution in the water column kept the seawater pCO2 undersaturated with respect to the atmosphere in spite of increased salinity, TA and TCO2 associated with sea ice growth. Results indicate that ikaite export from sea ice and its dissolution in the underlying seawater can potentially hamper the effect of oceanic acidification on the aragonite saturation state (Waragonite) in fall and in winter in ice-covered areas, at the time when Waragonite is smallest.
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2017027027 Chipman, Melissa L. (University of Illinois, Program in Ecology, Evolution, and Conservation Biology, Urbana, IL) and Hu, Feng Sheng. Novel disturbance regimes in the Arctic; paleoecological records of fire and permafrost thaw from alaskan tundra [abstr.]: in Geological Society of America, 2016 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 48(7), Abstract no. 291-6, 2016. Meeting: Geological Society of America, 2016 annual meeting & exposition, Sep. 25-28, 2016, Denver, CO.
Anthropogenic warming has resulted in profound environmental changes in the Arctic that may increase the vulnerability of the large carbon stocks in permafrost soils. Disturbance processes such as wildfire and thermal degradation of permafrost (i.e., thermo-erosion) have increased in both frequency and magnitude in recent decades. These disturbance processes may interact with one another, exacerbating ecosystem response beyond the direct impacts of warming alone. Paleoecological reconstructions from lake sediments can provide information on the long-term dynamics of tundra disturbance regimes. We present several reconstructions of wildfire and thermo-erosion from tundra ecoregions of Alaska, based on the analyses of charcoal, isotopes, lithology, X-Ray fluorescence, and X-Ray diffraction on lake-sediment cores. Paleofire reconstructions from tundra ecoregions that span a broad range of modern vegetation and climate show spatial heterogeneity in fire regimes, with mean fire-return intervals ranging from 140 to 6050 years. In some ecoregions, these past fire-return intervals are longer than fire cycles estimated from modern observations, suggesting higher rates of burning over the recent past. On the Alaskan North Slope, where fires are rare, we identified ten episodes of shoreline thermo-erosion over the past 6000 years that coincided with periods of warm summer temperatures. In contrast, records of fire and thermo-erosion from the Noatak Watershed, a high-fire ecoregion, suggest that thermo-erosion (14 episodes over the past 3000 years) was facilitated by watershed fires. Furthermore, these records show that shoreline thermo-erosional features formed ~20 years after fire events, suggesting a lagged response of permafrost thawing to climate-driven fire activity. These records provide valuable new information for understanding the natural variability, drivers, and interactions of tundra disturbances, which is critical given the rapidly changing state of the Arctic and the potential for novel disturbance regimes in tundra ecosystems.
2017022758 Fleisher, P. Jay (State University of New York-Oneonta, Department of Earth and Atmospheric Sciences, Oneonta, NY). Structures resembling ice-wedge casts suggest discontinuous permafrost during Laurentide retreat, central New York State [abstr.]: in Geological Society of America, 2016 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 48(7), Abstract no. 121-6, 2016. Meeting: Geological Society of America, 2016 annual meeting & exposition, Sept. 25-28, 2016, Denver, CO.
Structures resembling ice-wedge casts occupy siltstone bedrock joints on upland divides 10 kilometers south of the last major Laurentide advance into the eastern Susquehanna drainage of central NYS. They are similar in scale and structural configuration to ice-wedge casts found in Arctic permafrost. No similar features are found within glacial or post-glacial deposits. As with classic periglacial ice-wedge casts, these range from 30 cm to 1.5 m in width near the surface and taper downward to depths of 2 to 3 m where they narrow to thin seams. However, confinement within bedrock joints precludes polygonal distribution. Bedding in the host siltstone is sharply upturned at the wedge tops in marginal deformation that diminishes with depth. The extent of deformation appears to be directly proportional to wedge thickness. In all cases the deformation fades laterally within two meters of the wedge. Vertical sorting within all wedges exhibits coarser clasts near the top, fining downward. Several wedges contain vertically oriented zones suggesting multiple phases of development by filling from above accompanied by collapse of overlying lodgment till. Fragments of host bedrock dominate the coarse clastic filling, whereas the finer fraction contains erratic lithologies similar to those found in overlying till. Paleoclimate interpretation suggests discontinuous permafrost in uplands that predates Laurentide readvance circa 18,000 years.
2017025430 Levy, Joseph (University of Texas, Institute for Geophysics, Austin, TX) and Schmidt, Logan. Linking permafrost and active layer surface properties to thermokarst risk [abstr.]: in Geological Society of America, 2016 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 48(7), Abstract no. 286-7, 2016. Meeting: Geological Society of America, 2016 annual meeting & exposition, Sep. 25-28, 2016, Denver, CO.
How do the structure, composition, and physical properties of permafrost and active layer soils affect their susceptibility to rapid thaw and thermokarst subsidence? Spatial variability in the hydraulic and physical properties of active layer soils influences shallow groundwater flow through cold-desert hydrological systems, which in turn determines how heat, water, solutes, and carbon are moved into and out of polar landscapes. We measured the saturated hydraulic conductivity (k), grain-size distribution, and thermal properties (e.g., diffusivity, D) of >50 soil samples from the McMurdo Dry Valleys (MDV), Antarctica, in order to determine what processes drive soil hydraulic conductivity in a simple, mineral soil-dominated natural hillslope laboratory, and how soil hydrological properties compare to soil thermal properties and landscape-scale processes such as thermokarst erosion (measured via ground-based and airborne imaging and LiDAR). We find that both the hydraulic conductivity and the grain size distribution of soils are organized longitudinally along MDV valley axes. Soils down-valley near the coast have a higher percentage of fine-sized sediments (fine sand, silt, clay) and lower hydraulic conductivities than soils collected up-valley. Soils collected mid-valley have intermediate amounts of fines and conductivity values consistent with a hydrogeologic gradient spanning the valley from high inland to low near the coast. These results suggest that the organization of modern soil properties in Taylor Valley is a relict signature from past glaciations that have deposited tills of decreasing age towards the mouth of the valley, modified by fluvial activity acting over microclimate and geological gradients. Importantly, we show that water-holding soils show a strong, positive feedback between water content and thermal diffusivity, meaning that where low-k, high-D soil properties overlap in terrestrial Antarctic settings, rapid thawing and disruption of ground ice can occur as meltwater advects heat into permafrost-affected soils and accelerates conductive thaw.
2017025425 López, Robin D. (Lawrence Berkeley National Laboratory, Earth and Environmental Sciences, Berkeley, CA); Wu, Yuxin; Ulrich, Craig; Chou, Chunwei Nick; Kneafsey, Timothy J. and McKnight, Catherine. Investigating the link between hydraulic conductivity and soil characteristics of permafrost cores for the next generation ecosystem experiment (NGEE)-Arctic [abstr.]: in Geological Society of America, 2016 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 48(7), Abstract no. 286-2, 2016. Meeting: Geological Society of America, 2016 annual meeting & exposition, Sep. 25-28, 2016, Denver, CO.
The Arctic environment is rich with permafrost. However, as Earth experiences changes in its global temperature, there is a critical concern of permafrost thawing in the Arctic tundra. This could result in the release of vast stores of organic material locked frozen within the permafrost. The research efforts of this group is just one of many components that aims to address the overall goal of developing a predictive model of the Arctic ecosystem in response to climate change, as part of the Next Generation Ecosystem Experiment (NGEE)-Arctic. Specifically, permafrost samples derived from the Arctic at the Barrow Environmental Observatory in northern Alaska are evaluated for various properties, including hydraulic conductivity. Hydraulic conductivity is a fundamental parameter in understanding and predicting movement of water through soils. Additionally, lab analysis of soil yields key information that could possibly be correlated with hydraulic conductivity. One of which is soil particle analysis. Particle analysis is a qualitative and quantitative measurement performed in the field and laboratory, respectively. In the case of this particular research project, a laser diffraction method is utilized to conduct the soil particle analysis. Differences observed in soil analysis amongst samples, can offer indications on a soils ability to retain moisture, organic material concentration, and infiltration rate. The research group aims to develop a reasonable connection interlinking properties of soil particle analysis, hydraulic conductivity, and geomorphic features. Ideally, this ultimately will provide better insight of surface and subsurface water movement that is vital in predicting permafrost thaw. As well, these contributions will assist in developing a predictive model for climate feedback in the Arctic environment.
2017029830 Minsley, Burke J. (U. S. Geological Survey, Crustal Geophysics and Geochemistry Science Center, Denver, CO); Pastick, Neal J.; Wylie, B. K.; Brown, Dana R. N. and Kass, M. Andy. Geophysical evidence for non-uniform permafrost degradation after fire across boreal landscapes [abstr.]: in Geological Society of America, 2016 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 48(7), Abstract no. 310-9, 2016. Meeting: Geological Society of America, 2016 annual meeting & exposition, Sep. 25-28, 2016, Denver, CO.
Fire can be a significant driver of permafrost change in boreal landscapes, altering the availability of soil carbon and nutrients that have important implications for future climate and ecological succession. However, not all landscapes are equally susceptible to fire-induced change. As fire frequency is expected to increase in the high latitudes, methods to understand the vulnerability and resilience of different landscapes to permafrost degradation are needed. We present a combination of multi-scale remote sensing, geophysical, and field observations that reveal details of both near-surface (<1 m) and deeper impacts of fire on permafrost. Along 23 transects that span burned-unburned boundaries in different landscape settings within interior Alaska, subsurface imaging indicates locations where permafrost appears to be resilient to disturbance from fire, areas where warm permafrost conditions exist that may be most vulnerable to future change, and also where permafrost has thawed. High-resolution geophysical data corroborate remote sensing interpretations of near-surface permafrost, and also add new high-fidelity details of spatial heterogeneity that extend from the shallow subsurface to depths of about 10 m. Data collected along each transect include observations of active layer thickness (ALT), organic layer thickness (OLT), plant species cover, electrical resistivity tomography (ERT), and downhole Nuclear Magnetic Resonance (NMR) measurements. Results show that post-fire impacts on permafrost can be variable, and depend on multiple factors such as fire severity, soil texture, and soil moisture.
2017030039 Iskorkina, A. A. (National Research Tomsk Polytechnic University, Institute of Natural Resources, Department of Geophysics, Tomsk, Russian Federation); Isaev, V. I. and Terre, D. A. Assessment of Mesozoic-Kainozoic climate impact on oil-source rock potential (West Siberia): in Problems of geology and subsurface development (Ivanova, G. M., editor), IOP Conference Series. Earth and Environmental Science, 27(1), Paper no. 012023, illus. incl. 5 tables, 9 ref., 2015. Meeting: XIX international scientific symposium in honor of Academician M. A. Usov, April 6-10, 2015, Tomsk, Russian Federation.
Based on paleotemperature modeling, the evaluation of the effect of Neo-Pleistocene permafrost rock thickness on geothermal regime of the Bazhenov deposits has been performed. It has been stated that permafrost about 300 m in thickness must be considered for appropriate reconstruction of geothermal history of source rocks in the southeast areas of West Siberia. This condition is relevant to a consistent consideration of oil-generation phase history and can prevent underestimation (to 25%) of hydrocarbon-in-place resources. Copyright Published under license by IOP Publishing Ltd
2017025429 Fountain, Andrew G. (Portland State University, Geology and Geography, Portland, OR); Levy, Joseph; Obryk, Maciej K.; Gooseff, Michael; Van Horn, Dave; Glennie, Craig; Diaz, Juan Fernandez and Lyons, W. Berry. Dramatic topographic changes in the McMurdo Dry Valleys, Antarctica [abstr.]: in Geological Society of America, 2016 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 48(7), Abstract no. 286-6, 2016. Meeting: Geological Society of America, 2016 annual meeting & exposition, Sep. 25-28, 2016, Denver, CO.
Field observations of coastal and lowland regions in the McMurdo Dry Valleys (MDV) suggest they are on the threshold of rapid topographic change due to thermokarst erosion and subsidence. In contrast, the high elevation upland landscapes in the MDV represent some of the most stable surfaces on Earth. A number of landscapes have undergone dramatic and unprecedented landscape changes over the past decade and the commonality between all changes appears to be sediment on ice acting as a catalyst for melting. To document the magnitude and spatial pattern of these changes we compared a 2001 LiDAR elevation model to one we flew in 2014. Results showed extensive fluvial erosion and deposition. The Garwood River (Garwood Valley) had incised >3 m into massive ice permafrost, smaller streams in Taylor Valley have experienced widespread erosion of down-cutting and/or bank undercutting, and regional buried ice deposits in all coastal valleys have been ablating to form thermokarst ponds and slumps. The glaciers have been thinning in the ablation zone and becoming rougher. We hypothesize that these ice-related changes result from warming soils due to increased solar radiation during the 1990s, a period of decreasing summer air temperatures. The time series of the summer air temperatures and elevated solar radiation have shown no significant trends since. The cause of increasing solar radiation is probably due to increasing atmospheric transmissivity in the years after the eruption of Mt. Pinatubo. The warming soils also warmed the stream waters which enhanced thermal erosion of the permafrost and deposits of buried massive ice. We hypothesize that the trigger for the deep down cutting of the Garwood and other rivers was probably the unusual melt season of 2001/02 when a flood of water eroded the channel bottom close to the massive ice permafrost. Taken together, these changes are probably triggering important responses in fluvial hydrology, geochemistry, and biological community structure and function in this region. Work is underway to investigate these responses. The observed changes do not appear to be linked to climate warming but rather to climate variability. However, the changes do provide a harbinger of what to expect if and when climate warming envelops the McMurdo Dry Valleys.
2017025424 Gooseff, Michael (University of Colorado-Boulder, Institute of Arctic and Alpine Research, Boulder, CO); Godsey, Sarah; Lewkowicz, Antoni G. and Bowden, W. Breck. Recent permaforst degradation in response to a changing Arctic climate; lessons from the North Slope of Alaska [abstr.]: in Geological Society of America, 2016 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 48(7), Abstract no. 286-1, 2016. Meeting: Geological Society of America, 2016 annual meeting & exposition, Sep. 25-28, 2016, Denver, CO.
The changing climate of the Arctic is causing changes to surface energy fluxes, which is in turn causing permafrost to degrade. On the North Slope of Alaska, we have tracked several permafrost degradation features for over 7 years, assessing both impacts to downstream waters and ground temperature regimes. These features include large thaw slumps and deeply incised ice-wedges that have thawed. In their active degradation periods, these features release significant amounts of sediment and nutrients, with direct impacts to receiving waters. Shallow (<3 m) ground temperatures are dynamic during this period, with variable annual means that are highly sensitive to surface conditions. However, after the first couple of years, as features stabilize and vegetation begins to re-grow within them, release of sediment and nutrients drops off substantially, and ground temperatures tend to be a bit more buffered from surface energy balance changes. While these features are remarkable when fresh (and even as they begin to 'recover'), their substantial impacts on the landscape and river networks tend to occur in 'pulses' of a few years, prior to a period of stabilization and re-vegetation that is likely to last beyond a decade.
2017026570 Savichev, O. G. (Tomsk Polytechnic University, Natural Resource Institute, Tomsk, Russian Federation); Matveenko, I. A. and Ivanova, E. V. Conditions of contaminant distribution in the wetland water of western Siberia (the Russian Federation): in All-Russian scientific conference with international participation on Contemporary issues of hydrogeology, engineering geology and hydrogeoecology in Eurasia (Shvartsev, S. L., prefacer), IOP Conference Series. Earth and Environmental Science, 33(1), Paper no. 012023, illus. incl. 1 table, sketch map, 10 ref., March 2016. Meeting: International conference on "Modern problems of hydrology, geological engineering and hydrogeoecology of Eurasia", Nov. 23-27, 2015, Tomsk, Russian Federation.
The models of pollutants' distribution in the wetland waters of Western Siberia (Tomsk Oblast, Russia) have been considered. The models' application allows describing the observed changes in the chemical composition of active layer of wetland waters with satisfactory accuracy. With these models, the most significant impact of sewage discharge on the local wetland water composition is observed in wetland edge area of up to 150-300 m in width. Even in this area it is possible to minimize the impact of sewage discharge on the wetlands provided the concentration in sewage water is 1.14-1.3 time more than the background concentration. Copyright Published under licence by IOP Publishing Ltd.
2017029137 Brandt, Laurie (CPG, DOWL, Montrose, CO). Geotechnical engineering considerations regarding climate change in the intermountain West [abstr.]: in AIPG 53rd national conference; Land of geologic confluences and cultural crossroads (von Gonte, Susan, chairperson; et al.), AIPG Annual Meeting - Program, 53, p. 24-25, 2016. Meeting: AIPG 53rd national conference; Land of geologic confluences and cultural crossroads, Sept. 10-13, 2016, Santa Fe, NM.
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