September 2017 Permafrost Alert
The U.S. Permafrost Association is pleased to announce the availability of an updated searchable database on permafrost-related publications. The American Geosciences Institute, with support from the National Science Foundation, has migrated the previous Cold Regions Bibliography to a new platform. Included are the US Permafrost Association supported Monthly Permafrost Alerts dating back to 2011. The Bibliography is searchable at : www.coldregions.org.
Have a look for your favorite topic, location and/or author. For example, a search using permafrost and Barrow found 146 references dating back to at least 1952 and up to the more recent September 2015 Seventh Canadian Permafrost Conference.
The individual Monthly Permafrost Alerts are found on the US Permafrost Association website : http://www.uspermafrost.org/monthly-alerts.shtml.
Browse by Reference Type:
Serial | Conference | Report
2017081149 Huang, Yuanyuan (University of Oklahoma, Department of Microbiology and Plant Biology, Norman, OK); Jiang, Jiang; Ma, Shuang; Ricciuto, Daniel; Hanson, Paul J. and Luo, Yiqi. Soil thermal dynamics, snow cover, and frozen depth under five temperature treatments in an ombrotrophic bog; constrained forecast with data assimilation: Journal of Geophysical Research: Biogeosciences, 122(8), p. 2046-2063, illus. incl. 1 table, 65 ref., August 2017.
Accurate simulation of soil thermal dynamics is essential for realistic prediction of soil biogeochemical responses to climate change. To facilitate ecological forecasting at the Spruce and Peatland Responses Under Climatic and Environmental change site, we incorporated a soil temperature module into a Terrestrial ECOsystem (TECO) model by accounting for surface energy budget, snow dynamics, and heat transfer among soil layers and during freeze-thaw events. We conditioned TECO with detailed soil temperature and snow depth observations through data assimilation before the model was used for forecasting. The constrained model reproduced variations in observed temperature from different soil layers, the magnitude of snow depth, the timing of snowfall and snowmelt, and the range of frozen depth. The conditioned TECO forecasted probabilistic distributions of soil temperature dynamics in six soil layers, snow, and frozen depths under temperature treatments of +0.0, +2.25, +4.5, +6.75, and +9.0°C. Air warming caused stronger elevation in soil temperature during summer than winter due to winter snow and ice. And soil temperature increased more in shallow soil layers in summer in response to air warming. Whole ecosystem warming (peat + air warmings) generally reduced snow and frozen depths. The accuracy of forecasted snow and frozen depths relied on the precision of weather forcing. Uncertainty is smaller for forecasting soil temperature but large for snow and frozen depths. Timely and effective soil thermal forecast, constrained through data assimilation that combines process-based understanding and detailed observations, provides boundary conditions for better predictions of future biogeochemical cycles. Abstract Copyright (2017), . American Geophysical Union. All Rights Reserved.
2017084521 Camill, Philip (Bowdoin College, Department of Environmental Studies Program and Earth and Oceanographic Science, Brunswick, ME); Umbanhowar, Charles E., Jr.; Geiss, Christoph; Edlund, Mark B.; Hobbs, Will O.; Dupont, Allison; Doyle-Capitman, Catherine and Ramos, Matthew. The initiation and development of small peat-forming ecosystems adjacent to lakes in the north central Canadian low arctic during the Holocene: Journal of Geophysical Research: Biogeosciences, 122(7), p. 1672-1688, illus. incl. 1 table, sketch map, 60 ref., July 2017.
Small peat-forming ecosystems in arctic landscapes may play a significant role in the regional biogeochemistry of high-latitude systems, yet they are understudied compared to arctic uplands and other major peat-forming regions of the North. We present a new data set of 25 radiocarbon-dated permafrost peat cores sampled around eight low arctic lake sites in northern Manitoba (Canada) to examine the timing of peat initiation and controls on peat accumulation throughout the Holocene. We used macrofossils and charcoal to characterize changes in the plant community and fire, and we explored potential impacts of these local factors, as well as regional climatic change, on rates of C accumulation and C stocks. Peat initiation was variable across and within sites, suggesting the influence of local topography, but 56% of the cores initiated after 3000 B.P. Most cores initiated and remained as drier bog hummock communities, with few vegetation transitions in this landscape. C accumulation was relatively slow and did not appear to be correlated with Holocene-scale climatic variability, but C stocks in this landscape were substantial (mean = 45.4 kg C m-2), potentially accounting for 13.2 Pg C in the Taiga Shield ecozone. To the extent that small peat-forming systems are underrepresented in peatland mapping, soil organic carbon (SOC) stocks may be underestimated in arctic regions. Mean fire severity appeared to be negatively correlated with C accumulation rates. Initiation and accumulation of soil C may respond to both regional and local factors, and substantial lowland soil C stocks have the potential for biogeochemical impacts on adjacent aquatic ecosystems. Abstract Copyright (2017), . American Geophysical Union. All Rights Reserved.
2017084528 Chang, Ruiying (Chinese Academy of Sciences, Institute of Mountain Hazards and Environment, Chengdu, China); Wang, Genxu; Yang, Yuanhe and Chen, Xiaopeng. Experimental warming increased soil nitrogen sink in the Tibetan permafrost: Journal of Geophysical Research: Biogeosciences, 122(7), p. 1870-1879, illus. incl. 1 table, 71 ref., July 2017.
In permafrost soil, warming regulates the nitrogen (N) cycle either by stimulating N transformation or by enhancing cryoturbation, the mixture of soil layers due to repeated freeze thaw. Here N isotopic values (d15N) of plants and the soil were investigated in a 7 year warming experiment in a permafrost-affected alpine meadow on the Qinghai-Tibetan Plateau. The results revealed that warming significantly decreased the d15N in the plant (aboveground and belowground parts) and different soil fractions (clay and silt fraction, aggregate, and bulk soil). The decreased soil d15N was associated with an increase in soil N stock due to greater N fixation. The incremental N retention in plants and soil mineral-associated fractions from warming resulted in a decrease in soil inorganic N, which constrains the role of nitrification/denitrification in soil d15N, suggesting a restrained rather than an open N cycle. Furthermore, enhanced cryoturbation under warming, identified by a downward redistribution of 137Cs into deeper layers, promoted N protection from transformation. Overall, the decrease in soil d15N indicated higher rates of N input through fixation relative to N loss through nitrification and denitrification in permafrost-affected ecosystems under warming conditions. Abstract Copyright (2017), . American Geophysical Union. All Rights Reserved.
2017080513 Coles, Anna E. (University of Saskatchewan, School of Environment and Sustainability, Saskatoon, SK, Canada); McConkey, B. G. and McDonnell, J. J. Climate change impacts on hill slope runoff on the Northern Great Plains, 1962-2013: Journal of Hydrology, 550, p. 538-548, illus. incl. 1 table, sketch map, 49 ref., July 2017.
On the Great Plains of North America, water resources are being threatened by climatic shifts. However, a lack of hillslope-scale climate-runoff observations is limiting our ability to understand these impacts. Here, we present a 52-year (1962-2013) dataset (precipitation, temperature, snow cover, soil water content, and runoff) from three 5 ha hillslopes on the seasonally-frozen northern Great Plains. In this region, snowmelt-runoff drives c. 80% of annual runoff and is potentially vulnerable to warming temperatures and changes in precipitation amount and phase. We assessed trends in these climatological and hydrological variables using time series analysis. We found that spring snowmelt-runoff has decreased (on average by 59%) in response to a reduction in winter snowfall (by 18%), but that rainfall-runoff has shown no significant response to a 51% increase in rainfall or shifts to more multi-day rain events. In summer, unfrozen, deep, high-infiltrability soils act as a 'shock absorber' to rainfall, buffering the long-term runoff response to rainfall. Meanwhile, during winter and spring freshet, frozen ground limits soil infiltrability and results in runoff responses that more closely mirror the snowfall and snowmelt trends. These findings are counter to climate-runoff relationships observed at the catchment scale on the northern Great Plains where land drainage alterations dominate. At the hillslope scale, decreasing snowfall, snowmelt-runoff, and spring soil water content is causing agricultural productivity to be increasingly dependent on growing season precipitation, and will likely accentuate the impact of droughts.
2017084524 Khosh, Matthew S. (University of Texas at Austin, Marine Science Institute, Austin, TX); McClelland, James W.; Jacobson, Andrew D.; Douglas, Thomas A.; Barker, Amanda J. and Lehn, Gregory O. Seasonality of dissolved nitrogen from spring melt to fall freezeup in Alaskan Arctic tundra and mountain streams: Journal of Geophysical Research: Biogeosciences, 122(7), p. 1718-1737, illus. incl. 3 tables, sketch map, 113 ref., July 2017.
Predicting the response of dissolved nitrogen export from Arctic watersheds to climate change requires an improved understanding of seasonal nitrogen dynamics. Recent studies of Arctic rivers emphasize the importance of spring thaw as a time when large fluxes of nitrogen are exported from Arctic watersheds, but studies capturing the entire hydrologic year are rare. We examined the temporal variability of dissolved organic nitrogen (DON) and dissolved inorganic nitrogen (DIN) concentrations in six streams/rivers in Arctic Alaska from spring melt to fall freezeup (May through October) in 2009 and 2010. DON concentrations were generally high during snowmelt and declined as runoff decreased. DIN concentrations were low through the spring and summer and increased markedly during the late summer and fall, primarily due to an increase in nitrate. The high DIN concentrations were observed to occur when seasonal soil thaw depths were near maximum extents. Concurrent increases in DIN and DIN-to-chloride ratios suggest that net increases from nitrogen sources contributed to these elevated DIN concentrations. Our stream chemistry data, combined with soil thermistor data, suggest that downward penetration of water into seasonally thawed mineral soils, and reduction in biological nitrogen assimilation relative to remineralization, may increase DIN export from Arctic watersheds during the late summer and fall. While this is part of a natural cycle, improved understanding of seasonal nitrogen dynamics is particularly important now because warmer temperatures in the Arctic are causing earlier spring snowmelt and later fall freezeup in many regions. Abstract Copyright (2017), . American Geophysical Union. All Rights Reserved.
2017080524 Krogh, Sebastian A. (University of Saskatchewan, Centre for Hydrology, Saskatoon, SK, Canada); Pomeroy, John W. and Marsh, Philip. Diagnosis of the hydrology of a small Arctic basin at the tundra-taiga transition using a physically based hydrological model: Journal of Hydrology, 550, p. 685-703, illus. incl. 8 tables, sketch map, 109 ref., July 2017.
A better understanding of cold regions hydrological processes and regimes in transitional environments is critical for predicting future Arctic freshwater fluxes under climate and vegetation change. A physically based hydrological model using the Cold Regions Hydrological Model platform was created for a small Arctic basin in the tundra-taiga transition region. The model represents snow redistribution and sublimation by wind and vegetation, snowmelt energy budget, evapotranspiration, subsurface flow through organic terrain, infiltration to frozen soils, freezing and thawing of soils, permafrost and streamflow routing. The model was used to reconstruct the basin water cycle over 28 years to understand and quantify the mass fluxes controlling its hydrological regime. Model structure and parameters were set from the current understanding of Arctic hydrology, remote sensing, field research in the basin and region, and calibration against streamflow observations. Calibration was restricted to subsurface hydraulic and storage parameters. Multi-objective evaluation of the model using observed streamflow, snow accumulation and ground freeze/thaw state showed adequate simulation. Significant spatial variability in the winter mass fluxes was found between tundra, shrubs and forested sites, particularly due to the substantial blowing snow redistribution and sublimation from the wind-swept upper basin, as well as sublimation of canopy intercepted snow from the forest (about 17% of snowfall). At the basin scale, the model showed that evapotranspiration is the largest loss of water (47%), followed by streamflow (39%) and sublimation (14%). The models streamflow performance sensitivity to a set of parameter was analysed, as well as the mean annual mass balance uncertainty associated with these parameters.
2017084522 Mitzscherling, Julia (German Research Centre for Geosciences, Section 5.3 Geomicrobiology, Potsdam, Germany); Winkel, Matthias; Winterfeld, Maria; Horn, Fabian; Yang, Sizhong; Grigoriev, Mikhail N.; Wagner, Dirk; Overduin, Pier P. and Liebner, Susanne. The development of permafrost bacterial communities under submarine conditions: Journal of Geophysical Research: Biogeosciences, 122(7), p. 1689-1704, illus., 84 ref., July 2017.
Submarine permafrost is more vulnerable to thawing than permafrost on land. Besides increased heat transfer from the ocean water, the penetration of salt lowers the freezing temperature and accelerates permafrost degradation. Microbial communities in thawing permafrost are expected to be stimulated by warming, but how they develop under submarine conditions is completely unknown. We used the unique records of two submarine permafrost cores from the Laptev Sea on the East Siberian Arctic Shelf, inundated about 540 and 2500 years ago, to trace how bacterial communities develop depending on duration of the marine influence and pore water chemistry. Combined with geochemical analysis, we quantified total cell numbers and bacterial gene copies and determined the community structure of bacteria using deep sequencing of the bacterial 16S rRNA gene. We show that submarine permafrost is an extreme habitat for microbial life deep below the seafloor with changing thermal and chemical conditions. Pore water chemistry revealed different pore water units reflecting the degree of marine influence and stages of permafrost thaw. Millennia after inundation by seawater, bacteria stratify into communities in permafrost, marine-affected permafrost, and seabed sediments. In contrast to pore water chemistry, the development of bacterial community structure, diversity, and abundance in submarine permafrost appears site specific, showing that both sedimentation and permafrost thaw histories strongly affect bacteria. Finally, highest microbial abundance was observed in the ice-bonded seawater unaffected but warmed permafrost of the longer inundated core, suggesting that permafrost bacterial communities exposed to submarine conditions start to proliferate millennia after warming. Abstract Copyright (2017), . American Geophysical Union. All Rights Reserved.
2017080496 Wang Genxu (Chinese Academy of Sciences, Institute of Mountain Hazards and Environment, Chengdu, China); Mao Tianxu; Chang Juan; Song Chunlin and Huang Kewei. Processes of runoff generation operating during the spring and autumn seasons in a permafrost catchment on semi-arid plateaus: Journal of Hydrology, 550, p. 307-317, illus. incl. 2 tables, sketch map, 49 ref., July 2017.
There is a lack of knowledge about how to quantify runoff generation and the hydrological processes operating in permafrost catchments on semi-arid plateaus. To understand how freeze-thaw cycles affect runoff generation processes in permafrost catchments, a typical headwater catchment with continuous permafrost on the Tibetan Plateau was measured. A new approach is presented in this study to account for runoff processes on the spring thawing period and autumn freezing period, when runoff generation clearly differs from that of non-permafrost catchments. This approach introduces a soil temperature-based water saturation function and modifies the soil water storage curve with a soil temperature threshold. The results show that surface soil thawing induced saturation excess runoff and subsurface interflow account for approximately 66-86% and 14-34% of total spring runoff, respectively, and the soil temperature significantly affects the runoff generation pattern, the runoff composition and the runoff coefficient with the enlargement of the active layer. The suprapermafrost groundwater discharge decreases exponentially with active layer frozen processes during autumn runoff recession, whereas the ratio of groundwater discharge to total runoff and the direct surface runoff coefficient simultaneously increase. The bidirectional freezing of the active layer controls and changes the autumn runoff processes and runoff composition. The new approach could be used to further develop hydrological models of cold regions dominated by permafrost.
2017084523 Wu Xiaodong (Chinese Academy of Sciences, Northwest Institute of Eco-Environment and Resources, Lanzhou, China); Fang Hongbing; Zhao Yonghua; Smoak, Joseph M.; Li Wangping; Shi Wei; Sheng Yu; Zhao Lin and Ding Yongjian. A conceptual model of the controlling factors of soil organic carbon and nitrogen densities in a permafrost-affected region on the eastern Qinghai-Tibetan Plateau: Journal of Geophysical Research: Biogeosciences, 122(7), p. 1705-1717, illus. incl. 4 tables, sketch maps, 71 ref., July 2017.
Many investigations of the preservation of soil organic carbon (SOC) in permafrost regions have examined roles of geomorphology, pedogenesis, vegetation cover, and permafrost within particular regions. However, it is difficult to disentangle the effects of multiple factors on the SOC in permafrost regions due to the heterogeneity in environmental conditions. Based on data from 73 soil study sites in permafrost regions of the eastern Qinghai-Tibetan Plateau, we developed a simple conceptual model, which relates SOC to topography, vegetation, and pedogenesis. We summarized the dominant factors and their controls on SOC using 31 measured soil physiochemical variables. Soil texture explains approximately 60% of the variations in the SOC stocks for the upper 0-2 m soil. Soil particle size closely correlates to soil moisture, which is an important determinant of SOC. Soil salinity and cations are important factors as well and can explain about 10% of the variations in SOC. The SOC and total nitrogen (TN) stocks for the 1-2 m depths have larger uncertainties than those of upper 1 m soil layer. The vegetation, pH, and bulk density mainly affects SOC and TN stocks for the upper 1 m soil layers, while the active layer thickness and soil particle size have greater influence on SOC and TN stocks for the 1-2 m soils. Our results suggest that the soil particle size is the most important controller of SOC pools, and the stocks of SOC and TN are strongly effected by soil development processes in the permafrost regions of the eastern Qinghai-Tibetan Plateau. Abstract Copyright (2017), . American Geophysical Union. All Rights Reserved.
2017080298 Herndon, Elizabeth (Kent State University, Department of Geology, Kent, OH); AlBashaireh, Amineh; Singer, David; Roy Chowdhury, Taniya; Gu, Baohua and Graham, David. Influence of iron redox cycling on organo-mineral associations in Arctic tundra soil: Geochimica et Cosmochimica Acta, 207, p. 210-231, illus. incl. 4 tables, 107 ref., June 15, 2017. Includes appendices.
Arctic tundra stores large quantities of soil organic matter under varying redox conditions. As the climate warms, these carbon reservoirs are susceptible to increased rates of decomposition and release to the atmosphere as the greenhouse gases carbon dioxide (CO2) and methane (CH4). Geochemical interactions between soil organic matter and minerals influence decomposition in many environments but remain poorly understood in Arctic tundra systems and are not considered in decomposition models. The accumulation of iron (Fe) oxyhydroxides and organo-iron precipitates at redox interfaces may be particularly important for carbon cycling given that ferric iron [Fe(III)] species can enhance decomposition by serving as terminal electron acceptors in anoxic soils or inhibit microbial decomposition by binding organic molecules. Here, we examine chemical properties of solid-phase Fe and organic matter in organic and mineral horizons within the seasonally thawed active layer of Arctic tundra on the North Slope of Alaska. Spectroscopic techniques, including micro-X-ray fluorescence (mXRF) mapping, micro-X-ray absorption near-edge structure (mXANES) spectroscopy, and Fourier transform infrared spectroscopy (FTIR), were coupled with chemical sequential extractions and physical density fractionations to evaluate the spatial distribution and speciation of Fe-bearing phases and associated organic matter in soils. Organic horizons were enriched in poorly crystalline and crystalline iron oxides, and approximately 60% of total Fe stored in organic horizons was calculated to derive from upward translocation from anoxic mineral horizons. Ferrihydrite and goethite were present as coatings on mineral grains and plant debris, and in aggregates with clays and particulate organic matter. Minor amounts of ferrous iron [Fe(II)] were present in iron sulfides (i.e., pyrite and greigite) in mineral horizon soils and iron phosphates (vivianite) in organic horizons. Concentrations of organic carbon in the organic horizons (28 ± 5 wt.% C) were approximately twice the concentrations in the mineral horizons (14 ± 2 wt.% C), and organic matter was dominated by base-extractable and insoluble organics enriched in aromatic and aliphatic moieties. Conversely, water-soluble organic molecules and organics solubilized through acid-dissolution of iron oxides comprised <2% of soil organic C and were consistent with a mixture of alcohols, sugars, and small molecular weight organic acids and aromatics released through decomposition of larger molecules. Integrated over the entire depth of the active layer, soils contained 11 ± 4 kg m-2 low-density, particulate organic C and 19 ± 6 kg m-2 high-density, mineral-associated organic C, indicating that 63 ± 19% of organic C in the active layer was associated with the mineral fraction. We conclude that organic horizons were enriched in poorly crystalline and crystalline iron oxide phases derived from upward translocation of dissolved Fe(II) and Fe(III) from mineral horizons. Precipitation of iron oxides at the redox interface has the potential to contribute to mineral protection of organic matter and increase the residence time of organic carbon in arctic soils. Our results suggest that iron oxides may inhibit organic carbon degradation by binding low-molecular-weight organic compounds, stabilizing soil aggregates, and forming thick coatings around particulate organic matter. Organic matter released through acid-dissolution of iron oxides could represent a small pool of readily-degradable organic molecules temporarily stabilized by sorption to iron oxyhydroxide surfaces. The distribution of iron in organic complexes and inorganic phases throughout the soil column constrains Fe(III) availability to anaerobic iron-reducing microorganisms that oxidize organic matter to produce CO2 and CH4 in these anoxic environments. Future predictions of carbon storage and respiration in the arctic tundra should consider such influences of mineral stabilization under changing redox conditions.
2017080951 Wang Lei (Chinese Academy of Sciences, Institute of Tibetan Plateau Research, Beijing, China); Zhou Jing; Qi Jia; Sun Litao; Yang Kun; Tian Lide; Lin Yanluan; Liu Wenbin; Shrestha, Maheswor; Xue, Yongkang; Koike, Toshio; Ma Yaoming; Li Xiuping; Chen Yingying; Chen, Deliang; Piao Shilong and Lu Hui. Development of a land surface model with coupled snow and frozen soil physics: Water Resources Research, 53(6), p. 5085-5103, illus. incl. 5 tables, 53 ref., June 2017.
Snow and frozen soil are important factors that influence terrestrial water and energy balances through snowpack accumulation and melt and soil freeze-thaw. In this study, a new land surface model (LSM) with coupled snow and frozen soil physics was developed based on a hydrologically improved LSM (HydroSiB2). First, an energy-balance-based three-layer snow model was incorporated into HydroSiB2 (hereafter HydroSiB2-S) to provide an improved description of the internal processes of the snow pack. Second, a universal and simplified soil model was coupled with HydroSiB2-S to depict soil water freezing and thawing (hereafter HydroSiB2-SF). In order to avoid the instability caused by the uncertainty in estimating water phase changes, enthalpy was adopted as a prognostic variable instead of snow/soil temperature in the energy balance equation of the snow/frozen soil module. The newly developed models were then carefully evaluated at two typical sites of the Tibetan Plateau (TP) (one snow covered and the other snow free, both with underlying frozen soil). At the snow-covered site in northeastern TP (DY), HydroSiB2-SF demonstrated significant improvements over HydroSiB2-F (same as HydroSiB2-SF but using the original single-layer snow module of HydroSiB2), showing the importance of snow internal processes in three-layer snow parameterization. At the snow-free site in southwestern TP (Ngari), HydroSiB2-SF reasonably simulated soil water phase changes while HydroSiB2-S did not, indicating the crucial role of frozen soil parameterization in depicting the soil thermal and water dynamics. Finally, HydroSiB2-SF proved to be capable of simulating upward moisture fluxes toward the freezing front from the underlying soil layers in winter. Abstract Copyright (2017), . American Geophysical Union. All Rights Reserved.
2017082550 Siegert, Martin J. (Imperial College London, Grantham Institute and Department of Earth Science and Engineering, London, United Kingdom); Kulessa, Bernd; Bougamont, Marion; Christoffersen, Poul; Key, Kerry; Andersen, Kristoffer R.; Booth, Adam D. and Smith, Andrew M. Antarctic subglacial groundwater; a concept paper on its measurement and potential influence on ice flow: in Exploration of subsurface Antarctica; uncovering past changes and modern processes (Siegert, Martin J., editor; et al.), Special Publication - Geological Society of London, 461, illus. incl. sects., 88 ref., May 25, 2017. (Online First).
Is groundwater abundant in Antarctica and does it modulate ice flow? Answering this question matters because ice streams flow by gliding over a wet substrate of till. Water fed to ice-stream beds thus influences ice-sheet dynamics and, potentially, sea-level rise. It is recognized that both till and the sedimentary basins from which it originates are porous and could host a reservoir of mobile groundwater that interacts with the subglacial interfacial system. According to recent numerical modelling, up to half of all water available for basal lubrication, and time lags between hydrological forcing and ice-sheet response as long as millennia, may have been overlooked in models of ice flow. Here, we review evidence in support of Antarctic groundwater and propose how it can be measured to ascertain the extent to which it modulates ice flow. We present new seismoelectric soundings of subglacial till, and magnetotelluric and transient electromagnetic forward models of subglacial groundwater reservoirs. We demonstrate that multifaceted and integrated geophysical datasets can detect, delineate and quantify the groundwater contents of subglacial sedimentary basins and, potentially, monitor groundwater exchange rates between subglacial till layers. The paper thus describes a new area of glaciological investigation and how it should progress in future.
2017081243 Bosch, Anna (University of Tuebingen, Department of Geosciences, Tubingen, Germany); Schmidt, Karsten; He Jinsheng; Doerfer, Corina and Scholten, Thomas. Potential CO2 emissions from defrosting permafrost soils of the Qinghai-Tibet Plateau under different scenarios of climate change in 2050 and 2070: Catena (Giessen), 149(Part 1), p. 221-231, illus. incl. 5 tables, sketch maps, 90 ref., February 2017.
Permafrost soils store enormous quantities of organic carbon. Especially on the alpine Qinghai-Tibet Plateau, global warming induces strong permafrost thawing, which strengthens the microbial decomposition of organic carbon and the emission of the greenhouse gas carbon dioxide (CO2). Enhanced respiration rates may intensify climate warming in turn, but the magnitude of future CO2 emissions from this data-scarce region in a changing climate remains highly uncertain. Here, we aim at an area-wide estimation of future potential CO2 emissions for the permafrost region on the Qinghai-Tibet Plateau as key region for climate change studies due to its size and sensitiveness. We calculated four potential soil respiration scenarios for 2050 and 2070 each. Using a regression model, results from laboratory experiments and C stock estimations from other studies, we provide an approximation of total potential soil CO2 emissions on a regional scale ranging from 737.90 g CO2 m-2 y-1-4224.77 g CO2 m-2 y-1. Our calculations as first estimate of thawing-induced CO2 emissions (51.23 g CO2 m-2 y-1-3002.82 g CO2 m-2 y-1) from permafrost soils of the Qinghai-Tibet Plateau under global warming appear to be consistent to measurements of C loss from thawing permafrost soils measured within other studies. Thawing-induced soil CO2 emissions from permafrost soils with a organic C content ranging from 2.42 g C kg-1 to 425.23 g C kg-1 increase general soil respiration by at least about one third on average at a temperature of 5 °C. Differences between scenarios remain < 1% and thawing-induced CO2 emissions generally decrease over time comparing 2015, 2050 and 2070. With this spatial approximation at a regional scale, a first area-wide estimate of potential CO2 emissions for 2050 and 2070 from permafrost soils of the Qinghai-Tibet Plateau is provided. This offers support of assessing potential area-specific greenhouse gas emissions and more differentiated climate change models.
2017081236 Hu Guangyin (Northwest Institute of Eco-Environment and Resources, Lanzhou, China); Yu Lupeng; Dong Zhibao; Jin Huijun; Luo Dongliang; Wang Yixuan and Lai Zhongping. Holocene aeolian activity in the headwater region of the Yellow River, northeast Tibet Plateau, China; a first approach by using OSL dating: Catena (Giessen), 149(Part 1), p. 150-157, illus. incl. table, sketch maps, 48 ref., February 2017.
The Headwater Region of the Yellow River (HRYR) is the catchment upstream of Duoshi Gorge, covering an area of 29,588 km2. The HRYR is located in the northeastern Tibet Plateau with an altitude higher than 4000 m above sea level, and is especially sensitive to climate change. Since the late 19th century, the mean annual temperature in Tibet Plateau has increased sharply. As a result of increasing air temperature, a significant number of environmental problems have occurred during the past decades, including aeolian desertification. In recent decades, aeolian desertification has become a severe environmental problem in the Tibet Plateau due to permafrost degradation, because permafrost plays an important role in maintaining the grassland vegetation. With the increase in ground temperature, the aeolian activity in the HRYR is likely to become more serious. However, the history of aeolian activity in the HRYR remains unknown due to a lack of chronological studies. In this study, 15 Optical Stimulated Luminescence (OSL) ages from three typical sections were used to reveal the history of aeolian activities in the HRYR during the Holocene. All of the OSL ages were late Holocene, and the oldest age is 2.13 ± 0.16 ka BP. The relative young OSL ages and deep aeolian sediment indicated very high sedimentation rates in the late Holocene, especially after around 1 ka BP. The intensive aeolian activity and low TOC content indicate a drier climate in the late Holocene. The well-sorted sediments and similar grain size distributions of the three sections imply their similar wind regimes. Based on the evolution history of the Yellow River's headward erosion, it is inferred that little aeolian activity occurred in this region during the early and mid-Holocene.
2017076917 Taylor, Alan E. (Alan E. Taylor Geophysics, North Saanich, BC, Canada); Dallimore, S. R.; Hill, P. R.; Issler, D. R.; Blasco, S. and Wright, F. Numerical model of the geothermal regime on the Beaufort shelf, Arctic Canada since the last interglacial: Journal of Geophysical Research: Earth Surface, 118(4), p. 2365-2379, illus. incl. 2 tables, sketch map, 63 ref., December 2013.
A finite element geothermal model is developed for the outer Mackenzie Delta-Beaufort Sea shelf to predict permafrost evolution since the Last Interglacial ~130-116 kaBP(cal). The purpose is to reconcile sparse observations of the depth and extent of ice-bonded permafrost with sediment properties and the paleoenvironment. Sea level curves determine, as a function of time, areas of the shelf that were subaerially exposed, promoting permafrost aggradation, and areas that were submerged, promoting permafrost degradation. Assuming as a model starting point that a paleoclimate similar to today persisted through the Last Interglacial, permafrost subsequently aggrades in depth and advances seaward from the present shoreline to the shelf/slope bathymetric break by the Last Glacial Maximum (LGM) ~26 kaBP(cal). Modeled permafrost exhibits reduced growth in depth and seaward progression that correlate with early and middle Wisconsin stillstands in sea level. Following the LGM and rise in sea level, offshore permafrost degrades and permafrost base rises ~100 m to its present depth of ~600 m. The offshore limit of modeled ice-bonded permafrost lies at the ~95 m isobath, within 1 km of the bathymetric shelf/slope break. The model replicates features of offshore permafrost body observed seismically and demonstrates that warm outflow from the Mackenzie River depresses the upper surface of offshore permafrost by tens of meters to the 20 m isobath. Although Pleistocene permafrost predated the Wisconsinan, the model demonstrates that the paleoenvironment of the last 125,000 years is sufficient to develop the depth, seaward extent, and principal features of the permafrost body. Abstract Copyright (2013), . American Geophysical Union. All Rights Reserved.
2017078698 Schuur, E. A. G. (University of Florida, Gainesville, FL); Abbott, B. W.; Bowden, W. B.; Brovkin, V.; Camill, P.; Canadell, J. G.; Chanton, J. P.; Chapin, F. S., III; Christensen, T. R.; Ciais, P.; Crosby, Benjamin T.; Czimczik, C. I.; Grosse, G.; Harden, J.; Hayes, D. J.; Hugelius, G.; Jastrow, J. D.; Jones, J. B.; Kleinen, T.; Koven, C. D.; Krinner, G.; Kuhry, P.; Lawrence, D. M.; McGuire, A. D.; Natali, S. M.; O'Donnell, J. A.; Ping, C. L.; Riley, W. J.; Rinke, A.; Romanovsky, V. E.; Sannel, A. B. K.; Schadel, C.; Schaefer, K.; Sky, J.; Subin, Z. M.; Tarnocai, C.; Turetsky, M. R.; Waldrop, M. P.; Walter Anthony, K. M.; Wickland, K. P.; Wilson, C. J. and Zimov, S. A. Expert assessment of vulnerability of permafrost carbon to climate change: Climatic Change, 119(2), p. 359-374, illus., 46 ref., July 2013.
Approximately 1700 Pg of soil carbon (C) are stored in the northern circumpolar permafrost zone, more than twice as much C than in the atmosphere. The overall amount, rate, and form of C released to the atmosphere in a warmer world will influence the strength of the permafrost C feedback to climate change. We used a survey to quantify variability in the perception of the vulnerability of permafrost C to climate change. Experts were asked to provide quantitative estimates of permafrost change in response to four scenarios of warming. For the highest warming scenario (RCP 8.5), experts hypothesized that C release from permafrost zone soils could be 19-45 Pg C by 2040, 162-288 Pg C by 2100, and 381-616 Pg C by 2300 in CO2 equivalent using 100-year CH4 global warming potential (GWP). These values become 50% larger using 20-year CH4 GWP, with a third to a half of expected climate forcing coming from CH4 even though CH4 was only 2.3% of the expected C release. Experts projected that two-thirds of this release could be avoided under the lowest warming scenario (RCP 2.6). These results highlight the potential risk from permafrost thaw and serve to frame a hypothesis about the magnitude of this feedback to climate change. However, the level of emissions proposed here are unlikely to overshadow the impact of fossil fuel burning, which will continue to be the main source of C emissions and climate forcing. Copyright 2013 Springer Science+Business Media Dordrecht and The Author(s)
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2017077612 Schoeffler, Anne Farley (Seton Catholic School, Middle School Science, Hudson, OH). Bringing polar research into the classroom [abstr.]: in Geological Society of America, Northeastern Section, 52nd annual meeting; Geological Society of America, North-Central Section, 51st annual meeting, Abstracts with Programs - Geological Society of America, 49(2), Abstract no. 2-6, 2017. Meeting: Geological Society of America, Northeastern Section, 52nd annual meeting; Geological Society of America, North-Central Section, 51st annual meeting, March 19-21, 2017, Pittsburgh, PA.
PolarTREC is a teacher-researcher partnership designed to increase the gathering and dissemination of knowledge about polar regions. This PolarTREC teacher joined a research team investigating the ecological consequences of climate change in Greenland in 2016. She will share first-hand experience of field methodology, climatic conditions, glacial melt, and ecosystem impacts. She has developed resources to be used in the middle school classroom including student hands-on activities exploring permafrost melt, glacial melt, biodiversity, and range changes of organisms; these are available. Teacher research experience gives teachers the opportunity to develop investigative skills as well as content knowledge, and bringing these into the classroom helps develop student engagement in science and global stewardship. PolarTREC is managed by the Arctic Research Consortium of the United States and funded by the National Science Foundation.
2017080193 Bennett, Georgina L. (Colorado State University, Department of Geosciences, Fort Collins, CO); Roering, Joshua J.; Mackey, Benjamin; Handwerger, Alexander; Schmidt, David A. and Guillod, Benoit P. Historic drought puts the brakes on earthflows in Northern California [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract EP33E-03, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Understanding and predicting landslide response to climate change are significant challenges for Earth scientists, with landslides killing at least 5000 people each year around the world and costing 17% of the annual losses from all natural disasters. Much research on landslide response to climate surrounds their response to extreme rainfall events and melting permafrost, both of which are predicted to increase with climate change. However, landslide response to drought, also predicted to increase, remains largely unexplored. Further research on landslide response to drought as a climatic forcing event is needed to better understand the variable response of landslides, and more generally, geomorphic and hydrologic processes to climate change. California's ongoing drought reached historic proportions in 2015 with widespread consequences on the state's resources. We assessed the drought's impact on 98 deep-seated, slow-moving landslides in Northern California. We used a novel combination of aerial photograph analysis, satellite interferometry, and satellite pixel tracking to measure earthflow velocities spanning 1944-2015 for comparison with the Palmer Drought Severity Index, a proxy for soil moisture and pore pressure. We find that earthflow velocities reached a historical low in the extreme 2012-2015 drought, though their deceleration began at the turn of the century in response to a longer-term moisture deficit. Significantly, our analysis implies depth-dependent sensitivity of earthflows to climate forcing, with thicker earthflows reflecting longer-term climate trends and thinner earthflows exhibiting less systematic velocity variations. These findings have implications for our understanding of mechanical-hydrologic controls on earthflow movement as well as for predicting the response of slow-moving landslides to climate change.
2017080008 Ferguson, J. E. (University of California Irvine, Irvine, CA). Identifying key concepts and student misconceptions related to the cryosphere [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract ED51C-0808, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
The cryosphere is a vital part of the earth system which is undergoing very rapid change as a result of anthropogenic climate change. Melting ice and thawing permafrost have severe consequences for our society from dwindling freshwater supplies to accelerating sea level rise and climate change. It is therefore important that both geoscience majors and also the broader undergraduate population develop a better understanding of the cryosphere. However, in various locations around the world, students rarely encounter ice and snow in their everyday life and many undergraduate students have misconceptions about how the cryosphere functions. In several scientific fields the creation of concept inventories, including the geoscience concept inventory, has been extremely helpful in allowing instructors to assess student learning and the success of new instructional strategies. This project aims to take the first steps towards creating a cryosphere concept inventory by 1) reporting expert opinions about the key concepts related to the cryosphere, and 2) by examining undergraduate student understanding of the cryosphere using open-ended and multiple choice questions in large (»350-450 student) general education classes at the University of California, Irvine.
2017077265 Grosse, G. (Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research, Potsdam, Germany) and Nitze, I. Mapping permafrost change hot-spots with Landsat time-series [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract C42B-08, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Recent and projected future climate warming strongly affects permafrost stability over large parts of the terrestrial Arctic with local, regional and global scale consequences. The monitoring and quantification of permafrost and associated land surface changes in these areas is crucial for the analysis of hydrological and biogeochemical cycles as well as vegetation and ecosystem dynamics. However, detailed knowledge of the spatial distribution and the temporal dynamics of these processes is scarce and likely key locations of permafrost landscape dynamics may remain unnoticed. As part of the ERC funded PETA-CARB and ESA GlobPermafrost projects, we developed an automated processing chain based on data from the entire Landsat archive (excluding MSS) for the detection of permafrost change related processes and hotspots. The automated method enables us to analyze thousands of Landsat scenes, which allows for a multi-scaled spatio-temporal analysis at 30 meter spatial resolution. All necessary processing steps are carried out automatically with minimal user interaction, including data extraction, masking, reprojection, subsetting, data stacking, and calculation of multi-spectral indices. These indices, e.g. Landsat Tasseled Cap and NDVI among others, are used as proxies for land surface conditions, such as vegetation status, moisture or albedo. Finally, a robust trend analysis is applied to each multi-spectral index and each pixel over the entire observation period of up to 30 years from 1985 to 2015, depending on data availability. Large transects of around 2 million km2 across different permafrost types in Siberia and North America have been processed. Permafrost related or influencing landscape dynamics were detected within the trend analysis, including thermokarst lake dynamics, fires, thaw slumps, and coastal dynamics. The produced datasets will be distributed to the community as part of the ERC PETA-CARB and ESA GlobPermafrost projects. Users are encouraged to provide feedback and ground truth data for a continuous improvement of our methodology and datasets, which will lead to a better understanding of the spatial and temporal distribution of changes within the vulnerable permafrost zone.
2017077264 Iwahana, Go (University of Alaska Fairbanks, Fairbanks, AK). InSAR detection and field evidence for thermokarst after a tundra wildfire, using ALOS-PALSAR [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract C42B-04, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Thermokarst is the process of ground subsidence caused by either the thawing of ice-rich permafrost or the melting of massive ground ice. The consequences of permafrost degradation associated with thermokarst for surface ecology, landscape evolution, and hydrological processes have been of great scientific interest and social concern. Part of a tundra patch affected by wildfire in northern Alaska (27.5 km2) was investigated here, using remote sensing and in situ surveys to quantify and understand permafrost thaw dynamics after surface disturbances. A two-pass differential InSAR technique using L-band ALOS-PALSAR has been shown capable of capturing thermokarst subsidence triggered by a tundra fire at a spatial resolution of tens of meters, with supporting evidence from field data and optical satellite images. We have introduced a calibration procedure, comparing burned and unburned areas for InSAR subsidence signals, to remove the noise due to seasonal surface movement. In the first year after the fire, an average subsidence rate of 6.2 cm/year (vertical) was measured. Subsidence in the burned area continued over the following two years, with decreased rates. The mean rate of subsidence observed in our interferograms (from 24 July 2008 to 14 September 2010) was 3.3 cm/year, a value comparable to that estimated from field surveys at two plots on average (2.2 cm/year) for the six years after the fire. These results suggest that this InSAR-measured ground subsidence is caused by the development of thermokarst, a thawing process supported by surface change observations from high-resolution optical images and in situ ground level surveys.
2017077266 Kaeaeb, Andreas (University of Oslo, Department of Geosciences, Oslo, Norway); Altena, Bas and Mascaro, Joseph. Micro-satellite constellations for monitoring cryospheric processes and related natural hazards [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract C43D-01, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Currently, several micro-satellite constellations for earth-observation are planned or under build-up. Here, we assess the potential of the well-advanced Planet satellite constellation for investigating cryospheric processes. In its final stage, the Planet constellation will consist of ~150 free-flying micro-satellites in near-polar and ISS orbits. The instruments carry RGB+NIR frame cameras that image the Earth surface in nadir direction with resolutions of 3-5 m, covering ~20 ´ 13 km per image. In its final set-up, the constellation will be able to image the (almost) entire land surface at least once per day, under the limitation of cloud cover. Here, we explore new possibilities for insight into cryospheric processes that this very high repeat cycle combined with high image resolution offer. Based on repeat Planet imagery we derive repeat glacier velocity fields for example glaciers in the northern and southern hemispheres. We find it especially useful to monitor the ice velocities near calving fronts and simultaneously detect changes of the front, pointing to calving events. We also explore deformation fields over creeping mountain permafrost, so-called rockglaciers. As a second, very promising cryospheric application we suggest monitoring of glacier and permafrost related natural hazards. In cases such as temporary lakes, lake outbursts, landslides, rock avalanches, visual information over remote areas and at high frequencies are crucial for hazard assessment, early warning or disaster management. Based on several examples, we demonstrate that massive micro-satellite constellations such Planet's are exactly able to provide this type of information. As a third promising example, we show how such high-repeat optical satellite data are useful to monitor river ice and related jams and flooding. At certain latitudes, the repeat frequency of the data is even high enough to track river ice floes and thus water velocities.
2017077308 Kuznetsova, Elena (Norwegian University of Science and Technology, Trondheim, Norway). Thermal properties and unfrozen water content of frozen volcanic ash as a modelling input parameters in mountainous volcanic areas [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract C53B-0706, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Volcanic eruptions are one of the major causes of the burial of ice and snow in volcanic areas. This has been demonstrated on volcanoes, e.g. in Iceland, Russia, USA and Chile, where the combination of a permafrost-favorable climate and a thin layer of tephra is sufficient to reduce the sub-tephra layer snow ablation substantially, even to zero, causing ground ice formation and permafrost aggradation. Many numerical models that have been used to investigate and predict the evolution of cold regions as the result of climatic changes are lacking the accurate data of the thermal properties-thermal conductivity, heat capacity, thermal diffusivity-of soils or debris layers involved. The angular shape of the fragments that make up ash and scoria makes it inappropriate to apply existing models to estimate bulk thermal conductivity. The lack of experimental data on the thermal conductivity of volcanic deposits will hinder the development of realistic models. The decreasing thermal conductivity of volcanic ash in the frozen state is associated with the development and presence of unfrozen water films that may have a direct mechanical impact on the movement or slippage between ice and particle, and thus, change the stress transfer. This becomes particularly significant during periods of climate change when enhanced temperatures and associated melting could weaken polythermal glaciers and affect areas with warm and discontinuous permafrost, and induce ice or land movements, perhaps on a catastrophic scale. In the presentation, we will summarize existing data regarding: (i) the thermal properties and unfrozen water content in frozen volcanic ash and cinder, (ii) the effects of cold temperatures on weathering processes of volcanic glass, (iii) the relationship between the mineralogy of frozen volcanic deposits and their thermal properties -and then discusses their significance in relation to the numerical modelling of glaciers and permafrost's thermal behavior.
2017077310 Mithan, H. T. (Cardiff University, Cardiff, United Kingdom); Hales, T. C.; Cleall, P. and Constantine, J. A. Regional scale classification of landforms and understanding their surface processes using digital elevation model-derived thematic maps in Arctic landscapes [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract C53B-0710, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
With the onset of global warming and the subsequent thawing of permafrost, the Arctic is set to see a substantial change in the occurrence of surface processes. In permafrost and periglacial regions our current understanding of landform process, morphology, and landform interaction with climate has come from local empirical studies. However, there are few studies which have attempted to automate the mapping of landform processes and to understand their spatial distribution at a regional scale. The aims of this research are to demonstrate (1) the efficacy of using generalised linear models (GLM) in classifying an Arctic landscape into landform types, using only the characteristic surface features (geomorphometric parameters) of the landforms. (2) Quantify the extent of landform processes in the Arctic. (3) Understand how geomorphometric parameters can help to explain the processes controlling the formation of Arctic landforms, at a regional scale. To train the GLM, nine landform types were mapped from a 400 km2 study site in the glaciated valley of Adventdalen, Svalbard. Each landform type was mapped and digitised using a combination of satellite imagery and a geomorphological map. Eight geomorphometric parameters were derived for each landform type using a 10 m spatial resolution digital elevation model (DEM). For each landform type the classifier was trained on 70% and tested on the other 30%. Selected landscapes in Svalbard and Alaska were classified using the trained GLM. The highest accuracy scores for the GLM were achieved using a combination of three geomorphometric parameters: surface roughness, slope gradient, and relative local relief. These results provide an insight into the possible mechanisms driving the formation of Arctic landforms and demonstrate the applicability of the model for use in slope instability studies and landscape classification in other Arctic regions.
2017077272 Mohammed, Aaron (University of Calgary, Calgary, AB, Canada); LeBlanc, Freda; Cey, Edwin E. and Hayashi, Masaki. Vadose zone dynamics governing snowmelt infiltration and groundwater recharge in a seasonally frozen, semi-arid landscape [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract C51D-0687, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Snowmelt infiltration and vadose zone fluxes in seasonally frozen soils are strongly affected by meteorological and soil moisture dynamics occurring during the preceding fall and winter, and complex processes controlling soil hydraulic and thermal regimes. In order to predict their effects on hydrologic processes such as run-off generation, groundwater recharge and plant-water availability in cold regions, an improved understanding of the mechanisms governing coupled water and heat fluxes in the unsaturated zone is needed. Field and laboratory studies were conducted to investigate snowmelt infiltration and groundwater recharge through partially frozen ground over a range of climate and soil conditions in the Canadian Prairies. Meteorological and subsurface field measurements at three sites were combined with laboratory infiltration experiments on frozen undisturbed soil-columns to provide insights into the hydraulic and thermal processes governing water movement. Analysis reveals that antecedent moisture content and thermal profiles both strongly affect subsurface dynamics during infiltration of snowmelt. Preferential flow is also a critical parameter, as both thermal and hydraulic responses were observed at depth prior to complete ground thaw in the field; as well as drainage outflow from the frozen soil column experiments under certain conditions. Results indicate that both diffuse (matrix) and preferential (macropore) flow play significant roles in the infiltration and redistribution of snowmelt water under frozen soil conditions, and shallow groundwater recharge. This study highlights the critical subsurface factors and processes that control infiltration and groundwater recharge in these seasonally frozen landscapes.
2017079890 Overeem, Irina (University of Colorado at Boulder, Boulder, CO); Jafarov, Elchin E.; Piper, Mark and Schaefer, Kevin M. Development of a permafrost modeling cyberinfrastructure [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract ED13C-0944, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Permafrost is seen as an essential Arctic climate indicator, and feedback of thawing permafrost to the global climate system through the impacts on the global carbon cycle remain an important research topic. Observations can assess the current state of permafrost, but models are eventually essential to make predictions of future permafrost extent. The purpose of our project, which we call PermaModel, is to develop an easy-to-access and comprehensive cyberinfrastructure aimed at promoting and improving permafrost modeling. The PermaModel Integrated Modeling Toolbox (IMT) includes three permafrost models of increasing complexity. The IMT will be housed within the existing cyberinfrastructure of the Community Surface Dynamics Modeling System (CSDMS), and made publically accessible through the CSDMS Web Modeling Tool (WMT). The WMT will provide easy online access to students, scientists, and stakeholders who want to use permafrost models, but lack the expertise. We plan to include multiple sets of sample inputs, representing a variety of conditions and locations, to enable immediate use of the IMT. We present here the first permafrost model, which is envisioned to be the most suitable for teaching purposes. The model promotes understanding of a 1D heat equation and permafrost active layer dynamics under monthly temperature/climate drivers in an online environment. Modeling labs are presented through the CSDMS Educational Repository and we solicit feedback from faculty for further design of these resources.
2017077274 Painter, Scott L. (Oak Ridge National Laboratory, Oak Ridge, TN); Coon, Ethan; Jan, Ahmed; Moulton, John D.; Thornton, Peter E. and Wilson, Cathy J. Future needs and strategies for coupled permafrost and terrestrial hydrology simulations [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract C51E-05, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Permafrost degradation in a warming climate has the potential to adversely affect Arctic infrastructure and produce carbon and energy feedbacks to the atmosphere. The need to understand those potential impacts and feedbacks has prompted recent efforts to develop integrated surface/subsurface thermal hydrology simulation capability for permafrost-affected regions. We will summarize the current state and future needs for physically based permafrost thermal hydrology simulators. Four priority needs beyond the current state of the art have been identified: capability to represent dynamic topography caused by melting of massive ground ice, improved numerical performance of physically based simulators, approaches for representing effects of subgrid variability in regional to pan-Arctic scale simulations, and representation of thermal effects of vegetation changes. Strategies and ongoing efforts to implement the needed capability will also be described. This work was supported by the Next Generation Ecosystem Experiment (NGEE-Arctic) project, and the Interoperable Design of Extreme-scale Application Software (IDEAS) Project. NGEE-Arctic is supported by the Office of Biological and Environmental Research in the DOE Office of Science.
2017080219 Silhan, Karel. Recent increase in debris flow activity in the Tatras Mountains; results of high-mountain environmental changes? [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract EP41A-0893, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Debris flows are very frequent geomorphic agents that form the relief of the High Tatras Mountains. The knowledge of their history is based on lichenometric dating, historical orthophotos and incomplete archival records. Nevertheless, complete chronologies of debris flows at an annual resolution for the Tatras Mountains have not yet been reconstructed. Accordingly, dendrogeomorphic research in the southern region of the mountains (the Great Cold Valley and Small Cold Valley) was undertaken to reconstruct regional year-to-year chronologies of debris flows, which would present unique perspectives on the debris flow activity. A total of 474 scars on the stems and branches of 414 P. mugo were dated with seasonal precision (the best tool for distinguishing debris flow scars from snow avalanche scars) in 12 debris flow tracks. 22 debris flows over the last circa 30 years (the valid chronological range) in six event years were reconstructed. A significant increase in debris flow activity (verified using historical orthophotos) has occurred since AD 2007 (21 of 22 events occurred during the last decade). Two basic spatial patterns of debris flow activity were identified: regional events with at least five debris flows in one or both valleys and local events with a maximum of two debris flows per year. Based on reports by several authors, increases in extreme precipitation events during the last decade have been observed, but debris flows have not occurred even during the most extreme precipitation events in the study area. Preparatory factors must play an important role at this stage. A significant increase in summer and autumn temperatures at the turn of the 21st century has been reported in the High Tatras Mountains. This could accelerate (dis)continuous permafrost thawing in the source zones, increase the amount of material for the next transport and influence the increase in debris flow activity.
2017077267 Steiner, Nicholas (City College of New York, New York, NY); McDonald, Kyle C.; Podest, Erika.; Dinardo, Steven J. and Miller, Charles E. Characterization of surface properties over permafrost soils using a high resolution mid-infrared camera as part of the Carbon in the Arctic Vulnerability Experiment (CARVE) [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract C43D-06, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Freeze/thaw and hydrologic cycling have important influence over surface processes in Arctic ecosystems and in Arctic carbon cycling. The seasonal freezing and thawing of soils bracket negative and positive modes of CO2 and CH4 flux of the bulk landscape. Hydrologic processes, such as seasonal inundation of thawed tundra create a complex microtopography where greenhouse-gas sources and sinks occur over short distances. Because of a high spatial variability hydrologic features must be mapped at fine resolution. These mappings can then be compared to local and regional scale observations of surface conditions, such as temperature and freeze/thaw state, to create better estimates of these important surface fields. The Carbon in the Arctic Vulnerability Experiment (CARVE) monitors carbon gas cycling in Alaskan using aircraft-deployed gas sampling instruments along with remote sensing observations of the land surface condition. A nadir-pointed, forward looking infrared (FLIR) imager mounted on the CARVE air-craft is used to measure upwelling mid-infrared spectral radiance at 3-5 microns. The FLIR instrument was operated during the spring, summer and fall seasons, 2013 through 2015. The instantaneous field of view (IFOV) of the FLIR instrument allows for a sub-meter resolution from a height of 500 m. High resolution data products allows for the discrimination of individual landscape components such as soil, vegetation and surface water features in the image footprint. We assess the effectiveness of the FLIR thermal images in monitoring thawing and inundation processes at very high resolutions. Analyses of FLIR datasets over focused study areas emphasizing exploration of the FLIR dataset utility for detailed land surface characterization as related to surface moisture and temperature. Emphasis is given to the Barrow CMDL station site and employ the tram-based data collections there. We will also examine potential at other high latitude sites of interest, e.g. Atqasuk, Ivotuk Alaska and tundra polygon sites under study by collaborators at UT Austin. The combination of high resolution temperature observations with associated estimates of temperature from other instruments can be used to discriminate hydrologic from temperature features in the mid-infrared to produce a high-resolution hydrology product.
2017077312 Wang, Kang (University of Colorado at Boulder, Institute of Arctic and Alpine Research, Boulder, CO); Jafarov, Elchin E.; Schaefer, Kevin M.; Clow, Gary D.; Piper, Mark; Stewart, Scott; Overeem, Irina and Cyrus, Jason. Interactive modeling of permafrost in Alaska [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract C53B-0716, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
Permafrost distribution and evolution are critically important for scientists, engineers, policy makers, indigenous communities, and the general public. There is an urgent need to investigate permafrost dynamics via modeling using emerging new data products. However, the availability of such models to the community of permafrost scientists is quite limited. We developed an online modeling tool that provides an easy access to several permafrost models. The tool is based on the Community Surface Dynamics Modeling System Modeling (CSDMS) Framework platform. We employed one of the online permafrost models to study permafrost distribution and dynamics in Alaska. The model was forced by using ERA-Interim dataset with a spatial resolution of 0.125´0.125°, including air temperature, snow depth, snow density, and volumetric soil water content. We provide a general parameterization of soil thermal parameters based on soil textures. We validated modeled active layer thickness (ALT) using observations of ~15 years (2001-2015) from more than 40 CALM sites across Alaska. Results show a good agreement with observations. We quantified model uncertainty using Monte Carlo sampling method on parameters of soil and snow. Using near-surface temperature and precipitation data from the Coupled Model Intercomparison ProjectPhase 5 (CMIP5), our results indicate a wide permafrost degradation in Alaska over next 40 to 50 years.
2017080199 Ward, Melissa Karine (McGill University, Montreal, QC, Canada) and Pollard, Wayne H. Monitoring thermokarst activity and landscape change in the Eureka Sound Lowlands, Ellesmere Island, Nunavut [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract EP41A-0901, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
The Eureka Sound Lowlands is an area underlain with over 500 m of ice-rich permafrost largely composed of massive ground ice and ice wedge polygons with a thin active layer of a mean thickness of 57cm. The region has a polar desert climate, with a mean annual air temperature of -19°C, and approximately 67mm of annual precipitation (falling mostly as snow). The area has an Environment Canada Weather Station (located at Eureka at 79°59'N, 85°56'W) that has been conducting daily meteorological measurements since it was founded in 1947. The area is sensitive to increasing summer temperatures as observed during the summer of 2012: as one of the warmest summer on record, there was a three-fold increase in thermokarst (collapse of the land surface from melting ground ice) with the accelerated collapse of ice wedge polygon troughs and widespread development of retrogressive thaw slumps. This study monitors thermokarst activity within the area using air photos from 1959, 1974 and 1982, satellite imagery (WorldView2) from 2009 and 2012, and annual air surveys (since 1989). Thermokarst activity between 2013 and 2016 has been monitored in the field using a differential GPS (Global Positioning System) to survey headwall locations of retrogressive thaw slumps. The purpose of this study is to provide a detailed baseline of landscape processes to compare future landscape changes resulting from thermokarst in the area.
2017083959 West, Nicole (Central Michigan University, Mount Pleasant, MI); Kirby, Eric; Nyblade, Andrew and Brantley, Susan L. Microclimate controls on the evolution of critical zone architecture in the Susquehanna Shale Hills Critical Zone Observatory [abstr.]: in AGU 2016 fall meeting, American Geophysical Union Fall Meeting, 2016, Abstract EP41F-04, December 2016. Meeting: American Geophysical Union 2016 fall meeting, Dec. 12-16, 2016, San Francisco, CA.
The functioning and structure of the critical zone is largely controlled by the formation of regolith - the physically and chemically altered material formed from in situ parent bedrock. Therefore, understanding how regolith production and transport respond to perturbations in climate and/or tectonic forcing remains a first-order question in critical zone science. At the Susquehanna Shale Hills Critical Zone Observatory (SSHO), high resolution LiDAR-derived topographic data and depths to hand auger refusal reveal a systematic asymmetry in hillslope gradient and mobile regolith thicknesses; both are greater on north-facing hillslopes. Hydrologic and geochemical studies of at the SSHO also suggest asymmetric sediment transport, fluid flow, and mineral weathering with respect to hillslope aspect. Here, we combine shallow seismic surveys completed along 4 hillslope transects (2 north-facing and 2-south facing), 2 ridgetops transects, and subsurface observations in boreholes to investigate the role of climate in inducing fracturing and priming the development of the observed asymmetry. Comparisons of shallow p-wave velocities with borehole and pit observations suggest the presence of three distinct layers at SSHO: 1) a deep, high velocity layer that is consistent with largely unweathered shale bedrock immediately overlain by 2) an intermediate velocity layer that is consistent with fractured and chemically altered bedrock, and 3) a shallow, slow velocity layer that is consistent with mobile material or shallow soil. Shallow p-wave velocity profiles suggest differences in thickness for both the mobile and immobile regolith material with respect to aspect. Patterns of p-wave velocities with depth are consistent with patterns of fracture densities observed in boreholes and with predictive cracking intensity models related to frost action. Similarly, p-wave velocity profiles correspond with chemical depletion profiles measured in the SSHO subsurface. These data suggest that the feedbacks between chemical weathering and the physical structure of the critical zone at SSHO may be driven by microclimate asymmetry over geologic time.
2017082402 Paull, C. K. (Monterey Bay Aquarium Research Institute, Moss Landing, CA); Dallimore, S. R.; Gwiazda, R.; Caress, D. W.; Lundsten, E.; Anderson, K.; Riedel, M. and Melling, H. Submarine permafrost dynamics along the Arctic Shelf edge [abstr.]: in 35th international geological congress; abstracts, International Geological Congress, Abstracts = Congrès Géologique International, Résumés, 35, Abstract 218, 2016. Meeting: 35th international geological congress, Aug. 27-Sept. 4, 2016, Cape Town, South Africa.
Recent exploration in the Canadian Beaufort Sea offshore of the Tuktoyaktuk Peninsula has revealed a remarkable coalescence of seafloor morphologic features (pingos, pockmarks, slope parallel ridges, and slide scars), which form a band rimming the shelf edge and upper slope. Detailed investigations utilizing a Autonomous Underwater Vehicle (AUV) to provide 1-m grid bathymetric and Chirp profile, supported by sediment cores and Remotely Operated Vehicle observations, have been made to determine the origins of these features. We infer the concentrated band of features to be related to on-going degradation of relict permafrost under the shelf, the expulsion of the released waters, and the formation of ground ice within the near seafloor sediments. These all have geohazard implications, which may be unique to the Arctic setting. A distinctive seafloor morphology occurs along a ~95 km long stretch of the shelf edge in the Beaufort Sea within a band between 100 and 200 m water depths characterized by circular topographic features (similar to Pingos), that are up to 10 m high and ~50 in diameter, occur in places at a density of ~6 per km2. Circular and crescent shaped topographic depressions (similar to Pockmarks), which are up to 20 m deep, occur at a density of ~1 per km2, within this band. Between these topographic highs and ridges the upper layers contain laterally continuous reflector packages that are similar to those that occur below 200 m water depths, but with variable dips and some even dipping to the southeast back into the regional slope. To the west of this band there is an extensive area of disturbed topography approximately 24 km wide which is made up of several large coalesced landslide features with headwall scarp frequently occurring along the ~150 m contour. These topographic features are developed within Holocene sediments, indicating they formed within the submarine environment. Pore waters sampled in 20 sediment cores taken from 90 to 220 m water depths in this area characteristically freshen with sub-bottom depth, indicating the shelf edge and upper slope associated with this dynamic seafloor environment are bathed in brackish waters. Two unusual environmental factors pre-condition the sediment dynamics, which are unique to Arctic continental margin settings. First, during the sealevel lowstand associated with the last glaciation the exposed shelf experienced ~-20°C mean annual surface temperatures, which resulted in substantial permafrost formation. The postglacial marine transgression imposed a large thermal change as the mean annual sea bottom temperatures are =-1.8°C. This thermal disturbance is still propagating into the subsurface, stimulating the decomposition of both terrestrial permafrost and gas hydrate at depth, which liberates water and methane. Models and observations indicate some areas of the Beaufort Shelf are still underlain by a >600 m thick wedge of relict ice-bonded permafrost and methane hydrate down to >1000 m depths. This wedge of relict permafrost is inferred to extend out to the glacial shelf edge (~120 m) and is coincident with the distinctive topography. Second, the bottom seawater temperatures that imping on the seafloor at the shelf edge in the Beaufort Sea are <-1.4°C, cold enough to refreeze brackish pore water within near seafloor sediments. Buoyant brackish ground water supplied from the base of decomposing relict permafrost is hypothesized to migrate along the base of the relict permafrost, to emerge at the shelf edge and refreeze when it encounters the colder seafloor. Sediment deformation caused by intra-sediment ice growth has uplifted the seafloor and created numerous pingos and deformation ridges. Deformation is also enhanced by settlement following thaw consolidation along the outer edge of the decomposing relict permafrost, producing the pockmark depressions. The dynamics of ice formation and decomposition within the near seafloor sediments collectively weaken the sediments within this zone leaving them prone to failure along the edge of the decaying relict permafrost wedge.
2017079428 Remy, P. P. (Université de Lorraine, Laboratory of Physical Chemistry and Microbiology for the Environment, Villers-les-Nancy, France); Lanceleur, Laurent; Billard, P.; Schäfer, J. and Jorand, F. P. A. Contribution of microbial compartments (biofilms, suspended matters, surface sediments) to monomethylmercury formation in subarctic thermokarst (Nunavik, Quebec) and temperate (Lorraine, France) ponds [abstr.]: in Goldschmidt abstracts 2016, V.M. Goldschmidt Conference - Program and Abstracts, 26, p. 2610, 2016. Meeting: Goldschmidt 2016, June 26-July 1, 2016, Yokohama, Japan.
2017079561 Sato, H. (Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan); Kobayashi, H.; Iwahana, G. and Ohta, T. Endurance of larch forest in eastern Siberia under warming trends [abstr.]: in Goldschmidt abstracts 2016, V.M. Goldschmidt Conference - Program and Abstracts, 26, p. 2743, 2016. Meeting: Goldschmidt 2016, June 26-July 1, 2016, Yokohama, Japan.
2017082140 Steele, Liam J. (Open University, Department of Physical Sciences, Milton Keynes, United Kingdom); Balme, M. R. and Lewis, S. R. Regolith-atmosphere water vapour interaction at Gale Crater: in 47th lunar and planetary science conference, Abstracts of Papers Submitted to the Lunar and Planetary Science Conference, 47, Abstract no. 1944, illus. incl. sketch maps, 9 ref., 2016. Meeting: 47th lunar and planetary science conference, March 21-25, 2016, Woodlands, TX.
2017082007 Kolaczek, Piotr (Adam Mickiewicz University, Department of Biogeography and Palaeoecology, Poznan, Poland); Galka, Mariusz; Karpinska-Kolaczek, Monika and Lutynska, Monika. Late pleniglacial and late glacial lake-mire transformations in south-eastern Poland reflected in aquatic and wetland vegetation changes: in Climate change and impacts between 8,000 and 60,000 years ago in Central and Eastern Europe (Persoiu, Aurel, editor; et al.), Quaternary International, 388, p. 39-50, illus. incl. strat. cols., 2 tables, sketch map, 117 ref., November 19, 2015. Meeting: INTIMATE workshop on Terrestrial records from central Eastern Europe for the last glacial-interglacial transition, March 7-9, 2013, Cluj Napoca, Romania.
This paper presents reconstruction of lake/mire vegetation changes recorded in a continuous profile, which spans the Late Pleniglacial and Late Glacial in south-eastern Poland. This is done on the basis of pollen, non-pollen palynomorphs (NPPs), plant macrofossils and diatom evidence. Initially, a small eutrophic lake, which originated and developed through permafrost thawing, existed at the site from ca. 14,910 cal. BP. The lake was characterized by mass algae blooms and wide taxonomic diversity of Potamogeton representatives. The succession of submersed macrophytes started with the appearance of Characeae and ranged from communities composed of taxa preferring alkaline conditions and the thin organic layer at the bottom, such as Potamogeton filiformis and Potamogeton praelongus, to those requiring alkaline-neutral waters with a thick organic layer (e.g. Potamogeton alpinus, Potamogeton friesii, Potamogeton obtusifolius and Potamogeton pectinatus). Despite the alkaline pH of water in the lake, there were also suitable niches for Nuphar pumila, a taxon associated with acidic waters. About 13,730 cal. BP a rich fen developed within the lake basin where Carex was prevalent, with more oligotrophic patches being occupied by Sphagnum mosses. The water table of this mire fluctuated, which is visible in the irregular occurrences of NPPs suited to an aquatic environment. The local vegetation points to slightly alkaline conditions on the fen. An eutrophic water body reappeared ca. 12,700 cal. BP and was functioning at least until ca. 11,620 cal. BP. This alteration of palaeoecosystem created niches for Ranunculus sceleratus in the shoreline section of the water body. The algae content and Potamogeton diversity was significantly smaller than in the water body that had existed there during the Late Pleniglacial and early Late Glacial. The succession of submersed macrophytes was the reverse of that of the initial water body. Taxa preferring more neutral-acidic conditions, such as P. alpinus, appeared at the onset of the renewed lake. Together with the accumulation of a layer of calcareous-detritus gyttja there was the spread of more 'alkaline' taxa, such as P. pectinatus and Myriophyllum spicatum. The present study revealed a lack of diatoms in the deposits along the entire length of the profile. In the case of peat section it stems from limited niches for their occurrence in fen habitats and their consequent low concentrations in peat deposits. However, the problem of the diatoms' absence in lacustrine sediments remains unsolved. Abstract Copyright (2015) Elsevier, B.V.
2017082012 Starkel, Leszek (Polish Academy of Sciences, Department of Geomorphology and Hydrology of Mountains and Uplands, Cracow, Poland); Michczynska, Danuta J.; Gebica, Piotr; Kiss, Timea; Panin, Andrei and Persoiu, Ioana. Climatic fluctuations reflected in the evolution of fluvial systems of central-Eastern Europe (60-8 ka cal BP): in Climate change and impacts between 8,000 and 60,000 years ago in Central and Eastern Europe (Persoiu, Aurel, editor; et al.), Quaternary International, 388, p. 97-118, illus. incl. sects., geol. sketch maps, 160 ref., November 19, 2015. Meeting: INTIMATE workshop on Terrestrial records from central Eastern Europe for the last glacial-interglacial transition, March 7-9, 2013, Cluj Napoca, Romania.
In general, the evolution of fluvial systems in Central-Eastern Europe reflects the main phases of climatic changes during the period of 60-8 ka cal BP registered in Greenland ice cores and their isotopic 18O curves. The Greenland isotope curve shows many more wiggles and stages than the fluvial record of the same time, especially during the Interpleniglacial phase. In Central-Eastern Europe, we observe several deviations from those climatic trends, connected with different factors, among which are the long distance of the region from the Atlantic Ocean and an increase in continentality. At times, this region was occupied by permafrost although the coexisting warm summers during a part of the studied period enabled the presence of a forest cover. These factors together controlled the specific features of the fluvial regime and sediment load reflected in alternating trends to erosion or aggradation and from meandering to braiding. The permafrost influenced snowmelt floods and tendency to braiding. The dense vegetation (with trees) reduced the supply of sediments and stabilized the meandering channels. Very distinct changes occurred in the river valleys that drain the mountains, where ceaseless fluctuations of vegetation vertical zones were present, especially during the unstable Interpleniglacial when the supply of load from the higher vegetation zones was increased. This system, controlled by the climate and plant vegetation, was modified by other factors including tectonics, wind activity during dry periods, blocking of valleys by ice sheets, meltwater supply, and sea level fluctuations of two reservoirs. Abstract Copyright (2015) Elsevier, B.V.
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2017081044 Genet, Hélène (University of Alaska, Fairbanks, AK); He, Yujie; McGuire, A. David; Zhuang, Qianlai; Zhang, Yujin; Biles, Frances E.; D'Amore, David V.; Zhou, Xiaoping and Johnson, Kristopher D. Terrestrial carbon modeling; baseline and projections in upland ecosystems: in Baseline and projected future carbon storage and greenhouse-gas fluxes in ecosystems of Alaska (Zhu, Zhiliang, editor; et al.), U. S. Geological Survey Professional Paper, Rep. No. P 1826, p. 105-132, illus. incl. 11 tables, sketch maps, 82 ref., 2016.
2017081040 McGuire, A. David (U. S. Geological Survey, Fairbanks, AK); Rupp, T. Scott; Kurkowski, Tom and Stackpoole, Sarah. Baseline and projected future carbon storage and greenhouse-gas fluxes in ecosystems of Alaska; introduction: in Baseline and projected future carbon storage and greenhouse-gas fluxes in ecosystems of Alaska (Zhu, Zhiliang, editor; et al.), U. S. Geological Survey Professional Paper, Rep. No. P 1826, p. 5-16, illus. incl. sketch maps, 54 ref., 2016.
2017081042 Wylie, Bruce K. (U. S. Geolgoical Survey, Sioux Falls, SD); Pastick, Neal J.; Johnson, Kristopher D.; Bliss, Norman and Genet, Hélène. Soil carbon and permafrost estimates and susceptibility to climate change in Alaska: in Baseline and projected future carbon storage and greenhouse-gas fluxes in ecosystems of Alaska (Zhu, Zhiliang, editor; et al.), U. S. Geological Survey Professional Paper, Rep. No. P 1826, p. 53-76, illus. incl. 6 tables, sketch maps, 61 ref., 2016.
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