2018039700 Gao Tanguang (Lanzhou University, Key Laboratory of Western China's Environmental System, Lanzhou, China); Zhang Tingjun; Guo, Hong; Hu Yuantao; Shang Jianguo and Zhang Yulan. Impacts of the active layer on runoff in an upland permafrost basin, northern Tibetan Plateau: PLoS One, 2018(e0192591), illus. incl. 1 table, geol. sketch map, 45 ref., February 22, 2018.
The paucity of studies on permafrost runoff generation processes, especially in mountain permafrost, constrains the understanding of permafrost hydrology and prediction of hydrological responses to permafrost degradation. This study investigated runoff generation processes, in addition to the contribution of summer thaw depth, soil temperature, soil moisture, and precipitation to streamflow in a small upland permafrost basin in the northern Tibetan Plateau. Results indicated that the thawing period and the duration of the zero-curtain were longer in permafrost of the northern Tibetan Plateau than in the Arctic. Limited snowmelt delayed the initiation of surface runoff in the peat permafrost in the study area. The runoff displayed intermittent generation, with the duration of most runoff events lasting less than 24 h. Precipitation without runoff generation was generally correlated with lower soil moisture conditions. Combined analysis suggested runoff generation in this region was controlled by soil temperature, thaw depth, precipitation frequency and amount, and antecedent soil moisture. This study serves as an important baseline to evaluate future environmental changes on the Tibetan Plateau.
2018036697 Sobota, Ireneusz (Nicolaus Copernicus University, Polar Research Center, Torun, Poland); Weckwerth, Piotr; Grajewski, Tomasz; Dziembowski, Michal; Gren, Katarzyna and Nowak, Marcin. Short term changes in thickness and temperature of the active layer in summer in the Kaffioyra region, NW Spitsbergen, Svalbard: Catena (Giessen), 160, p. 141-153, illus. incl. 2 tables, geol. sketch maps, 50 ref., January 2018.
This article focuses on short-term changes in the thermal conditions and thickness of the active layer during the summer season of 2015, observed in test fields located in the tundra and the beach areas in the Kaffioyra region Svalbard. The purpose was also to attempt a detailed analysis of short-term relationships between the rate and the dynamic of ground thaw and air temperature, as well as to determine the influence of the local surface features and geological structures on the thaw rate. Active layer thickness in the Kaffioyra region is considerably diversified both spatially and temporally. Throughout the analysed timeframe average ground temperatures on the beach and in the tundra were above zero and a delayed response of ground temperature to changes in air temperature was generally observed. The increase in the thickness of the active layer on the beach was 0.8 cm per day, whereas in the tundra it averaged 1.3 cm. One essential factor conditioning the short-term variability of the thickness and thermal conditions of an active layer is the activity of contemporary morphogenetic processes, which affect the dynamic of changes in the morphology of permafrost areas and their geological structure. Examples of such changes can be found in coastal zones exposed to tidal activity and undergoing glacial processes. The research demonstrated the substantial influence of local morphology and lithological and geological structures of the active layer on the variable thaw intensity and thickness growth rate in the tundra and beach environments.
2018040802 Wu, Yuxin (Lawrence Berkeley National Laboratory, Climate and Ecosystem Sciences Division, Berkeley, CA); Nakagawa, Seiji; Kneafsey, Timothy J.; Dafflon, Baptiste and Hubbard, Susan. Electrical and seismic response of saline permafrost soil during freeze-thaw transition: Journal of Applied Geophysics, 146, p. 16-26, illus. incl. sects., 69 ref., November 2017.
We conducted laboratory studies on the geophysical signals from Arctic saline permafrost soils to help understand the physical and mechanical processes during freeze-thaw cycles. Our results revealed low electrical resistivity (<20 Wm) and elastic moduli (7.7 GPa for Young's modulus and 2.9 GPa for shear modulus) at temperatures down to ~-10°C, indicating the presence of a significant amount of unfrozen saline water under the current field conditions. The spectral induced polarization signal showed a systematic shift during the freezing process, affected by concurrent changes of temperature, salinity, and ice formation. An anomalous induced polarization response was first observed during the transient period of supercooling and the onset of ice nucleation. Seismic measurements showed a characteristic maximal attenuation at the temperatures immediately below the freezing point, followed by a decrease with decreasing temperature. The calculated elastic moduli showed a non-hysteric response during the freeze-thaw cycle, which was different from the concurrently measured electrical resistivity response where a differential resistivity signal is observed depending on whether the soil is experiencing freezing or thawing. The differential electrical resistivity signal presents challenges for unfrozen water content estimation based on Archie's law. Using an improved formulation of Archie's law with a variable cementation exponent, the unfrozen water content estimation showed a large variation depending on the choice of the resistivity data during either a freezing or thawing cycle. Combining the electrical and seismic results, we suggest that, rather than a large hysteresis in the actual unfrozen water content, the shift of the resistivity response may reflect the changes of the distribution pattern of the unfrozen water (or ice) in the soil matrix during repeated freeze and thaw processes. Collectively, our results provide an improved petrophysical understanding of the physical and mechanical properties of saline permafrost during freeze-thaw transitions, and suggest that large uncertainty may exist when estimating the unfrozen water content using electrical resistivity data.
2018040573 Carrivick, Jonathan L. (University of Leeds, School of Geography and Water, Leeds, United Kingdom) and Heckmann, Tobias. Short term geomorphological evolution of proglacial systems: in Sediment cascades in cold climate geosystems (Morche, David, editor; et al.), Geomorphology, 287, p. 3-28, illus. incl. 3 tables, sketch maps, 265 ref., June 15, 2017.
Proglacial systems are amongst the most rapidly changing landscapes on Earth, as glacier mass loss, permafrost degradation and more episodes of intense rainfall progress with climate change. This review addresses the urgent need to quantitatively define proglacial systems not only in terms of spatial extent but also in terms of functional processes. It firstly provides a critical appraisal of prevailing conceptual models of proglacial systems, and uses this to justify compiling data on rates of landform change in terms of planform, horizontal motion, elevation changes and sediment budgets. These data permit us to produce novel summary conceptual diagrams that consider proglacial landscape evolution in terms of a balance of longitudinal and lateral water and sediment fluxes. Throughout, we give examples of newly emerging datasets and data processing methods because these have the potential to assist with the issues of: (i) a lack of knowledge of proglacial systems within high-mountain, arctic and polar regions, (ii) considerable inter- and intra-catchment variability in the geomorphology and functioning of proglacial systems, (iii) problems with the magnitude of short-term geomorphological changes being at the threshold of detection, (iv) separating short-term variability from longer-term trends, and (v) of the representativeness of plot-scale field measurements for regionalisation and for upscaling. We consider that understanding of future climate change effects on proglacial systems requires holistic process-based modelling to explicitly consider feedbacks and linkages, especially between hillslope and valley-floor components. Such modelling must be informed by a new generation of repeated distributed topographic surveys to detect and quantify short-term geomorphological changes.
2018040577 Kociuba, Waldemar (Maria Curie Sklodowska University, Faculty of Earth Sciences and Spatial Management, Lublin, Poland). Assessment of sediment sources throughout the proglacial area of a small Arctic catchment based on high-resolution digital elevation models: in Sediment cascades in cold climate geosystems (Morche, David, editor; et al.), Geomorphology, 287, p. 73-89, illus. incl. 3 tables, geol. sketch map, 75 ref., June 15, 2017.
The article presents calculations of quantitative modifications of the morphology of selected subsystems of a glacial valley through: (i) identification of the spatial distribution of important sources of sediment, (ii) assessment of the spatiotemporal variety of sediment volume and landform morphology, and (iii) assessment of the role of particular subsystems in sediment distribution. The study involved a comparison of the results of field measurements from 2010 to 2013 performed in the Scott Glacier catchment (10.1 km2) in NW Wedel Jarlsberg Land (Spitsbergen). The assessment of the landform surface changes was performed by means of a precise Terrestrial Laser Scanning (TLS) survey. The applied field and post-processing techniques for oblique laser scanning permitted the acquisition of digital elevation data at a resolution 0.01 m and density >500 pt m-2. This allowed the development of a detailed terrain model, and balancing spatial quantitative changes in six research test areas (10,000 m2) located within two subsystems of the catchment in a cascade arrangement. In the alluvial valley-floor subsystem, the survey covered: 1) the glacier terminus, 2) the intramarginal outwash plain, 3) the extramarginal braid-plain and 4) the alluvial fan, and in the slope subsystem: 5) the erosional-depositional slope in the gorge through terminal moraines, and 6) the solifluction slope. Three zones differing in terms of the spatiotemporal dynamics of geomorphic processes were distinguished within the two analysed valley subsystems. In the valley floor subsystem, these are: (i) the zone of basic supply (distribution throughout the melting season) and (ii) the redeposition zone (distribution particularly during floods), and in the slope subsystem: (iii) zone of periodical supply (distributed mainly in periods of increased precipitation and rapid increases in temperature in summer and during snow avalanches in winter). The glacier and the landforms of the channel and valley floor, as well as slope sediments transported as a result of mass wasting processes and activity of the active permafrost layer, constitute important sources of sediment supply over a short/3-year timescale. Evidence of major changes of the surface morphology (slopes, floodplain and channel platform) resulted in varied sediment budgets. The subtraction of consecutive DEMs of the test areas located in the alluvial valley subsystem revealed downstream spatial and volumetric differentiation, from the predominance of erosion (79% of volume; 43% of area) to the dominance of deposition (90/91%, respectively) in upper part of the valley floor to erosion predominance in the central (88/95%) and lower (87/82%) part of valley floor. The test areas located on the slope subsystem showed the opposite relationship: deposition dominance (88% of volume; 80% of area) in the upper gorge and erosion dominance (99/99%, respectively) in the lower part (solifluction slopes). The analysis of short-time repeated surveys (3-week survey) where volumes were calculated following DEM subtraction showed increased deposition (82% of volume; 79% of area) for the alluvial fan, and for solifluction slopes (70/57%, respectively).
2018040574 Messenzehl, Karoline (University of Bonn, Department of Geography, Bonn, Germany); Meyer, Hanna; Otto, Jan-Christoph; Hoffmann, Thomas and Dikau, Richard. Regional scale controls on the spatial activity of rockfalls (Turtmann Valley, Swiss Alps); a multivariate modeling approach: in Sediment cascades in cold climate geosystems (Morche, David, editor; et al.), Geomorphology, 287, p. 29-45, illus. incl. 6 tables, sketch maps, 175 ref., June 15, 2017.
In mountain geosystems, rockfalls are among the most effective sediment transfer processes, reflected in the regional-scale distribution of talus slopes. However, the understanding of the key controlling factors seems to decrease with increasing spatial scale, due to emergent and complex system behavior and not least to recent methodological shortcomings in rockfall modeling research. In this study, we aim (i) to develop a new approach to identify major regional-scale rockfall controls and (ii) to quantify the relative importance of these controls. Using a talus slope inventory in the Turtmann Valley (Swiss Alps), we applied for the first time the decision-tree based random forest algorithm (RF) in combination with a principal component logistic regression (PCLR) to evaluate the spatial distribution of rockfall activity. This study presents new insights into the discussion on whether periglacial rockfall events are controlled more by topo-climatic, cryospheric, paraglacial or/and rock mechanical properties. (i) Both models explain the spatial rockfall pattern very well, given the high areas under the Receiver Operating Characteristic (ROC) curves of >0.83. Highest accuracy was obtained by the RF, correctly predicting 88% of the rockfall source areas. The RF appears to have a great potential in geomorphic research involving multicollinear data. (ii) The regional permafrost distribution, coupled to the bedrock curvature and valley topography, was detected to be the primary rockfall control. Rockfall source areas cluster within a low-radiation elevation belt (2900-3300 m a.s.l,) consistent with a permafrost probability of >90%. The second most important factor is the time since deglaciation, reflected by the high abundance of rockfalls along recently deglaciated (<100 years), north-facing slopes. However, our findings also indicate a strong rock mechanical control on the paraglacial rockfall activity, declining either exponentially or linearly since deglaciation. The study demonstrates the benefit of combined statistical approaches for predicting rockfall activity in deglaciated, permafrost-affected mountain valleys and highlights the complex interplay between rock mechanical, paraglacial and topo-climatic controls at the regional scale.
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2018039328 Batchelor, Cameron J. (University of Wisconsin at Madison, Department of Geology, Madison, WI); Orland, I. J.; Marcott, Shaun A.; Slaughter, Richard and Edwards, Lawrence. A high-precision U-Th chronology of calcite deposition at Cave of the Mounds, Wisconsin, and its implications for climate and permafrost in the late Pleistocene [abstr.]: in Geological Society of America, 2017 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 49(6), Abstract no. 122-2, 2017. Meeting: Geological Society of America, 2017 annual meeting & exposition, Oct. 22-25, 2017, Seattle, WA.
Permafrost forms when mean annual air temperatures are consistently below freezing, and plays a critical role in a diverse array of environmental and climatic systems, including terrestrial carbon storage (Billings, 1987) and subglacial ice sheet processes (Cutler et al., 2000). Our understanding of late Pleistocene permafrost extent in the upper Midwest is temporally restricted to the last 25 ka and primarily derived from radiocarbon dates. Fortunately, expansive areas of the upper midcontinent of North America are underlain by cave carbonates (speleothems), which can be precisely dated using the 230Th-234U chronometer to 600 ka (Edwards et al., 1987). Since speleothem growth requires water, and therefore temperatures above freezing, these deposits can be used as a tool to constrain the extent of past permafrost and to better reconstruct pre-Last Glacial Maximum (LGM) climate near the Laurentide Ice Sheet (LIS) margin. Seventeen speleothem samples were collected from well-distributed areas throughout Cave of the Mounds; a cave located in the unglaciated Driftless Area of southwestern Wisconsin. This cave represents an ideal study site because it is located <20 km from the maximum extent of the LIS margin during the LGM. A total of 132 U-series dates were analyzed and span several glacial-interglacial cycles, ranging from 257-2.2 ka. Over this time period, these data demonstrate only a single period of no calcite growth (hiatus) from 33 to 14 ka that overlaps Marine Isotope Stage (MIS) 2. The end of this hiatus (14 ka) corresponds with previously published geomorphological observations that constrain the onset of permafrost retreat in this area (Mickelson et al., 1983; Attig et al., 1989; Clayton et al, 2001). Our results also demonstrate that prior to the MIS 2 hiatus, continuous calcite growth occurred for ~220 ka at Cave of the Mounds. We conclude that over the last three LIS advances (MIS 2, 6, 8), the only significant duration of continuous permafrost in southwestern Wisconsin occurred relatively late during the last glacial period, which has major implications since this is the first dataset constraining permafrost extent in this region prior to the LGM.
2018039046 Boelck, Sandra (Max Planck Institute for Biogeochemistry, Department of Biogeochemical Systems, Jena, Germany); Goeckede, Mathias; Hildebrandt, Anke; Vonk, Jorien and Heimann, Martin. Hydrological patterns in warming permafrost; comparing results from a control and drained site on a floodplain tundra near Chersky, Northeast Siberia [abstr.]: in European Geosciences Union general assembly 2017, Geophysical Research Abstracts, 19, Abstract EGU2017-9101, 2017. Meeting: European Geosciences Union general assembly 2017, April 23-28, 2017, Vienna, Austria.
Permafrost areas represent a major reservoir for organic carbon. At the same time, permafrost ecosystems are very susceptible to changing climate conditions. The stability of this reservoir, i.e. changes in lateral and vertical carbon fluxes in permafrost ecosystems, largely depends on groundwater level, temperature and vegetation community. Particularly during summer when the soil thaws and a so-called active layer develops, fluctuations in carbon flux rates are often dominantly driven by water availability. Such dry soil conditions are expected to become more frequent in the future due to deepening active layers as a consequence of climate change. This could result in degradation of polygonal tundra landscape properties with channelled water transport pathways. Therefore, water table depth and the associated groundwater fluxes are crucial to understand transport patterns and to quantify the lateral export of carbon through an aquatic system. Consequently, a fundamental understanding of hydrological patterns on ecosystem structure and function is required to close the carbon balance of permafrost ecosystems. This study focuses on small-scale hydrological patterns and its influencing factors, such as topography and precipitation events. Near Chersky, Northeast Siberia, we monitored (i) a control site of floodplain tundra, and (ii) a drained site, characterised by a drainage ring which was constructed in 2004, to study the effects of water availability on the carbon cycle. This experimental disturbance simulates drainage effects following the degradation of ice-rich permafrost ecosystems under future climate change. Continuous monitoring of water table depth in drained and control areas revealed small-scale water table variations. At several key locations, we collected water samples to determine the isotopic composition (d18O, dD) of surface water, suprapermafrost groundwater and precipitation. Furthermore, a weir at the drainage ditch was constructed to directly measure the discharge of the drained system. This hydrological sampling programme was complemented by continuous monitoring of atmospheric vertical turbulent carbon fluxes and meteorological conditions by two eddy-covariance towers on each site. Our results from the hydrological sampling campaign of summer 2016 indicate that total discharge through the drained system was mainly driven by precipitation events as well as modified evaporative loss due to temperature changes. The distributed network of groundwater gauges allows deriving lateral, local scale groundwater flow direction and its spatial variability, as well as the response to precipitation events within different parts of this ecosystem. Isotopic analysis of water samples showed the contribution of specific end member water sources, and how these vary across the season while the active layer deepens. Future research will focus on carbon fluxes, distribution and sources in relation to hydrological patterns. [Copyright Author(s) 2017. CC Attribution 3.0 License: https://creativecommons.org/licenses/by/3.0/legalcode]
2018039219 Carey, Anne E. (Ohio State University, School of Earth Sciences, Columbus, OH); Zorn, Matija; Ticar, Jure; Lipar, Matej; Welch, Susan A. and Lyons, W. Berry. Chemostratigraphy of karst ice, Paradana Cave, Slovenia [abstr.]: in Geological Society of America, 2017 annual meeting & exposition, Abstracts with Programs - Geological Society of America, 49(6), Abstract no. 32-10, 2017. Meeting: Geological Society of America, 2017 annual meeting & exposition, Oct. 22-25, 2017, Seattle, WA.
Velika Ledena Jama v Paradani or Paradana Cave, is the best-known ice cave in Slovenia. Its entrance sits at 1135 m.a.s.l. in the High Dinaric Karst Plateau, Trnovski gozd, in Western Slovenia. The cave is 7311 m long and 858 m deep. The entrance to the cave is a funnel-like depression formed by collapse. Ice occurs in the entrance to the cave and down to depths of approximately 100 m below the entrance. Based on measurements of air movements and temperatures, ice formation has been attributed exclusively to air circulation. During the middle to late 19th century, ice was extracted from the cave as an economic product. It has been reported that just in a single year, in 1867, 800 m3 of ice had been extracted and sold to the coastal city of Trieste. Since at least the 1950s the amount of ice in the entrance area has been observed to wax and wane. In the mid-20th century the amount of ice was estimated to be ~4000 m3 and in the beginning of the 21st century at ~2000 m3. In July 2017, we sampled a 230 cm vertical profile of ice in the north-west section of the Entrance Chamber. The ice samples were thawed and one aliquot was taken for d18O and dD analyses. Other aliquots were filtered and analyzed for major cations and anions, H4SiO4, nitrate and soluble reactive phosphate. In addition to the ice samples, two melt water pools sitting on ice within the cave were sampled for the same constituents as noted above. The motivation for this work is to (1) describe the biogeochemical character of the ice; (2) compare the ice chemical characteristics to the regional groundwater and spring water; (3) attempt to discern the relative age and timing of ice accumulation in the cave; and (4) determine the significance of ice as a possible source of palaeoclimatic information. Because this ice cave is considered a form of permafrost, we seek to document its future fate in a warming climate. The biogeochemical data will be presented and discussed within this climate framework.
2018041461 Castro-Morales, Karel (Max Planck Institute for Biogeochemistry, Germany); Kaiser, Sonja; Kleinen, Thomas; Kwon, Min Jung; Kittler, Fanny; Zaehle, Sönke; Beer, Christian and Göckede, Mathias. Year-round methane emissions from permafrost in a North-east Siberian region [abstr.]: in European Geosciences Union general assembly 2017, Geophysical Research Abstracts, 19, Abstract EGU2017-8852, 2017. Meeting: European Geosciences Union general assembly 2017, April 23-28, 2017, Vienna, Austria.
In recent decades, permafrost regions in northern latitudes are thawing as a response of climate warming. Soils in permafrost areas contain vast amounts of organic material that is released into the environment after thaw, providing new labile material for bacterial decomposition. As a result, higher production of methane in the anoxic soil layers and within anaerobic wetlands is anticipated, and this will be further released to the atmosphere. In order to assess the current large-scale methane emissions from a wetland permafrost-thaw affected area, we present results of year-round simulated methane emissions at regional scale for a section at the Russian far Northeast in Siberia, located in the low Arctic tundra and characterized by continuous permafrost. For this we use a newly developed process-based methane model built in the framework of the land surface model JSBACH. The model contains explicit permafrost processes and an improved representation of the horizontal extent of wetlands with a hydrological model (TOPMODEL). Model simulated distribution and horizontal extent of wetlands is evaluated against high-resolution remote sensing data. Total and individual regional methane emissions by ebullition, molecular diffusion, plant-mediated and emissions through snow are presented for 2014 and 2015. The model shows a reasonable seasonal transition between the individual methane emission paths. Most of the methane emissions to the atmosphere occur in summer (July, August, September), with the peak of the emissions during August. In this month, plant-mediated transport is the dominant emission path with about 15 mg CH4 m-2 d-1 in 2014, followed by ebullition (7 mg CH4 m-2 d-1) accounting for about half of the emissions thorough plants. Molecular diffusion is a minor contributor with only 0.006 mg CH4 m-2 d-1 at the peak of the summer emissions. Methane emissions through snow occur only during spring, fall and winter months, with higher emissions in spring and autumn (max. 2 mg CH4 m-2 d-1) when the thickness of the snow layer starts to melt or accumulate, respectively. The performance of the model was evaluated by comparing the modeled total methane emissions from a section of the Kolyma river floodplain near Chersky, against methane fluxes obtained from eddy covariance (for 2014 and 2015) and chambers (for June - August 2014) measured in the same area. Model results agree well with observations, with the highest emissions during August each year with 92.3 mg CH4 m-2 d-1 from eddy fluxes, 72.5 mg CH4 m-2 d-1 from chambers and 79.0 mg CH4 m-2 d-1 from the model in 2014, while 64.4 mg CH4 m-2 d-1 from eddy and 66.3 mg CH4 m-2 d-1 from the model in August 2015. The model underestimates winter emissions by up to 15 mg CH4 m-2 d-1, however a better agreement is observed in April 2014. To understand the shortcomings of the model against observations, the heterogeneity between model grid cells will be discussed. [Copyright Author(s) 2017. CC Attribution 3.0 License: https://creativecommons.org/licenses/by/3.0/legalcode]
2018041296 Chiarle, Marta (CNR, Istituto di Ricerca per la Protezione Idrogeologica, Italy); Berro, Daniele Cat; Mercalli, Luca; Mortara, Giovanni and Nigrelli, Guido. Slope instabilities occurred at high elevation in the Italian Alps in 2016; regional landscape fragility and meteorological framework [abstr.]: in European Geosciences Union general assembly 2017, Geophysical Research Abstracts, 19, Abstract EGU2017-8498, 2017. Meeting: European Geosciences Union general assembly 2017, April 23-28, 2017, Vienna, Austria.
The Italian side of the Alps includes some of the most fascinating and, at the same time, fragile landscapes of the European Alps (e.g. the Mont Blanc Massif, the Matterhorn and the Dolomites). The relatively low latitude and the prevalence of the exposure to the South, together with a decrease of approximately 10% of the precipitation in the last 100 years, have exacerbated more than in other parts of the European Alps the consequences of climate warming on the cryosphere. It is a fact that many Italian ridges extend in the lower fringe of the permafrost and that glacier shrinkage since the end of the Little Ice Age has been dramatic, up to the almost complete deglaciation of most of the south-western and eastern Italian Alps. In view of this, and of the fact that 2016 has been declared as the warmest year on record globally, we analyze the natural instability events that occurred in 2016 in the Italian Alps at high elevation (> 1500 m a.s.l.). More than 20 events have been reported in the period March-October, mostly in the western and eastern Italian Alps. Rockfalls significantly outweigh other types of instabilities, but ice falls, glacial outburst floods and debris flows have also been documented. The properties and spatial occurrence of these instability processes will be discussed, as well as the synoptic meteorological context in which they developed, in order to contribute to the discussion on how ongoing environmental changes are influencing the response of glaciated and recently deglaciated slopes to meteorological forcing, and thus hazard occurrence. [Copyright Author(s) 2017. CC Attribution 3.0 License: https://creativecommons.org/licenses/by/3.0/legalcode]
2018041083 Cicoira, Alessandro (University of Zurich, Department of Geography, Zurich, Switzerland); Vieli, Andreas; Faillettaz, Jerome and Wirz, Vanessa. Investigating seasonal variations in rock glacier dynamics [abstr.]: in European Geosciences Union general assembly 2017, Geophysical Research Abstracts, 19, Abstract EGU2017-7546, 2017. Meeting: European Geosciences Union general assembly 2017, April 23-28, 2017, Vienna, Austria.
Periglacial monitoring has highlighted seasonal and inter-annual variations in rock glacier dynamics. Temperature forcing, through heat conduction, has been proposed as one of the key processes to explain these kinematics variations. But this mechanism has not yet been quantitatively assessed against real-world data. We present a numerical model that couples heat conduction and an empirical creep model for ice-rich frozen soils (Arenson, 2005). We use this model to investigate the dynamic response of alpine permafrost to external temperature variations. We compare the modeling with the PERMOS monitoring network data, which include several years of borehole temperature data and variations in surface velocity. These data allow us to conduct a direct comparison and test our model. We are able to model velocity variations from temperature forcing in the right order of magnitude but, in general, these are underestimated, in particular for thicker rock-glaciers. [Copyright Author(s) 2017. CC Attribution 3.0 License: https://creativecommons.org/licenses/by/3.0/legalcode]
2018039021 De Blasio, Fabio (University of Milano-Bicocca, Department of Earth and Environmental Sciences, Milan, Italy); Dattola, Giuseppe and Crosta, Giovanni Battista. Modelling rock fragmentation of extremely energetic rockfalls [abstr.]: in European Geosciences Union general assembly 2017, Geophysical Research Abstracts, 19, Abstract EGU2017-9020, 2017. Meeting: European Geosciences Union general assembly 2017, April 23-28, 2017, Vienna, Austria.
Extremely energetic rockfalls (EER) are phenomena for which the combination of a large volume (at least some thousands of m) and a free fall height of hundreds of metres, results in a large released energy. We fix a threshold value of around 1/50 of kilotons to define such a type of events. Documented examples include several events with different size in the Alps (Dru, 2005, 2011, 265,000, 59,200 m3; val Fiscalina - Cima Una, 2007, 40,000 m3; Thurwieser 2004, ca 2 Mm3; Cengalo, 2011, 1.5*105 m3 in 2016, in Switzerland; Civetta, 2013, ca 50,000 m3;), in the Apennines (Gran Sasso, 2006, 30,000 m3), Rocky Mountains (Yosemite, Happy Isles, 38,000 m3), and Himalaya. EERs may become more frequent on steep and sharp mountain peaks as a consequence of permafrost thawing at higher altitudes. In contrast to low energy rockfalls where block disintegration is limited, in EERs the impact after free fall causes an immediate and efficient release of energy much like an explosion. The severe disintegration of the rock and the corresponding air blast are capable of snapping trees many hundreds of metres ahead of the fall area. Pulverized rock at high speed can abrade tree logs, and the resulting suspension flow may travel much further the impact zone, blanketing vast surrounding areas. Using both published accounts of some of these events and collecting direct data for some of them, we present some basic models to describe the involved processes based on analogies with explosions and explosive fragmentation. Of the initial energy, one part is used up in the rock disintegration, and the rest is shared between the shock wave and air blast. The fragmentation energy is calculated based on the fitting of the dust size spectrum by using different probabilistic distribution laws and the definition of a surface energy and by considering the involved strain rate. We find the fragmentation is around one third of the initial boulder energy. Finally, we evaluate the velocity of the corresponding cloud generated by the powder suspension and compare with the information available in literature. keywords: EER, Rockfalls, Disintegration number, Omographic distribution [Copyright Author(s) 2017. CC Attribution 3.0 License: https://creativecommons.org/licenses/by/3.0/legalcode]
2018039041 Dean, Joshua F. (University of Stirling, Department of Biological and Environment Sciences, Stirling, United Kingdom); Billett, Michael F.; Dinsmore, Kerry J.; Garnett, Mark H. and van der Velde, Ype. Arctic catchment releases mostly young aquatic carbon despite complete thawing of old organic-rich permafrost soils during growing season [abstr.]: in European Geosciences Union general assembly 2017, Geophysical Research Abstracts, 19, Abstract EGU2017-9093, 2017. Meeting: European Geosciences Union general assembly 2017, April 23-28, 2017, Vienna, Austria.
Radiocarbon (14C) dating of dissolved organic carbon (DOC) in Arctic freshwaters has been used as a crucial tool for detecting old C mobilised from thawing permafrost, but DO14C in major Arctic rivers is usually quite young. New methods for the collection of both CO2 and CH4 from inland waters allow novel observation of dissolved 14CO2 and 14CH4 alongside DO14C, and provide a more sensitive method than aquatic OC alone - published Arctic freshwater 14C studies to date focus only on DOC, particulate OC, or ebullition CH4/CO2. The mobilisation of old C sourced from deepening permafrost soil active-layers into Arctic freshwaters has the potential to form a significant positive climate feedback. We compare 14C in DOC, dissolved CO2 and dissolved CH4 at five time points over a single growing season from streams, ponds and lakes underlain by continuous permafrost in the western Canadian Arctic. Using age distribution analysis based on atmospheric 14CO2 records, we estimated the age of aquatic C that would otherwise be labelled as "modern" due to the 14C bomb peak. We then calculated the vertical and lateral C fluxes in the study systems, and estimated the proportion derived from old permafrost C. The upper organic-rich soils are the dominant hydrologic pathway, which were completely thawed by late season, and we hypothesised that mobilisation of older, deeper organic soil C would be visible in the aquatic 14C by late in the growing season. Early in the season, median aquatic DO14C and CO2 ages were 65-131 years old (all 14C ages reported here are years before sampling date). By the end of the season, DO14C was 156-271 years old, while CO2 was 113-161 years old, demonstrating that aquatic C ages reflect the mobilisation of thawing older permafrost C. CH4 concentrations were generally low throughout and only two dates were obtained: 202 and 1,970 years old. Overall there was limited evidence of very old permafrost organic C, which comprised 0-10% of vertical and lateral aquatic fluxes. Our results demonstrate that permafrost thaw will result in the mobilisation of old C into the aquatic phase as DOC, CO2 and CH4, but also indicate potential resilience within these systems in response to climate change. [Copyright Author(s) 2017. CC Attribution 3.0 License: https://creativecommons.org/licenses/by/3.0/legalcode]
2018041363 Garcia-Garcia, Almudena (Memorial University of Newfoundland, Environmental Science Program, St. John's, NL, Canada); Cuesta-Valero, Francisco José; Beltrami, Hugo; Mondéjar, Carlos and Finnis, Joel. Ground heat flux within the PMIP3/CMIP5 last millennium simulations and estimates from geothermal data [abstr.]: in European Geosciences Union general assembly 2017, Geophysical Research Abstracts, 19, Abstract EGU2017-8642, 2017. Meeting: European Geosciences Union general assembly 2017, April 23-28, 2017, Vienna, Austria.
The proper simulation of the energy partitioning at the surface, both as storage within the ground and energy fluxes from the surface, is crucial for the accurate representation of land-surface processes and related climate feedback mechanisms (e.g. permafrost thaw and soil carbon stability). We analyze the changes in ground heat flux over the last millennium as simulated by the PMIP3/CMIP5 General Circulation Models (GCMs). The following three methods were used to estimate ground heat flux: 1) using the surface energy balance, that is from the difference between net-radiation, latent and sensible heat fluxes, 2) calculations based on Surface Air Temperature (SAT), Surface Temperature (ST) and Ground Surface Temperature at 0.5m and at 1m (GST), and 3) inferences from temperature at two soil depths (GST at 0.5m and GST at 1m). Results show large regional variability among models and methods. Global estimates of ground heat flux from the surface energy balance differ significantly from values obtained from geothermal data over the second half of the last century. Such disagreement may be indicative of a change in the partitioning of the energy within historical simulations of the PMIP3/CMIP5 GCMs. The lack of observational data and the challenges of measuring soil fluxes highlight the value of geothermal database as a potentially valuable source of information for evaluating long-term models performance. [Copyright Author(s) 2017. CC Attribution 3.0 License: https://creativecommons.org/licenses/by/3.0/legalcode]
2018041382 Harding, Poppy (University College London, Department of Geography, London, United Kingdom); Mackay, Anson; Bezrukova, Elena and Shchetnikov, Alexander. Ecosystem resilience to abrupt late Quaternary change in continental southern Siberia [abstr.]: in European Geosciences Union general assembly 2017, Geophysical Research Abstracts, 19, Abstract EGU2017-8684, 2017. Meeting: European Geosciences Union general assembly 2017, April 23-28, 2017, Vienna, Austria.
Quaternary climate variability is dominated by long term orbital forcing along with abrupt sub-Milankovitch events on the scales of millennia to centuries, driven by internal feedback mechanisms, volcanic forcing and fluctuating solar activity. Although these are well documented in the North Atlantic region, their expression is poorly understood in Siberia, particularly in relation to abrupt climatic events. Siberia has the world's highest level of continentality offering an opportunity to study changes remote from oceanic influences and improving understanding of interactions between the Siberian High and other atmospheric systems including the Aleutian Low, Arctic oscillation and Icelandic Low1 and ENSO2. Understanding of palaeoenvironmental change in Siberia is essential due to the region's high sensitivity to climatic change, with warming rates considerably higher than the global average over the past 50 years3, triggering significant environmental changes, including permafrost degradation, shifts in the forest-steppe biome, increases in forest fires and warming of seasonally ice-covered lakes. Additionally, the region provides essential palaeoenvironmental context for early hominins, for example at globally important sites such as Denisova cave4, and megafauna extinctions5. This presentation outlines ongoing work at Lake Baunt, SE Siberia including: key quaternary climate forcings, the site and its regional context, the key methods and preliminary results. These include a dated record back to 30ka BP (based on multiple 14C dates and Bayesian age modelling), multiproxy indicators of palaeoproductivity (e.g. biogenic silica and diatom analyses) and lake mixing regimes (inferred from diatom analyses). Together these highlight several key Quaternary fluctuations potentially correlated to events recorded in Greenland Ice Cores (GS2, GS2.1, GI1, GS1), and these are considered against key Quaternary records including those from nearby Lake Baikal and Hulu Cave in east China. Our analyses suggest that teleconnections between the Siberian High and the East Asian monsoon are also significant for this study, with Lake Baunt showing a relationship between productivity and variability in strength of the Siberian High. References: Tubi, A. & Dayan, U. (2013). Int. J. Climatol. 33, 1357-1366. Park, T.-W. et al. (2014). Clim. Dyn. 45, 1207-1217. Tingley, M. P. & Huybers, P. (2013). Nature 496, 201-5. Krause, J. et al.. (2010). Nature 464, 894-7. Stuart, A. J. et al. (2004). Nature 431, 684-9. [Copyright Author(s) 2017. CC Attribution 3.0 License: https://creativecommons.org/licenses/by/3.0/legalcode]
2018036798 Jin Xiaoying (Cold and Arid Regions Environmental and Engineering Research Institute, China) and Jin Huijun. Effects of permafrost degradation on vegetation in the Source Area of the Yellow River NE Qinghai Tibetan Plateau [abstr.]: in European Geosciences Union general assembly 2017, Geophysical Research Abstracts, 19, Abstract EGU2017-4223, 2017. Meeting: European Geosciences Union general assembly 2017, April 23-28, 2017, Vienna, Austria.
Permafrost degradation caused by climate warming has markedly changed ecological environment in the Source Area of the Yellow River, in the northeast of the Qinghai Tibetan Plateau. However, related research about ecological impact of permafrost degradation is limited in this area. More attentions should be paid to the impact of permafrost degradation on alpine grassland. In this study vegetation characteristics (plant species composition, vegetation cover and biomass, etc.) at different permafrost degradation stages (as represented by the continuous and discontinuous permafrost zone, transitional zone, and seasonally frozen ground zone) is investigated. The results showed that (1) there are total 64 species in continuous and discontinuous permafrost zone, transitional zone, and seasonally frozen ground zone, and seasonally frozen ground zone has more species than transitional zone and permafrost zone, (2) sedge is the dominant species in three zones. But Shrub only presented in the seasonally frozen ground zone. These results suggest that permafrost degradation affect the species number and species composition of alpine grassland. [Copyright Author(s) 2017. CC Attribution 3.0 License: https://creativecommons.org/licenses/by/3.0/legalcode]
2018036796 Michel, Roberto (Universidade Estadual de Santa Cruz, Brazil); Andrade, Andre; Simas, Felipe; Silva, Tassio; Loureiro, Diego and Schaefer, Carlos. Nine year active layer thermal monitoring at Fildes Peninsula, King George Island, maritime Antarctica [abstr.]: in European Geosciences Union general assembly 2017, Geophysical Research Abstracts, 19, Abstract EGU2017-4219, 2017. Meeting: European Geosciences Union general assembly 2017, April 23-28, 2017, Vienna, Austria.
Most global circulation models predict enhanced rates of climate change, particularly temperature increase, at higher latitudes witch are currently faced with rapid rates of regional climate change (Convey 2006, Vaughan et al. 2003, Quayle et al. 2002), Antarctic ecosystems are expected to show particular sensitivity and rapid responses (Freckman and Virginia 1997, Quayle et al. 2002, 2003). The active layer and permafrost are important components of the cryosphere due to their role in energy flux regulation and sensitivity to climate change (Kane et al., 2001; Smith and Brown, 2009). Compared with other regions of the globe, our understanding of Antarctic permafrost is poor, especially in relation to its thermal state and evolution, (Bockheim, 1995, Bockheim et al., 2008). The active layer monitoring site was installed in the summer of 2008, and consists of thermistors (accuracy 0.2 °C) arranged in a vertical array (Turbic Eutric Cryosol 60 m asl, 10.5 cm, 32.5 cm, 67.5 cm and 83.5 cm). All probes were connected to a Campbell Scientific CR 1000 data logger recording data at hourly intervals from March 1st 2008 until November 30th 2012. We calculated the thawing days (TD), freezing days (FD); thawing degree days (TDD) and freezing degree days (FDD); all according to Guglielmin et al. (2008). The active lawyer thickness was calculated as the 0 °C depth by extrapolating the thermal gradient from the two deepest temperature measurements (Guglielmin, 2006). The temperature at 10.5 cm reaches a maximum daily average (5.6 °C) in late January 2015, reaching a minimum (-9.6 °C) in in early August 2011, at 83.5 cm maximum daily average (0.6 °C) was reached in mid March 2009 and minimum (-5.5 °C) also in early August 2011. The years of 2008, 2009 and 2011 recorded thaw days at the bottom of the profile (62 and 49 in 2009 and 2011), and logged the highest soil moisture contents of the time series (62%, 59% and 63%). Seasonal variability of the active layer shows disparities between different years, especially in bottom most layer, where high summer temperatures trigger a increase in soil moisture content that can endure for several seasons. The winter of 2014 also deserves special attention, being the mildest winter recorded during the studied period; in July minimum monthly temperatures were -3.2 °C and -1.9 °C at 10.5 cm and 83.5 cm, it experienced 17 FD summing -0.61 FDD, average for the whole period was -7.5 °C, -3.9 °C, 27 FD and -55 FDD (2008 also had a mild winter but still hold 21 FD and -0,88 FDD at 83.5 cm in July). The summer of 2009 was the warmest facing 31 thawing days and summing 105 thawing degree days at 10.5 cm in January (28.7 thawing days and 66.3 thawing degree days average). The profile showed a increase in soil water content annual during warm summers, persisting for the following seasons, average is 44 % in 2008, 32 % in 2012 closing the time series with a annual average of 27 % in 2016, all values at 83.5 cm. Active layer thickness varied between 86 cm (max of 2015, March) and 117 cm (max of 2009, March). The active layer thermal regime over a 9 year period at Fildes Peninsula shows great variation between years, 2008, 2009 and 2011 presenting warm summers and 2014 being abnormally warm during Winter. Temperature fluctuations can affect the active layer in depth and the effects of warmer temperatures in the bottom of the profile can increase soil water content for several seasons. [Copyright Author(s) 2017. CC Attribution 3.0 License: https://creativecommons.org/licenses/by/3.0/legalcode]
2018041018 Oliva, Marc (University of Lisbon, Institute of Geography and Spatial Planning, Lisbon, Portugal); Serrano, Enrique; Ruiz-Fernández, Jesús; Gómez-Ortiz, Antonio and Palacios, David. Paraglacial dynamics in Little Ice Age glaciated environments in the Iberian Peninsula [abstr.]: in European Geosciences Union general assembly 2017, Geophysical Research Abstracts, 19, Abstract EGU2017-6757, 2017. Meeting: European Geosciences Union general assembly 2017, April 23-28, 2017, Vienna, Austria.
Three Iberian mountain ranges encompassed glaciers during the Little Ice Age (LIA): the Pyrenees, Cantabrian Mountains and Sierra Nevada. The gradual warming trend initiated during the second half of the XIX century promoted the progressive shrinking of these glaciers, which completely melted during the first half of the 20th century in the Cantabrian Mountains and Sierra Nevada and reduced by 80% of their LIA extent in the Pyrenees. Currently, the formerly glaciated environments are located within the periglacial belt and still present to a major or lesser degree signs of paraglacial activity. LIA moraines are devoid of vegetation and composed of highly unstable sediments that are being intensely mobilized by slope processes. Inside the moraines, different landforms and processes generated following LIA glacial retreat have generated: (i) buried ice trapped within rock debris supplied from the cirque walls, which has also generated rock glaciers and protalus lobes; (ii) semi-permanent snow fields distributed above the ice-patches remnants of the LIA glaciers, and (iii) small periglacial features such as frost mounds, sorted circles and solifluction landforms generated by processes such as solifluction and cryoturbation. Present-day morphodynamics is mostly related to seasonal frost conditions, though patches of permafrost have formed in some areas in contact with the buried ice. This "geomorphic permafrost" is undergoing a process of degradation since it is not balanced with present-day climate conditions. This is reflected in the occurrence of multiple collapses and subsidences of the debris cover where the frozen bodies sit. In the highest areas of the Pyrenees there is a permafrost belt next to the small glaciated environments in the highest massifs. Finally, we propose a model for paraglacial activity in Iberian mountain ranges and compare it to other mid-latitude mountain environments as well as to other past deglaciation stages. [Copyright Author(s) 2017. CC Attribution 3.0 License: https://creativecommons.org/licenses/by/3.0/legalcode]
2018041333 Steiner, Matthias (Technische Universität Wien, Departement of Geodesy and Geoinformation, Vienna, Austria); Maierhofer, Theresa; Pfeiler, Stefan; Chwatal, Werner; Behm, Michael; Reisenhofer, Stefan; Schöner, Wolfgang; Straka, Wolfgang and Orozco, Adrian Flores. Active and passive seismic investigations in alpine permafrost at Hoher Sonnblick (Austria) [abstr.]: in European Geosciences Union general assembly 2017, Geophysical Research Abstracts, 19, Abstract EGU2017-8578, 2017. Meeting: European Geosciences Union general assembly 2017, April 23-28, 2017, Vienna, Austria.
Different geophysical measurements have been applied at the Hoher Sonnblick study area to gain information about permafrost distribution as well as heterogeneities controlling heat circulation, in the frame of the OAW-AtmoPerm project, which aims at the understanding the impacts of atmospheric extreme events on the thermal state of the active layer. Electrical Resistivity Tomography (ERT) has been widely accepted as a suitable method to characterize permafrost processes; however, limitations are imposed due to the challenges to inject high current densities in the frozen periods and the loss of resolution of electrical images at depth require the application of further geophysical methods. To overcome such problems, we investigate here the application of active and seismic methods. Seismic campaigns were performed using permanent borehole and temporarily installed surface geophones. A total of 15 borehole geophones are installed at depths of 1 m, 2 m, 5 m, 10 m and 20 m in three boreholes which are separated by a horizontal distance of 30 m between each other. Active measurements utilized 41 surface and 15 borehole geophones and a total of 199 excitation points. Surface geophones were laid out along two crossing lines with lengths of 92 m and 64 m, respectively. The longer line was placed directly along the borehole transect and the shorter one was oriented perpendicular to it. Hammer blows were performed with a spacing of 1 m inline the geophones and 4 m in crosslines rotated by 45 degrees, permitting 3D acquisition geometry. In addition to the active sources, data loggers connected to the borehole geophones permitted the collection of continuous 36-hours datasets for two different thermal conditions. Seismic ambient noise interferometry is applied to this data and aims at the identification of velocity changes in the subsurface related to seasonal changes of the active layer. A potential source of ambient seismic energy is the noise excited by hikers and the activity from the nearby cable cars station. Results obtained from the 3D-hammer seismics and interferometry are compared and benchmarked against each other. Changes in the seismic velocities in the subsurface permitted the delineation of the active layer and improved permafrost investigation when combined with ERT monitoring. Seismic results were then interpreted together with those obtained with ERT monitoring, electromagnetic induction (EMI) and ground-penetrating radar (GPR). [Copyright Author(s) 2017. CC Attribution 3.0 License: https://creativecommons.org/licenses/by/3.0/legalcode]
2018041438 Zhu Liping (Chinese Academy of Sciences, Institute of Tibetan Plateau Research, China) and Qiao Baojin. Estimation of lake water storage change and its linkage to increased mass on the Tibetan Plateau [abstr.]: in European Geosciences Union general assembly 2017, Geophysical Research Abstracts, 19, Abstract EGU2017-8805, 2017. Meeting: European Geosciences Union general assembly 2017, April 23-28, 2017, Vienna, Austria.
In this study, we estimated water storage change of 282 lakes (> 10 km2) by an empirical equation based on Shuttle Radar Topography Mission (SRTM) DEM and Landsat images in the endorheic basin of inner Tibetan Plateau (ITP). Lakes water storage had increased by 107.5 Gt (8.27 Gt/y) from 2000 to 2013, 89.4 % of increased water storage was mainly concentrated in four regions and 126 large lakes (> 50 km2) occupied 90.6 % of total water storage change. Mass increased rate of ITP was 4.38 Gt/y derived from Gravity Recovery and Climate Experiment (GRACE) satellite data during 2003-2009, which could explain 53 % of lake expansion. A little contribution to lake from permafrost degradation based on Active-layer depth (ALD) model. Increased glacial meltwater with rising temperature, which didn't increase mass of ITP, made an equivalent contribution to lake expansion with precipitation and evaporation. [Copyright Author(s) 2017. CC Attribution 3.0 License: https://creativecommons.org/licenses/by/3.0/legalcode]
2018036432 Harder, Silvie R. (McGill University, Montreal, QC, Canada); Roulet, Nigel T.; Strachan, Ian B.; Crill, Patrick M. and Pelletier, Luc. Carbon and energy fluxes from a spatially heterogeneous permafrost peatland [abstr.]: in Joint assembly AGU-GAC-MAC-CGU; abstracts listing, Abstract Volume (Geological Association of Canada), 38, p. 89, 2015. Meeting: Joint assembly of the American Geophysical Union, Geological Association of Canada, Mineralogical Association of Canada, and Canadian Geophysical Union, May 3-7, 2015, Montreal, QC, Canada.
2018036433 Malhotra, Avni (McGill University, Montreal, QC, Canada); Roulet, Nigel T. and Moore, Tim R. Critical changes to peatland carbon biogeochemistry following permafrost thaw [abstr.]: in Joint assembly AGU-GAC-MAC-CGU; abstracts listing, Abstract Volume (Geological Association of Canada), 38, p. 89-90, 2015. Meeting: Joint assembly of the American Geophysical Union, Geological Association of Canada, Mineralogical Association of Canada, and Canadian Geophysical Union, May 3-7, 2015, Montreal, QC, Canada.
2018036411 Zheng Wang (McGill University, Montreal, QC, Canada); Roulet, Nigel T. and Moore, Tim R. CH4 flux changes with permafrost thaw in a subartic peatland [abstr.]: in Joint assembly AGU-GAC-MAC-CGU; abstracts listing, Abstract Volume (Geological Association of Canada), 38, p. 53, 2015. Meeting: Joint assembly of the American Geophysical Union, Geological Association of Canada, Mineralogical Association of Canada, and Canadian Geophysical Union, May 3-7, 2015, Montreal, QC, Canada.
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