Displays

Subsea permafrost on the Arctic Shelf originates as terrestrial permafrost which was submerged by ocean water following sea level rise during deglaciation. The thickness and depth of subsea permafrost are not well known on the circumpolar scale. Subsea frozen sediments contain organic carbon as well as preventing the upward diffusion of carbon-containing greenhouse gases. Thawing of subsea permafrost – which may accelerate as a consequence of global warming – makes this carbon available for release to the ocean-atmosphere system and thus constitutes a positive feedback to global warming. Present estimates of the carbon associated with subsea permafrost range over two orders of magnitude and are thus highly uncertain and the amount of stored organic carbon potentially huge. Due to the long time scales involved in thawing permafrost, subsea permafrost may become – especially in a future with low anthropogenic carbon emissions – a significant contributor to global carbon releases and thus to an enhanced global warming.

The best tool for estimating the effects of future carbon releases are the Earth System Models (ESMs) which, however, are – due to their computational demands – not well suited for the long time scale of build-up and degradation of subsea permafrost. We therefore apply a novel two-model approach. The multiple glacial-cycle model Submarine Permafrost Map (SuPerMap) was used to obtain the pre-industrial distribution of permafrost based on 1D modelling of heat flow driven by glacial, marine and aerial surface upper boundary conditions. This state was then used to initialize JSBACH, the land surface component of the MPI Earth System Model (MPI-ESM), which was extended to allow subsea permafrost applications. JSBACH was used to generate present-day and near-future permafrost thaw by applying historical and future scenario forcings from the MPI-ESM runs performed within the Coupled Model Intercomparison Project, CMIP6. As a first step we here present the modelled physical state (temperature and ice content profiles) of the subsea sediments on the Arctic Shelf in the pre-industrial and present states as well as in the near future. SuPerMap generated a region of cryotic (<0°C) sediment on the Arctic Shelf of 2.5 million km², more than 80% of which lay north of Eastern Siberia. In the JSBACH simulations, permafrost thawing rates accelerate after the mid-20^th century. From about 2060 onwards, the choice of shared social-economic pathway (SSP) determines the rate of thaw and up to about 1/3 of the pre-industrial cryotic area is lost before year 2100. Regional aspects of the SSP projections will be presented.

How to cite: Wilkenskjeld, S., Overduin, P., Miesner, F., Puglini, M., and Brovkin, V.: Integrating subsea permafrost into an Earth System Model (MPI-ESM), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8473, https://doi.org/10.5194/egusphere-egu2020-8473, 2020.

The ground surface over permafrost area subsides and uplifts annually due to the seasonal thawing and freezing of active layer. GPS Interferometric Reflectometry (GPS-IR) has been successfully applied to the signal-to-noise ratio (SNR) observations to retrieve elevation changes of frozen ground surface at Barrow, Alaska. In this study, the method is extended to include GLONASS and Galileo SNR observations. Based on the multiple SNR observations collected by SG27 in Barrow, the multiple GNSS-IR time series of ground surface elevation changes during snow-free days from late June to middle October in year 2018 are obtained at daily intervals. All the three time series show a similar pattern that the ground subsided in thaw season followed by uplifts in freezing season, which is well characterized by the previous composite physical model using thermal indexes. Fitted with the composite model, the amplitude of the GPS-derived elevation changes during the snow-free days is suggested to be 3.3 ± 0.2 cm. However, the time series of GLONASS-IR and Galileo-IR measurements are much noisier than that of GPS-IR due to their inconsistent daily satellite tracks. Applied with a specific strategy in the composite model fitting, the amplitudes of GLONASS- and Galileo-derived elevation changes are estimated to be 4.0 ± 0.3 cm and 3.9 ± 0.5 cm, respectively. Then, GLONASS-IR and Galileo-IR time series are reconstructed in turn with the fitting coefficients. Moreover, the occurrences of the short-term variations in time series of GNSS-IR measurements are found to coincidence with the precipitation events, indicating the hydrologic control on the movements of frozen ground surface. The results presented in this study show the feasibility to combine multiple GNSS to densely monitor frozen ground surface deformations, and provide an insight to understand the impacts of both thermal and hydrologic forces on the frozen ground dynamics.

How to cite: Hu, Y.: Ground surface elevation changes estimated using multiple GNSS signal-to-noise ratio observations over permafrost area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6841, https://doi.org/10.5194/egusphere-egu2020-6841, 2020.

Permafrost is a widespread thermal subsurface phenomenon in polar and high mountain regions and was defined as an essential climatic variable (ECV) by the Global Climate Observing System (GCOS). The Swiss Permafrost Monitoring Network was started in the year 2000 as an unconsolidated network of sites from research projectsand as the first national long-term observation network for permafrost it is an early component of the Global Terrestrial Network for Permafrost (GTN-P). After 20 years of operation, development and evaluation, PERMOS holds the largest and most diverse collection of mountain permafrost data worldwide and has a role model regarding its structure and organization. PERMOS aims at the systematic long-term documentation of the state and changes of mountain permafrost in the Swiss Alps. The scientific monitoring strategy is now based on three observation elements: ground-surface and subsurface temperatures, changes in subsurface ice content, and permafrost creep velocities. These three elements complement each other in a landform-based approach to capture the influence of the topography as well as the surface and subsurface conditions of different landforms on the ground thermal regime. These influences are considered to be more relevant than regional climatic conditions in the small country.

Over the past 20 years, all observation elements indicate a clear warming trend of mountain permafrost in the Swiss Alps. Borehole temperatures generally increase at 10 and 20 m depth. This warming trend was intensified after 2009 and temporarily interrupted following winters with a thin and late snow cover, particularly winter 2016. Further, the trend is more pronounced at cold permafrost sites like rock glacier Murtèl-Corvatsch, where an increase of +0.5°C has been observed at 20 m over the past 30 years. For permafrost temperatures close to 0 °C, climate warming does not result in significant temperature increase but is masked by phase changes and latent heat effects. These result in significant changes in ice content, which can be registered by electrical resistivity tomography (ERT). Further, the warming trend of mountain permafrost in the Swiss Alps is corroborated by increasing creep rates of rock glaciers, which follow an exponential relationship with ground temperatures. In this contribution, we present and discuss the key results from two decades of mountain permafrost monitoring within the PERMOS network. In addition to the measurement data, we identified considerable challenges for long-term monitoring network of mountain permafrost based on experience collected over two decades. The acquisition of reliable data at a limited number of stations in extreme environments with difficult access requires robust strategies, standards and traceability for the entire data acquisition chain: installation > measurement > raw data > processing > archiving and, finally, reporting.

How to cite: Noetzli, J. and Pellet, C.: 20 years of mountain permafrost monitoring in the Swiss Alps: key results and major challenges, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10903, https://doi.org/10.5194/egusphere-egu2020-10903, 2020.

Peat plateaus are a major type of permafrost landscape in Arctic and Siberian lowlands. They represent a substantial pool of several hundreds of petagrams of organic carbon that has the potential to contribute to the Permafrost Carbon Feedback. The thermal response of these soils to the climate signal is complex and implies the interaction of various surface and subsurface processes operating at a very small spatial scale involving water, snow and heat fluxes and surface subsidence. As these processes have the ability to generate feedbacks between each other and trigger non-linear evolutions of the landscape, they challenge our abilities to measure and model them.

Peat plateaus in Northern Norway have been actively degrading over at least the last 60 years. They thus offer a precious opportunity to measure and model the degradation patterns they exhibit. We present new topographical observations derived from drone-based photogrammetry that we acquired for one site in Northern Norway. Over a period of 3 years, these Digital Elevation Models allows quantifying precisely the surface subsidence and resulting lateral degradation of the peat plateaus. In a second time, we use the land surface model CryoGrid to model the observed patterns. The model is able to (i) simulate the snow fluxes and the water and heat sub-surface fluxes within the plateau and between the plateau and the surrounding wet mire and to (ii) represent the soil surface subsidence due to excess ice melt in the soil. We implement a set up that discretize the interface between the peat plateaus and the wet mire and force the Surface Energy Balance module of the model with climatic data derived from regional atmospheric modelling.

Our simulations manage to reproduce the degradation speed we observe in our topographical data. We also present a sensitivity analysis of the degradation speed to snow cover and to the geometry of the peat plateaus and show how the feedbacks between the dynamical topography and the lateral fluxes of snow and water can trigger rapid permafrost thawing and fast degradation of permafrost landscapes.

How to cite: Westermann, S., Martin, L., Nitzbon, J., Aas, K., Scheer, J., Eiken, T., and Etzelmüller, B.: Measuring and modelling thermal erosion patterns of peat plateaus in northern Norway, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10183, https://doi.org/10.5194/egusphere-egu2020-10183, 2020.

Snow depth increases observed in some artic regions and its insulations effects have led to a winter-warming of permafrost-containing peatlands. Permafrost thaw and the temperature-dependent decomposition of previously frozen carbon (C) is currently considered as one of the most important feedbacks between the artic and the global climate system. However, the magnitude of this feedback remains uncertain because winter effects are rarely integrated and predicted from mechanisms active in both surface (young) and thawing deep (old) peat layers.

Laboratory incubation studies of permafrost soils, in situ carbon flux measurements in ecosystem-scale permafrost thaw experiments, or measurements made across naturally degrading permafrost gradients have been used to improve our knowledge about the net effects of winter-warming in permafrost C storage. The results from these studies, however, are biased by imprecision in long-term (decadal to millennial) effects due to the short time scale of the experiments. Gradient studies may show longer-term responses but suffer from uncertainties because measurements are usually taken during the summer, thus ignoring the long cold season. The need for robust estimates of the long-term effect of permafrost thaw on the net C balance, which integrates year-round C fluxes sets the basis of this study.

Here, we quantified the effects of long-term in situ permafrost thaw in the net C balance of a permafrost-containing peatland subjected to a 10-years snow manipulation experiment. In short, we used a peat age modelling approach to quantify the effect of winter-warming on net ecosystem production as well as on the underlying changes in surface C inputs and losses along the whole peat continuum. Contrary to our hypothesis, winter-warming did not affect the net ecosystem production regardless of the increased old C losses. This minimum overall effect is due to the strong reduction on the young C losses from the upper active layer associated to the new water saturated conditions and the decline in bryophytes. Our findings highlight the need to incorporate long-term year-round responses in C fluxes when estimating the net effect of winter-warming on permafrost C storage. We also demonstrate that thaw-induced changes in moisture conditions and plant communities are key factors to predicting future climate change feedbacks between the artic soil C pool and the global climate system.

How to cite: Olid, C., Klaminder, J., Monteux, S., Johansson, M., and Dorrepaal, E.: Decade of permafrost thaw in a subarctic palsa mire alters carbon fluxes without affecting net carbon balance, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21805, https://doi.org/10.5194/egusphere-egu2020-21805, 2020.

During the past several decades, Arctic regions warmed almost twice as much as the global average temperature. Simultaneously in the high northern latitudes, observations indicate a decline in permafrost extend and landscape modifications due to permafrost degradation. Climate projections suggest an accelerated soil warming, and consequently deepening of the active layer thickness in the near future. Except air temperature, two other parameters i.e. precipitation and snow depth are the most important climatic parameters affecting the thermal state and extend of the permafrost. The key research question of this study is whether or not certain climatic conditions can be identified that can be considered as an extreme event relevant for permafrost degradation. Here we apply data mining techniques on meteorological re-analysis to develop a coherent framework for the identification of extreme climate conditions relevant for active soil layer deepening and a decline of permafrost extend.
Several key types of events have been classified based on various combinations of temperature, precipitation and snow depth statistics. Then, the respective events have been identified in ERA-Interim reanalysis and evaluated against in situ observations in West Siberia region. The evaluation proved that the developed algorithm could successfully detect relevant extreme climate conditions in meteorological re-analysis dataset. It also indicated possibilities to improve the algorithm by refining definitions of extreme events. Refinement of algorithm is currently work in progress as well as the evaluation against satellite observations and a hierarchy of numerical models. Nevertheless, the method is applicable for all kinds of gridded climatological datasets that contain air temperature, precipitation and snow depth.

Acknowledgement
This work is funded in the frame of ERA-Net plus Russia. TSU is supported by MOSC RF # 14.587.21.0048 (RFMEFI58718X0048), AWI and HZG are supported by BMBF (Grant no. 01DJ18016A and 01DJ18016B), and WUT by a grant of the Romanian National Authority for Scientific Research and Innovation, CCDI-UEFISCDI, project number ERANET-RUS-PLUS-SODEEP, within PNCD III

How to cite: Georgievski, G., Hagemann, S., Sein, D., Drozdov, D., Gravis, A., Romanovsky, V., Nicolsky, D., Onaca, A., Ardelean, F., Chețan, M., and Dornik, A.: Climate extremes relevant for permafrost degradation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-16115, https://doi.org/10.5194/egusphere-egu2020-16115, 2020.

Ground surface subsidence caused by the melt of excess ice is a key geomorphic process in permafrost regions. Subsidence can damage infrastructure, alter ecology and hydrology, and influence carbon cycling. The Geological Survey of Canada maintains a network of thaw tubes in northwestern Canada, which records annual thaw penetration, active-layer thickness, and ground surface elevation changes at numerous sites. Measurements from the early 1990s from 17 sites in the Mackenzie Delta area have highlighted persistent increases in thaw penetration in response to rising air temperatures. These increases in thaw penetration have been accompanied by significant ground surface subsidence (~5 to 20 cm) at 10 ice rich sites, with a median subsidence rate of 0.4 cm a^-1 (min: 0.2, max: 0.8 cm a^-1). Here we present preliminary results comparing these long-term field data to simulations for two observation sites using the Northern Ecosystem Soil Temperature (NEST) model. NEST has been modified to include a routine that accounts for ground surface subsidence caused by the melt of excess ground ice. The excess ice content of upper permafrost in the simulations was estimated based on ratios between thaw penetration and subsidence measured at each thaw tube. The NEST simulations begin in 1901, and there is little ground surface subsidence until the 1980s. The simulated rate of ground surface subsidence increases in the 1990s. The modelled ground surface subsidence is in good agreement with the measured annual magnitudes and longer-term patterns over the measurement period from 1992 to 2017. This preliminary assessment indicates that the modified NEST model is capable of predicting gradual thaw subsidence in ice-rich permafrost environments over decadal timescales.

How to cite: O'Neill, H. B. and Zhang, Y.: Simulation and validation of long-term ground surface subsidence in continuous permafrost, western Arctic Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20012, https://doi.org/10.5194/egusphere-egu2020-20012, 2020.

Recent intensification of slope thermokarst is transforming permafrost preserved glaciated landscapes and causing significant downstream effects. In this paper we: A) Describe the thaw-related mechanisms driving the evolution of slope to stream connectivity; B) define the watershed patterns of thermokarst intensification; and C) project the cascade of effects through the Arctic drainage networks of northwestern Canada. The power-law relationships between disturbance area and volume, and thickness of permafrost thawed, in conjunction with a time-series of disturbance mapping show that the non-linear intensification of slope thermokarst is mobilizing vast stores of previously frozen glacial sediments linking slopes to downstream systems. Mapping across a range of catchment scales indicates that slope thermokarst predominantly affects first and second order streams. Slope sediment delivery now frequently exceeds fluvial transport capacity of these streams by several orders of magnitude indicating long-term perturbation. Mapping shows slope thermokarst is directly affecting over 6760 km of stream segments, over 890 km of coastline and over 1370 lakes across the 1,000,000 km² Arctic drainage basin from continuous permafrost of northwestern Canada. The downstream projection of thermokarst disturbance increases affected lakes by a factor of 4 and stream length by a factor of 7, and suggests that fluvial transfer has the potential to yield numerous thermokarst impact zones across coastal areas of western Arctic Canada. The Prince of Wales Strait between Banks and Victoria Islands is identified as a hotspot of downstream thermokarst effects, and the Peel and Mackenzie rivers stand out as principle conveyors of slope thermokarst effects to North America’s largest Delta and to the Beaufort Sea. The distribution of slope thermokarst and the fluvial pattern of sediment mobilization signal the climate-driven rejuvenation of post-glacial landscape change and the triggering of a time-transient cascade of downstream effects. Geological legacy and the patterns of continental drainage dictate that terrestrial, freshwater and marine environments of western Arctic Canada will be a hotspot of climate-driven change through the coming centuries. 

How to cite: Kokelj, S., Kokoszka, J., van der Sluijs, J., Rudy, A., Tunnicliffe, J., Shakil, S., Tank, S., and Zolkos, S.: Slope thermokarst transforms permafrost preserved glacial landscapes and effects propagate through Arctic drainage networks. , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12498, https://doi.org/10.5194/egusphere-egu2020-12498, 2020.

Vast areas of the Arctic host ice-rich permafrost, which is becoming increasingly vulnerable to terrain-altering thermokarst in a warming climate. Among the most rapid and dramatic changes are retrogressive thaw slumps. These slumps evolve by a retreat of the slump headwall during the summer months, making them detectable by comparing digital elevation models over time using the volumetric change as an indicator. Despite the availability of many topographic InSAR observations to generate digital elevation models, there is currently no method to map and analyze retrogressive thaw slumps. 
Here, we present and assess a method to detect and monitor thaw slumps using time-series of elevation models (DEMs), generated from single-pass InSAR observations, which have been acquired across the Arctic at high resolution since 2011 by the TanDEM-X satellite pair.  At least three observations over this timespan are available with a spatial resolution of about 12 meter and the height sensitivity of 0.5-2 meter. We first difference the generated digital elevation and detect significant elevation changes taking the uncertainty estimates of each elevation measurement into account. In the implementation of the processing chain we focused on making it as automated as much as possible to be able to cover large areas of the northern hemisphere. This includes detecting common problems with the data and apply appropriate algorithms to obtain DEMs with high accuracy. Additionally we implemented methods to deal with problematic features like wet-snow, vegetation and water bodies. After generating the DEMs we us DEM differencing followed by a blob detection and cluster algorithm to detect active thaw slumps. To improve the accuracy of our method we apply and compare different machine learning methods, namely a simple threshold method, a Random Forest and a Support-Vector-Machine. To estimate the accuracy of our method we use data from past studies as well as a classification based on optical satellite data.
The obtained locations of thaw slumps can be used as a starting point to extract important slump properties, like the headwall height and volumetric change, which are currently not available on regional scales. Additionally to the thaw slump detection, we show first results of the thaw slump property extraction for thaw slumps located in Northern Canada (Peel Plateau, Mackenzie River Delta, Banks Island, Ellesmere Island). 

How to cite: Bernhard, P., Zwieback, S., Leinss, S., and Hajnsek, I.: Monitoring rapid permafrost thaw using elevation models generated from satellite radar interferometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6965, https://doi.org/10.5194/egusphere-egu2020-6965, 2020.

The Mackenzie-Delta Region is known for strong morphological activity in context of global warming and permafrost degradation, which reveals in a large number of retrogressive thaw slumps. These are frequently found along the shorelines of inland lakes and the coast; however, this geomorphological phenomenon also occurs at inland ​​streams and creeks of the Peel Plateau and the Richardson Mountains, located in the southwest of the delta. Here several active retrogressive thaw slumps are found of which some have reached an extent of several hectares, e.g. the mega slump at the Dempster Creek.

In this study we investigated a recent retrogressive thaw slump at the edge of the Richardson Mountains close to the Dempster Highway to determine the subsurface properties using non-invasive geophysical methods. We performed three-dimensional Ground Penetrating Radar (GPR) surveys, as well as quasi-three-dimensional Electrical Resistivity Tomography (ERT) surveys in order to investigate the subsurface characteristics adjacent to the retreating headwall of the slump. These measurements provide information on the topography of the permafrost table, ice content and/or water pathways on top, within or under the permafrost layer. Additionally, we performed manual measurements of the active layer thickness for validation of the geophysical models. The approach was complemented by the analysis of high-resolution photogrammetric digital elevation models (DEM) that were generated using in situ drone acquisitions.

The measured active layer depths show a strong influence of the relief and especially of small creeks on the permafrost table topography. Likely, this influence also is the primary trigger for the initial slump activity. In addition, the ERT measurements show strong variations of the electrical resistivity values in the upper few meters, which are indicative for heterogeneities, also within the ice-rich permafrost body. Especially noticeable is a layer of low resistivity values in an area adjacent to the slump headwall. This layer is found at depths between 4m to 7m, which approximately corresponds to the base of the headwall. Here, the low resistivity values could be indicative for an unfrozen or water-rich layer below the ice-rich permafrost. Consequently, this layer may have contributed to the initial formation of the slump and is important for the spatial extension of the slump.

These results present new insights into the subsurface of an area adjacent to an active retrogressive thaw slump and may contribute to a better understanding of slump development.

How to cite: Kunz, J., Kneisel, C., Ullmann, T., and Baumhauer, R.: Multi-methodological investigation of a retrogressive thaw slump in the Richardson Mountains, Northwest Territories, Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14201, https://doi.org/10.5194/egusphere-egu2020-14201, 2020.

The Peel Plateau in northwestern Canada hosts some of the fastest growing “mega slumps”, retrogressive thaw slumps exceeding 2000 m² in area. The region is located at the former margin of the Laurentide ice sheet and its landscape is dominated by ice-rich hummocky moraines. Rapid permafrost thaw resulting from enhanced warming and increases in summer precipitation has been identified as a major driver of sediment mobilization in the area, with some of the largest slumps relocating up to 10⁶ m³ of previously frozen sediments into fluvial networks. The biogeochemical transformation of this thawed substrate within fluvial networks may represent a source of CO₂ to the atmosphere and have a large impact on downstream ecosystems, yet its fate is currently unclear. Concentrations of dissolved organic matter are lowered in slump-impacted streams, while the particle loads increase. Here, we aim to characterize the mobilized material and its sources by analyzing active layer, Holocene and Pleistocene permafrost, debris (recently thawed, still at the headwall) and slump outflow samples from four different slumps on the Peel Plateau. We use sediment properties (mineral surface area, grain size distribution), carbon isotopes (¹³C, ¹⁴C) and molecular markers (solvent-extractable lipids, lignin phenols, cutin acids, non-extractable compound classes analyzed by pyrolysis-GCMS) in order to assess the composition and quality of the mobilized sediment and organic matter and thereby improve our understanding of their fate and downstream effects. Preliminary results show that organic matter content and radiocarbon age in debris and outflow from all four slumps are dominantly derived from Holocene and Pleistocene permafrost soils with a smaller influence of the organic-rich active layer. Degradation proxies based on extractable lipid and lignin biomarkers suggest Holocene and Pleistocene permafrost organic matter to be more matured than the fresh plant material found in the active layer, while debris and outflow samples show a mixed signal. For the non-extractable organic matter, aromatics and phenols make up the largest fraction of all samples. Lignin markers are almost exclusively found in the active layer samples, which also contain a larger proportion of polysaccharides, while N-containing compounds and alkanes make up the remaining 2-25 % with no obvious patterns. Active layer soils also have the highest median grain sizes, whereas Pleistocene permafrost soils consist of much finer mineral grains. Samples collected at the slump outflow are significantly more homogeneous (i.e., showing a narrower grain size distribution) than any of the other samples. We thus infer that both organic matter degradation and hydrodynamic sorting during transport play a role within these slump features; determining their relative magnitudes will be crucial to better assess potential feedbacks of these increasingly abundant “mega slumps” to changing climate.

How to cite: Bröder, L., Keskitalo, K., Zolkos, S., Shakil, S., Tank, S., Tesi, T., van Dongen, B., Haghipour, N., Eglinton, T., and Vonk, J.: Characterization of mobilized sediments and organic matter in retrogressive thaw slumps on the Peel Plateau, NWT, Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7176, https://doi.org/10.5194/egusphere-egu2020-7176, 2020.

Underlain by ice-rich permafrost, the Peel Plateau in western Canada is highly susceptible to rapid permafrost degradation in the form of retrogressive thaw slumps and has experienced a non-linear intensification in the area, volume, and thickness of permafrost thawed since 2002. These slumps tend to occur along stream networks, which flow directly into the Peel River, through the Mackenzie Delta, and into the Beaufort Sea. Thus, lateral transport of previously sequestered organic carbon from these features has the potential to propagate far downstream. Upstream-downstream comparisons have shown that thaw slumps mobilize material to stream systems primarily in the form of particulate organic carbon (POC), increasing organic carbon yields by orders of magnitude, and switching stream networks to particle-dominated systems. Furthermore, the bulk POC released from slumps can be upwards of 10,000 ¹⁴C years old, and base-extracted fluorescence measurements suggest material is more reworked since terrestrial production compared to upstream material.

To determine how far this effect propagates downstream we measured particulate and dissolved organic carbon (DOC) fluxes across stream transects extending 0.4 to 1 km downstream of thaw slumps in 1^st to 2^nd order streams and found no consistent decrease in TSS or POC fluxes with transit downstream.  In addition, we measured the composition (%POC, C:N, fluorescence, D¹⁴C) and flux of DOC and POC within the ~1100 km² Stony Creek watershed, examining tributary streams representing different vegetative, slump-density, and geological units in addition to the Stony Creek mainstem, to determine contributions to downstream flux. We found organic carbon fluxes were dominated by slump-mobilized POC at all points downstream of disturbance, and that these organic carbon fluxes were greater than any non-disturbed tributary stream. The ¹⁴C age of POC along the Stony Creek mainstem increased by thousands of years with the introduction of slump inputs and remained similarly depleted in ¹⁴C at the watershed outlet. Using historical suspended sediment, POC, and discharge data for the 75,000 km² Peel River drainage basin containing the Stony Creek watershed, we will examine whether there have been increases in instantaneous sediment and POC fluxes during the thaw season to track the trends of intensifying slump activity that have been documented on the Peel Plateau. Constraining the downstream effect of these abrupt, localized disturbances may improve detection and prediction of change that will likely cascade through the region over the coming decades.

How to cite: Shakil, S., Tank, S., Kokelj, S., and Vonk, J.: Downstream persistence of particulate organic carbon released from thaw slumps on the Peel Plateau, NT, Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10567, https://doi.org/10.5194/egusphere-egu2020-10567, 2020.

Around the Arctic Ocean there are many stretches of coastline composed of ice-rich sediments. With the dramatic climatic, oceanic and terrestrial changes that are currently occurring, there is considerable concern over the stability of these coasts and how they are being altered. With the complexity that permafrost conditions add to the coastal setting, modelling erosion involves a more detailed understanding of the physical and thermal conditions as well as the sedimentological and wave action processes. This research examines the role that the shallow water energy balance plays in preserving sub-bottom massive ice as the coastline retreats and the implications it has for secondary subsea disturbance once the water depth increases.

The study area was Peninsula Point which is approximately 10 km west of Tuktoyaktuk, NWT, Canada. The massive ice and retrogressive thaw slumps at this location are some of the more dramatic examples of the impact of ice-rich permafrost on coastal processes in the Arctic. By mapping the area with satellite and aerial imagery and conducting repeat ground penetrating radar surveys (GPR) over a 30 year period, the long-term character of coastal retreat above, and below, the water line is revealed. In winter, the GPR was pulled behind a snowmobile along transects on land, across the shoreline and out onto the near shore area of the Beaufort Sea. This provided the stratigraphic continuity between the terrestrial and sub-sea settings. The GPR revealed the massive ice and sedimentary architecture, from which vertical and lateral relationships to the coastline were determined. The roles of erosion, re-sedimentation and shallow-water thermodynamics in the degradation and preservation of massive ground ice were revealed. Using this new information, modeling of the coastal retreat and sediment contributions to the ocean demonstrated a much more complex system than previously assumed.

How to cite: Moorman, B.: Submarine preservation of massive tabular ground ice by coastal retrogressive thaw slumps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11343, https://doi.org/10.5194/egusphere-egu2020-11343, 2020.

Changing environmental conditions in the Arctic have profound impacts on permafrost coasts, which erode at great pace. Although numbers exist on annual carbon and sediment fluxes from coastal erosion, little is known on how terrestrial organic matter (OM) is transformed by thermokarst and –erosional processes on transit from land to sea. Here, we investigated a retrogressive thaw slump (RTS) on Qikiqtaruk - Herschel Island in the western Canadian Arctic. The RTS was classified into an undisturbed, disturbed and nearshore zone and systematically sampled along transects. Collected sediments were analyzed for organic carbon (OC), nitrogen (N), stable carbon isotopes (δ13C-OC) and ammonium. C/N-ratios, δ13C-signatures and ammonium concentrations were used as general indicator for OM degradation. Permafrost sediments from the RTS headwall and mud lobe sediments from the thaw stream outlet were incubated to further assess OM degradation and potential greenhouse gas formation during slumping and upon release into the nearshore zone. Our results show that OM concentrations significantly decrease upon slumping in the disturbed zone with OC and N decreasing by >70% and >50%, respectively. Whereas δ13C-signatures remain fairly stable, C/N-ratios decrease significantly and ammonium concentrations increase slightly in fresh slumping material. Nearshore sediments have low OM contents and a terrestrial signature comparable to disturbed sites on land. The incubations show that carbon dioxide (CO2) forms quickly from thawing permafrost deposits and mud debris with ~2-3 mg CO2 per gram dry weight being cumulatively produced within two months. We suggest that the initial strong decrease in OM concentration after slumping is caused by a combination of OC degradation, dilution with melted massive ice and immediate offshore transport via the thaw stream. After stabilization in the slump floor, recolonizing vegetation takes up N from the disturbed sediment. Upon release into the nearshore zone, larger portions of OM are directly deposited in marine sediments, where they further degrade or being buried. The incubations indicate that CO2 is rapidly produced upon slumping and potentially continues to form within the nearshore zone that receives eroded material. We conclude that coastal RTS systems profoundly change the characteristic of modern and ancient permafrost terrestrial OM during transit from land to sea - a process which is likely linked to the production of greenhouse gases. Our study provides valuable information on the potential fate of terrestrial OM along eroding permafrost coasts under the trajectory of a warming Arctic.

How to cite: Tanski, G., Lantuit, H., Wagner, D., Knoblauch, C., Ruttor, S., Radosavljevic, B., Wolter, J., Fritz, M., Strauss, J., Irrgang, A. M., Ramage, J., Sachs, T., and Vonk, J. E.: Retrogressive thaw slumps along permafrost coasts transform organic matter before release into the Arctic Ocean , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8806, https://doi.org/10.5194/egusphere-egu2020-8806, 2020.

With the increased availability and coverage of high resolution satellite imagery, characterizing processes at the pan-Arctic scale is now possible. This baseline pan-Arctic product will enable us to highlight areas for future research efforts and to standardize observations that are currently locally or regionally focused. The ArcticDEM project (www.arcticdem.org) has released a large collection of 2 meter resolution Digital Elevation Models (DEMs) for all land areas above 60 °N. These DEMs are created using high resolution (~0.5 m) stereo paired satellite images (by DigitalGlobe and include Worldview- 1 (launched 2007), 2 (2009), 3 (2014) and GeoEye-1 (2008) satellites). Using repeat DEMs, we are developing algorithms for automated detection to identify and quantify land surface topographic changes from Arctic volcano eruptions and mass wasting events to create a pan-Arctic mass wasting inventory, including retrogressive thaw slumps. Currently, retreat rates reported for retrogressive thaw slumping activity differ between studies, and our dataset will enable rates to be standardized for slump activity after 2007. Furthermore, our mass wasting inventory will enable us to investigate the triggers of mass wasting events and to analyze the linkages to the contributing factors including climate, topography, and geology. We will be presenting preliminary results focusing specifically on retrogressive thaw slumps, including time series analysis for topographic change detection and using field observations for validation. We welcome collaborators who can share the field or remote sensing observations to aid in our validation efforts.

How to cite: Dai, C., Jones, M., Howat, I., Liljedahl, A., Lewkowicz, A., and Freymueller, J.: Using ArcticDEM to identify and quantify pan-Arctic retrogressive thaw slump activity, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12142, https://doi.org/10.5194/egusphere-egu2020-12142, 2020.

Retrogressive thaw slumps (RTS) occur from the mass wasting of ice-rich permafrost. These horseshoe-shaped features have an ablating or retreating ice-rich headwall with fluidized sediment that is transported along the RTS floor. RTS can remain active for up to decades and enlarge as the headwall retreats. With observed increases in RTS number, rates and sizes in recent decades, there is a need to understand these highly dynamic landforms, however there is a general lack of detailed field observations of RTSs. We monitored 3 RTS for over half of the 2017 thaw period by setting up and tracking survey transects on a near daily basis. We correlated mean daily and cumulative retreat to mean daily air temperature (MDAT), total daily precipitation (TDP) and thawing degree days (TDD) using various polynomial regressions and Pearson correlation techniques. Our results show that July retreat was highly variable and periods of increased RTS retreat did not always align with periods of increased air temperature. Also, multiple periods of increased retreat could occur within a single period of increased air temperature. These retreat trends were observed to be largely driven by sediment redistribution in the RTS floor. Retreat rates decreased suddenly in early August, indicating a threshold of either air temperature, solar radiation or a combination of both must be reached for increased retreat rates. There was a statistically significant correlation between daily mean and mean cumulative retreat with MDAT (p < 0.001) and TDD (p < 0.001 and < 0.0001) but not with TDP. Correlating mean cumulative retreat and cumulative TDD using polynomial regression (quadratic and cubic) generated R² values greater than 0.99 for all 3 sites as these variables account for past and current conditions within the monitoring period, as well as lag responses of retreat. This suggests the potential of accurately modelling RTS retreat with minimal field data (air temperature and headwall position), however this is currently restricted to individual RTSs and only within short time scales. We tested this idea by modelling 2 weeks of cumulative retreat in 2018 for 2 of our sites we monitored using the 2017 regression equations. Percent prediction error was 8% at one site and 16% at the other. Monitoring RTS on a daily scale allows RTS behaviour and trends to be identified that may be obscured at annual time scales. With the widespread increased numbers of RTSs being observed around the Arctic, understanding their dynamics is critical as these landforms impact surrounding ecosystems and infrastructure which will be exacerbated with climate change.  

How to cite: Ward Jones, M., Jones, B., and Pollard, W.: Daily monitoring of retrogressive thaw slumps in the Fosheim Peninsula, Ellesmere Island, Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-360, https://doi.org/10.5194/egusphere-egu2020-360, 2020.

Thermal denudation is a combination of the processes responsible for the formation of retrogressive thaw slumps (cryogenic earth flows) and thermocirques. Thermocirques are the depressions with a semi-circle shape resulting from tabular ground ice thaw. Environments characteristic of Сentral parts of Yamal and Gydan peninsulas forming the so called  Kara sub-latitudinal transect, are favorable to activation of thermal denudation. The key factors are continuous permafrost distribution and shallow occurrence of tabular ground ice.

An increase in ground temperature and active layer thickness in 2012-2013 cause the intensification of thermal denudation along Kara sub-latitudinal transect. Field studies in the area of “Vaskiny Dachi” research station as well as remote sensing of 2018 data demonstrates the presence of both active and stabilized thermocirques during.

This research presents preliminary results of collecting and analyzing the distribution of more than 400 landforms caused by thermal denudation identified in central Yamal and central Gydan peninsulas. Coastal thermodenudation landforms were not taken into account to exclude the influence of wave erosion in this study. Such work became possible due to free of charge satellite images with a very high spatial resolution available at the service Yandex.Maps (https://yandex.ru/maps/).

In Yamal peninsula, we identified 63 active and 53 stabilized thermodenudation landforms, in Gydan peninsula, 169 active and 166 stabilized, respectively. Active thermodenudation features concentrate in the western and southern parts of central Yamal, while stabilized dominate in western and central parts. In central Gydan both active and stabilized features of thermal denudation are located at northwestern part and are distributed more evenly compared to Yamal. Northern border of all identified thermodenudation features for both Yamal and Gydan peninsulas is located at 71 degrees North, and the southern border at 69 degrees North. Despite the difficulties of visual interpretation of thermal denudation features, we defined the majority of them as thermocirques, most of which are located along lake coastlines. Such indication was also confirmed by in-situ data collected during multiyear field campaigns in the study area. These results reveal a prevalence of thermal denudation features in the study area and the collected data gives us an opportunity for spatial analysis of their distribution.

The reported study was partially funded by RFBR according to the research project #18-05-60222 

How to cite: Nesterova, N., Khomutov, A., Kalyukina, A., and Leibman, M.: The specificity of thermal denudation feature distribution on Yamal and Gydan peninsulas, Russia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-746, https://doi.org/10.5194/egusphere-egu2020-746, 2020.

The activation of retrogressive thaw slumps is associated with slope surface stability disturbances, or with an increase in the depth of seasonal thawing, that can reach the top of surface-near ground ice. Most retrogressive thaw slumps are confined to terraced slope surfaces that have been undercut and started to retreat due to lateral river erosion or wave action along lake, river or sea shores. Subsequent long-term retrogressive that slump growth depends on constant removal of material from the slope foot by river water or sea waves.

We have studied the current dynamics of coastal destruction and retrogressive thaw slumps in the western (Kolguev Island) and one of the eastern-most (Novaya Sibir’ Island) occurrences of tabular ground ice in the Eurasian Arctic. A wide set of multi-temporal optical earth observation data of high and very-high spatial resolution (SPOT 6 & 7, GeoEye, WorldView, Kompsat, Prism, Formosat, and Resurs) was used. We modified the TanDEM-X DEM (12 m) for relief reconstruction of earlier stage relief settings to ensure consistent orthorectification of oblique viewing satellite imagery. All raw images were terrain-corrected and georeferenced using a comprehensive block adjustment.

In the western part of Kolguev Island retrogressive thaw slump average retreat rates of different thermocirque features varied from 0.7 to 7.9 m/year in 2002-2018. Maximum rates reached 14.5-15.1 m/year. On the Novaya Sibir’ Island thermocirques averaged retreat rates in 2007-2018 varied from 3.3 to 8.5 m/year, maximum rates were up to 15.5 m/year.

Besides dependence of thermocirque occurrence on local ground ice conditions, external forcing on coastal dynamics and thermocirque retreat has been analysed for air temperature and sea ice fluctuations through sums of positive daily mean air temperature and the duration of the open-water period variability for specific periods bracketed by image acquisition dates. Ice conditions in the coastal zone (app. near 50 km of coastal line) of the studied areas were analyzed according to microwave satellite OSI-450 and OSI-430 datasets. We assumed the open-water season as the period when sea ice concentration was less than 15%. Around Kolguev Island, over the 2006-2018 there has been not statistically significant linear trend for open-water period - median value of linear trend is 2.5 days/year with different sea ice conditions off the south and north coasts of the island. At the same time, an increase in the annual sum of positive daily mean  air temperature is noted. For the period 2006-2018, the linear trend was 23.2 degree/year. That is why, for Kolguev Island, we expect at least a sustained level of substantially stronger retreat rates when compared with the past, if not a further increase in thermal denudation intensity and thermocirque growth, and strong and steady rates of coastal destruction due to wave action. Further research will focus on identifying commonalities and differences between the two study regions with respect to hydrometeorological and permafrost conditions.

Supported by RFBR grants № 18-05-60080 and 18-05-60221, and by DFG grant № WE4390/7-1.

How to cite: Kizyakov, A., Günther, F., Zimin, M., Sonyushkin, A., Zhdanova, E., Wetterich, S., and Medvedev, A.: Retrogressive thaw slumps in areas with tabular ground ice on Kolguev (Barents Sea) and Novaya Sibir’ (East-Siberian Sea) Islands, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7611, https://doi.org/10.5194/egusphere-egu2020-7611, 2020.

The Arctic has warmed twice as fast as the globe and sea-ice extent has decreased, causing permafrost to thaw and the duration of the open-water period to extend. This combined effect increases the vulnerability of the Arctic coast to erosion, which in turn releases substantial amounts of carbon to both the ocean and the atmosphere, potentially contributing to further warming due to a positive climate-carbon cycle feedback. Therefore, Arctic coastal erosion is an important process of the global carbon cycle.

Comprehensive modelling studies exploring Arctic coastal erosion within the Earth system are still in their infancy. Here, we describe the development of a semi-empirical Arctic coastal erosion model and its coupling with the Max Planck Institute Earth System Model (MPI-ESM). We also present preliminary results for historical and future climate projections of coastal erosion rates in the Arctic. The coupling consists on the exchange of a combination of driving forcings from the atmosphere and the ocean, such as surface air temperature, winds and sea-ice concentration, which result in annual coastal erosion rates. In a further setp, organic matter from the eroded permafrost is provided to the ocean biogeochemistry model and, consequently, to the global carbon cycle including atmospheric CO₂.

How to cite: Nielsen, D. M., Baehr, J., Brovkin, V., and Dobrynin, M.: Representing Arctic coastal erosion in the Max Planck Institute Earth System Model (MPI-ESM), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10477, https://doi.org/10.5194/egusphere-egu2020-10477, 2020.

In the last century the number of retrogressive thaw slumps has doubled in some arctic regions, e.g. Herschel Island, Yukon Territory, Canada [Lantuit and Pollard, 2008]. Retrogressive thaw slumps are a common thermocarst landform along the coast of Herschel Island [Lantuit and Pollard, 2005]. However mechanical conditions leading to the evolution of those retrogressive thaw slumps are poorly understood.

For a better understanding of internal thermal processes in these retrogressive thaw slumps we implemented different electrical resistivity profiles (ERT). They cross the focused thaw slump longitudinally and transversally. We compared about 2 km of new ERT-data from 2019 with the same transects from 2011 to gain information about the temperature distribution and the temperature changes in the slump ground.

The aim for our study is to gain a profound understanding of the strong and deep thermal disturbances generated by retrogressive thaw slumps and how they change over time, leading to a possible polycyclicality of these slumps.

Lantuit, H., and W. H. Pollard (2005), Temporal stereophotogrammetric analysis of retrogressive thaw slumps on Herschel Island, Yukon Territory, Nat. Hazards Earth Syst. Sci. 5 (3), 413–423.

Lantuit, H., and W. H. Pollard (2008), Fifty years of coastal erosion and retrogressive thaw slump activity on Herschel Island, southern Beaufort Sea, Yukon Territory, Canada, Geomorphology 95 (1-2), 84–102.

How to cite: Eppinger, S., Krautblatter, M., Lantuit, H., and Fritz, M.: Thermal behaviour of retrogressive thaw slumps over time revealed by ERT - an example from Herschel Island, Canada, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17801, https://doi.org/10.5194/egusphere-egu2020-17801, 2020.

Rapid and sustained warming of the northern high latitudes has led to increased permafrost thaw and retrogressive thaw slump (RTS) activity in some areas of the Arctic. Thaw slumps are common in the Tuktoyaktuk Coastlands (Northwest Territories, Canada) and expose relict ice wedge polygon networks that contain a long-term record of winter precipitation isotopes. Notably, the stable isotope geochemistry of ice wedges can be used as a paleotemperature proxy for the winter season, a seasonality that is largely missing from current understandings of Holocene paleoclimate change in the Arctic.

In this study, we sampled lateral cross-sections of four relict ice wedges from RTS exposures at coastal sites on Hooper Island, Pelly Island, Richards Island and near Tuktoyaktuk. Ice blocks capturing the entire growth sequences of the ice wedges (i.e., ice wedge center to ice-sediment contact) were collected by chainsaw and kept frozen in field coolers, and later sub-sampled at high-resolution in a cold lab. The ice wedges were sub-sampled at 1-1.5 cm horizontal resolution, integrating ~1-3 ice veins per sample on average. We analysed the stable hydrogen- and oxygen-isotope ratios (δ²H and δ¹⁸O) of each sample (N = 803). The age of the ice was estimated by AMS-DO¹⁴C dating of 6 to 10 samples per ice wedge, evenly distributed across each wedge to capture the full range of ages. A composite δ¹⁸O record spanning the period 7,400-600 cal yr BP was also constructed using the dated samples only (N = 36). The all-sample co-isotope (δ²H-δ¹⁸O) data are defined by regression line that is remarkably similar to the Local Meteoric Water Line, suggesting the ice wedges reliably preserve the isotopic composition of local precipitation, which is strongly influenced by mean air temperatures. The composite record shows an increase in δ¹⁸O over the last 7,400 years which we interpret as a long-term warming trend of the mean winter climate. This warming trend is largely explained by increasing November-April insolation at 69°N, a result that is corroborated by two independent high-resolution ice wedge records from the Siberian Arctic and is also in agreement with model-based simulations of the winter climate. This record, the first of its kind in the North American Arctic, provides a more seasonally holistic perspective on Holocene climate change and highlights the potential to use permafrost isotope records to fill paleoclimate knowledge gaps in Arctic regions were more traditional precipitation isotope archives (e.g., ice cores) do not exist.

How to cite: Porter, T., Holland, K., Froese, D., and Kokelj, S.: Long-term warming of Holocene winter temperatures in the Canadian Arctic recorded in stable water isotope ratios of ice wedges, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12181, https://doi.org/10.5194/egusphere-egu2020-12181, 2020.

Dating of ancient permafrost is essential for understanding permafrost stability and interpreting past climate and environmental conditions over Pleistocene timescales but faces substantial challenges to geochronology.

Here, we date permafrost from the world’s largest retrogressive thaw slump at Batagay in the Yana Upland, East Siberia (67.58 °N, 134.77 °E). The slump headwall exposes four generations of ice and sand-ice (composite) wedges that formed synchronously with permafrost aggradation. The stratigraphy differentiates into a Lower Ice Complex (IC) overlain by a Lower Sand Unit, an Upper IC and an Upper Sand Unit. Two woody beds below and above the Lower Sand Unit represent the remains of two episodes of taiga forest development prior to the Holocene forest. Thus, the ancient permafrost at Batagay potentially provides one of the longest terrestrial records of Pleistocene environments in western Beringia.

We apply four dating methods to the permafrost deposits to disentangle the chronology of the Batagay permafrost archive – optically-stimulated luminescence (OSL) dating of quartz and post-infrared-stimulated luminescence (pIR-IRSL) dating of feldspar as well as accelerator mass spectrometry-based Cl-36/Cl dating of wedge ice and radiocarbon dating of organic material.

The age information obtained so far indicates that the Batagay permafrost sequence is discontinuous and that the Lower IC developed well before MIS 7, the overlying Lower Sand Unit formed during MIS 6, and the Upper IC and the Upper Sand Unit formed both during MIS 3-2.

Additional sampling for all dating approaches presented here took place in spring 2019, and is part of ongoing research to enhance the geochronology of the exceptional palaeoenvironmental archive of the Batagay megaslump.

How to cite: Wetterich, S., Murton, J. B., Toms, P., Wood, J., Blinov, A., Opel, T., Fuchs, M. C., Merchel, S., Rugel, G., Gärtner, A., and Savvinov, G.: Multi-method dating of ancient permafrost of the Batagay megaslump, East Siberia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2999, https://doi.org/10.5194/egusphere-egu2020-2999, 2020.

In recent years, permafrost ground ice (i.e. ice wedges and pore ice) has been frequently utilized as a paleoclimate archive for the Late Pleistocene and Holocene, mainly using stable isotopes from water as proxies for local air temperatures. Due to their formation processes (frost cracking in winter and crack infilling mainly with snowmelt in spring), ice wedges have a unique winter seasonality, whereas pore ice integrates summer or annual precipitation.

The world’s largest retrogressive thaw slump at Batagay in the Yana Upland, East Siberia (67.58 °N, 134.77 °E), provides unique access to Late and Middle Pleistocene permafrost formations usually deeply buried in the frozen ground. The Batagay megaslump exposes syngenetic ice wedges and composite wedges (ice–sand wedges) along with pore ice in four cryostratigraphic units: (1) the Lower Ice Complex, (2) the Lower Sand, (3) the Upper Ice Complex, and (4) the Upper Sand.

Here, we present ground-ice stable-isotope data from all four units. This dataset is accompanied by precipitation stable-isotope values from winter snowpack and summer rain as a first stable-isotope framework for this region.

The high continentality of the study region with – extremely low winter temperatures – is clearly reflected by the stable-isotope composition for ice wedges from the Upper Ice Complex (MIS 3) and nearby Holocene ice wedges. Both are much more depleted than for any other ice-wedge study site in East Siberia. The ice wedges from the Lower Ice Complex are likely the oldest ice wedges (>0.5 Ma) ever analyzed isotopically and also point to very cold winter climate during formation. Stable-isotope signatures of composite wedges and pore ice are less distinctive and require detailed studies of formation processes and seasonality.

How to cite: Opel, T., Wetterich, S., Meyer, H., and Murton, J.: Ground-ice stable-isotope paleoclimatology at the Batagay megaslump, East Siberia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3748, https://doi.org/10.5194/egusphere-egu2020-3748, 2020.

With the ongoing Arctic warming, permafrost thaw accelerated during the last decade as much as it is now a global concern for biodiversity loss, food webs and biogeochemical cycling. This rapid permafrost degradation forms features such as massive retrogressive thaw slumps that give access to exceptional records for Quaternary biodiversity change investigations. The Batagay megaslump located in northern Yakutia, East Siberia, is the world’s largest thawslump known to date, and along its ~55m high headwall it gives access to Late and Mid Pleistocene permafrost deposits up to more than 500 kyrs in age. During an expedition to this unique site in 2017, sediment samples were collected with ages from more than 500 kyrs to modern time for the analysis of ancient DNA (aDNA). Our aim is to characterise the biodiversity and changes over geological timescales of this region in East Siberia. Using the aDNA extracted from these ancient environmental samples, we first performed a metabarcoding analysis (chloroplast trnL) to investigate past vegetation composition. We then performed a shotgun metagenomic analysis, which enabled a much higher depth of sequence data and allowed us to access the entire biodiversity, from Eukaryotes to Prokaryotes, Archaea and Viruses. This approach opened up new horizons, making it possible not only to investigate biodiversity composition and changes but also to infer on potential interactions across taxa and kingdoms. Both methods together allowed comparison and ensured robustness of the results obtained. We present here one of the very first studies done on the global, past and modern, biodiversity of permafrost regions which holds an enormous potential to reveal new insights into the evolution of this fragile ecosystem.

How to cite: Courtin, J., Perfumo, A., Stoof-Leichsenring, K., and Herzschuh, U.: Characterisation of East Siberian paleodiversity based on ancient DNA analyses of the Batagay megaslump exposure, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21041, https://doi.org/10.5194/egusphere-egu2020-21041, 2020.

The Batagay mega slump is the largest active thaw slump on the planet. Enormously rapid thermal erosion gave access to permafrost sediments that deposited since the Middle Pleistocene. Permafrost is an excellent medium for the preservation of ancient organic matter. The Batagay exposure is well known for some spectacular findings of Pleistocene megaherbivore carcasses including the youngest steppe bison found in Eurasia so far, dated to 8.2 ka BP. The extraordinarily long sequence of Pleistocene deposits in Batagay is therefore an excellent archive of the palaeoenvironmental history in the Yana highlands - a region with uniquely stable cold-continental climate known as the pole of cold in the northern hemisphere. This region is regarded as refugial area for extrazonal steppe plants and now extinct large grazers together constituting the Pleistocene mammoth steppe, which covered vast areas in high and mid latitudes of the northern hemisphere during cold stages. Modern vegetation around the study site consists of light taiga mainly composed of larch, shrub alder, shrub birches and stone pine. To understand the processes that resulted in the demise of Pleistocene megafauna and in the biological turnover during the late Quaternary, we reconstructed vegetation and environmental conditions during the two climate extremes of the late Pleistocene, the onset of the last glacial maximum and the last interglacial using remains of plants and insects preserved in organic-rich material. The results from studies of plant material gathered in a fossil ground squirrel nest suggest that grassland vegetation corresponding to modern meadow steppes in Central Yakutia and northern Mongolia existed in the study area during the last cold stage. During the last interglacial, open coniferous woodland similar to modern larch taiga was the primary vegetation at the site. Abundant charcoal indicates wildfire events during the last interglacial. Zoogenic disturbances of the local vegetation were indicated by the presence of ruderal plants, especially by the abundant nitrophytic Urtica dioica, suggesting that the area was an interglacial refugium for large herbivores. Meadow steppes, which formed the primary vegetation during cold stages and provided potentially suitable pastures for herbivores, were a significant constituent of the plant cover in the Yana Highlands also under the full warm stage conditions of the last interglacial. Consequently, meadow steppes occurred in the Yana Highlands during the entire investigated timespan of the Pleistocene documenting a remarkable environmental stability. The documented fossil record also proves that modern steppe occurrences in the Yana Highlands did not establish as late as in the Holocene, as suggested by some scholars, but instead are relicts of a formerly continuous steppe belt extending from Central Siberia to Northeast Yakutia during the Pleistocene.

How to cite: Kienast, F., Ashastina, K., Kuzmina, S., and Rudaya, N.: Vegetation at the northern pole of cold during the climate extremes of the late Pleistocene: fossil records from the Batagay mega thaw slump, Yakutia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20513, https://doi.org/10.5194/egusphere-egu2020-20513, 2020.

Cryogenic processes, especially “warm” significantly affect the reliability of the northern infrastructure. Thermoerosion is the process of destruction of the banks or ground massives constructed by the permafrost and ground ice, by thermal and mechanical influence of the running water. Tazovskiy peninsula, where the largest gas production facilities are located, is referred in Russia as “The kingdom of the thermoerosion”.

The geodetical level of the surface on Tazovskiy peninsula varies between 15–20 m. and 60–80 m., but the thermoerosion processes are very active. The area exposed to thermoerosion was 10–15% of the territory in the beginning of 1980^th and actively enlarges.

The period of the maximum active layer thaw depth is August, when the precipitation amount is the highest, which coupled with the raising trend of the air temperature (0.8°C per decade) (IPCC, 2014) and growing temperature (up to 1.5-2^o warmer) of the upper permafrost layers, results in the ground destruction. The appearance of the thermoerosion process we clarify by the highly blurred sediments at the surface: the upper Quaternary silty iced (up to 40–60%) sands or sandy loams. The other auspicious factor is polygonal ice systems formed by iced peatlands (2–3 m of depth) serving as the positions of the future thermoerosion cuts. Our investigations showed that in the raising probability of the erosion occurrence, weak root systems of the shrubs and grasses can not cope with the process.

The factor that significantly intensify the speed of the thermoerosion is active snow melting in May–beginning of June. Together with increasing snowiness of the winters it additionally activies the processes of gullies formation. The conducted field works during the snowmelt revealed lumpy collapsing of the big ground blocks near the lateral sides of the watercourses which was the main reason of erosion speed boost. The blocks remained frozen, the rate of the lateral erosion was 15–20 cm/per day, the widths was up to  1.5–2 m.

We started to observe dynamics of the thermoerosion in early 2000’s. The rate of the gullies growing on the right side of the r. Nyudya-Adlyurdyepoka was up to 10 m. per year. The length of the gully was 60 m. in 2006 and it was U-shaped. In 2016 the gully had length of 80 m.. The profile of the gully became V-shape everywhere, the gully was branched out and the steepness of the edges increased. More detailed characteristics of the other representative gullies development will be consider in this research.

Our study showed that construction and exploitation of the road systems between the deposit fields entailed the formation of linear overmoistured zones near the roads and formed new thermoerosion systems.  

 Satellite data showed that territory occupied by thermoerosion processes raised by 15–20 % in the last 40 years. It is due to climatic changes, the active exploitation of the technogenic systems on iced and easily blurred soils.

This work is supported by the RFBR project â„–18-05-60080 «Dangerous nival-glacial and cryogenic processes and their impact on infrastructure in the Arctic»

How to cite: Tolmanov, V.: Thermoerosion process on Tazovskiy peninsula. Factors and dynamics., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-825, https://doi.org/10.5194/egusphere-egu2020-825, 2020.

Between 2016 and 2018, Gagnon and Allard (2019) investigated the impact of climate change on winter ice-wedge (IW) cracking frequency and IW morphology. In this study, they revisited 16 sites in the Narsajuaq valley (Canada) that were extensively studied between 1989 and 1991. Climate warming only started around 1993 whence mean annual air temperatures started to rise from -10 °C then to about -6 °C nowadays. This gave the unique opportunity to observe and measure changes by directly comparing field data with data pre-dating a climate warming of known amplitude. They found that based on IW tops, the active layer reached depths that were 1.2 to 3.4 times deeper than in 1991, which led to the widespread degradation of IW in the valley. Whereas 94% of the IWs unearthed in 1991 showed multiple recent growth structures, only 13% of the IWs unearthed in 2017 still had such features.

However, about half of the IWs in 2017 had ice veins connecting them to the base of the active layer, an indication that the recent cooling trend (2010-now) in the region was enough to reactivate frost cracking and IW growth. This shows that the soil system can respond quickly to short-term climate variations. For this study, we aimed to determine how changes in surface temperatures affected active-layer thickness (ALT) and dynamics over the past 25 years in order to understand the timing and reaching times of ground temperature thresholds for soil cracking and IW degradation. We used TONE, a one-dimensional finite-element thermal model, to simulate ground temperatures over the past 25 years. A monthly mean air temperature from a reanalysis (1948-2016) was combined with data from a weather station about 9 km west of the study area (2002-2018) to simulate the soil temperature profiles of four typical soil types found in the valley: thick sandy peat cover, thick peat cover, thin sandy peat cover, and fluvial sands.

Our results show that ALT variations were predominantly controlled by changes in thawing season air temperature with regards to the previous year. As soon as 1998, the active layer had already reached the main stages of the IWs, i.e. the largest and oldest part composing the IWs, but it is only from 2006 that the main stages started melt until 2010, an exceptionally warm year. Based on soil temperature thresholds, our results show that IWs remained active until around 2006. This means that as the active layer deepened and caused IW tops degradation, freezing season temperatures were still cold enough to induce soil cracking and IW growth in width. After 2010, the cooling trend was enough to reactivate the IWs from as a soon as 2011. This study shows that prior to advanced degradation, IWs can melt substantively and remain active at the same time as long as freezing season temperatures are cold enough to induce soil contraction cracking. However, it is likely that pulse events such as ground collapse will cause positive feedbacks contributing to rapid IW degradation before the soil completely stops cracking.

How to cite: Gagnon, S. and Allard, M.: Modelled (1990-2100) Variations in Active-Layer Thickness and Ice-Wedge Activity Near Salluit, Nunavik (Canada) , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1428, https://doi.org/10.5194/egusphere-egu2020-1428, 2020.

Climate change has a strong impact on periglacial regions and intensifies the degradation of mountain permafrost. This can result in instabilities of steep rock walls as rock- and ice-mechanical properties are modified. Besides altitude and the related air temperature, latitude is a crucial factor, as solar radiation has a strong impact on the energy transfer processes from the atmosphere to the ground. It can differ significantly in intensity and time over latitudinal positions and exposures of frozen rock slopes.

In this project, we suggest improving the parametrization of short-wave and long-wave radiation in thermal models for permafrost degradation. To achieve this, we will analyze temperature data of surface temperature loggers from Southern Norway to Svalbard. In total, 37 loggers were installed between 2010 and 2017. The field sites display enormous latitudinal gradients as well as topographic settings. Furthermore, they provide hourly data, allowing us to set up short-stepped time series for examination of solar radiation angles at varying latitudes.

The data is used to set up a transient heat-flow model (CryoGrid) to simulate the local thermal regime. The model takes into account varying input of short-wave radiation due to aspect, slope angle and time as well as long-wave radiation under different sky-view factors. Finally, the influence of solar radiation on permafrost degradation in steep rock walls is investigated.

How to cite: Schmidt, J., Westermann, S., Etzelmüller, B., and Magnin, F.: The influence of radiative forcing on permafrost temperatures in Arctic rock walls, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2416, https://doi.org/10.5194/egusphere-egu2020-2416, 2020.

In the permafrost-affected landscape, surface and near-surface water movement links areas of higher elevation with lowlands and surface water bodies. Water supply is dominated by snow melt and is thus highly seasonal, as most water moves on the frozen surface in spring, passing only a thin layer of thawed soil. Soluble nutrients mobilized by soil thaw may thus be transported laterally from upslope to downslope ecosystems, which in nutrient-limited cold ecosystems may affect vegetation, ecosystem respiration and surface-atmosphere interaction. In a nitrogen (N) limited ecosystem, however, released inorganic N may in reality not travel far downslope.
This study quantifies the potential effect of the snowmelt water nutrient transport by tracing dissolved N in meltwater moving downslope on the frozen surface in a W Greenlandic slope with a snow fan supplying meltwater throughout most of the summer. We use the stable isotopes ¹⁵N and D applied simultaneously on top of the frozen surface upslope in a combined solution to investigate the behavior of water and dissolved N flow patterns. We further address the effect of season by tracing N supplied in the early thaw season (30 cm to the frozen surface) and in the late thaw season (90 cm to the frozen surface). Monitoring the slope in detail, we then use the numerical coupled heat-and-mass transfer Coup model to simulate the biotics and abiotics of the receiving ecosystem and study the importance of the lateral N input and the effect of increased N transport in a warmer future.  
About 50 % of the N tracer was retained in the ecosystem immediately below injection in the early growing season (30 cm active layer), whereas about 35 % was retained in the later growing season (90 cm active layer). Most of the applied ¹⁵N was rapidly immobilized by microbes and into the bulk soil, whereas only a few percentages was taken up by the vegetation. D recovery seemed to follow the pattern of microbial N uptake, suggesting that N and D moved physically from the frozen surface and to the immediate subsoil together.

Modelling the ecosystem based on measured N and C pool sizes, meteorology, soil temperature and –moisture revealed a large N constrain on vegetation growth. The current observed vegetation could not be explained with the measured pools alone, suggesting an “invisible” source of N to support the observed vegetation. We conclude that a substantial fraction of lateral N input is transported further downslope, but that increases in N release and transport might not affect vegetation immediately, as most supplied N ends in the soil pool. Vegetation in the receiving ecosystem relies on an external N source, which could be dissolved N transported by snowmelt water on the frozen surface. Snowmelt redistribution of N in the landscape may thus be a factor to account for when studying N cycling in a spatial context.

How to cite: Rasmussen, L. H., Ambus, P., Zhang, W., Jansson, P. E., Michelsen, A., and Elberling, B.: Slope hydrology and permafrost: The effect of snowmelt N transport on downslope ecosystem, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2927, https://doi.org/10.5194/egusphere-egu2020-2927, 2020.

Recent field and modelling studies indicate that a fully-coupled, multi-dimensional, thermo-hydraulic (TH) approach is required to accurately model the evolution of permafrost-impacted landscapes and groundwater systems. However, the relatively new and complex numerical codes being developed for coupled non-linear freeze-thaw systems require validation. This issue was first addressed within the InterFrost IPA Action Group, by means of an intercomparison of thirteen numerical codes for two-dimensional TH test cases (TH2 & TH3). The main results (cf. Grenier et al. 2018 and wiki.lsce.ipsl.fr/interfrost) demonstrate that these codes provide robust results for the test cases considered.

The second phase of the InterFrost project is devoted to the simulation of a cold-room reference experiment based on test case TH2 (Frozen Inclusion). In a first implementation phase of the experimental setup, the initial frozen inclusion was inserted in the setup prior to the complete filling of the porous medium and the flow initiation. The thermal evolution of the system was monitored by thermistors located at the center of the initial inclusion and along the downgradient centerline. This setup provided optimal conditions to control the initial experiment geometries but resulted in slight differences in the initialization time for different experiments.

In a second implementation strategy, we now consider “in place” generation of an initial frozen inclusion through a cooling coil. The initial frozen inclusion is obtained after the initial cooling time and its initial thermal state is measured by means of an array of thermistors. In a second step, the flow is initiated, and the thermal evolution is monitored through an array of 11 thermistors (within the initial position and downgradient).

The experimental setup and an overview of all monitoring results as well as preliminary numerical simulations are presented. In an attempt to prevent formerly observed drifts in total water flowrates, the porous medium is renewed for each single experiment considering some key experimental conditions (full-flow vs. no-flow). A repetition of experiments provides an estimation of experimental uncertainty bounds. Derived results and conclusions from this experiment will form the basis for the next phase within the InterFrost validation exercise.

How to cite: Grenier, C. and Costard, F.: InterFrost Project Phase 2: Updated experiment results for the validation of Cryohydrogeological codes (Frozen Inclusion), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4865, https://doi.org/10.5194/egusphere-egu2020-4865, 2020.

Quantification of ground ice is particularly crucial for understanding permafrost systems. The volumetric ice content is however rarely estimated in permafrost studies, as it is particularly difficult to retrieve. Geophysical methods have become more and more popular for permafrost investigations due to their capacity to distinguish between frozen and unfrozen regions and their complementarity to standard ground temperature data. Geophysical methods offer both a second (or third) spatial dimension and the possibility to gain insights on processes happening near the melting point (ground ice gain or loss at the melting point). Geophysical methods, however, may suffer from potential inversion imperfections and ambiguities (no unique solution). To reduce uncertainties and improve the interpretability, geophysical methods are standardly combined with ground truth data or other independent geophysical methods. We developed an approach of joint inversion to fully exploit the sensitivity of seismic and electrical methods to the phase change of water. We choose apparent resistivities and seismic travel times as input data of a petrophysical joint inversion to directly estimate the volumetric fractions of the pores (liquid water, ice and air) and the rock matrix. This approach was successfully validated with synthetic datasets (Wagner et al., 2019). This joint inversion scheme warrants physically-plausible solutions and provides a porosity estimation in addition to the ground ice estimation of interest. Different petrophysical models are applied to several alpine sites (ice-poor to ice-rich) and their advantages and limitations are discussed. The good correlation of the results with the available ground truth data (thaw depth and ice content data) demonstrates the high potential of the joint inversion approach for the typical landforms of alpine permafrost (Mollaret et al., 2020). The ice content is found to be 5 to 15 % at bedrock sites, 20 to 40 % at talus slopes, and up to 95 % at rock glaciers (in good agreement to the ground truth data from boreholes). Moreover, lateral variations of bedrock depth are correctly identified according to outcrops and borehole data (as the porosity is also an output of the petrophysical joint inversion). A time-lapse version of this petrophysical joint inversion may further reduce the uncertainties and will be beneficial for monitoring and modelling studies upon climate-induced degradation.

References:

Mollaret, C., Wagner, F. M. Hilbich, C., Scapozza, C., and Hauck, C. Petrophysical joint inversion of electrical resistivity and refraction seismic applied to alpine permafrost to image subsurface ice, water, air, and rock contents. Frontiers in Earth Science, 2020, submitted.

Wagner, F. M., Mollaret, C., Günther, T., Kemna, A., and Hauck, C. Quantitative imaging of water, ice, and air in permafrost systems through petrophysical joint inversion of seismic refraction and electrical resistivity data. Geophysical Journal International, 219 (3):1866–1875, 2019. doi:10.1093/gji/ggz402.

How to cite: Mollaret, C., Wagner, F. M., Hilbich, C., and Hauck, C.: Quantification of ground ice through petrophysical joint inversion of seismic and electrical data applied to alpine permafrost, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7489, https://doi.org/10.5194/egusphere-egu2020-7489, 2020.

The surface energy balance is one of the most important influencing factors for the ground thermal regime. It is therefore crucial to understand the interactions of the individual heat fluxes at the surface and within the subsurface layers as well as their relative impacts. A unique set of high-altitude meteorological measurements has been analysed to determine the energy balance at three mountain permafrost sites in the Swiss Alps, where data is being collected since the late 1990s in collaboration with the Swiss Permafrost Monitoring (PERMOS). The three stations have a standardized equipment with sensors for four-component radiation, air temperature, humidity, wind speed and direction as well as ground temperatures and snow height. The three sites differ considerably by their surface and ground material composition ranging from a coarse blocky active layer above ice supersaturated permafrost at rock glacier Murtèl-Corvatsch to deeply weathered micaceous shales, which are covered by fine grained debris of sandy and silty material with a low ice content at the Northern slope of Schilthorn summit. The third site at the Stockhorn plateau shows intermediate ice contents and heterogeneous surface conditions with medium-size debris, fine grained material and outcropping bedrock. Ice content estimation and general ground characterisation are based on geophysical surveying and borehole drilling.

The energy fluxes are calculated based on around two decades of field measurements. While the determination of the radiation budget and the ground heat flux is comparatively straightforward (by the four-component radiation sensor and thermistor measurements within the boreholes, respectively), larger uncertainties exist for the determination of sensible and latent turbulent heat fluxes. They are therefore determined on the one hand by the bulk aerodynamic method using the bulk Richardson number to describe the stability of the surface layer relating the relative effects of buoyancy to mechanical forces and on the other hand by the bowen ratio method.

Results show that mean air temperature at Murtèl-Corvatsch (1997–2018, elevation 2600 m asl.) is –1.66°C and has increased by about 0.7°C during the observation period. The Schilthorn (1999–2018, elevation 2900 m asl.) site shows a mean air temperature of –2.48°C with a mean increase of 1.0°C and the Stockhorn (2003–2018, elevation 3400 m asl.) site shows lower air temperatures with a mean of –5.99°C with an increase of 0.6°C. Measured net radiation, as the most important energy input at the surface, shows substantial differences with mean values of 33.41 Wm^-2 for Murtèl-Corvatsch, 40.65 Wm^-2 for Schilthorn and 24.88 Wm^-2 for Stockhorn. The calculated turbulent fluxes show values of around 7 to 12 Wm^-2 using the bowen ratio method and 8 to 18 Wm^-2 using the bulk method at all sites. Large differences are observed regarding the energy used for melting of the snow cover: at Schilthorn a value of 12.41 Wm^-2, at Murtèl-Corvatsch of 7.31 Wm^-2 and at Stockhorn of 3.46 Wm^-2 is calculated reflecting the differences in snow height at the three sites.

How to cite: Hoelzle, M., Hauck, C., Noetzli, J., Pellet, C., and Scherler, M.: Long-term energy balance measurements at three different mountain permafrost sites in the Swiss Alps, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8076, https://doi.org/10.5194/egusphere-egu2020-8076, 2020.

Ground thermal regime in cold environments is key to understanding the effects of climate change on surface–atmosphere feedbacks. The northern Eurasia, covering over half of terrestrial areas north of 40°N, is sensitive to the ongoing climate change due to underlain permafrost and seasonal frost. Here, we quantify the recent ground thermal dynamics and variations over northern Eurasia by compiling measurements of soil temperature data over 457 sites at multiple depths from 1975-2016. Our analysis shows that the mean annual ground temperature has significant warming trends by 0.30–0.31 °C/decade at depths of 0.8, 1.6, and 3.2 m. We found that the changes in annual maximum ground temperatures were more pronounced than mean annual ground temperatures with a weakened warming magnitude (0.40 to 0.31°C/decade) from upper to lower ground. Our results also suggest the substantial differences in warming magnitudes through parameters and depths over different frost-related areas. The ground over continuous permafrost area warmed faster than non-continuous permafrost and seasonal frost areas in shallow ground (0.8 and 1.6 m depth) but slower in deeper ground (3.2 m). Our study highlights the varied ground temperature evolutions at multiple depths and different frost-related ground, suggesting the importance of separated discussions on different frost-affected ground in application and future research. Noteworthy, the results indicate that the significant ground warming can promote greenhouse gas emissions from soil to atmosphere, further accelerating climate change.

How to cite: Chen, L., Aalto, J., and Luoto, M.: Recent ground thermal dynamics and variations in northern Eurasia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9106, https://doi.org/10.5194/egusphere-egu2020-9106, 2020.

Recent studies have highlighted water supply as a driving factor for rock glacier deformation velocities. In parallel, numerous observations of correlating mean annual air- or ground temperatures and rock glacier velocities have been reported. We investigated the connection between rock glacier temperatures and –hydrology and found that there is no contradiction between both hypotheses. We observed that water supply to the shear horizon of rock glaciers is highly correlated to their mean annual temperatures and – even more pronounced – to their temperatures during early winter. The rock glacier temperatures influence the amount of water supplied to the shear horizon to a lesser extent, but strongly determine the duration of the water supply. The main external influencing factor on rock glacier dynamics found next to atmospheric warming was early winter snow cover. Our results are based on deformation- and borehole temperature measurements of four Swiss rock glaciers.

How to cite: Kenner, R., Pruessner, L., Beutel, J., Limpach, P., and Phillips, M.: Why rock glacier deformation velocities correlate with both ground temperatures and water supply at multiple temporal scales, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9534, https://doi.org/10.5194/egusphere-egu2020-9534, 2020.

The rate of climate warming in North-West Siberia is among the highest in the world and this trend is especially pronounced in summer [1]. Analysis of permafrost thermal conditions in this area provides plausible scenarios of permafrost degradation also elsewhere. An increase in the summer mean temperature together with the prolongation of the warm season results in the increase of the thawing degree-days enhancing thawing of permafrost. Here we present the results of decadal temperature observations from three boreholes near Nadym, North-West Siberia. We further use the results and the observed cryolithological structure of soils in two boreholes to model the long-term evolution of the deep permafrost under two climate scenarios, RCP2.6 (climate action, fast reduction of CO₂ emissions) and RCP8.5 (‘business as usual’). Both borehole sites have a topmost high-porosity, high-ice content layer of peat which helps prolonging the degradation. The main difference between the boreholes is snow cover resulting from the difference of borehole positions (one is located on the top of the hill). Our results suggest that under RCP8.5 scenario permafrost will degrade in both boreholes. On the contrary, under RCP2.6 scenario permafrost will degrade in one borehole with the deeper snow cover, where it already shows the signs of degradation. For the other borehole, the model predicts that permafrost will not degrade within the next 300 years, although the permafrost temperatures are eventually above -1°C.

[1] Frey K.E. & Smith L.C. Recent temperature and precipitation increases in West Siberia and their association with the Arctic Oscillation. Polar Research 22(2), 287–300 (2003).

How to cite: Ezhova, E., Kukkonen, I., Suhonen, E., Ponomareva, O., Gravis, A., Gennadinik, V., Miles, V., Drozdov, D., Lappalainen, H., Melnikov, V., and Kulmala, M.: Modelling of long-term permafrost evolution in the discontinuous permafrost zone of North-West Siberia, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10325, https://doi.org/10.5194/egusphere-egu2020-10325, 2020.

With climate warming shrubs can grow on high-Arctic tundra. This impacts many terms of the energy budget, resulting in a modification of the permafrost thermal regime. The summer surface albedo is decreased. The winter surface albedo is decreased because shrubs protrude above the snow. Winter conductive fluxes through the snow are reduced because shrubs trap snow, increasing snow depth. Shrubs also favor both snow melt in fall and spring and depth hoar formation in fall and winter, and both these factors affect snow thermal conductivity. Soil thermal properties may also be affected because of increased moisture.  We have measured many terms of the energy budget at Bylot Island, 73°N, Canada, at a herb tundra site and in a nearby large willow shrub patch. Monitored variables include radiation, snow and soil thermal conductivity and standard atmospheric variables. We observe that soil temperature at 15 cm depth is 1.5°C warmer under shrubs on a yearly average. The energetics of both sites are simulated using SurfexV8 including the detailed snow model Crocus. Combining observations and simulations indicates that the increased soil moisture under shrubs, by delaying  freezing by one month in fall, is an important factor in winter soil warming. Summer temperature is also markedly warmer under shrubs because of lower albedo and because the shrub understory is less insulating than on herb, which facilitates warming. These results show that investigating shrub impact using manipulations such as shrub removal is questionable because it does not restore pre-shrub understory and moisture.

How to cite: Domine, F., Lackner, G., Belke-Brea, M., Sarrrazin, D., and Nadeau, D.: Does shrubs growth in the high-Arctic lead to permafrost warming?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10837, https://doi.org/10.5194/egusphere-egu2020-10837, 2020.

Borehole soundings have revealed a warming of mountain permafrost of up to 1°C during recent decades. There is evidence that the increase in air temperature has favored the solute release from active rock glaciers, and pronounced changes in water quality of headwaters in the Alps have been described. Here, we report on solute concentrations of selected streams and springs in the vicinity of an active rock glacier in the Central European Alps (Lazaun, Italy). Stream water sampling started in 2007, and samples were analysed for major ions and heavy metals. We compare surface freshwaters of different origin and chemical characteristics, i.e. outflows of active and fossil rock glaciers, a spring emerging from a moraine and an ice glacier fed stream. Substance concentrations were highest in springs impacted by active rock glaciers, and dissolved ions increased up to a factor of 3 through the summer season. This pattern reflects a seasonally varying contribution to runoff by the melting winter snow pack, summer precipitation, baseflow and ice melt. Intense geochemical bedrock weathering of freshly exposed mineral surfaces, which are due to the downhill movement of the active rock glacier, is considered as a major reason for the high ion and metal concentrations in late summer runoff. In addition, solutes contained in the ice matrix of the rock glacier are released due to enhanced melting of rock glacier ice. On the contrary, minimum substance concentrations without any seasonal variability were found in the moraine spring.

How to cite: Nickus, U., Thies, H., Krainer, K., and Tessadri, R.: Rock glacier impact on high-alpine freshwater chemistry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12707, https://doi.org/10.5194/egusphere-egu2020-12707, 2020.

Snow depth increases observed and predicted in the sub-arctic are of critical importance for the dynamics of lowland permafrost and vegetation. Snow acts as an insulator that protects vegetation but may lead to permafrost degradation. In the Abisko area, in northernmost Sweden, there has been an increasing trend in snow depth during the last Century. Downscaled climate scenarios predict an increase in precipitation by 1.5 - 2% per decade for the coming 60 years. The observed changes in snow cover have affected peat mires in this area as thawing of permafrost, increases in active layer thickness and associated vegetation changes have been reported during the last decades. An experimental manipulation was set up at one of these lowland permafrost sites in the Abisko area (68°20’48’’N, 18°58’16’’E) 15 years ago, to simulate projected future increases in winter precipitation and to study their effect on permafrost and vegetation. The snow cover has been more than twice as thick in manipulated plots compared to control plots and it has had a large impact on permafrost and vegetation. It resulted in statistically significant differences in mean winter and minimum ground temperatures between the control and the manipulated plots. Already after three years there was a statistically significant difference between active layer thickness in the manipulated plots compared to the control plots. In 2019, the active layer thickness in the control plots were around 70 cm whereas in the manipulated plots it was 110 cm. The increased active layer thickness has led to surface subsidence due to melting of ground ice in all the manipulated plots. The increased snow thickness has prolonged the duration of the snow cover in spring with up to 22 days. However, this loss in early season photosynthesis was well compensated for by the increased absorption of PAR and higher light use efficiency throughout the whole growing seasons in the manipulated plots. Eriophorum vaginatum is a species that has been especially favored in the manipulated plots. It has increased both in number and in size. Underneath the soil surface, the roots have also been affected. There has been a strong increase in total root length and growth in the active layer, and deep roots has invaded the newly thawed permafrost in the manipulated plots. The increased active layer thickness has also had an effect on the bacterial community composition in the newly thawed areas. According to past, century-long patterns of increasing snow depth and projections of continuing increases, it is very likely that the changes in permafrost and vegetation that have been demonstrated by this experimental treatment will occur in the future under natural conditions.

How to cite: Johansson, M., Åkerman, J., Blume-Werry, G., Callaghan, T. V., Christensen, T. R., Monteux, S., and Dorrepaal, E.: 15 years of snow manipulation reveals huge impact on lowland permafrost and vegetation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13137, https://doi.org/10.5194/egusphere-egu2020-13137, 2020.

Arctic ecosystems outpace the global rate of temperature increases and are exceptionally susceptible to global warming. Concerns are raising that CO₂ and CH₄ released from thawing permafrost upon warming may induce a positive feedback to climate change. This is based on the assumption, that microbial activity increases with warming and does not acclimate over time. However, we lack a mechanistic understanding of carbon and nutrient fluxes including their spatial control in the very heterogeneous Arctic landscape. The objective of this study therefore was to elucidate the microbial controls over soil organic matter decomposition in different horizons of the active layer and upper permafrost. We investigated different landscape units (high-centre polygons, low-centre polygons and flat polygon tundra) in two small catchments that differ in glacial history, at the Yukon coast, Northwestern Canada.

In total, 81 soil samples were subjected to short-term (eight weeks) incubation experiments at controlled temperature (4 °C and 14 °C) and moisture conditions. Heterotrophic respiration was assessed weekly, whereas physiological parameters of soil microbes and their temperature response (Q₁₀) were determined at the end of the incubation period. Microbial growth was estimated by measuring the incorporation of ¹⁸O from labelled water into DNA and used to calculate microbial carbon use efficiencies (CUE). Microbial biomass was determined via chloroform fumigation extraction. Potential activities of extracellular enzymes involved in C, N, P and S cycling were measured using microplate fluorimetric assays.

Cumulative heterotrophic respiration of investigated soil layers followed the pattern organic layers > upper frozen permafrost > cryoturbated material > mineral layers in both catchments. Microbial respiration responded strongly in all soils to warming in all soils, but the observed response was highest for organic layers and cryoturbated material at the beginning and end of the experiment. Average Q₁₀ values at the beginning of the experiment varied between 1.7 to 4.3 with differences between horizons but converged towards Q₁₀ values between 2.0_min to 2.9_max after eight weeks of incubation. Even though microbial biomass C did not change with warming, microbial mass specific growth was enhanced in organic, cryoturbated and permafrost soils. Overall, warming resulted in a 65% reduced CUE in organic horizons.

Our results show no indication for physiological acclimatization of permafrost soil microbes when subjected to 8-weeks of experimental warming. Given that the duration of the season in which most horizons are unfrozen is rarely longer than 2 months, our results do not support an acclimation of microbial activity under natural conditions. Instead, our data supports the current view of a high potential for prolonged carbon losses from tundra soils with warming by enhanced microbial activity.

This work is part of the EU H2020 project “Nunataryuk”.

How to cite: Martin, V., Wagner, J., Speetjens, N., Lodi, R., Horak, J., Urbina-Malo, C., Mohrlok, M., Rottensteiner, C., a' Campo, W., Durstewitz, L., Tanski, G., Fritz, M., Lantuit, H., Hugelius, G., and Richter, A.: How do microorganisms from permafrost soils respond to short-term warming?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13452, https://doi.org/10.5194/egusphere-egu2020-13452, 2020.

Among mountainous landforms, rock glaciers are mostly abundant in periglacial areas, as tongue-shaped heterogeneous bodies. By measuring physical properties sensitive to useful hydro-mechanical parameters of the medium, a wide range of geophysical methods provides interesting tools to characterize and monitor rock glaciers at large scale⁽¹⁾. However, the need of high resolution temporal monitoring reduces the choice of such methods.

Passive seismic monitoring systems have the potential to overcome these difficulties, as recently shown on the Gugla rock glacier⁽²⁾. Indeed, seismological networks provide continuous recordings of both seismic ambient noise and microseismicity. From spectral analysis, we track resonance frequencies and modal parameters that are directly linked to elastic properties of the system, which evolve according to its rigidity and its density⁽³⁾⁽⁴⁾. Here, we propose to evaluate the potential of this methodology on two rock glaciers (Laurichard and Gugla) located in the Alps, at elevations where climatic forcing influences their internal structures and consequently their dynamics.

For both sites, we succeed in tracking and monitoring resonance frequencies of vibrating modes during several years. These frequencies show seasonal variations, indicating a freeze-thawing effect on elastic properties of the structure.

Assuming vibrating systems, we perform 2D mechanical modeling of rock glaciers, which fits well the recorded resonant frequencies. By modeling the increase of rigidity due to freezing in wintertime, seasonal variations are also mimicked. Differences between observed and modeled values, together with the variability of the results over sites, are discussed.

We finally compare the results of modal analysis with those from Ground Penetrating Radar surveys, in order to converge on a consistent view of these rock glaciers and their freeze-thawing cycles.

References

• (1) Kneisel, C., Hauck, C., Fortier, R., Moorman, B., (2008). Advances in geophysical methods for permafrost investigations. Permafrost and Periglacial Processes 19, 157–178. https://doi.org/10.1002/ppp.616
• (2) Guillemot A., Baillet L., Helmstetter A., Larose E., Garambois S., Mayoraz R., (2019). Seismic monitoring in the Gugla rock glacier (Switzerland): ambient noise correlation, microseismicity and modelling, Geophysical Journal International, submitted.
• (3) Roux Ph., Guéguen Ph., Baillet L., Hamze A. (2014). Structural-change localization and monitoring through a perturbation-based inverse problem, The Journal of the Acoustical Society of America 136, 2586; https://doi.org/10.1121/1.4897403
• (4) Larose E., C. S. (2015). Environmental seismology: What ca we learn on earth surface processes with ambient noise. Journal of Applied Geophysics, 116, 62-74.

How to cite: Guillemot, A., Baillet, L., Garambois, S., Bodin, X., Larose, É., Helmstetter, A., and Mayoraz, R.: Towards mechanical modeling of rock glaciers from modal analysis of passive seismic data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13874, https://doi.org/10.5194/egusphere-egu2020-13874, 2020.

Qinghai-Tibet Plateau (QTP) has the largest high-altitude permafrost zone in the middle and low latitudes. Substantial hydrologic changes have been observed in the Yangtze River source region and adjacent areas in the early 21st century. Permafrost on the QTP has undergone degradation under global warming. The ground leveling observation site near Tangula (33°04′N, 91°56′E) located in the degraded alpine meadow indicates that the ground has subsided 50mm since 2011. The contribution of permafrost degradation and loss of ground ice to the hydrologic changes is however still lacking. This study monitors the permafrost changes by applying the Small BAseline Subset InSAR (SBAS-InSAR) technique using C-band Sentinel-1 datasets during 2014-2019. The ground deformation over permafrost terrain is derived in spatial and temporal scale, which reflects the seasonal freeze-thaw cycle in the active layer and long-term thawing of ground ice beneath the active layer. Results show the seasonal thaw displacement exhibits a strong correlation with surficial geology contacts. The ground leveling data is used to validate the ground deformation monitoring results. Then, the ground deformation characteristics are analyzed against the landscape units. Last, the long-term inter-annual displacement value is used to estimate the water equivalent of ground ice melting.

How to cite: Wang, L., Zhao, L., Zhou, H., Liu, S., Huang, X., and Wang, C.: Monitoring permafrost changes in the Yangtze River source region of the Qinghai-Tibetan Plateau using differential SAR interferometry, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13906, https://doi.org/10.5194/egusphere-egu2020-13906, 2020.

Geophysical methods and especially electrical techniques have been used for permafrost detection and monitoring since more than 50 years. In the beginning, the use of Vertical Electrical Soundings (VES) allowed the detection of ice-rich permafrost due to the clear contrast between the comparatively low-resistive active layer and the high-resistive permafrost layer below. Only after the development of 2-dimensional tomographic measurement and processing techniques (Electrical Resistivity Tomography, ERT), in the late 1990’s, electrical imaging was widely applied for a large range of different permafrost applications, including ice content quantification and permafrost monitoring over different spatial scales. Regarding ERT monitoring, the comparatively large efforts needed for continuous and long-term measurements implies that there are still only few continuous ERT monitoring installations in permafrost terrain worldwide. One of the exceptions is a network of six permafrost sites in the Swiss Alps that have been constantly monitored in the context of the Swiss Permafrost Monitoring Network (PERMOS) since 2005, enabling the analysis of the long-term change in the ground ice content and associated thawing and freezing processes (Mollaret et al. 2019).

On the contrary, a much larger number (estimated to be > 500) of permafrost sites exist worldwide, where singular ERT (or VES) measurements have been performed in the past - many of them published in the scientific literature. These data sets are neither included in a joint database nor have they been analysed in an integrated way. Within a newly GCOS Switzerland-funded project we address this important historical data source. Whereas singular ERT data from different permafrost occurrences are not easily comparable due to the local influence of the geologic material on the obtained electrical resistivities, their use as baseline for repeated measurements and subsequent processing and interpretation in a climatic context is highly promising and can be effectuated with low efforts.

In this presentation we will show evidence that singular ERT surveys in permafrost terrain can indeed be repeated and jointly processed after long time spans of up to 20 years, yielding a climate signal of permafrost change at various sites and on different landforms. Examples are given from various field sites in Europe and Antarctica, and the results are validated with borehole data, where available. We believe that a joint international data base of historical ERT surveys and their repetitions would add an important data source available for permafrost studies in the context of climate change.

Mollaret, C., Hilbich, C., Pellet, C., Flores-Orozco, A., Delaloye, R. and Hauck, C. (2019): Mountain permafrost degradation documented through a network of permanent electrical resistivity tomography sites. The Cryosphere, 13 (10), 2557-2578.

How to cite: Hauck, C., Hilbich, C., Mollaret, C., and Pellet, C.: Permafrost monitoring by reprocessing and repeating historical geoelectrical measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14047, https://doi.org/10.5194/egusphere-egu2020-14047, 2020.

Surface state information, derived from ASCAT microwave sensors (C-band scatterometer), were empirically linked to in-situ arctic ground temperature measurements. The resulting FT2T-regressionmodel was established using the sum of days of year frozen and in-situ mean annual ground temperatures, both at specific depths and years. Regionally, the model showed the best results in Scandinavia and northern Russia with less than 1°C difference to the in-situ data. Overall, the results were valid for most depths and regions, with a slight tendency for underestimation of the ground temperatures on the Eurasian continent (about -1°C) and an overestimation on the American continent up to 2 °C.  The most northern parts of Greenland, the Canadian High Arctic Islands and Alaska, however, showed a high positive bias of more than 10°C. Reasons for this overshooting include the limited amount of measurements in those regions, the oceanic influence and possibly snow cover effects. 
Due to the inaccessibility of many arctic regions, in-situ data availability is still sparse and if available not harmonized. We used the currently revised annual ground temperature dataset from CCI+ Permafrost, which combines in-situ data from the GTNP-database, RosHydroMet and additional regional arctic ground temperature datasets (e.g. Nordicana). The resulting determination coefficients of the FT2T-model showed 55% explained variance at shallow borehole-depths below 80cm and decrease with depth to around 25% at 20 meters. This suggests that the sum of frozen days of year delivers better result at shallow depths in the active layer than at the actual permafrost table. The RMSE showed a dependency on the spread of measurement stations considered in the model calibration step. The more input regions we could use, the larger the RMSE got due to the increase of variability in the input data. Inevitably, it’s the in-situ information which enables the translation between ground temperatures and microwave backscatter and thus it fundamentally affects the accuracy of the result.

How to cite: Kroisleitner, C., Bartsch, A., Heim, B., and Wiezorek, M.: The potential of satellite derived surface state to empirically estimate pan-arctic ground temperature at specific depths and the essential role of in-situ data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15162, https://doi.org/10.5194/egusphere-egu2020-15162, 2020.

Freeze-thaw processes induced in the vicinity of borehole heat exchangers (BHE) as a result of operating temperatures below 0 °C can significantly affect the compound structure consisting of the BHE pipes, the cement-based grouting material as well as the surrounding soil. The hydraulic integrity of such systems is not ensured anymore and its thermal efficiency could be impaired. However, the knowledge on freezing and thawing processes in porous media, such as the grout and unconsolidated rock materials, is still incomplete. The content of unfrozen water has a strong impact on material properties influencing the overall heat and mass transfer processes. Moreover, freezing strongly depends on various boundary conditions such as soil type or pore water chemistry. Accordingly, it is essential to have adequate information about the freezing interval for different boundary conditions, which describe the transition from pure liquid water to the ice phase and vice versa.

Therefore, a thermo-hydraulic-mechanical (THM) experiment has been developed and is used to gain a more detailed insight into freezing processes in artificial grouts and unconsolidated rock materials. It consists of a modified triaxial test system, which can carry cylindrical samples with a diameter of up to 100 mm and a height of up to 200 mm. A confining pressure of up to 16 bar can be gained by a plunger system. The confining pressure liquid (water-glycol-mixture) can be tempered down to -25 °C and is used to induce freezing conditions on the lateral surface of the sample. Mechanical parameters such as the freeze pressure are recorded by an axial load sensor and a displacement sensor. Besides, the radial deformation can be observed by the volume displacement of the confining liquid. Moreover, the hydraulic conductivity of the sample is determined according to DIN EN ISO 17892 (2019). The fluid temperatures during the flow-through experiment can be varied between 5 °C and 25 °C to represent natural groundwater temperatures. In addition to that, the freeze-thaw experiment is equipped with an ultrasonic measurement device: In the observed temperature range, the wave velocity in solid particles is constant and not affected by temperature changes. However, with descending temperature, the ice content increases, which leads to an improved cross-linking of the solid soil particles. As a consequence, the bulk P-wave velocity increases with decreasing unfrozen water content. Hence, this relationship can be used to determine the content of unfrozen water during a freeze-thaw cycle.

At this time, the first experiments are conducted with this novel device. Consequently, initial results will be presented at the conference. Moreover, the results of the THM experiments will be implemented in numerical models, which allow for an upscaling of the experimental findings to real scale applications.

How to cite: Hesse, J. C., Schedel, M., Welsch, B., and Sass, I.: THM Experiment for the Investigation of Freeze-Thaw Processes in Soils and Grouting Materials, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18276, https://doi.org/10.5194/egusphere-egu2020-18276, 2020.

With climate change and the associated continuing recession of glaciers, water security, especially in regions depending on the water supply from glaciers, is threatened. In this context, the understanding of permafrost distribution and its degradation is of increasing importance as it is currently debated whether ground ice can be considered as a significant water reservoir and as an alternative resource of fresh water that could potentially moderate water scarcity during dry seasons in the future. Thus, there is a pressing need to better understand how much water is stored as ground ice in areas with extensive permafrost occurrence and how meltwater from permafrost degradation may contribute to the hydrological cycle in the region.

Although permafrost and permafrost landforms in the Central Andes are considered to be abundant and well developed, the data is scarce and understanding of the Andean cryosphere lacking, especially in areas devoid of glaciers and rock glaciers.

In the absence of boreholes and test pits, geophysical investigations are a feasible and cost-effective technique to detect ground ice occurrences within a variety of landforms and substrates. In addition to the geophysical surveys themselves, upscaling techniques are needed to estimate ground ice content, and thereby future water resources, on larger spatial scales. To contribute to reducing the data scarcity regarding ground ice content in the Central Andes, this study focuses on the permafrost distribution and the ground ice content (and its water equivalent) of two catchments in the semi-arid Andes of Chile and Argentina. Geophysical methods (Electrical Resistivity Tomography, ERT and Refraction Seismic Tomography, RST) were used to detect and quantify ground ice in the study regions in the framework of environmental impact assessments in mining areas. Where available, ERT and RST measurements were quantitatively combined to estimate the volumetric ground ice content using the Four Phase Model (Hauck et al., 2011). Furthermore, we developed one of the first methodologies for the upscaling of these geophysical-based ground ice quantifications to an entire catchment in order to estimate the total ground ice volume in the study areas.

In this contribution we will present the geophysical data, the upscaling methodology used to estimate total ground ice content (and water equivalent) of permafrost areas, and some first estimates of total ground ice content in rock glacier and rock glacier free areas and compare them to conventional estimates using remotely sensed data.

Hauck, C., Böttcher, M., and Maurer, H. (2011). A new model for estimating subsurface ice content based on combined electrical and seismic datasets, The Cryosphere, 5: 453-468.

How to cite: Mathys, T., Hilbich, C., Koenig, C. E. M., Arenson, L., and Hauck, C.: Upscaling of geophysical measurements: A methodology for the estimation of the total ground ice content at two study sites in the dry Andes of Chile and Argentina, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18397, https://doi.org/10.5194/egusphere-egu2020-18397, 2020.

Warming of mountain permafrost leads to growth of active layer thickness and reduction of rock wall stability. The subsequent increase of instable rock volumes can have disastrous or even fatal consequences, especially when cascading events are simultaneously triggered. This growth of climate-change-connected hazard, together with the recent increase of exposition of infrastructure and people, poses the alpine environments at a high risk, which needs to be monitored. Laboratory-calibrated Electrical Resistivity Tomography (ERT) has shown to provide a sensitive record for frozen vs. unfrozen conditions, presumably being the most accurate quantitative permafrost monitoring technique in permafrost areas where boreholes are not available.

The data presented here are obtained at the Steintälli ridge in Switzerland, which presents highly vulnerable permafrost conditions. A consistent 3D field set-up, the robust temperature calibration and the quantitative inversion scheme allow to compare measurements from the longest time series (2006-2019) of ERT in steep bedrock. A direct link to mechanical changes measured with tape extensometer is provided. Comparison of repeated hourly measurements as well as Wenner and Schlumberger arrays are also shown here, in order to increase the robustness of the delivered results.

Confirming the long-term observation from air temperatures, results from multiple parallel transects show an average resistivity reduction of 22%, concentrated at deeper layers of the permafrost lens. The permafrost area in the 3D cross sections also decreased from 30 to 10% (about 500 to 150m² in our transects), with losses mainly localized on the south-east part of the study site, but in some cases also extending to the north face. 

How to cite: Scandroglio, R. and Krautblatter, M.: Climate-change-induced changes in steep alpine permafrost bedrock. 13 years of 3D-ERT at the Steintälli ridge, Switzerland., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18808, https://doi.org/10.5194/egusphere-egu2020-18808, 2020.

Rock wall permafrost has been increasingly regarded since the early 2000s in reason of the growing frequency and magnitude of bedrock failures from mountain permafrost areas. One of the main current challenges to better assess its degradation and the failure mechanisms is the understanding of hydraulic processes, i.e. water infiltration and circulation in the fractures. Indeed, recent thermal and mechanical models have considered a homogeneous and ice-saturated rock medium, overlooking water-related processes which may act along fractures when water percolates. But observations of water stains alongside ice bodies in several rock fall scars point out the need to gain knowledge about such processes.

Recent development in numerical codes allow to fully couple thermal and hydraulic processes, and have so far mostly been used to investigate polar permafrost terrains. In this communication, we will present a first attempt to couple thermal and hydraulic processes in a numerical model of high-alpine bedrock permafrost. This entails designing a new modelling approach accounting for heterogeneous (fractured) and non-saturated areas in the rock medium, as well as water outlets and fracture intersections to permit water circulation. We implement Richards equations in the Finite Element simulation system Feflow (DHI-WASY) to model variably saturated flow and advective-conductive heat transports combined with phase change processes. We simulate heat and mass transports in a 2D geometry (vertical cross-section) reflecting the Aiguille du Midi settings (3842 m a.s.l., Mont Blanc massif, European Alps). The model is forced with climate time series partially constructed out of measured air temperature and assumptions about previous climate period. Steady freezing occurring between 1550 and 1850 AD (Little Ice Age) points out the role of fractures in the freezing rate, as fractures favor infiltration of cold water from the surface, acting as freezing corridors. Under thawing, water movements are enabled in the unfrozen upper parts of the model geometry through a partially saturated domain, whereas the lower part remains saturated. In the thawed zones, fractures that are not completely filled by ice can accelerate water circulation and create thawing corridors.

In this communication, we will present the modelling approach and the preliminary results. We will show that our numerical investigations bear strong potential to address thermal and mechanical effects of water infiltration (from snow melting and rain) and circulation in the frozen bedrock.

How to cite: Magnin, F., Josnin, J.-Y., Ravanel, L., and Deline, P.: Modelling water-related processes in rock wall permafrost , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19575, https://doi.org/10.5194/egusphere-egu2020-19575, 2020.

In the context of climate change, permafrost degradation is a key variable in understanding rock slope failures in high mountain areas. Permafrost degradation imposes a variety of environmental, economic and humanitarian impacts on infrastructure and people in high mountain areas. Therefore, new high-quality monitoring and modelling strategies are needed.

Electrical Resistivity Tomography (ERT) is the predominant permafrost monitoring technique in high mountain areas. Its high temperature sensitivity for frozen vs. unfrozen conditions, combined with the resistivity-temperature laboratory calibration on Wettersteinkalk (Zugspitze) (Krautblatter et al. 2010) gives us quantitative information on site-specific rock wall temperatures (Magnin et al. 2015). Long-term ERT-Measurements (2007/2014 – now) were taken at the Kammstollen along the northern Zugspitze rock face. Two high-resistivity bodies along the investigation area reach resistivity values ≥10^4.5Ωm (∼−0.5 °C), indicating frozen rock, displaying a core section with resistivities ≥10^4.7Ωm (∼−2 °C) (Krautblatter et al., 2010). We can differentiate seasonal variability, seen by laterally aggrading and degrading marginal sections (Krautblatter et al., 2010) and singular effects due to environmental factors and extreme weather events.

Here, we present a new local high-resolution numerical, process-orientated thermo-geophysical model (TGM) for steep permafrost rock walls. The model links apparent resistivities, the ground thermal regime and meteorological forcings as seasonality and long-term climate change to validate the ERT and project future conditions. The TGM comprises a surface energy balance model, conductive energy transport, turbulent and seasonal heat fluxes (sensible, latent, melt and rain heat fluxes) including phase-change, as well as a multi-phase rock wall composition.

Finally, we can reproduce the natural temperature field in the rock wall, assess the spatial-temporal permafrost evolution in alpine rock walls, validate the ERT measurements via the new TGM and the applicability of the laboratory derived resistivity-temperature relationship by Krautblatter et al. (2010) for natural rock-wall conditions.

Krautblatter, M., Verleysdonk, S., Flores-Orozco, A. & Kemna, A. (2010): Temperature- calibrated imaging of seasonal changes in permafrost rock walls by quantitative electrical resistivity tomography (Zugspitze, German/Austrian Alps). J. Geophys. Res. 115: F02003.

Magnin, F., Krautblatter, M., Deline, P., Ravanel, L., Malet, E., Bevington, A. (2015): Determination of warm, sensitive permafrost areas in near-vertical rockwalls and evaluation of distributed models by electrical resistivity tomography. J. Geophys. Res. Earth Surf., 120, 745-762.

How to cite: Schroeder, T., Scandroglio, R., Stammberger, V., Wittmann, M., and Krautblatter, M.: New multi-phase thermo-geophysical model: Validate ERT-monitoring & assess permafrost evolution in alpine rock walls (Zugspitze, German/Austrian Alps), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19984, https://doi.org/10.5194/egusphere-egu2020-19984, 2020.

Permafrost exists in the highest mountains of SE Europe (South Carpathians, Rila, Pirin) in small isolated patches, where local topography and landforms provide conditions for winter ground cooling and for shading and ground thermal isolation during summer.

We present a summary of the present state of mountain permafrost in the study area by analyzing the results of ERT (electrical resistivity tomography) and GPR (ground penetrating radar) profiles together with thermal measurements of ground surface and air performed at the sites of documented permafrost occurrence. The results are put in context with recent climate evolution by a decade of thermal measurements in the South Carpathians and three years in the Rila and Pirin Mountains.

Despite differences in air temperature and snow cover timing and thickness the permafrost extent remains constant at the study sites. The active layer is thick (between 5-10 m), whereas the permanently frozen layers vary in thickness even for the same study site, and are relatively thin compared to sites located in the Alps or the Andes, indicating that the existing permafrost is in imbalance with the current climate. Snow cover is probably the most important factor in seasonal evolution, controlling both the winter cooling and the summer thermal decupling of ground and air temperature. Recent evolution shows a tendency of shifting the snow cover period with later deposit and later thaw which favors permafrost conditions. We also observe a significant difference between Southern Carpathians and Rila and Pirin mountains, with snow patches lasting until late summer, August or September, in the later.

However snow cover present strong local variations in terms of thickness and isolating proprieties which makes it the least study and least understood factor in mountain permafrost dynamics in SE Europe.

How to cite: Sirbu, F., Onaca, A., Ardelean, F., Magori, B., and Urdea, P.: Present state of marginal mountain permafrost in South Eastern Europe, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20066, https://doi.org/10.5194/egusphere-egu2020-20066, 2020.