CR4.4

CR4 EDI
Subglacial and supraglacial processes of ice sheets, ice shelves and glaciers 

Supraglacial and subglacial processes play a key role in the structure, motion and stability of Earth’s ice masses. Such processes broadly relate to supraglacial hydrology (concerning the generation and movement of meltwater at the ice surface), subglacial hydrology (including the formation and operation of flow pathways beneath the ice), and subglacial processes (including deformation and erosion and its consequences for ice mass motion and the glacial-geomorphological record). This session brings together observational and modelling contributions that concern any such processes and/or interactions between them.

This session is a merger of initial sessions CR4.4 ‘Subglacial environment of ice sheets and glaciers’ and CR4.5 ‘Hydrology of ice shelves, ice sheets and glaciers - from the surface to the base’. The session is divided into three time blocks: (1) supraglacial hydrology, (2) subglacial hydrology, and (3) subglacial sedimentary processes.

Solicited authors: Jennifer Arthur, Kasia Warburton, Mohammed Reza Ershadi

Convener: Sammie BuzzardECSECS | Co-conveners: Rebecca Schlegel, Ian Hewitt, Robert Bingham, Martin WearingECSECS, Bryn Hubbard, Gabriela RaczECSECS
Presentations
| Fri, 27 May, 08:30–11:50 (CEST), 13:20–16:39 (CEST)
 
Room 1.15/16

Presentations: Fri, 27 May | Room 1.15/16

Chairpersons: Jennifer Arthur, Riley Culberg
Subglacial Hydrology
08:30–08:31
08:31–08:38
|
EGU22-1236
|
Virtual presentation
Anne Felden, Daniel Martin, and Esmond Ng

Water flowing under ice sheets and glaciers can have a strong influence on ice dynamics, particularly through pressure changes, suggesting that a comprehensive ice-sheet model should include the effect of basal hydrology. Modeling subglacial hydrology remains a challenge however, mainly due to the range of spatial and temporal scales involved - from subglacial channels to vast subglacial lakes. Additionally, subglacial drainage networks dynamically evolve over time. To address some of these challenges, we have developed an Adaptive Mesh Refinement (AMR) model based on the Chombo software framework. We extend the model proposed by Sommers and others, (2018) with a few changes to accommodate the transition from unresolved to resolved elements. We handle the strong non-linearities present in the equations by resorting to an efficient non-linear Full Approximation Scheme (FAS-MG) algorithm.  We outline the details of the algorithm and present convergence analysis results demonstrating its effectiveness. Additionally, we present results validating our approach, using test cases from the SHMIP inter-comparison project (2018). We finish by discussing ongoing work related to the coupling of SUHMO with the BISICLES AMR ice-sheet model.

How to cite: Felden, A., Martin, D., and Ng, E.: SUHMO: an AMR SUbglacial Hydrology MOdel , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1236, https://doi.org/10.5194/egusphere-egu22-1236, 2022.

08:38–08:45
|
EGU22-424
|
ECS
|
On-site presentation
Kevin Siu, Christine Dow, Mathieu Morlighem, Felicity McCormack, and Tim Hill

The Greenland and Antarctic ice sheets have differing climates, which makes surface melt a significant hydrological source in Greenland but not currently in Antarctica. Due to changing climate and warming air temperatures, Antarctica is predicted to experience more surface meltwater in the future. This will likely lead to surface features common in Greenland today, such as supraglacial lakes and moulins, to also form over grounded ice in Antarctica. Moulins in particular are important because they will route this surface melt into basal drainage networks. The resulting change in subglacial drainage characteristics and water volumes will potentially have far-reaching impacts on ice dynamics, ice shelf melt, grounding line stability, and ultimately global sea level rise. To examine this, we model the hydrological system in Wilkes Subglacial Basin, East Antarctica with the future climate in mind by incorporating moulins and surface melt to try to understand the impact that this will have on ice sheet and ice shelf dynamics. We use predictive data generated by the Community Climate System Model 4 (CCSM4) for surface runoff in Antarctica for the year 2100 as inputs to the Glacier Drainage System (GlaDS) subglacial hydrology model. We compare the modelling results from two different Representative Concentration Pathway (RCP) scenarios, RCP 2.6 and RCP 8.5. Moulin locations are predicted using current strain rates along preferential surface hydrology flow pathways and we also compare modelling results with different numbers and locations of moulins. Preliminary results show that even under the lower RCP 2.6 scenario, surface water input significantly alters basal drainage rates, channel extent, and water pressure near the grounding line. The changes are focussed during the modelled summer melt season with the hydrological system settling towards its current state over winter. This demonstrates that the future state of the climate will have an impact on the subglacial hydrology of Antarctica and, in turn, on ice flow speeds and ice shelf melt rates near the grounding line.

How to cite: Siu, K., Dow, C., Morlighem, M., McCormack, F., and Hill, T.: Modelling Subglacial Hydrology under Future Climate Scenarios in Wilkes Subglacial Basin, Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-424, https://doi.org/10.5194/egusphere-egu22-424, 2022.

08:45–08:52
|
EGU22-4926
|
Virtual presentation
Basile de Fleurian, Richard Davy, and Petra M. Langebroek

In recent years, temperatures over the Greenland ice sheet have been rising, leading to an increase in surface melt. This increase however can not be reduced to a simple number. Throughout the recent years we have seen some extreme melt seasons with melt extending over the whole surface of the ice sheet (2012) or melt seasons of lower amplitudes but with a longer duration (2010). The effect of those variations on the subglacial system and hence on ice dynamic are poorly understood and are still mainly deduced from studies based on mountain glaciers.

Here we apply the Ice-sheet and Sea-level System Model (ISSM) to a synthetic glacier with a geometry similar to a Greenland ice sheet land terminating glacier. The forcing is designed such that it allows to investigate different characteristics of the melt season such as its length or intensity. Subglacial hydrology and ice dynamics are coupled within ISSM allowing to study the response of the system in terms of subglacial water pressure and the final impact on ice dynamics. Of particular interest is the evolution of the distribution of the efficient and inefficient component of the subglacial drainage system which directly impacts the water pressure evolution at the base of the glacier. We note that the initiation of the melt season and the intensity of the melt at this period is a crucial parameter when studying the dynamic response of the glacier to different melt season characteristics.

From those results, we can infer a more precise evolution of the dynamics of land terminating glaciers that are heavily driven by their subglacial drainage system. We also highlight which changes in the melt season pattern would be the most damageable for glacier stability in the future.

How to cite: de Fleurian, B., Davy, R., and Langebroek, P. M.: Is longer or warmer melt season a more important driver of ice dynamics., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4926, https://doi.org/10.5194/egusphere-egu22-4926, 2022.

08:52–08:59
|
EGU22-5140
|
ECS
|
On-site presentation
Hanwen Zhang, Timothy Davis, Richard Katz, Laura Stevens, and Dave May

Basal crevasses are macroscopic structural discontinuities at the base of ice sheets and glaciers. Sticky patches (also referred to as sticky spots) are regions of high basal shear stress caused by low subglacial water pressure or topographic high of the bedrock. Motivated by observations, we hypothesise that in the presence of basal water pressure, spatial variations in basal shear stress on the sticky patches can promote and localise basal crevassing. In the theoretical context of linear elastic fracture mechanics, we develop a model evaluating the effect of shear stress variation on the growth of basal crevasses, finding that the existence of sticky patches can promote mixed-mode basal crevassing on the downstream end. By simulating the quasi-static growth of such mixed-mode basal crevasses, we find that such crevasses tend to incline upstream and propagate along a specific path, which can be approximated by the principal stress trajectories in the uncracked ice. A detailed exploration on the dimensionless parameter space indicates that the crevassing is controlled by three parameters—the flotation fraction, the relative magnitude of excess shear stress, and the relative size of the sticky patch. Inspired by the crevassing in the elastic model, we also explore the propagation of basal crevasses using the viscoelastic rheology.

How to cite: Zhang, H., Davis, T., Katz, R., Stevens, L., and May, D.: Basal hydrofractures near sticky patches, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5140, https://doi.org/10.5194/egusphere-egu22-5140, 2022.

08:59–09:06
|
EGU22-12718
|
On-site presentation
Mauro Werder

Subglacial flow routing, which simply routs water down the Shreve potential (i.e. the hydraulic potential assuming that water pressure equals a fraction of ice overburden pressure), is probably the most widely used subglacial drainage model.  It is easy to use via many ready-to-use implementations, does not suffer from numerical issues, such as non-convergence, and is fast.

Here I present two improvements to this venerable model: (1) the spatial uncertainties in the input fields (surface and bed topography, water input) and the model parameter (fraction between water pressure and floation pressure) are taken into account by representing them as Gaussian random fields. This a allows to assess the impact of these uncertainties by running Monte Carlo simulations.  (2) the dependence of the ice melting point on the pressure (leading to the so-called supercooling effects) can lead to deflections in the flow directions where descending flow-paths are favoured over ascending ones.  I present a framework on how this effect can be taken into account in subglacial flow routing.

To showcase the improved model, I present results from applying it to catchments of Antarctica which show that the sizes of sub-catchments can have uncertainties of several order of magnitudes.  This demonstrates the need of using such an improved model to make predictions of fluxes, including their uncertainties, into subglacial lakes or at the grounding line.

How to cite: Werder, M.: Subglacial water flow routing v2.0: taking uncertainties and supercooling effects into account, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12718, https://doi.org/10.5194/egusphere-egu22-12718, 2022.

09:06–09:13
|
EGU22-9202
|
Presentation form not yet defined
Christian Juncher Jørgensen, Sarah Elise Sapper, Thomas Blunier, Vasileios Gkinis, and Jesper Riis Christiansen

Emission of CH4 and CO2 was recently discovered at the western margin of the Greenlandic Ice Sheet (GrIS) 1,2. While knowledge on both carbon sources, extent and magnitude of these emissions are still very limited, the previous studies indicate that a primary driver for emission is degassing of dissolved and pressurized gases in the meltwater as it reaches the glacial margin. In this way we suggest that glacial hydrology plays a key role in regulating emission on both temporal and spatial scale.

In our studies of subglacial CH4 and CO2 emissions we have so far observed that the seasonal variations in meltwater discharge is correlated to both the magnitude of gas concentrations as well as timing of emissions3,4. We propose that the seasonal variations in the connectivity of subglacial channels to both 1) pockets of sediment with CH4 and CO2 production from both anaerobic and aerobic biological processes and 2) supraglacial meltwater via englacial conduits could be a mechanism, which could explain the overall temporal and seasonal patterns of gas concentrations observed at the glacial margin.

We hypothesize that by observing hydrological and geochemical processes at the margin together with CH4 and CO2 in high frequency over the melt season it can be inferred how subglacial hydrological processes regulate biogeochemical and carbon turnover processes. Knowledge on these mechanism and processes are important for future upscaling CH4 and CO2 emission to seasonal periods and larger spatial scales through modeling as well as the assessment of the potential importance of subglacial carbon emissions to the climate system.

Here, we will present data that couples meltwater discharge to measurements of dissolved CH4 and gaseous CH4 and CO2 as well as campaign measurements of water geochemistry and its isotopic composition. Preliminary data shows that CH4 and CO2 export display a clear diurnal signal in response to variations in the composition of melt water discharge. EC measurements and isotopic composition of melt water show a dominance of surface meltwater to subglacial meltwater, but clear diurnal trends in the mixing between these two water sources can be deduced from both isotope and elemental geochemistry of the meltwater.

1. Christiansen, J. R. & Jørgensen, C. J. First observation of direct methane emission to the atmosphere from the subglacial domain of the Greenland Ice Sheet. Sci. Rep. 8, 16623 (2018).

2. Lamarche-Gagnon, G. et al. Greenland melt drives continuous export of methane from its bed. Nature 73–77 (2018). doi:10.1038/s41586-018-0800-0

3. Jørgensen, C. J., Mønster, J., Fuglsang, K. & Christiansen, J. R. Continuous methane concentration measurements at the Greenland Ice Sheet-atmosphere interface using a low-cost low-power metal oxide sensor system. Atmos. Meas. Tech. Discuss. 13, 3319–3328 (2020).

4. Christiansen, J. R., Röckmann, T., Popa, M. E., Sapart, C. J. & Jørgensen, C. J. Carbon emissions from the edge of the Greenland Ice sheet reveal subglacial processes of methane and carbon dioxide turnover. J. Geophys. Res. Biogeosciences 1–13 (2021). doi:10.1029/2021jg006308

How to cite: Jørgensen, C. J., Sapper, S. E., Blunier, T., Gkinis, V., and Christiansen, J. R.: Temporal relationship between meltwater discharge and CH4 and CO2 emissions from the Greenland Ice Sheet., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9202, https://doi.org/10.5194/egusphere-egu22-9202, 2022.

09:13–09:20
|
EGU22-8644
|
ECS
|
On-site presentation
Annegret Pohle, Mauro A. Werder, Dominik Gräff, and Daniel Farinotti

The englacial and subglacial drainage system exerts key controls on glacier dynamics.  However, due to its inaccessibility, it is still only poorly understood and more detailed observations are important, particularly to validate and tune physical models describing its dynamics.

By creating artificial glacier moulins - boreholes connected to the subglacial drainage system and supplied with water from surface streams - we present a novel method to monitor the evolution of englacial hydrological systems with high temporal resolution.  Here, we use artificial moulins as representations for vertical, pressurised, englacial R-channels.  From tracer and pressure measurements we derive time series of the hydraulic gradient, discharge, flow speed and channel cross-sectional area.  Using these, we compute the Darcy-Weisbach friction factor, obtaining values which increase from 0.1 to 13 within five days of channel evolution (corresponding to a Manning friction factor of 0.03 to 0.3 s m-1/3).

Furthermore, we simulate the growth of the channel cross-sectional area using different temperature gradients.  The comparison to our measurements largely supports the common assumption that the temperature follows the pressure melting point.  The deviations from this behaviour are analysed using various heat transfer parameterisations to assess their applicability.

Finally, we discuss how artificial moulins could be combined with glacier-wide tracer experiments to constrain parameters of subglacial drainage more precisely. The presented approach allows to accurately quantify the englacial transit time of the tracer and thus, in turn, to quantify the subglacial transit time; something which has not been achieved to date.

How to cite: Pohle, A., Werder, M. A., Gräff, D., and Farinotti, D.: Using artificial moulins to characterise englacial R-channels, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8644, https://doi.org/10.5194/egusphere-egu22-8644, 2022.

09:20–09:27
|
EGU22-3182
|
ECS
|
On-site presentation
Alessio Nogarotto, Riko Noormets, Teena Chauhan, Florence Colleoni, Gesine Mollenhauer, Francesco Muschitiello, Lucilla Capotondi, Claudio Pellegrini, Simon Belt, and Tommaso Tesi

The subglacial environment and its characteristics are of primary importance for the behaviour and the stability of ice sheets; however, the mechanisms that take place beneath ice sheets still need to be accurately quantified. Here we present the results of a multi-proxy, biogeochemical analysis carried out on a marine sediment core (HH11-09GC) from the northern Svalbard continental slope, encompassing the last 30 ka. During Termination I, our results suggest a persistent polynya-like environment with significant input of terrigenous organic matter. Indeed, the amount of land-derived material during this period is comparable to that found in the immediate proximity of the major Siberian river mouths during modern times. Alkenone fingerprint suggests that the origin of the terrigenous material could be related to an as yet unidentified freshwater body located in the White Sea/Pechora Basin region, at the margin of the Svalbard Barents Sea Ice Sheet; therefore, the environmental conditions at the base of the ice sheet were suitable for the existence of a large subglacial water drainage. According to our data, this drainage network was able to carry huge amounts of water and sediments beneath the ice sheet and, subsequently, discharge them thousands of kilometres away from their origin. This could represent the first evidence of a pervasive, highly connected subglacial drainage network in the Barents Sea region. Our results may shed new insights on the magnitude of subglacial drainage systems, and thus have important implications with regards to ice sheet modelling.

How to cite: Nogarotto, A., Noormets, R., Chauhan, T., Colleoni, F., Mollenhauer, G., Muschitiello, F., Capotondi, L., Pellegrini, C., Belt, S., and Tesi, T.: Terrestrial biomarkers in sediments from the continental slope of Nordaustlandet, Svalbard reveal unprecedented subglacial meltwater drainage during the Last Termination, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3182, https://doi.org/10.5194/egusphere-egu22-3182, 2022.

09:27–09:34
|
EGU22-7222
|
ECS
|
On-site presentation
Rasmus Bahbah Nielsen, Louise Sandberg Sørensen, Sebastian Bjerregaard Simonsen, Natalia Havelund Andersen, Anne Munck Solgaard, Nanna Bjørnholt Karlsson, Jade Bowling, Amber Leeson, Jenny Maddalena, Malcolm McMillan, Noel Gourmelen, Alex Horton, and Birgit Wessel

Subglacial lakes may form beneath ice sheets and ice caps, given the availability of water and appropriate bedrock and surface topography to capture the water. On a regional scale, these lakes can modulate the freshwater output to the ocean by acting as reservoirs that may periodically drain and recharge. Several such active subglacial lakes have been documented under the Antarctic ice sheet, while only a few are observed under the Greenland ice sheet. The small size of the hydrologically active subglacial lakes in Greenland compared to those in Antarctica, puts additional demands on our mapping capabilities to resolve in great detail the evolving surface topography over these lakes to document their temporal behavior. Here, we explore the potential of combining CryoSat-2 swath data and high resolution DEMs generated from TanDEM-X scenes and ArcticDEM strips to improve our knowledge of the evolution of four active subglacial lake sites previously documented in the literature. We find that the DEM data complement each other well in terms of time and resolution and thus provide new information about the subglacial lake activity, though the small size of the collapse basins is challenging for CS2, and we are only able to derive useful CS2 data for the two largest of the four investigated lakes. Based on these data sets we can e.g. conclude that the collapse basin at Flade Isblink was actually as deep as 95 m when it formed, which is 30 m deeper than previously documented.  We also present evidence of a new active subglacial lake in Southwest Greenland.

How to cite: Bahbah Nielsen, R., Sandberg Sørensen, L., Bjerregaard Simonsen, S., Havelund Andersen, N., Munck Solgaard, A., Bjørnholt Karlsson, N., Bowling, J., Leeson, A., Maddalena, J., McMillan, M., Gourmelen, N., Horton, A., and Wessel, B.: Improved monitoring of subglacial lake activity in Greenland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7222, https://doi.org/10.5194/egusphere-egu22-7222, 2022.

09:34–09:41
|
EGU22-11500
|
ECS
|
Presentation form not yet defined
Modelling Antarctic subglacial hydrological response of the Pine Island/Thwaites drainage basin
(withdrawn)
Elise Kazmierczak and Frank Pattyn
09:41–09:48
|
EGU22-7234
|
Virtual presentation
Thomas Kleiner, Yannic Fischler, Raban Emunds, Lennart Oestreich, Christian Bischof, Jeremie Schmiedel, Roiy Sayag, and Angelika Humbert

Simulating the hydrological systems underneath ice sheets and glaciers is important for estimating the freshwater flux into the ocean as well as inferring the characteristics of the hydrological system and its impact on ice sheet dynamics. In particular, simulations of the subglacial hydrological system in high temporal and spatial resolution and coupled to ice sheet models are needed to investigate the formation of ice streams. In order to be able to run simulations efficiently, both codes need to be parallelised. To this end, we present our approach for a parallelised version of the confined-unconfined aquifer system (CUAS) model (Beyer et al., 2018) that was established as a python code. CUAS is simulating an effective porous medium layer, in which the transmissivity indicates if the flow is channelised. Transmissivity is evolving by melt, creep and cavity opening. A fully implicit finite difference scheme is used for the hydraulic head while an explicit Euler time step is used for the transmissivity. 

The new CUAS-MPI version is written in C++ and instrumented for performance measurements. The parallelisation is done with MPI, where we take advantage of PETSc data structures and linear equation system solvers. The code has been designed to be coupled to the Ice Sheet and Sea-level system Model (ISSM) using preCICE (precice.org). 

Pumping tests that are widely used in applied groundwater hydrology are performed to test the model implementation including the boundary conditions and to compare with the analytical solutions. We further present test applications to the Greenland Ice Sheet, with the major focus on performance, rather than on characteristics of the hydrological system.

How to cite: Kleiner, T., Fischler, Y., Emunds, R., Oestreich, L., Bischof, C., Schmiedel, J., Sayag, R., and Humbert, A.: CUAS-MPI - A parallelised version of the confined-unconfined aquifer system model applied to the Greenland Ice Sheet, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7234, https://doi.org/10.5194/egusphere-egu22-7234, 2022.

09:48–10:00
Coffee break
Chairpersons: Rasmus Bahbah Nielsen, Mauro Werder
Supraglacial Hydrology
10:20–10:21
10:21–10:31
|
EGU22-731
|
ECS
|
solicited
|
On-site presentation
Jennifer Arthur, Chris Stokes, Stewart Jamieson, Rachel Carr, Amber Leeson, and Vincent verjans

Antarctic supraglacial lakes (SGLs) have been linked to ice shelf collapse and the subsequent acceleration of inland ice flow. These processes are difficult to capture in numerical ice sheet models, but those that include them project higher sea-level contributions from Antarctica. However, observations of SGLs in Antarctica remain relatively scarce and their seasonal variability is largely unknown, making it difficult to assess whether some ice shelves are close to thresholds of stability under climate warming. Here, we quantify the variability in SGL distributions and volumes across the entire East Antarctic Ice Sheet around the peak of seven consecutive melt seasons (2014-2020). We investigate potential climatic controls on SGL development and near-surface (i.e. firn) conditions generated by ERA5 climate reanalysis and the Community Firn Model forced by the regional climate model MARv3.11. Interannual variability in SGL volume is >200% on some ice shelves, but patterns are highly asynchronous. More extensive, deeper SGLs correlate with higher summer (December-January-February) air temperatures, but comparisons with modelled melt and runoff are complex. However, we find that modelled January melt and the ratio of November firn air content to summer melt are important predictors of SGL volume on some potentially vulnerable ice shelves, suggesting large increases in SGLs should be expected under future atmospheric warming. 

How to cite: Arthur, J., Stokes, C., Jamieson, S., Carr, R., Leeson, A., and verjans, V.: Large interannual variability in supraglacial lakes around East Antarctica, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-731, https://doi.org/10.5194/egusphere-egu22-731, 2022.

10:31–10:38
|
EGU22-2884
|
ECS
|
Highlight
|
Virtual presentation
Peter Tuckett, Jeremy Ely, Andrew Sole, Stephen Livingstone, James Lea, and Julie Jones

Understanding the distribution and evolution of surface meltwater on the Antarctic Ice Sheets is vital in enabling us to predict how the ice sheet will respond to a warming climate. The majority of Antarctic surface meltwater studies have typically been limited by either spatial or temporal scale. We have overcome these limitations by using a fully automated method to map surface meltwater across the entire Antarctic continent between 2006 and 2021 at a monthly temporal resolution. Furthermore, by accounting for variability in both cloud cover and satellite image coverage, we have generated the first consistent and continuous multi-year time series of Antarctic-wide surface meltwater to date. Here, we present results from analysis of this dataset, including long-term trends in surface meltwater extent, comparison between surface meltwater area and modelled melt, and associations between surface meltwater area and climatic factors. Regression analysis shows strong correlations between surface meltwater area and modelled snowmelt around the ice sheet margin, increasing our confidence in regional climate models to predict future melt conditions. Synoptic scale climate regimes, such as the Southern Annular Mode, exert a strong controlling factor on surface meltwater area totals on an annual basis. However, regional climatic processes and melt-albedo feedbacks can have strong second-order influences on localised melt rates, resulting in high variability in meltwater coverage, especially in parts of East Antarctica. This multi-year dataset offers the opportunity to explore surface meltwater evolution at local, catchment and continental scales, and will be of widespread use in understanding the operation of surface hydrological systems.

How to cite: Tuckett, P., Ely, J., Sole, A., Livingstone, S., Lea, J., and Jones, J.: Monthly Antarctic-wide surface meltwater evolution between 2006 and 2021, and its links to climate, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2884, https://doi.org/10.5194/egusphere-egu22-2884, 2022.

10:38–10:45
|
EGU22-3004
|
ECS
|
Highlight
|
On-site presentation
Riley Culberg, Winnie Chu, and Dustin Schroeder

The growth of shallow, low-permeability ice slabs in Greenland’s firn is known to increase surface meltwater runoff by hindering vertical percolation. However, the partitioning of meltwater between local impoundment, downslope runoff, and drainage to the ice sheet bed is still poorly constrained. Northwest Greenland is a particularly interesting study area for understanding the role of englacial hydrology because ice-penetrating radar surveys have identified coexisting ice slabs and firn aquifers in this region. These results suggest that ice slabs may not necessarily preclude local firn water storage. However, the mechanism that would allow these two distinct facies to develop together is unclear.

               To examine the relationship between firn aquifers and ice slabs in Northwest Greenland, we analyzed six-years of NASA Operation IceBridge radar data between 2011 and 2017. These observations show that isolated, short-lived water pockets frequently develop beneath the ice slabs and over time refreeze to form kilometer-scale ellipsoidal buried ice masses. These ice blobs covered ~14% of the 1176 radar line-kms flown in 2017 and analysis of Landsat imagery between 2000 and 2016 shows they are spatially correlated with visible runoff in supraglacial lakes, streams, or massive slush swamps. High-resolution optical satellite imagery also shows that surface crevassing is widespread in this region and that many of the ice blobs are associated with moulins or lake drainage events in the 2012 melt season. This suggests that ice blobs form where fractures create high permeability pathways through the ice slab through which surface meltwater can drain into the relict firn. In the short term, this process impounds water and heat in the upper 30 meters of the ice column, reducing surface runoff and limiting the immediate impact of surface melt on local ice dynamics. However, on longer timescales, this efficient filling of pore space beneath supraglacial flow paths may lead to more efficient surface hydrology and full ice thickness hydrofracture at high elevations. 

How to cite: Culberg, R., Chu, W., and Schroeder, D.: Shallow Fracture Buffers High Elevation Runoff in Northwest Greenland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3004, https://doi.org/10.5194/egusphere-egu22-3004, 2022.

10:45–10:52
|
EGU22-4526
|
ECS
|
On-site presentation
Mariel Dirscherl, Andreas Dietz, and Claudia Kuenzer

Earth Observation (EO) provides a wealth of data for the monitoring of the Antarctic continent. In this context, data of the Sentinel-1 Synthetic Aperture Radar (SAR) and optical Sentinel-2 satellite missions of the European Copernicus programme deliver valuable information on key ice sheet parameters including the location of the calving front and grounding line, the ice velocity and elevation as well as the Antarctic surface hydrological network. The monitoring of the latter is crucial for an improved understanding of processes such as hydrofracture triggering ice shelf collapse and ultimately ice flow accelerations and increased ice discharge. To establish a monitoring service for supraglacial lake extent delineation in Sentinel-1 SAR and optical Sentinel-2 imagery, a fully automated processing chain based on machine learning and deep learning was developed and integrated within the internal processing infrastructure of the German Aerospace Center (DLR).

Here, we present first results of the implemented machine learning processing pipeline over six major Antarctic ice shelves. In particular, the full archive of Sentinel-1 and Sentinel-2 was exploited to provide bi-weekly supraglacial lake extent mappings during 2015-2021 at unprecedented 10 m spatial resolution. The results over Antarctic Peninsula ice shelves reveal comparatively low lake coverage in 2015-2018 and high lake coverage during summers 2019-2020 and 2020-2021. Over East Antarctic ice shelves, supraglacial lake extents fluctuated more substantially with comparatively high lake coverage during most of 2016-2019 and low lake coverage throughout melting season 2020-2021. Further, the data reveal a coupling between supraglacial lake formation and the near-surface climate, the local glaciological setting and large-scale atmospheric modes.

The final data products on Antarctic supraglacial lake extent dynamics during 2015-2021 are available via the GeoService of the Earth Observation Center (EOC) at DLR. To establish a near-real-time monitoring service on supraglacial lake dynamics in the future, the full processing pipeline is currently refined and data products will be made readily available for download via the EOC GeoService. In this context, we are building upon the expertise of the Polar Monitor project and IceLines, a processor for automated calving front extraction over the Antarctic coastline.

How to cite: Dirscherl, M., Dietz, A., and Kuenzer, C.: Artificial intelligence for the monitoring of Antarctic supraglacial lake dynamics in 2015-2021 using Sentinel-1 SAR and optical Sentinel-2 data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4526, https://doi.org/10.5194/egusphere-egu22-4526, 2022.

10:52–10:59
|
EGU22-4688
|
ECS
|
Presentation form not yet defined
The Seasonal Evolution of the Supraglacial Hydrologic Network at Humboldt Glacier, Northwest Greenland.
(withdrawn)
Lauren Rawlins, David Rippin, Andrew Sole, Stephen Livingstone, and Kang Yang
10:59–11:06
|
EGU22-5463
|
ECS
|
On-site presentation
Sophie de Roda Husman, Zhongyang Hu, Stef Lhermitte, Bert Wouters, and Peter Kuipers Munneke

Surface meltwater is becoming an increasing driver for ice shelf disintegration and consequent mass loss from the AIS. In this regard, monitoring surface melt over Antarctic ice shelves can enhance our understanding of their stability. Earth Observation (EO) satellites provide decadal records of land dynamics over Antarctica, and have been applied in surface melt monitoring. Thereby, they hold a potential to monitor the spatiotemporal evolution of surface melt over the entire AIS. Among the wealth of EO satellites, scatterometer and radiometer observations are most frequently used for surface melt detection, followed by SAR and optical data. Most studies used observations from a single satellite to study surface melt, while specific sensor characteristics (e.g., spatial resolution, overpass time, penetration depth) largely influence the potential for detecting surface melt. Therefore, we compare differences in melt detection between radiometer, scatterometer, SAR and optical sensors to assess the opportunities and challenges in observing surface melt for different EO satellites. We apply state-of-the-art melt detection algorithms to radiometer (Special Sensor Microwave Imager/Sounder, SMMIS), scatterometer (Advanced Scatterometer, ASCAT), Synthetic Aperture Radar (SAR; Sentinel-1), and optical (Moderate Resolution Imaging Spectroradiometer, MODIS) data over the Larsen B+C and Amery Ice Shelves for the 2015-2020 melt seasons. We construct melt timeseries and spatial maps using the melt detection algorithms. and intercompare the spatiotemporal patterns of detected melt. Finally, we compare areas with different melt patterns with auxiliary data sets (i.e., Regional Atmospheric Climate Model (RACMO2), Digital Elevation Models (DEM), high resolution optical imagery). Our results show that the largest differences in detected melt between the EO satellites can be linked to physical properties of the surface, sensor properties and atmospheric conditions. Over the blue ice areas, MODIS indicates more surface melt than the other sensors, as they miss blue ice areas due to either a coarse spatial resolution or the applied detection algorithms. However, over the ice shelves, MODIS detects significantly less surface melt, which can be attributed to the very high cloud obstruction frequency over AIS. Based on this intercomparison, we discuss the opportunities and challenges for melt detection across the AIS regarding the choice of different sensors and the chosen melt detection algorithms. We conclude that merging observations from different satellites (e.g. using machine learning) would further strengthen our knowledge on the presence of surface melt across the AIS, since this combines the strengths of specific sensors based on their sensor characteristics and the area of interest.

How to cite: de Roda Husman, S., Hu, Z., Lhermitte, S., Wouters, B., and Kuipers Munneke, P.: Earth Observation for Surface Melt Monitoring over Antarctic Ice Shelves: Opportunities and Challenges , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5463, https://doi.org/10.5194/egusphere-egu22-5463, 2022.

11:06–11:13
|
EGU22-10904
|
Presentation form not yet defined
Jiangjun Ran and Pavel Ditmar

The Greenland ice sheet (GrIS) is currently losing mass, as a result of complex mechanisms of ice-climate interaction that need to be understood for reliable projections of future sea level rise. Previous authors have intensively investigated the total GrIS mass balance, Surface Mass Balance (SMB), and ice discharge at different temporal scales. However, knowledge of the remaining mass variations due to supra-, en- and sub-glacier meltwater retention, is limited. In this study, we make a first attempt to quantify the temporal pattern of meltwater retention at different locations within the GrIS by analyzing the bedrock’s elastic response caused by meltwater mass variations. To that end, we use vertical displacements observed by Global Positioning System (GPS) stations. We estimate, for the first time, the evolution of meltwater storage variations at both the seasonal and inter-annual time scale. We find, among others, that the annual cycle of vertical displacements, after subtracting the signals related to SMB and other known mass transport processes, demonstrates at many GPS stations a consistent subsidence from May to July. This is an indication of a mass gain, which starts in May and peaks in July. We infer that this mass gain signal is due to the meltwater accumulation within the ice sheet. An in-depth investigation of this process by Geodetic data is critical for better understanding the hydrological cycle and the further evolution of the GrIS.

How to cite: Ran, J. and Ditmar, P.: GPS data reveal the evolution of liquid water  retention within the Greenland Ice Sheet at the seasonal and inter-annual time scale, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10904, https://doi.org/10.5194/egusphere-egu22-10904, 2022.

11:13–11:20
|
EGU22-2197
|
ECS
|
On-site presentation
Ilaria Tabone, Johannes Fürst, and Thomas Mölg

One of the consequences of rising temperatures observed in Northeast Greenland during the last decades is the increase in surface melting. Meltwater runoff can reach the bed and influence the ice flow regime through changes in basal conditions. Yet, depending on the drainage system, meltwater increase can have opposite effects on basal sliding and there is no consensus yet on the mechanisms that govern this hydrological switch. Here we present some advances in understanding the effects of surface meltwater percolation on ice dynamics at the Northeast Greenland Ice Stream (NEGIS) by investigating surface melt-basal sliding interactions at various temporal scales. To this end, we make use of a fully coupled model approach, comprising the finite-element ice-flow model Elmer/Ice and the hydrological scheme GlaDS. The latter is capable of representing the water drainage at all levels of the ice column. High resolution daily surface mass balance reconstructions available for the years 2014-2018 and simulated by the surface energy balance model COSIPY are used to force the ice-flow model. After first sensitivity tests aiming to explore the parameters of the ice-flow-hydrology system model, a fully coupled simulation for the period 2014-2018 is performed. This advanced modelling framework allows us to tackle the response of the NEGIS ice flow to seasonal and multi-annual variations in surface melt through changes in the drainage system.

How to cite: Tabone, I., Fürst, J., and Mölg, T.: Investigating the influence of increased meltwater runoff on basal sliding in Northeast Greenland. , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2197, https://doi.org/10.5194/egusphere-egu22-2197, 2022.

11:20–11:27
|
EGU22-7675
|
ECS
|
Presentation form not yet defined
Emily Glen, Alison Banwell, Jennifer Maddalena, Amber Leeson, Diarmuid Corr, and Mal McMillan

Mass loss from the Greenland Ice Sheet (GrIS) is predicted to contribute up to 10 cm to global sea level rise by 2100. This mass loss is due to both increased meltwater production and therefore increased runoff, which is occurring at higher elevations on the ice sheet, as well as ice-dynamical feedback processes such as supraglacial lakes (SGLs) draining rapidly to the ice sheet bed; enhancing basal sliding. Therefore, the specific processes through which SGLs drain has an important control on mass loss from the GrIS. This highlights the need for high-resolution, integrated datasets that provide a comprehensive view of supraglacial hydrological networks, including SGL drainage events, on the GrIS.

Here, we compare SGL characteristics and drainage dynamics of a southwestern sector of the GrIS throughout both an extreme high melt season (2019) and an extreme low melt season (2018). SGLs are delineated throughout both the summer seasons from Sentinel-2 and Landsat 8 optical imagery using threshold-based normalized difference water index (NDWI) methods followed by extensive manual enhancement to increase accuracy. SGL depths are calculated using a radiative transfer model and individual lake volume is determined. The resulting meltwater maps have a spatial resolution of 10 to 30 m and have a temporal resolution of weekly to fortnightly. The following SGL characteristics are determined: i) area; ii) volume; iii) elevation; iv) ice surface slope; and v) solidity. SGL drainage dynamics are analysed by tracking lakes through the duration of each melt season and determining if a lake drains rapidly by hydrofracture, slowly drains via channel incision and overflow, or does not drain and instead refreezes at the end of the melt season. To do this, we use the Fully Automated supraglacial lake area and volume tracking at enhanced resolution (FASTER) algorithm, developed by Williamson et al. (2018).

As temperatures continue to increase, the frequency of high melt years like 2019 will also increase. As such, it ever more important to understand supraglacial meltwater characteristics and dynamics in high melt seasons, especially compared to years with limited melt.

How to cite: Glen, E., Banwell, A., Maddalena, J., Leeson, A., Corr, D., and McMillan, M.: A comparison of supraglacial lake characteristics and drainage dynamics in Southwest Greenland between an extreme high, and an extreme low, melt season, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7675, https://doi.org/10.5194/egusphere-egu22-7675, 2022.

11:27–11:34
|
EGU22-820
|
Virtual presentation
Ted Scambos, Julie Miller, Riley Culberg, Christopher Shuman, Lynn Montgomery, Clément Miège, Marco Brogioni, and David Long

Water-saturated firn layers, or firn aquifers, have recently been identified from satellite microwave image time-series data in some western Antarctic Peninsula ice shelves. Subsequent field work on the Wilkins Ice Shelf (this work) and Müller Ice Shelf (MacDonell et al., 2021) has proven the existence of these perennial ice shelf firn aquifers. Most of the aquifer areas are maintained by seasonal meltwater recharge. Brine aquifers have been known for many decades in certain slow-moving ice shelves with shorter or absent melt seasons (e.g., McMurdo Ice Shelf). We present both satellite evidence of meltwater firn aquifers in several areas of the Antarctic Peninsula, and radar profile evidence consistent with extensive brine infiltration in the Abbott, Nickerson, and Shackleton Ice Shelves. These latter ice shelves had been previously identified as likely sites of widespread brine infiltration (Cook et al., 2018).

The hydrofracture-driven disintegration of the Wilkins Ice Shelf in February-March of 2008, and subsequent rapid calving events extending into the winter season, justify a closer look at the relative potential for fresh-water aquifers, brine aquifers, and surface melt ponds for inducing hydrofracture in ice shelves. The destructive impact of surface or near-surface meltwater on floating ice is now well-established and is implicated in the loss of the Larsen A and Larsen B ice shelves, and rapid late-stage disintegrations of several tabular icebergs. Brine-aquifer-induced disintegration was suspected for the Wilkins breakup (Scambos et al., 2009), but now appears to be related to the effects of a freshwater system. A question remains regarding the vulnerability of ice shelves with significant brine infiltration in an aquifer.

We will present field measurements from the Wilkins Ice Shelf and discuss the relative hydrofracturing potential of fresh water and brines under various scenarios pertinent to ice shelf stability. The potential for future expansion of fresh-water aquifers under warming coastal conditions, and the characteristics of a hypothetical transitioning from a cold brine aquifer to a fresh-water aquifer will be discussed.

 

Cook, S., Galton-Fenzi, B.K., Ligtenberg, S.R. and Coleman, R., 2018. Brief communication: widespread potential for seawater infiltration on Antarctic ice shelves. The Cryosphere12(12), 3853-3859, doi: 10.5194/tc-12-3853-2018.

MacDonell, S., Fernandoy, F., Villar, P. and Hammann, A., 2021. Stratigraphic analysis of firn cores from an antarctic ice shelf firn aquifer. Water, 13(5), 731, doi:10.3390/w13050731.

Scambos, T., Fricker, H.A., Liu, C.C., Bohlander, J., Fastook, J., Sargent, A., Massom, R. and Wu, A.M., 2009. Ice shelf disintegration by plate bending and hydro-fracture: Satellite observations and model results of the 2008 Wilkins ice shelf break-ups. Earth and Planetary Science Letters, 280(1-4), 51-60, doi:10.1016/j.epsl.2008.12.027.

How to cite: Scambos, T., Miller, J., Culberg, R., Shuman, C., Montgomery, L., Miège, C., Brogioni, M., and Long, D.: Antarctic Ice Shelf Aquifers:Characteristics and Potential Contributions to Ice Shelf Loss, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-820, https://doi.org/10.5194/egusphere-egu22-820, 2022.

11:34–11:41
|
EGU22-10584
|
ECS
|
Virtual presentation
Nathan Maier, Jonas Andersen, Jeremie Mouginot, Florent Gimbert, and Olivier Gagliardini

On land-terminating regions of ice sheets, large and transient changes in surface motion are not expected outside of summer due to the lack of concurrent melt forcing.  Here, we document the dynamic response to a cascading lake drainage that occurred during winter in Greenland using a high-resolution DInSAR timeseries (6-day) acquired from Sentinel-1 and optical imagery from Landsat-8 and Sentinel-2. A total of fifteen supraglacial lakes and several smaller supraglacial water features were identified to have drained during the event resulting in a velocity wave that propagates from the inland regions to the margin. Along the wave path, speeds increase up to three times pre-drainage velocities as the wave passes. Bifurcation of the velocity wave during the event implies at least two distinct subglacial flood pathways develop which drain from the margin over 100 km apart. By tracking the wavefront, we estimate the wave velocity through the event which we infer to be similar to the drainage velocity. Wave speeds of between 0.04 and 0.28 m s-1 suggests the subglacial flood propagates mainly through an inefficient drainage system. Using temporally overlapping portions of two DInSAR velocity maps which have an accuracy of greater than 0.1 m yr-1, we decompose the signal and demonstrate some of the motion is a result of surface uplift which constrains locations of likely flow pathways. Overall, our results demonstrate a sustained dynamic response to melt forcing can occur in the absence of surface melt. This indicates melt-induced ice motion changes are not limited to summer and transient winter dynamics might commonly occur as stored meltwater is released.

How to cite: Maier, N., Andersen, J., Mouginot, J., Gimbert, F., and Gagliardini, O.: Cascading supraglacial drainage observed to cause large-scale acceleration and uplift during winter in Greenland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10584, https://doi.org/10.5194/egusphere-egu22-10584, 2022.

11:41–11:50
Lunch break
Chairpersons: Bryn Hubbard, Rebecca Schlegel, Robert Bingham
13:20–13:27
|
EGU22-3047
|
ECS
|
On-site presentation
Lena Buth, Sanne Veldhuijsen, Bert Wouters, Stef Lhermitte, and Michiel van den Broeke

In recent years, the existence of firn aquifers in the Antarctic Peninsula (AP) has been confirmed by in situ observations. Due to their importance for understanding the hydrology of the Antarctic ice sheet, a more spatially comprehensive assessment of AP firn aquifers is desirable. The purpose of this study is to map firn aquifers in the AP from space using C-band Synthetic Aperture Radar imagery from ESA's Sentinel-1 mission. This product enables the detection of firn aquifers at 1 km2 resolution for the period 2017 to 2020. The method is based on quantifying the characteristic shape of the backscatter curve over time during the (partial) refreezing of the liquid water in the firn layer after each peak melt season. In this context, both seasonal aquifers and perennial aquifers are detected together, acknowledging that their backscatter signature in any given year is indistinguishable with the given method. With the new method, seasonal firn aquifers are being detected in the north and northwest of the AP, as well as on the Wilkins Ice Shelf and the George VI Ice Shelf. Imposing the aquifers to occur during all available years, as a proxy for perennial firn aquifers, limits their extent to the north and northwest AP. Both distributions agree well with model simulations. Further in situ and modelling studies and longer time series of satellite observations are needed to validate the results of this study.

How to cite: Buth, L., Veldhuijsen, S., Wouters, B., Lhermitte, S., and van den Broeke, M.: Satellite detection of firn aquifers in the Antarctic Peninsula, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3047, https://doi.org/10.5194/egusphere-egu22-3047, 2022.

13:27–13:34
|
EGU22-6570
|
ECS
|
Presentation form not yet defined
Meltwater flow through firn on the SW Greenland ice sheet
(withdrawn)
Nicole Clerx, Horst Machguth, Andrew Tedstone, Nicolas Jullien, and Nander Wever
13:34–13:41
|
EGU22-4909
|
Virtual presentation
Sebastian B. Simonsen, Nicolaj Hansen, Inès Otosaka, Baptiste Vandecrux, and Louise Sandberg Sørensen

The ESA 4DGreenland project has the objective of performing an integrated assessment of Greenland’s hydrology through maximizing the use of Earth observation (EO) data. However, as meltwater is activated on the surface of the Greenland ice sheet and percolates into the firn, the firn water storage and delayed runoff are unobservable from EO, and we must resort to modeling to quantify this component. 

The DTU-firn model has previously been used to quantify the change in firn air volume as a leading component of altimetric mass balance estimates and was initially tuned using firn core density observations. Here, we revisit the fundamentals of the model and perform model inversion using as many observational datasets as possible. This observational data ranges from direct measurements of firn compaction derived from “coffee-can” experiments, over traditional observation of densities and temperature from firn cores to regional observation of firn stratigraphy from airborne radar surveys. This large diversity in the data sources ensures the best possible constraints for capturing as many aspects as possible of the firn dynamics.  

One important model feature of the DTU-firn model is its ability to resolve individual precipitation events as model layers. This feature promotes the capability of retaining water and shows promising results in line with the in-situ observation. The updated DTU-firn model is therefore used within the 4DGreenland project to provide updated estimates of meltwater retention and delayed runoff as a function of the available water at the surface of the firn. Combined with results obtained by the HIRHAM- and MAR-firn models, it also enables better quantification of firn model uncertainties. Having built confidence in the model we can treat the retention and delayed runoff as a function of the available water at the surface of the firn. This then gives the possibility of using the observed surface melt, also acquired within 4DGreenland from satellite microwave data, in the assessments of Greenland’s hydrology and thereby increasing the useability of EO data.

How to cite: Simonsen, S. B., Hansen, N., Otosaka, I., Vandecrux, B., and Sandberg Sørensen, L.: Assessing firn water storage from a multi-data firn-model inversion, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4909, https://doi.org/10.5194/egusphere-egu22-4909, 2022.

13:41–13:48
|
EGU22-2296
|
ECS
|
Virtual presentation
Andrew Tedstone and Horst Machguth

Most of the Greenland ice sheet (∼78% to 92%) is underlain by porous snow and firn, into which meltwater can percolate and refreeze, or run off. However, the fate of meltwater in firn areas is poorly constrained. We identified the ice sheet’s annual visible runoff limits by mapping surface hydrological features in >25,000 Landsat satellite scenes. Between 1985–1992 and 2013–2020, the visible runoff limits along the west and north margins rose by 58–329 metres, expanding the visible runoff area by ~29%. Estimates using two different regional climate models suggest that the enlarged area has contributed from 190–264 Gt to 320–491 Gt of runoff since 1985, equivalent to as much as ∼10% of recent annual runoff from the west and north margins. However, the spread highlights that runoff processes in the percolation zone are a source of considerable uncertainty among the major models. We demonstrate that sustained excess melting since the 1990s has provided favourable conditions for anomalous near-surface firn densification. Much of the expanded visible runoff area is underlain by relatively impermeable and persistent ice slabs that have previously been identified by airborne radar campaigns. These slabs have recently enabled sustained runoff from higher elevations even in cooler summers. Our findings highlight that lateral runoff over densified near-surface firn is pervasive in several sectors of the ice sheet and therefore must be incorporated into future runoff projections.

How to cite: Tedstone, A. and Machguth, H.: Increasing surface runoff from Greenland's firn areas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2296, https://doi.org/10.5194/egusphere-egu22-2296, 2022.

13:48–13:52
Basal processes
13:52–13:53
13:53–14:03
|
EGU22-9915
|
ECS
|
solicited
|
Highlight
|
On-site presentation
M.Reza Ershadi, Reinhard Drews, Inka Koch, Falk Oraschewski, Rainer Prinz, Carlos Martin, and Olaf Eisen

Mapping the ice bed interface with radar is challenging in many alpine glaciers where the ice is temperate, and in-ice absorption is high. It is also difficult in selected regions of polar ice sheets such as near grounding zones and in ice streams where clutter and rough beds increase incoherent volume scattering. The lack of information for the ice geometry impedes our process understanding, e.g., basal sliding (requires knowledge about the basal roughness) and the routing of subglacial water flow (requires knowledge on basal smoothness). The lack of observations to constrain variations in ice thickness on the sub-kilometre scale is thus still a bottleneck to confidently predict ice dynamics and expected rates of sea-level rise.

A recent development in radioglaciology, namely the application of phase-coherent polarimetric radar, provides an excellent opportunity to overcome these limitations. Radar polarimetry has made significant strides in the last few years to constrain internal ice structure and their impact on the deformation of ice sheets, including the reconstruction of ice micro-structure parameters previously obtained from ice cores. Here, we suggest that the ice-bed interface can be identified in characteristic patterns of the polarimetric coherence phase. This new metric provides information in areas where the backscattered power amplitude does not show any signatures of the ice-bed interface. We provide examples for this across a wide range of glaciological settings, including cold (Colle Gnifetti, Switzerland) and temperate (Hintereisferner, Austria) alpine glaciers, thin grounding zones (Ekström Ice Shelf, East Antarctica) and thick ice domes (Dome C, East Antarctica). If this holds, then the ice thickness mapping in challenging glaciological settings should preferably be done using a quad-polarimetric acquisition geometry. For ground-based surveys, this can be done using an autonomous ice rover, for which we provide a proof-of-concept study on the Ekström Ice Shelf in Antarctica.

How to cite: Ershadi, M. R., Drews, R., Koch, I., Oraschewski, F., Prinz, R., Martin, C., and Eisen, O.: Mapping the bed in challenging radar environments on alpine glaciers and ice sheets using radar polarimetry, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9915, https://doi.org/10.5194/egusphere-egu22-9915, 2022.

14:03–14:10
|
EGU22-7594
|
ECS
|
On-site presentation
Helen Ockenden, Rob Bingham, Andrew Curtis, Daniel Goldberg, and Antonios Giannopoulos

The West Antarctic Ice Sheet has the potential to contribute up to 3m of sea level rise over the next few centuries. There is considerable uncertainty over the rate at which ice loss will occur, caused in part by a lack of knowledge about the bed topography beneath the ice sheet, which influences ice flow and retreat. Since direct bed topography observations are often further apart than ice sheet models require, we explore instead what we can learn about bed topography from high resolution observations of the ice surface, which are openly available. We apply an inversion methodology based on linear perturbation theory and developed by Gudmundsson (2003, 2008) to ice surface data from Pine Island Glacier, and present the bed topography results. Comparison to high-resolution radar sounding of the bed topography of Pine Island Glacier from the iSTAR 2013-14 ground surveys allows us to assess the success of the inversion methodology. We identify regions of the glacier where the landforms we see are likely to be artefacts, and regions where unknown and interesting landforms are likely to exist. This methodology has the potential to be extremely useful in regions where direct observations of bed topography are sparse, and for identifying areas where more observations would be of particularly high benefit.   

How to cite: Ockenden, H., Bingham, R., Curtis, A., Goldberg, D., and Giannopoulos, A.: What can high resolution ice surface observations tell us about the bed topography of Pine Island Glacier, West Antarctica? , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7594, https://doi.org/10.5194/egusphere-egu22-7594, 2022.

14:10–14:17
|
EGU22-11291
|
ECS
|
On-site presentation
Rebecca Schlegel, Alex Brisbourne, Tavi Murray, Adam Booth, Andrew Smith, Roger Clark, and Edward King

Subglacial bedforms such as mega-scale glacial lineations and drumlins are commonly thought to form during active ice flow. They are often present in deglaciated areas with various elongation ratios, consisting of different materials , information which led to the development of different formation theories. However, these exposed examples were formed not only by subglacial processes during glaciation but also altered by processes during and after deglaciation. Here, we analyse in-situ properties and topography beneath Rutford Ice Steam, a fast flowing ice stream in West Antarctica to evaluate current theoretical models of bedform formation. We present a combination of seismic and radar data, including high-resolution 3D radar topography covering the upstream end of a bedform. Data acquisition and processing of the high-resolution 3D radar dataset result in a horizontal resolution of 24 m along- and across-track and a vertical resolution of 12 m. Using seismic acoustic impedance and calibrated radar reflectivity subglacial properties of the bedforms as well as the surrounding area are identified.

A depression around the upstream end of a 360 m wide, 50 m high and more than 13 km long bedform was observed for the first time analysing the high-resolution 3D radar topography.  The depression consists of a deepening up to 45 m deep and 360 m wide and is seen to extend around 10.5 km downstream. Radar reflectivity reveals that the material the depression is excavated into at least partly consists of low porosity material. Radar reflectivity and seismic acoustic impedance  along the bedform imply a stiffer upstream end which softens along flow. The subglacial topography and properties give evidence that the bedform and the depression are formed by a combination of  erosional and depositional processes. Both processes are likely interlinked, as implied by the comparable volume of the moat and the bedform at the upstream end of the bedform. Based on these observations we support or reject common bedform formation theories beneath Rutford Ice Stream.

How to cite: Schlegel, R., Brisbourne, A., Murray, T., Booth, A., Smith, A., Clark, R., and King, E.: Properties and High-Resolution Topography of Subglacial Bedforms Beneath a West Antarctic Ice Stream , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11291, https://doi.org/10.5194/egusphere-egu22-11291, 2022.

14:17–14:24
|
EGU22-2467
|
ECS
|
On-site presentation
Charlotte Carter, Michael Bentley, Stewart Jamieson, Neil Ross, Tom Jordan, and Julien Bodart

Understanding the subglacial bed topography of the Antarctic ice sheet is important for the boundary conditions of ice sheet modelling and the assessment of basal hydrological conditions. Moreover, inferring landscape evolution from the geomorphology can also provide insight into ice sheet inception and history. We utilise radio-echo sounding data from the BAS GRADES-IMAGE and TORUS radar surveys to geomorphologically interpret the bed topography in the Evans-Rutford Region of Antarctica, between the Ellsworth mountains and the southern Antarctic Peninsula. The GRADES-IMAGE survey is a legacy radar survey that has not yet been examined in detail in terms of subglacial bed topography and consists of 11,500 line kilometres of data along 22 lines. We have updated the subglacial bed picks to develop a new Digital Elevation Model of the region. Here we report preliminary results of the mapped subglacial landscape, with potential interpretations of the topographic patterns and landscape evolution. Geomorphological observations of the key features include identification of flat plateau surfaces at similar elevations, sitting between deep incised glacial troughs, some of which have potential tectonic controls.

How to cite: Carter, C., Bentley, M., Jamieson, S., Ross, N., Jordan, T., and Bodart, J.: Subglacial topography and landscape evolution from radio-echo sounding data in the Evans-Rutford Region, southern Antarctic Peninsula., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2467, https://doi.org/10.5194/egusphere-egu22-2467, 2022.

14:24–14:31
|
EGU22-247
|
ECS
|
Virtual presentation
Steven Franke, Niklas Neckel, Tamara Annina Gerber, Hannes Eisermann, Jölund Asseng, Daniel Steinhage, Veit Helm, Olaf Eisen, Reinhard Drews, Graeme Eagles, Heinrich Miller, Dorthe Dahl-Jensen, and Daniela Jansen

Future sea-level predictions require that the history of the Antarctic Ice Sheet is well understood and constrained by observations. Much of the ice sheets’  ice-dynamic properties are governed by processes at the ice-bed interface which can be imaged with radar sounding surveys. Here we use a combination of ultra-wideband radio-echo sounding data, satellite radar and laser altimetry data, as well as electromagnetic waveform modeling to characterize the properties of the ice base and the evolution of the subglacial morphology of the Jutulstraumen drainage basin (western Dronning Maud Land, Antarctica). Based on the classification of the bed topography, we reconstruct the step-by-step modifications the subglacial landscape has experienced since the beginning of the glaciation of Antarctica, 34 million years ago. Between 2017 and 2020, we find evidence of active episodic cascade-like subglacial water transport along the subglacial valley network. In addition, our high-resolution radio-echo sounding data reveal a cluster of anomalous basal ice units whose material properties we constrain by electromagnetic waveform modeling. Through this, we aim to derive the physical conditions at the ice base, and establish a link to the subglacial hydrology system. The combination of these observations will represent an important step towards a better understanding of large-scale ice-sheet dynamics in western Dronning Maud Land.

How to cite: Franke, S., Neckel, N., Gerber, T. A., Eisermann, H., Asseng, J., Steinhage, D., Helm, V., Eisen, O., Drews, R., Eagles, G., Miller, H., Dahl-Jensen, D., and Jansen, D.: Ice-flow history and observations from the ice base of Jutulstraumen drainage basin (Antarctica), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-247, https://doi.org/10.5194/egusphere-egu22-247, 2022.

14:31–14:38
|
EGU22-3159
|
Virtual presentation
A vast preglacial valley network beneath the Greenland Ice Sheet
(withdrawn)
Joseph MacGregor, Winnie Chu, William Colgan, Beáta Csathó, Mark Fahnestock, Denis Felikson, Nanna Karlsson, Emma MacKie, Mathieu Morlighem, Guy Paxman, Kirsty Tinto, and Lijing Wang
14:38–14:45
|
EGU22-11596
|
Presentation form not yet defined
The effects of basal topography and ice-sheet surface slope in a subglacial glaciofluvial deposition model
(withdrawn)
David Stevens, Jeremy Ely, Stephen Livingstone, Chris Clark, Frances Butcher, and Ian Hewitt
14:45–14:50
Coffee break
Chairpersons: Rebecca Schlegel, Bryn Hubbard
15:10–15:20
|
EGU22-11677
|
ECS
|
solicited
|
Highlight
|
Virtual presentation
Kasia Warburton, Duncan Hewitt, and Jerome Neufeld

The dynamics of soft-bedded glacial sliding over water-saturated tills are poorly constrained and difficult to realistically capture in large scale models. While experiments characterise till as a plastic material with a pressure dependent yield stress, large scale models rely on a viscous or power-law description of the subglacial environment to efficiently constrain the basal sliding rate of the ice. Further, the subglacial water pressure may fluctuate on annual to daily timescales, leading to transient adjustment of the till.

Here, we construct a continuum two-phase model of coupled fluid and solid flows, using Darcy flow to describe the movement of water through the pore space of the till that deforms according to a granular-inspired rheology. After calibrating our model against steady-state experiments, we force the model with a fluctuating effective pressure at the ice-till interface to infer the resulting relationships between basal traction, solid fraction, rate of deformation, and till flux. Shear dilation introduces internal pressure variations and transient dilatant strengthening emerges, leading to hysteretic behaviour in low-permeability materials.

Our model predicts a time-dependent effective sliding law, with permeability-dependent lag between changes in effective pressure and the sliding speed. This deviation from traditional steady-state sliding laws may play an important role in a wide range of transient ice-sheet phenomena, from glacier surges to the tidal response of ice streams. 

How to cite: Warburton, K., Hewitt, D., and Neufeld, J.: A time-dependent sliding law for granular till, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11677, https://doi.org/10.5194/egusphere-egu22-11677, 2022.

15:20–15:27
|
EGU22-512
|
ECS
|
Virtual presentation
Rebecca McCerery, John Woodward, Glen McHale, Kate Winter, Onoriode Esegbue, and Martin Jones

The driving mechanisms of glacier fast flow and the cyclical instability inherent in ice streams and surging glaciers are not fully understood, with current theories of sliding and basal deformation being insufficient in explaining glacier dynamics. Previous work on soil water repellency and interfacial physics shows that the incorporation of a lubricating oil into a sediment enhances the water repellent and water shedding properties. This can form a Slippery Liquid-Infused Porous Surface (SLIPS), whereby a liquid-liquid interface is created when the sediment is exposed to water resulting in extreme water shedding.

In Alberta, Canada, oil sands material has been detected in surficial sediment and in glacial sediments south of the Alberta Oil Sands deposits. It has been hypothesised that this material was eroded and transported subglacially during the Laurentide Glaciation. Here, sediments from the Central Alberta Ice Stream flow track in the former Laurentide Ice Sheet were analysed and compared to samples of the Alberta Oil Sands from mines and natural exposures using oil-oil correlation by gas chromatography-mass spectrometry. The results show evidence of Alberta Oil Sands throughout the Central Alberta Ice Stream flow track, in particular at the terminating margins to the east of Calgary and in the Cooking Lake area to the southeast of Edmonton. These results indicate glacial erosion and long-distance mobilisation of oil sands deposits from Northern Alberta. Three scenarios of SLIPS at the ice-bed interface caused by the presence of a lubricating oil at the bed can be assumed from these results; (i) an oil-wet macroscale SLIPS, (ii) a water-wet macroscale SLIPS, and (iii) a microscale SLIPS.  These SLIPS mechanisms would influence the degree of ice-bed coupling and therefore the proportion and rates of sliding and basal deformation. By understanding the physics occurring at the ice-bed interface it is possible to better predict glacier flow conditions. It is therefore critical that properties affecting wettability and water shedding of sediments such as the presence of an oil are considered in our understanding of transient flow conditions.

How to cite: McCerery, R., Woodward, J., McHale, G., Winter, K., Esegbue, O., and Jones, M.: Oil in glacial till as drivers of ice streaming and surging, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-512, https://doi.org/10.5194/egusphere-egu22-512, 2022.

15:27–15:34
|
EGU22-1487
|
Presentation form not yet defined
Accounting for transient effects in water pressure in sliding laws 
(withdrawn)
Olivier Gagliardini, Adrien Gilbert, Florent Gimbert, and Juan Pedro Roldan Blasco
15:34–15:41
|
EGU22-10053
|
Presentation form not yet defined
Regularized Coulomb friction laws and associated grounding line flux conditions
(withdrawn)
Frank Pattyn, Thomas Gregov, Elise Kazmierczak, and Maarten Arnst
15:41–15:48
|
EGU22-1801
|
Virtual presentation
Jane Hart, Kirk Martinez, Nathaniel Baurley, and Benjamin Robson

An understanding of subglacial processes are a vital component of ice-sheet models for sea level rise prediction as the use of different sliding laws can result in very different outcomes. In particular, the West Antarctic ice streams, are potentially unstable, and are underlain by soft (unconsolidated) beds, which have rarely been studied. Innovative in situ wireless subglacial experiments and web connected RTK GPS data from Iceland have shown that stick-slick motion can occur at different time scales throughout the whole year, and this allowed the quantification of different sedimentary processes. We investigate the results from four soft bedded glaciers. We compare the similarities and differences; and in particular describe the relationship with subglacial hydrological processes and temperature rise. We discuss the implications for ice sheet models and reconstructions of Quaternary sedimentary processes.

How to cite: Hart, J., Martinez, K., Baurley, N., and Robson, B.: Quantifying subglacial soft bed sedimentary processes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1801, https://doi.org/10.5194/egusphere-egu22-1801, 2022.

15:48–15:55
|
EGU22-12228
|
On-site presentation
Bryn Hubbard, Samuel Doyle, Poul Christoffersen, Thomas Chudley, and Robert Law

Enhanced ice velocity around the margins of the Greenland Ice Sheet is facilitated by the presence and pressure of subglacial meltwater. However, annual and longer-term velocity may be moderated by hydrological regulation, which reduces late melt-season and winter ice velocities following summers with relatively high surface melting and associated meltwater flux to the bed. While detail is lacking, hydrological regulation is likely driven by variations in the efficiency of subglacial drainage pathways and by associated variations in post-melt-season water retention at the glacier bed. Spatial variations in these processes may be viewed in terms of domains of differing degrees of hydrological connection to large subglacial meltwater channels. To date, a ‘well connected’ domain and an ‘isolated’ domain have been characterized, and an intermediate ‘weakly connected’ domain proposed. Generally, changes in the extent and/or pressurisation of the isolated domain are proposed as the driver of hydrological regulation. Yet, identifying the precise nature and timing of hydrological regulation, as well as the role of the weakly-connected domain, remain elusive.

             Here, we investigate the nature of the onset of hydrological regulation through a field experiment ~30 km from the terminus of Sermeq Kujalleq/Store Glacier, a fast-moving Greenlandic outlet glacier. We recorded simultaneous high-resolution time series of surface meltwater discharge, surface ice velocity and subglacial water pressure in two boreholes drilled at different distances from a substantial moulin. Analysis of the magnitude and timing of diurnal cycles and longer-term trends in all four records reveals that initially, in July, one borehole intersected the isolated subglacial domain and the other a ‘weakly-connected’ domain, with the latter showing a gradual decline in water pressure through the summer melt season. Transition to a winter state over the period ~10th – 20th August was marked by (i) a decrease in surface melting; (ii) a decrease in the amplitude of diurnal water pressure cycles in both boreholes, and (iii) a decrease in surface velocity. This transition was accompanied by an almost instantaneous (<1 d) switch in the borehole hitherto intersecting the weakly-connected domain to the isolated domain, evidenced by a 180° phase shift in the timing of its diurnal water pressure cycle. After this transition, diurnal cycles in all records diminish and both subglacial water pressure and ice surface velocity increase gradually through the winter.

                We conclude that ice velocity at our study location is at least partly governed by water pressure within a weakly-connected subglacial drainage domain. Water pressure here declines gradually through the melt season but increases after transition to hydraulic isolation, a transition that occurs over a period of only some days in the autumn. At the scale represented by records from individual boreholes the transition can occur over just some hours.

How to cite: Hubbard, B., Doyle, S., Christoffersen, P., Chudley, T., and Law, R.: Borehole-based insights into the nature and timing of hydrological-regulation at a fast-moving Greenlandic outlet glacier, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12228, https://doi.org/10.5194/egusphere-egu22-12228, 2022.

15:55–16:02
|
EGU22-3812
|
Virtual presentation
Andrew Sole, Benjamin Davison, and Stephen Livingstone

Ice motion within the land-terminating ablation zone of west Greenland typically follows a seasonal pattern with fastest flow in the spring as surface meltwater first accesses the hydraulically inefficient subglacial drainage system, followed by a gradual reduction in ice motion over the summer as efficient subglacial channels evacuate water stored over wide swathes of the subglacial environment. Minimum speeds occur in autumn, when surface meltwater delivery to the bed ceases, then, over winter, ice flow gradually recovers before the cycle repeats once again. This understanding is principally derived from high temporal resolution field observations with limited spatial coverage. It is now, however, possible to measure these seasonal patterns in detail over large spatial scales, enabling basin-scale comparisons between meltwater supply, subglacial hydrology and ice motion.

We present near continuous time-series of ice motion for a ~60,000 km2 portion of predominantly the land-terminating western margin of the Greenland Ice Sheet (with coverage extending up to 150 km from the margin in winter and 25 km in summer) between 2016 and 2022 at up to 12-day temporal resolution derived from Sentinel-1, Sentinel-2 and Landsat 8 imagery. We compare ice motion with surface melt magnitude and timing (derived from meteorological observations and a positive degree day model), theoretical subglacial water routing, and glaciological context (e.g. ice thickness).

Our results reveal clear spatial patterns in seasonal coupling between ice sheet hydrology and motion. Overall, the amplitude of the seasonal cycle of ice motion is generally greater closer to the ice margin as has been shown previously by field observations. There is, however, distinct variability between subglacial hydraulic catchments. Subglacial catchments whose principal drainage pathway has a high hydraulic potential gradient typically experience smaller peaks in summer ice motion, but more prominent autumn ice flow minima. Subglacial water flow in such catchments has more potential to create hydraulically efficient channels, which can both accommodate spikes in meltwater delivery with muted ice flow acceleration, and also reduce basal water pressure across a wider area of the ice bed as surface meltwater delivery declines.

As ice sheet surface mass balance becomes more negative and marginal ice thins fastest (where the ice is land-terminating), subglacial hydraulic gradients and subglacial discharge will both increase. Based on our findings, these changes may lead to smaller summer ice flow accelerations and bigger winter slow-downs, driving an overall decrease in mean annual ice motion. Our results also highlight the importance of careful selection of field sites for measuring ice motion and caution against scaling up from spatially limited observations.

How to cite: Sole, A., Davison, B., and Livingstone, S.: Spatial patterns in seasonal coupling between ice sheet hydrology and motion in west Greenland, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3812, https://doi.org/10.5194/egusphere-egu22-3812, 2022.

16:02–16:09
|
EGU22-3854
|
ECS
|
Virtual presentation
Matthew Jenkin, Davide Mancini, Floreana Miesen, Margaux Hofmann, Bryn Hubbard, Frédéric Herman, and Stuart N. Lane

Proglacial measurements of subglacial sediment export by meltwater are commonly used to estimate glacial erosion rates. Such estimates generally assume that subglacial meltwater flow is the dominant agent driving export and that eroded sediment is rapidly conveyed through subglacial drainage networks to the glacier outlet in efficient channels with large and generally-unsatisfied transport capacities. However, understanding of sediment transport processes under glaciers is limited, especially in the thin, snout-marginal zones of retreating temperate Alpine glaciers.

A growing body of field and model-based research from such systems challenges the theory that eroded sediment is rapidly evacuated. Conversely, Alpine glaciers develop intense diurnal and seasonal discharge variation leading to highly variable sediment transport competence and the moderation of sediment export by associated cycles of alluviation. This has important consequences for the timescales over which sediment export can be used as a reliable proxy for glacial erosion, though the problem remains that very little is known about when and under what conditions a glacier margin is capable of evacuating the sediment supplied to it.

This study attempts to elucidate sediment transport mechanisms and timescales in the main snout-marginal subglacial channel of glacier d’Otemma, Switzerland, by tracking 324 cobble-sized particles tagged with 433 MHz active radio transponders over the mid-to-late 2021 melt season. Tagged particles were injected into the channel via a 48 m deep borehole and were then tracked over a 350 m subglacial reach and a 150 m proglacial reach with a mobile antenna and stationary antenna arrays.

Only 86 particles (27%) were exported in 2021. Preliminary analyses indicate that cobble-sized particles generally have extended residence times in snout marginal zones (weeks to months), with no clear effect of particle size, shape or density on overall transport velocities. Ongoing work involves the daily localisation of particles using a signal strength-based algorithm, providing a unique record of the down-glacier transport of coarse particles in a subglacial channel. Repeat measurements will follow in 2022.

How to cite: Jenkin, M., Mancini, D., Miesen, F., Hofmann, M., Hubbard, B., Herman, F., and Lane, S. N.: Subglacial export of coarse sediment from temperate Alpine glaciers by meltwater, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3854, https://doi.org/10.5194/egusphere-egu22-3854, 2022.

16:09–16:16
|
EGU22-7817
|
ECS
|
Presentation form not yet defined
Providing constraints on Antarctic Subglacial Environments using Observations of Active Subglacial Lakes from Satellite Radar Altimetry
(withdrawn)
George Malczyk, Noel Gourmelen, Mauro Werder, Martin Wearing, and Daniel Goldberg
16:16–16:23
|
EGU22-4867
|
On-site presentation
Paul Winberry

The Totten Glacier is the main conduit for ice leaving the Aurora Subglacial Basin in East Antarctica. During December 2018 and January 2019, we deployed a 12 station broadband seismic array near the grounding zone of the Totten Glacier. Here we report on subglacial sedimentary structure and seismic activity recorded by this network. Previous gravity studies indicated the possibility that erosion had removed most of the subglacial sediments in the region. We use the receiver function analysis to reveal that 100-200 meters of subglacial sediment remain near the grounding zone. We also will summarize a range of glacier generated seismic activity recorded by the array. We find significant occurrence of tidally modulated near surface crevasse related events as well as basal stick-slip seismic activity. We will provide an overview into both the temporal and spatial variability of seismic activity and discuss implications for fast flow in the region.

How to cite: Winberry, P.: Seismic activity and subglacial sedimentary structure near the grounding zone of the Totten Glacier, East Antarctica , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4867, https://doi.org/10.5194/egusphere-egu22-4867, 2022.

16:23–16:30
|
EGU22-8007
|
ECS
|
Virtual presentation
Anders Damsgaard, Jenny Suckale, and Jan Piotrowski

Glacier flow has the potential to mobilize subglacial till, resulting in till deposition and subglacial landforms in glaciated areas. The subglacial till transport occurs when sedimentary beds are thawed and sufficiently weak relative to the glacial driving stress. As a consequence of till mobilization, soft-bedded and marine-terminating ice sheets are known to produce grounding-zone wedges. It has been hypothesized that these wedges may stabilize grounded ice in spite of rising sea level.

In order to test this hypothesis, we develop a fully coupled framework for simulating ice flow, glacier hydrology, and till advection. Ice flow and hydrology is handled with PISM, the three-dimensional, thermomechanical, parallel ice sheet model (Bueler and Brown, 2009; Winkelmann et al 2011). Till advection is computed with the cohesive non-granular fluidity method with pore-water pressure, which is consistent with Coulomb-frictional mechanics and stress-dependent shear-zone thickness (Damsgaard et al., 2020). We apply the model to various bed geometries and forcing scenarios, and show how subglacial landforms evolve and grounding-zone wedges form. The grounding-zone wedges prove to contribute conditional stabilization to the ice sheet, and this mechanism could limit the marine-ice sheet instabilities that may occur on reverse sloping beds.

 

References:

Bueler, E. and Brown, J. 2009 “Shallow shelf approximation as a “sliding law” in a”. J. Geophys. Res. Earth Surf. 114(F3)

Damsgaard, A., L. Goren and J. Suckale 2020 “Water pressure fluctuations control variability in sediment flux and slip dynamics beneath glaciers and ice streams”. Commun. Earth Environ. 1(66), 1–8. doi: 10.1038/s43247-020-00074-7

Winkelmann, R., M. A. Martin, M. Haseloff, T. Albrecht, E. Bueler, C. Khroulev and A. Levermann 2011 “The Potsdam Parallel Ice Sheet Model (PISM-PIK) - Part 1: Model description”. 5(3), 715–726. doi: 10.5194/tc-5-715-2011

How to cite: Damsgaard, A., Suckale, J., and Piotrowski, J.: Simulated formation of grounding-zone wedges and implications for ice-sheet stability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8007, https://doi.org/10.5194/egusphere-egu22-8007, 2022.

16:30–16:39