Supraglacial channels play a crucial role in glacial hydrology by transporting meltwater across ice sheets and ice shelves. Despite their importance, recent research has tended to focus on the storage of supraglacial meltwater (e.g., in lakes), and our understanding of the distribution and connectivity of channels is more limited, particularly in Antarctica. Here we investigate large supraglacial channels (i.e., width > 20 m) on five contrasting ice shelves in Antarctica during the melt seasons of 2020 and 2022. Supraglacial channels are mapped by applying an automated delineation method to Landsat-8 satellite imagery, and various metrics are calculated to comprehensively describe their fluvial morphometry. Results show that supraglacial channels are extensive on all five ice shelves, forming a total of 119 channel networks with significantly different drainage patterns. Channel networks exhibit relatively simple structures but large in extent and occur on low ice surface slopes (<0.001) and low elevations (< 70 m) where ice is slow-flowing (<150 m a^-1). The orientation of channels broadly coincides with the ice flow direction, and they are clearly influenced by surface flow structures (e.g., longitudinal flow-stripes), which appear to exert a clear control on both channel formation and their morphological properties. Future research will focus on temporal (i.e., seasonal and interannual) analysis of channels on each ice shelf by using Sentinel-2 imagery.

How to cite: Chen, J., Hodge, R., Jamieson, S., and Stokes, C.: Distribution and Morphometry of Large Supraglacial Channels on Five Antarctic Ice Shelves, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1076, https://doi.org/10.5194/egusphere-egu24-1076, 2024.

Supraglacial lakes are dynamic hydrological features that play a significant role in surface mass balance estimations. These lakes act as conduits for surface and subglacial runoff, the amount of which varies quite strongly based on the local surface temperature, rainfall, and snowpack thickness. Additionally, supraglacial lakes tend to undergo impactful events called rapid drainages, during which a crack opens at the lake bed, draining the meltwater to the glacier bed within hours or days. Not only does this contribute to glacier mass loss and freshwater influx into the ocean, but it can also cause temporary glacier speed-ups due to the reduction of friction on the glacier bed. Currently, the influencing factors involved in triggering these rapid drainages are minimally understood. This research firstly focuses on the comparison of several lake depth estimation methods in order to be able to accurately monitor seasonal lake development and quantify meltwater volumes. Secondly, the temporal and spatial variances in rapid drainages in Northeast Greenland, specifically over Zachariae Isstrom and Nioghalvfjerdsfjorden (79N Glacier), are evaluated in order to understand underlying causes and to quantify the amount of meltwater lost through them. 

Several established and novel supraglacial lake depth estimation methods are evaluated in this research, comprising of (1) a radiative transfer model based on Sentinel-2 data, (2) an empirical equation derived from ICESat-2 lake crossings and Sentinel-2 data, (3) an empirical equation derived from in situ sonar data gathered in Northeast Greenland and Sentinel-2 data, and (4) TanDEM-X elevation data. These four methods are directly compared on five supraglacial lakes in Northeast Greenland, highlighting the advantages and limitations of each method. Furthermore, the three methods based on Sentinel-2 imagery are applied to the peak melt dates in Northeast Greenland over the 2016 to 2022 melt seasons to understand seasonal variations. Finally, individual lakes are tracked throughout the seven melt seasons to allow for a detailed assessment of rapid drainage occurrences in the region. Overall, insight into the behavioral patterns and influencing factors involved with the rapid drainages of supraglacial lakes and the amount of meltwater lost from them has been gained. 

How to cite: Lutz, K., Sommer, C., Humbert, A., and Braun, M.: Evaluation of supraglacial lake depth estimation techniques using Sentinel-2, ICESat-2, TanDEM-X, and in situ data, along with an analysis of rapid drainage events over Northeast Greenland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2115, https://doi.org/10.5194/egusphere-egu24-2115, 2024.

Greenland’s crevasse fields transfer nearly half of the seasonal runoff to the bed of the ice sheet, with implications for ice rheology, subglacial hydrology, and subsequent feedbacks in ice dynamics. The hydrological behaviour of crevasses has been shown to be complex and spatially heterogenous, but the drainage mechanics are poorly understood, particularly in comparison to other water pathways (lake drainage, moulins, and finer-scale fractures). To better understand crevasse drainage processes at scale, we develop a convolutional neural network (CNN) to map water-filled crevasses from 10 metre resolution Sentinel-2 MSI imagery. Training and validation datasets are produced using NDWI-based approaches that are accurate but require time-consuming and scene-specific manual tuning. In contrast, our scaleable CNN approach allows for the seasonal and multiannual evolution of ponded crevasse fields to be efficiently monitored. After constructing a comprehensive, time-evolving dataset of crevasse field hydrology, we aim to quantify controls (strain rate, melt rate, etc.) on the time-evolving filling and drainage of crevasses. Our ultimate objective is to use these derived relationships to improve the parameterisation of spatially heterogenous crevasse hydrological behaviour into coupled models of Greenland Ice Sheet hydrology-dynamics. 

How to cite: Chudley, T., Winterbottom, T., Stokes, C., and Lea, J.: Mapping the hydrology of Greenland’s crevasses with deep learning , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6661, https://doi.org/10.5194/egusphere-egu24-6661, 2024.

Active subglacial and proglacial lakes drain and fill constantly, contributing to glacier and ice sheet mass balance in a way that is not always easy to quantify. Active subglacial lakes account for about 20% of the first worldwide subglacial lake inventory (published by Livingstone et al., 2022); however, none have been previously identified in the Canadian Arctic. Here, we report at least 28 drainage and fill events identified by analyzing time-stamped ArcticDEM elevation data. We stack all the available 2-m DEM strips (23,691 in total) from the latest ArcticDEM release (October 2022) and calculate the elevation change rate at every 15-m sized pixel in a reference grid. Glacier areas with the following signals are interpreted to be associated with the lake drainage or refill beneath the ice: (1) a significantly higher elevation change rate than the neighboring regions within the same glacier catchment, and (2) no adjacent zones showing reversed elevation change (to avoid surge event being misclassified). If such an area touches the glacier terminus, we interpret the elevation change to be governed by a proglacial lake where the floating ice terminus rises and falls when the lake level changes. These drainage and refill events are scattered throughout the region, from the North Ellesmere Icefields to Penny Ice Cap (South Baffin Island). Almost none of the lake locations have been previously reported, probably due to their small size (a few kilometers wide on average), but some of them caused significant ice elevation drops of up to 100 meters during a drainage event. It is not clear whether these significant drainage events produced outburst floods due to temporal sampling gaps in the data. Nevertheless, the water mass lost or gained during the events should be independently calculated from the land ice budget, and we should keep monitoring these newly discovered lakes for their potential impact on the ice flow dynamics and localized mass balances, especially in the context of rapid Arctic warming.

How to cite: Zheng, W. and Van Wychen, W.: Significant subglacial and proglacial lake drainages in the Canadian Arctic identified by time-stamped ArcticDEM strips, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6955, https://doi.org/10.5194/egusphere-egu24-6955, 2024.

The Soil Moisture and Ocean Salinity (SMOS) mission has been providing surface brightness temperatures (TB) at L-band since 2010. These measurements feed geophysical applications over the ice sheets including melt detection. The synergy between SMOS and other sensors operating at higher frequencies such as AMSR2 is furthermore promising to give insights on the percolation of meltwater in the snowpack and the presence of firn aquifers. However, most of the algorithms currently use the SMOS Level 3 (L3) gridded data which suffer from a coarse spatial resolution. To overcome this issue, we developed a new SMOS enhanced resolution TB dataset over Antarctica and Greenland which is further used to detect melt. The resolution enhancement process is based on the radiometer version of the Scatterometer Image Reconstruction (rSIR) algorithm which was previously successfully applied to SSM/I, SSMIS, AMSR and SMAP. Our methodology also takes advantage of the multi-incidence nature of SMOS measurements to use information with the best native resolution, i.e. low-incidence measurements (15-40°). We evaluated the effective spatial resolution to be ~30 km for the new SMOS enhanced TB maps. It is twice finer than the spatial resolution of the conventional SMOS L3 dataset (~60 km). Finally, a state-of-the-art melt detection algorithm was applied to both the enhanced resolution and the conventional L3 datasets. The new product unravels many localized melt patterns that were not detected using the SMOS L3, especially near the grounding lines of Antarctic ice shelves, due to smoothing of the TB between melting and non melting area. We also identify a clear aquifer signature over the ~25 km wide northern George 6 ice shelf in the Antarctic Peninsula thanks to the gain in resolution. The new SMOS enhanced resolution TB and melt products are posted on the same 12.5 km polar stereographic grid and are comparable to AMSR-E and 2 in terms of spatial resolution to facilitate further synergetic use of multi-frequency passive microwave datasets.

How to cite: Zeiger, P., Picard, G., Richaume, P., Rodriguez Fernandez, N., and Mialon, A.: Melt detection from SMOS enhanced resolution brightness temperatures on the Antarctic and Greenland ice sheets, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7605, https://doi.org/10.5194/egusphere-egu24-7605, 2024.

The potential impact of increased snowmelt and related hydrological processes on ice sheet stability has become a focus of academic attention. Hydro-fracture caused by liquid water is one of the main triggers of ice shelf disintegration. Recent discoveries of firn aquifer (FA) in the Wilkins Ice Shelf (WIS) have updated our understanding of surface hydrological processes, mass and energy balance. However, the limited field and airborne radar observations of FA cannot provide a complete picture of their distribution and characteristics. Microwave remote sensing is highly sensitive to the dielectric constant change caused by the dynamics in buried liquid water. However, it is challenging to obtain the buried depth of FA from space. In this study, the extent and depth to the water table (DWT) of FA are investigated with the combination of active and passive microwave observations, as well as airborne radar measurements. First, with the verification points from airborne radar, the extent of FA is mapped from satellite-derived snowmelt and accumulation conditions based on a K-Nearest Neighbors classification model (OA=97.2%, Kappa=0.94). Next, we use a Gaussian Process Regression model to estimate the DWT of FA (R=0.8, RMSE=2.17 m). The results show that FA occurred in most areas of WIS in 2014, with a DWT of 12.8±2.9 m. The DWT increased from north to south. Further study will examine the dynamics in FA and their hydro-fracture effect on ice shelf calving and the stability of the Antarctic ice sheet.

How to cite: Shang, X., Cheng, X., Zheng, L., Liang, Q., and Li, T.: Firn aquifer properties of Wilkins ice shelf from multi-source spaceborne microwave observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8534, https://doi.org/10.5194/egusphere-egu24-8534, 2024.

Recent research on the subglacial hydrology beneath the soft bedded West Antarctic Ice streams has shown the presence of a braided subglacial hydrology. We have been able to investigate the seasonal changes associated with a soft-bedded braided system from a series of instrumented temperate glaciers, and show there is a continuum between a subglacial channelized and braided system.

In particular, a braided subglacial river system can store summer meltwater, which is released during winter during positive degree days during winter (winter events) resulting in speed-ups. Here we show how recent increases in air temperature (and associated feedbacks such as proglacial lake growth), from a series of temperate soft-bedded glaciers, lead to potential changes in the subglacial hydrology and resultant glacier dynamics.

How to cite: Hart, J., Baurley, N., and Martinez, K.: Changes in soft bed subglacial hydrology associated with Climate Change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10739, https://doi.org/10.5194/egusphere-egu24-10739, 2024.

The snowpack and glaciers of the Himalaya-Karakoram range feed several major river systems in Asia which provide water to over one billion people. Glacial retreat, glacial lake outburst flooding (GLOFs), and glacial ice mass balance are all likely strongly affected by subglacial hydrology. Unfortunately, little is known about Himalayan glaciers due to their remoteness and the danger of doing field work there. Recent advances in subglacial hydrological modeling may allow us to shed more light on subglacial processes that lead to changes in ice mass balance and glacial lake flooding. We present the first application of the SHAKTI subglacial hydrology model to a Himalayan glacier. We model the subglacial drainage network of Shishper Glacier, located in Gilgit-Baltistan, Pakistan, to understand its seasonal evolution and history of surges and GLOFs. We find that the modeled seasonal evolution of Shishper's subglacial system follows a similar seasonal pattern to past observed and modeled subglacial systems. Additionally, a central Röthlisberger channel persists through the winter and serves as the basis for the subglacial drainage system throughout the melt season. We also investigate the 2017-2019 surge of Shishper glacier and find that subglacial hydrology, while likely an important component of surging, cannot provide a standalone explanation for surges. This work serves as a nucleus for future modeling work in the Himalayas and provides a new framework for studying the effects of climate change on glacier dynamics, water availability, and glacier-related hazards in the Himalaya-Karakoram (H-K) region.

How to cite: Narayanan, N., Sommers, A., Steiner, J., Chu, W., Siddique, M. A., Meyer, C., and Minchew, B.: Simulating Subglacial Hydrology: Insights into the Triggers of Surges and GLOFs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11819, https://doi.org/10.5194/egusphere-egu24-11819, 2024.

The 79° North Glacier (Nioghalvfjerdsbrae, 79NG) is one of three glaciers with a floating tongue in Greenland. Recent investigations indicate an increased subglacial discharge due to a considerably enlarged area of summer surface melt due to the warming of the atmosphere, resulting in increased water input to the base of glaciers. Consequently, ice velocities measured at the surface respond directly to changes in water pressure, revealing detailed insights about the ice dynamics. Global Navigation Satellite System, like GPS and Galileo, can observe ice velocities with high temporal resolution in horizontal and vertical directions.

We will present results from the 2022-2023 GNSS measurement campaign where two tinyBlack GNSS receivers were installed at 79NG. Firstly, data quality regarding common indicators like the number of tracked satellites, signal strength, and multipath will be discussed. Secondly, variations in the ice reflection characteristics will be presented based on the GNSS-reflectometry technique. The final processing was carried out as kinematic precise point processing (sampling rate 30s) using GFZ’s processing software EPOS.P8 and GFZ’s operational GNSS products. Thus, thirdly, the derived time series will be discussed with a focus on short-term variations in the surface velocity. We can link speed-up events in July 2022 to rapid lake drainage using optical satellite imagery and interferometrically derived digital elevation models.

How to cite: Männel, B., Humbert, A., Ramatschi, M., and Steinhage, D.: GNSS-based Observation of seasonal acceleration at 79°N Glacier (Greenland) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11852, https://doi.org/10.5194/egusphere-egu24-11852, 2024.

Approximately 50% of current mass loss from the Greenland Ice Sheet is from ice dynamics. It is important to understand the processes controlling ice dynamics to better calculate current rates of mass loss and predict rates into the future. Previous work has shown that both surface runoff and surface lake drainages control subglacial drainage development and therefore seasonal and annual velocities of the ice sheet, although few studies have considered these together. Here we analyse monthly patterns of runoff, lake drainages and ice velocities across a 6 753 km² land terminating part of the ice sheet between 2016 and 2021. We find that annual runoff is inversely correlated with annual velocity across the study area, supporting previous work showing the importance of subglacial drainage development in driving down water pressures and therefore basal sliding speeds. We also show that rapid surface lake drainages (a surrogate for moulin formation by hydrofracture) have an impact superimposed on the runoff control. 2016 and 2019 have comparably high annual runoff totals but the former experiences three times more rapid lake drainages than the latter, resulting in greater depressurisation of the subglacial drainage system, greater net summer slowdown and lower annual velocities. We also demonstrate ‘interannual subglacial memory’ with years succeeding high runoff years showing net summer speedup, higher winter velocities and higher annual velocities than might otherwise be expected. We identify, therefore, high runoff ‘depressurisation’ years and subsequent ’recharge’ years, with effects on seasonal and annual glacier velocities. Finally, we see localised impacts of lake drainages on spatial patterns of net summer speed up or slowdown, with lake drainages acting to depressurise cavities causing local slowdown in some instances, or recharge cavities causing local speedup in others. These processes should be considered for modelling of the future impacts of climate-controlled runoff on ice sheet dynamics and mass balance.

How to cite: Willis, I., Donaldson, L., and Dell, B.: Ice Velocity Response to Surface Melt and Lake Drainages at a Land-Terminating Margin of the Greenland Ice Sheet, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12186, https://doi.org/10.5194/egusphere-egu24-12186, 2024.

Subglacial lakes form beneath ice sheets and ice caps if water is available, and if bedrock and surface topography are able to retain the water. On a regional scale, the lakes modulate the timing and rate of freshwater flow through the subglacial system to the ocean by acting as reservoirs. More than one hundred hydrologically active subglacial lakes, that drain and recharge periodically, have been documented under the Antarctic Ice Sheet, while only approximately 20 active lakes have been identified in Greenland. Active lakes may be identified by local changes in ice topography caused by drainage or recharge of the lake beneath the ice. The small size of the Greenlandic subglacial lakes puts additional demands on mapping capabilities to resolve the evolving surface topography in sufficient detail to record their temporal behavior. Here, we explore the potential for using CryoSat-2 swath-processed data together with TanDEM-X digital elevation models to improve the monitoring capabilities of active subglacial lakes in Greenland. We focus on four subglacial lakes previously described in the literature, and combine the new data with ArcticDEMs to obtain improved measurements of the evolution of these four lakes.

We find that with careful tuning of the swath-processor and filtering of the output data, the inclusion of these new data together with the TanDEM-X data provides important information on lake activity, documenting, for example, that the ice surface collapse basin on Flade Isblink Ice Cap was 30 meters deeper than previously recorded. 

How to cite: Sandberg Sørensen, L., Simonsen, S., Havelund Andersen, N., Bahbah, R., Karlsson, N., Solgaard, A., Leeson, A., Maddalena, J., McMillan, M., Bowling, J., Gourmelen, N., Horton, A., and Wessel, B.: Improved Monitoring of Subglacial Lake Activity in Greenland using CryoSat-2 swath processed data and TanDEM-X DEMs. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12692, https://doi.org/10.5194/egusphere-egu24-12692, 2024.

Successful adaptation and mitigation of rising sea level demands improved constraints on emerging ice sheet processes controlling the magnitude and rate of sea level change in a warming climate. Therefore, it is vital to enhance the confidence in quantitative assessments of present-day ice sheet mass balance arising from meltwater generation and refine the explicit treatment of meltwater refreezing in firn densification models to evaluate the time evolution of runoff/retention and surface elevation change. The European Space Agency's Copernicus Imaging Microwave Radiometer (CIMR), scheduled for launch in 2028, responds to this need by measuring the brightness temperature (TB) at 1.4, 6.9, 10.7, 18.7, and 36.5 GHz frequencies multiple times a day over polar regions without gaps at the poles. These measurements can resolve the stratification of the seasonal meltwater from the immediate surface to the deeper firn layers. Furthermore, the 1.4 GHz TB is sensitive to the amount of meltwater.

We are developing retrieval algorithms using 1.4 GHz measurements from NASA Soil Moisture Active Passive (SMAP) and ESA Soil Moisture Ocean Salinity (SMOS) satellites and 6.9, 10.7, 18.7, and 36.5 GHz measurements from JAXA Advanced Microwave Scanning Radiometer – EOS (AMSR-E) and AMSR2 instruments on NASA Aqua and JAXA (Global Change Observation Mission – Water) GCOM-W satellites. In the algorithm development, we use ground measurements and coupled energy and mass balance models to test, calibrate, and validate the algorithm. The ground measurements include surface and subsurface measurements from PROMICE/GC-Net (Greenland) and other station and campaign data sets. The model suite includes locally calibrated and forced energy balance models and regionally forced models, such as the Ice Sheet System Model's Glacier Energy and Mass Balance module. The retrieved data product will provide twice-daily parameters such as meltwater amount, melt layer depth, and near-surface snow status (wet/dry) profile. It will also include seasonal parameters such as firn aquifer extent and evolution.

The meltwater algorithm for the CIMR mission will eventually encompass two satellites capable of monitoring diurnal melt-freeze cycles and perennial firn aquifers for at least a 15-year mission period. CIMR will measure all frequencies simultaneously, which will eliminate the uncertainties related to different observation times of the current instrument combinations, increase the revisit time of the L-band observations, and improve the spatial resolution of the 6.9, 10.7, 18.9, and 36.5 GHz channels compared to what is currently available.

How to cite: Colliander, A., Hossan, A., Harper, J., Vandecrux, B., Miller, J., Schlegel, N., Marshall, S., and Donlon, C.: Towards Ice Sheet and Ice Shelf Meltwater Profile Retrieval from Copernicus Imaging Microwave Radiometer (CIMR), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12972, https://doi.org/10.5194/egusphere-egu24-12972, 2024.

The Greenland Ice Sheet is a massive glacier that covers most of Greenland's surface and contains enough ice to raise the sea level by up to seven meters, if it melts due to climate change. Moreover, this melting could potentially lead to the disruption of the Atlantic Meridional Overturning Circulation (AMOC). For this reason, it is crucial to understand the processes that influence its melting. Meltponds, which form on its surface during the warmest months, are believed to potentially accelerate the melting process and its evolution significantly. Their variety of characteristics, can be seen as a result of a pattern-forming process that involves the interplay of multiple components, such as temperature, albedo, and mechanical processes. We employ a conceptual model of the Greenland ice sheet to unravel the possible role of such pattern formation related to meltponds in the context of global warming and climate change. This analysis is meant to contribute to a further understanding of possible essential processes influencing the future of the Greenland Ice Sheet.

How to cite: Cotronei, A. and Feudel, U.: Melt Pond Pattern Formation In Greenland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13358, https://doi.org/10.5194/egusphere-egu24-13358, 2024.

Perennial firn aquifers in Greenland are crucial for meltwater storage, significantly influencing ice-sheet hydrology. In Antarctica, although firn aquifers have been identified in situ, a comprehensive continent-wide overview is currently lacking. Using an advanced methodology that integrates multiple datasets, our pioneering study presents a 2 x 2 km resolution assessment of firn aquifer distribution in Antarctica.
The focal point of our analysis is the creation of a heat map of firn aquifer locations across Antarctica. In contrast to prior studies, reliant on traditional binary evaluations of aquifer presence or absence, our method addresses the inherent uncertainty associated with firn aquifer extent and overcoming challenges posed by the vast and remote Antarctic environment.
We use a Monte Carlo method that exploits multiple datasets as input, spanning from 2017 to 2021. Data includes Sentinel-1, Advanced SCATterometer (ASCAT), and statistically downscaled output from the RACMO2.3p2 climate model. Each of these datasets highlights a particular property of firn aquifers.
Our high-resolution heat map reveals a concentration of firn aquifers across the Antarctic Peninsula (AP). Elevated probabilities are observed along its northern, northwest, and western coastlines, as well as on the Wilkins, Müller, and part of George VI ice shelves. Beyond the AP, aquifer evidence is sparse, with only a few locations exhibiting slightly elevated probabilities, such as on the Abbot, Shackleton, and Holmes ice shelves.
Validation of the methodology applied in Greenland using Operation IceBridge (OIB) data demonstrates a 91% correspondence with observed aquifers, firmly establishing the robustness of our approach.
Leveraging the sustained accessibility of freely available C-band and scatterometer observations, complemented by modeling data, our approach allows for ongoing long-term monitoring of aquifer conditions, proving crucial to explore the response of the Antarctic ice sheet to climate change.

How to cite: Di Biase, V., Kuipers Munneke, P., de Roda Husman, S., Veldhuijsen, S., van den Broeke, M., Wouters, B., and Noël, B.: Firn aquifers in Antarctica: High-resolution mapping highlights predominance in the Antarctic Peninsula, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14576, https://doi.org/10.5194/egusphere-egu24-14576, 2024.

This study presents high resolution mapping of moulins located above three subglacial lakes at Isunguata Sermia. Moulins are the primary pathway for transferring supraglacial melt to englacial and subglacial environments. The formation of moulins has been explained by the flow of water into a notch, associated with glacier structures and incision of supraglacial streams, which are directly related to glacier morphology and dynamics. Meltwater input to subglacial systems, along with glacier dynamics, will in turn affect the development of subglacial meltwater networks, which control glacier morphology and dynamics. This study focusses on Isunguata Sermia, West Greenland, which has an active subglacial drainage system that includes distinct subglacial lakes. Hydrologically connected or active subglacial lakes may be directly influenced by water input from supraglacial to englacial systems via moulins during the ablation season.

Moulins were mapped using a combination of high resolution orthomosaics and digital elevation models derived from uncrewed aerial vehicle flights. Moulin locations and morphologies were compared with glacier structures, ice flow velocities, and bed topography. We reveal a distinct pattern of moulin locations relative to each subglacial lake and the locations of primary and secondary glacier structures an supraglacial hydrology. Furthermore, we also outline a clear morphological pattern, wherein morphology of moulins varies distinctly at with the location of each subglacial lake between vertical shafts, crevasse associated and keyhole morphology. These observations will be used to consider the efficiency of meltwater routing from the surface to the bed, and the potential for inputs to subglacial lakes, and the wider implications for varying ice flow velocity and evolution of the subglacial drainage system.

How to cite: Peacey, M., Livingstone, S., Doyle, S., Sole, A., Storrar, R., Edwards, L., Bagshaw, E., Chudley, T., Ross, N., Buzzard, S., Booth, A., Bianchi, G., Ing, R., Clason, C., Young, T. J., Thorpe, S., Gimbert, F., Le Bris, T., Barruol, G., and Gilbert, A. and the Cryoegg: Distribution and morphology of moulins at Isunnguata Sermia, West Greenland , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16236, https://doi.org/10.5194/egusphere-egu24-16236, 2024.

Ice shelves play a key role in buttressing upstream ice - modulating the flow of grounded ice into the ocean and in turn affecting ice sheet contribution to sea level. Iceberg calving, which has approximately equalled thinning in terms of mass loss from Antarctic ice shelves since 2007, is an important ablation process for balancing accumulation. However, rapid ice shelf disintegration, driven by surface melting, can dramatically impact grounded ice dynamics on relatively short time scales. In 2002, the Larsen B ice shelf lost ~60% of its area, following extensive surface melt ponding, observed over months.  This event has been associated with a ‘hydro-fracture’ mode of ice shelf collapse, where surface melt ponds enhance surface crevasse penetration, causing the ice shelf to disintegrate. Following the collapse of Larsen B, retreat of its largest tributary glacier increased by >50% over two years. Whilst surface melting on the scale that preceded Larsen B collapse has historically been limited to the North of the Antarctic Peninsula, under future anthropogenic warming, more of Antarctica’s ice shelf area could become vulnerable to hydro-fracture.

To quantify the role of ice shelf hydro-fracture in ice sheet response to warming, the PSU ice sheet model (PSUISM) incorporates a simple parameterisation of this process, as well as ice cliff failure following loss of buttressing. With its computationally tractable hydro-fracture parameterisation, PSUISM has been used to reproduce large long term Antarctic mass loss under periods of past warmth. It has also simulated high Antarctic contribution to future sea level. However, the break-up of Larsen B, which provides the observational basis for its hydro-fracture scheme, has been less well explored in PSUISM.

We present a suite of high-resolution simulations of the Larsen B ice shelf and its tributary glaciers. We explore the role of hydro-fracture parameters and a range of climate boundary conditions in driving ice shelf collapse. We also compare modelled ice shelf retreat, and grounded ice response, to available observational data. Finally, we explore modifications to the simple hydro-fracture scheme that can better capture Larsen B shelf collapse.

Ice shelf processes remain a key challenge in predicting future Antarctic ice sheet retreat. Despite advances in ice sheet modelling, capturing hydro-fracture in models capable of long integration times, at high resolution, remains a challenge. Our work explores how well the current approach in PSUISM captures the best observed ‘hydro-fracture’ driven ice shelf collapse, and how that impacts our understanding of existing projections.  

How to cite: ONeill, J. and Gasson, E.: Modelling the Hydro-fracture driven collapse of the Larsen B ice shelf, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16642, https://doi.org/10.5194/egusphere-egu24-16642, 2024.

The Greenland Ice Sheet is currently one of the primary contributors to the rise of sea levels . The Total Mass Balance (TMB) of the Greenland Ice Sheet can be decomposed into Surface Mass Balance (SMB) and ice discharge (D). At present, both terms contribute approximately equally to mass loss. However, it has been anticipated that surface losses will become more significant in the future (because coastal glaciers will retreat if the ice sheet continues to melt). Our understanding of SMB is currently notably based on polar regional climate models (RCMs) like MAR ("Modèle Atmosphérique Régional"), that simulates most of the different surface processes involved in SMB. However, one potential important process is currently missing in all model based estimates: the role of supraglacial lakes. The excess of meltwater is directly removed from the pixels by assuming that this mass fully runoffes towards the ocean in models until now. These lakes notably impact on the surface albedo of bare ice and could retain a part of produced surface meltwater that can refreeze at the beginning of winter or evaporate during summer (impacting them clouds and precipitation afterwards).

To evaluate the importance of supraglacial lakes as a potential SMB component needed to take into account, we have run MARv3.14 at very high resolution over the South-West of Greenland during the 2018-2019 hydrological year by allowing the produced surface meltwater in the ablation zone to remain liquid or solid above the surface in the bare ice areas where supraglacial lakes have been detected by MODIS.

How to cite: Timmermans, G. and Fettweis, X.: Impact of supraglacial lakes on the Greenland Ice Sheet Surface Mass Balance into the regional climate model MAR, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18932, https://doi.org/10.5194/egusphere-egu24-18932, 2024.

The presence of subglacial lubrication networks at the ice-bed interface is a key component for ice sheet dynamics. A subglacial network has the potential to facilitate rapid ice flow through reduction in basal friction, possibly resulting in the formation of surges and ice streams. A wide range of numerical models are designed to simulate the impact such networks on ice flow. Validating these models is crucial to ensure that the important subglacial physical processes are accurately resolved.

One class of subglacial network models is based on an effective porous medium (EPM) approach. A major component of such models involves a nonlinear diffusion equation for the subglacial water pressure, which include variable transmissivity that represent a range of subglacial and groundwater processes.

We present solutions to a generalized nonlinear diffusion equation that can model a wide range of flows of this kind. We use scaling analysis to find general similarity solutions and other solutions with explicit time-dependent transmissivity. We use this method to validate the parallel implementation of the Confined–Unconfined Aquifer System model (CUAS-MPI) for subglacial hydrology. The model is based on an effective porous media (EPM) approach. Our results show, that CUAS-MPI is able to accurately solve highly non linear flows, equivalent to cavity opening and creep closure terms in subglacial hydrology. Because of their generality, our solutions are readily applicable to other subglacial hydrology models that are based on the EPM approach. We anticipate that a validated hydrology model with our solutions can achieve more credible results in subglacial network simulations, and consequently in predicting ice sheet evolution.

How to cite: Schmiedel, J., Humbert, A., Kleiner, T., and Sayag, R.: Validation of effective subglacial hydrology models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19875, https://doi.org/10.5194/egusphere-egu24-19875, 2024.