CR2.4 | Hydrology of ice sheets, ice shelves and glaciers
EDI
Hydrology of ice sheets, ice shelves and glaciers
Convener: Ian Hewitt | Co-conveners: Gabriela Clara Racz, Alison Banwell, Sophie de Roda HusmanECSECS, Sammie Buzzard
Orals
| Wed, 17 Apr, 08:30–12:30 (CEST)
 
Room 1.61/62
Posters on site
| Attendance Wed, 17 Apr, 16:15–18:00 (CEST) | Display Wed, 17 Apr, 14:00–18:00
 
Hall X5
Posters virtual
| Attendance Wed, 17 Apr, 14:00–15:45 (CEST) | Display Wed, 17 Apr, 08:30–18:00
 
vHall X5
Orals |
Wed, 08:30
Wed, 16:15
Wed, 14:00
Dynamic subglacial, supraglacial and englacial water networks play a key role in the flow and stability of glaciers and ice sheets. The accumulation of meltwater on the surface of ice shelves has been hypothesized as a potential mechanism controlling ice-shelf stability, with ice-shelf collapse triggering substantial increases in discharge of grounded ice. Observations and modelling also suggest that complex hydrological networks occur at the base of glaciers and ice sheets and these systems play a prominent role in controlling the flow of grounded ice. This session tackles the urgent need to better understand the fundamental processes involved in glacial hydrology that need to be addressed in order to accurately predict future ice-sheet evolution and mass loss, and ultimately the contribution to sea-level rise.

We seek contributions from both the modelling and observational communities relating to any area of ice-sheet, ice-shelf, or glacier hydrology. This includes but is not limited to: surface hydrology, melt lake and river formation; meltwater processes within the ice and firn; basal hydrology; subglacial lakes; impacts of meltwater on ice-sheet stability and flow; incorporation of any of these processes into large-scale climate and ice-sheet models.

Session assets

Orals: Wed, 17 Apr | Room 1.61/62

Chairpersons: Sophie de Roda Husman, Gabriela Clara Racz
08:30–08:40
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EGU24-20925
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On-site presentation
Aneesh Subramanian, Devon Dunmire, Emam Hossain, Md Osman Gani, Alison Banwell, and Brendan Myers

Supraglacial lakes form on the surface of the Greenland Ice Sheet during the summer months and can directly impact ice sheet mass balance by removing mass via drainage and runoff or indirectly impact mass balance by influencing ice sheet dynamics. Here, we utilize the growing inventory of optical and microwave satellite imagery to automatically determine the fate of Greenland-wide supraglacial lakes during 2018 and 2019, a cool and warm melt season respectively. We use a machine learning time series classification approach to categorize lakes into four different categories: lakes that 1) refreeze, 2) rapidly drain, 3) slowly drain, and 4) become buried lakes at the end of the melt season. We find that during the warmer 2019, not only was the number of lake drainage events higher than in 2018, but also the proportion of lakes that drained was greater. By investigating mean lake depths for these four categories, we show that drained lakes were, on average, 22% deeper than lakes that refroze or became buried lakes. Interestingly, drained lakes had approximately the same maximum depth in 2018 and 2019; however, lakes that did not drain were 29% deeper in 2018, a cooler year. Our unique two-year dataset describing the fate of every Greenland supraglacial lake provides novel insight into lake drainage and refreeze in a relatively warm and cool year, which may be increasingly relevant in a warming climate.

How to cite: Subramanian, A., Dunmire, D., Hossain, E., Gani, M. O., Banwell, A., and Myers, B.: The fate of Greenland Ice Sheet supraglacial lakes in a warm and cool year, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20925, https://doi.org/10.5194/egusphere-egu24-20925, 2024.

08:40–08:50
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EGU24-16416
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On-site presentation
Angelika Humbert, Veit Helm, Ole Zeising, Niklas Neckel, Robert Salzano, Giulio Esposito, Matthias Braun, Holger Steeb, Julia Sohn, Matthias Bohnen, Ralf Müller, and Martin Rückamp

The mechanisms of drainage of supraglacial lakes are not yet fully understood. Here we present an indepth study of drainage characteristics of a 21km^2 large supraglacial lake in Northeast Greenland from its genesis in mid 1990s to 2023. We discuss the fracture modes involved in drainage and compare this to simulated principal stress fields. A particular focus of the presentation is the formation of gullies. Using high resolution optical satellite imagery (WV2 and Planet), we detect fracture networks at the surface. We find evidence for reactivation of former gullies in subsequent lake drainage events. In addition we present viscoelastic modelling of gullies at the surface that support the continued existence of open gullies at the surface. In vertical direction, we surveyed the glacier using airborne radio echo sounding in 2016, 2018 and 2021. This data reveals englacial channels and their remnants over the entire live span of the lake. 

How to cite: Humbert, A., Helm, V., Zeising, O., Neckel, N., Salzano, R., Esposito, G., Braun, M., Steeb, H., Sohn, J., Bohnen, M., Müller, R., and Rückamp, M.: Supraglacial lake drainage through gullies and fractures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16416, https://doi.org/10.5194/egusphere-egu24-16416, 2024.

08:50–09:00
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EGU24-13766
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ECS
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On-site presentation
Alamgir Hossan, Andreas Colliander, Julie Miller, Shawn Marshall, Joel Harper, and Baptiste Vandecrux

With the growing concern of climate change, an accurate estimation of the total meltwater amounts (MWA) in the Greenland ice sheet (GIS) becomes crucial for understanding the physical processes of the GrIS and its mass balance, thereby enabling accurate prediction of its contribution to the global sea-level rise. Satellite microwave radiometers have been widely used for monitoring ice sheet melting for the last four decades; nevertheless, quantification of total MWA, especially the sub-surface MWA, remains a challenge.

Here, we used the enhanced resolution L-band brightness temperature (TB) observations from the NASA Soil Moisture Active Passive (SMAP) mission to quantify the magnitude of the total MWA in GrIS for 2015-2023. Because of the larger penetration depth, L-band signals can track liquid water in deeper layers and provide a reliable estimate of surface-to-subsurface MWA, contrary to the higher frequency signals (18 or 37 GHz bands), which are limited to the top few centimeters of the surface snow. The algorithm uses vertically polarized (V-pol) TBs and an empirically derived adaptive thresholding technique to detect melt events. A simple microwave emission model, based on ice sheet radiative transfer, was used to simulate L-band TBs. The simulated TBs were then used in an inversion algorithm for MWA retrieval.

Finally, the retrieval was compared with the corresponding MWA derived from an ice sheet energy and mass balance (EMB) model which was forced by hourly in situ observations from the Programme for Monitoring of the Greenland Ice Sheet (PROMICE) automatic weather station (AWS) network. The model was initialized and constrained by the relevant ice core density and sub-surface temperature profiles. The retrievals generally demonstrate a stronger agreement with the in situ observations in the percolation zone than in the ablation and upper elevation regions. The radiometric sensitivity, meltwater process, and their spatiotemporal variability were analyzed. The results demonstrate the potential for advancing our understanding of ice sheet physical processes to better project Greenland’s contribution to global sea level rise in response to the warming climate.

How to cite: Hossan, A., Colliander, A., Miller, J., Marshall, S., Harper, J., and Vandecrux, B.: Measurement of the Total Meltwater Amount in the Greenland Ice Sheet Using SMAP L-band Radiometry , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13766, https://doi.org/10.5194/egusphere-egu24-13766, 2024.

09:00–09:10
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EGU24-6372
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ECS
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On-site presentation
Anna Puggaard, Nicolaj Hansen, Ruth Mottram, Thomas Nagler, Stefan Scheiblauer, Sebastian B. Simonsen, Louise S. Sørensen, and Anne M. Solgaard

Since the early 1990s, a decrease in the surface mass balance has contributed to about half of the observed Greenland Ice Sheet mass loss. Since surface melt is the primary driver of surface mass loss, an accurate representation of surface melt is crucial for understanding the surface mass balance and, ultimately, the total contribution to rising sea levels. Although Regional Climate Models (RCMs) can simulate ice-sheet-wide melt volume, significant variability exists among state-of-the-art RCMs, underpinning the need for validation of the melt. Here, we explore a novel processing of Advanced SCATterometer (ASCAT) data, which provides estimates of the spatiotemporal variability of melt extent across the Greenland Ice Sheet. We apply these new maps to pinpoint differences in the melt products from three RCMs. Using Programme for Monitoring of the Greenland Ice Sheet & Greenland Climate Network (PROMICE GC-net) air temperature observations, we evaluate how well RCM-modeled melt volume aligns with temperature measurements. With this evaluation, we establish thresholds for the RCMs to identify the amount of meltwater before it is observed at the AWS stations, thus allowing us to infer melt extent in RCMs. Results show that applying thresholds, informed by in-situ measurement, reduces the differences between ASCAT and RCMs and minimizes the discrepancies among RCMs. We leverage the differences between modeled melt extent and ASCAT-observed melt extent to further pinpoint (i) limitations in ASCAT's melt detection, including misclassification in the ablation zone as well as a temporal melt onset bias, and (ii) biases inherent in RCMs, including variability in albedo schemes, snow layer thickness, and temperature and radiation biases in the boundary forcing.

How to cite: Puggaard, A., Hansen, N., Mottram, R., Nagler, T., Scheiblauer, S., Simonsen, S. B., Sørensen, L. S., and Solgaard, A. M.: Intercomparison of melt observed by ASCAT and modeled by Greenland Regional Climate Models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6372, https://doi.org/10.5194/egusphere-egu24-6372, 2024.

09:10–09:20
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EGU24-9707
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ECS
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On-site presentation
Ryan Ing, Peter Nienow, Andrew Sole, Andrew Tedstone, and Kenneth Mankoff

Extreme melt and rainfall events can induce temporary acceleration of Greenland Ice Sheet motion, leading to increased advection of ice to lower elevations where melt rates are higher. In a warmer climate, these events are likely to become more frequent. In September 2022, unprecedented air temperatures caused multiple melt events over the Greenland Ice Sheet, generating the highest melt rates of the year. In this study we investigate the impact of these large late-season melt events on the ice dynamics of five land- and two marine-terminating outlet glaciers of the west Greenland Ice Sheet. The scale and timing of the largest event overwhelmed the subglacial drainage system, enhancing basal sliding and increasing ice velocities by up to ~240% relative to pre-event velocities. However, ice velocity returned rapidly to pre-event levels, and the speed-ups caused a regional increase in annual ice discharge of only ~2% compared to when the effects of the speed-ups on ice discharge were excluded. In contrast, the total annual runoff from the studied glaciers increased by 24%. Therefore, although late-season melt events are forecast to become more frequent and drive large amounts of runoff, their impact on net mass loss via ice discharge is minimal.

How to cite: Ing, R., Nienow, P., Sole, A., Tedstone, A., and Mankoff, K.: Minimal Impact of Late-Season Melt Events on Greenland Ice Sheet Annual Motion, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9707, https://doi.org/10.5194/egusphere-egu24-9707, 2024.

09:20–09:25
09:25–09:35
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EGU24-7667
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Highlight
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On-site presentation
Andrew Tedstone, Horst Machguth, Nicole Clerx, Nicolas Jullien, Hannah Picton, Julien Ducrey, Dirk van As, Paolo Colosio, Marco Tedesco, and Stef Lhermitte

Refreezing is an important component of the Greenland Ice Sheet's surface mass balance. At higher elevations of the ice sheet which are underlain by porous firn, meltwater percolates into the firn pore space where it refreezes in-situ, and therefore does not run off. However, in the last three decades, surface melting has increased at a faster rate than accumulation. In the percolation zone, this has caused anomalous densification of the firn pore space by meltwater percolation and refreezing, leading to metres-thick near-impermeable ice 'slabs' forming and causing the runoff limit to rise.

In-situ hydrological observations on ice slabs show that surface meltwater percolates through the seasonal snowpack to flow laterally at metres an hour through a slush matrix atop the ice slab. A saturated slush matrix on top of a cold ice slab therefore has the potential to accrete superimposed ice onto the slab surface.

We present the first measurements of superimposed ice formation (SIF) on top of ice slabs in the vicinity of the runoff limit on the K-Transect, south-west Greenland and quantify the impact of SIF on local surface mass balance and runoff. Next, we use vertical heat flow modelling to calculate the ability of an ice slab to refreeze surface melt during a melt season. With synthetic aperture radar observations, we estimate the contribution of residual stored meltwater to autumn-time refreezing. Finally, we assess the importance of SIF across all regions of the ice sheet underlain by ice slabs.

Our findings reveal widespread and substantial refreezing in areas that, at a first glance of recent satellite imagery, can appear to be dominated by runoff. Ice slabs undoubtedly enable surface runoff from higher elevations of the ice sheet. However, their cold content and their shallow surface slopes, promoting water retention, can also enable substantial refreezing. In our field area at the 2022-2023 runoff limit, net refreezing corresponded to roughly 50 % of melt. Ice-sheet-wide, ice slabs enable runoff but are also hotspots of refreezing, retaining around 27 Gt of melt as superimposed ice between 2017 and 2022.

How to cite: Tedstone, A., Machguth, H., Clerx, N., Jullien, N., Picton, H., Ducrey, J., van As, D., Colosio, P., Tedesco, M., and Lhermitte, S.: Superimposed ice formation reduces meltwater runoff from ice slab areas of the Greenland Ice Sheet , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7667, https://doi.org/10.5194/egusphere-egu24-7667, 2024.

09:35–09:45
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EGU24-11855
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ECS
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On-site presentation
Sanne Veldhuijsen, Willem Jan van de Berg, Peter Kuipers Munneke, Nicolaj Hansen, Fredrik Boberg, and Michiel van den Broeke

Perennial firn aquifers (PFAs) are year-round bodies of liquid water within firn. In Antarctica, they can cause hydrofracturing of ice shelves, leading to accelerated ice-sheet mass loss. PFAs were only recently discovered in the Antarctic Peninsula, at locations with high melt and snow accumulation rates. Likely, PFAs will expand in the future as both snowfall and melt increase. So far, this has not been considered when assessing the future vulnerability of Antarctic ice shelves. One could use a firn model to predict future Antarctic PFA evolution, but to do so for a wide range of climatic forcings is computationally expensive. Therefore, we set up a random forest emulator. The emulator represents both firn and surface climate processes, so that only 2 metre temperature and precipitation are required as input. To train the emulator, we use simulations of three scenarios (SSP1-2.6, SSP2-4.5 and SSP5-8.5) from firn densification model IMAU-FDM forced by the regional climate model RACMO2, which was driven by CESM2 in turn. The emulator successfully explains 98% of the PFAs variation, therefore we use its versatility and speed to predict Antarctic PFA evolution for 15 additional RCM/GCM model forcings. We find a range of solutions, highlighting the usefulness of the emulator. Until 2100, PFA occurrence remains restricted to ice shelves in the Antarctic Peninsula for SSP1-2.6 and SSP2-4.5. For SSP5-8.5, PFAs expand to the Bellingshausen Sea region in West-Antarctica, and to Enderby Land in East-Antarctica. The meteorological conditions in Enderby Land exhibit similarities to those observed in the Antarctic Peninsula. In contrast, Getz ice shelf, which experiences high snow accumulation rates, remains insensitive to PFA formation, because it is rather cold. Our results highlight the sensitivity of relatively warm, high-accumulation ice shelves to future PFA formation and subsequent hydrofracturing.

How to cite: Veldhuijsen, S., van de Berg, W. J., Kuipers Munneke, P., Hansen, N., Boberg, F., and van den Broeke, M.: Exploring the future expansion of perennial firn aquifers in Antarctica using a random forest emulator, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11855, https://doi.org/10.5194/egusphere-egu24-11855, 2024.

09:45–09:55
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EGU24-1052
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ECS
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On-site presentation
Tilly Woods and Ian Hewitt

The weathering crust is a porous layer of ice found at an ice sheet surface, formed by shortwave radiation penetrating below the surface and causing internal melting. It is a dynamic hydrological system that acts to transport meltwater, impurities, and microbes across the ice sheet surface into larger-scale hydrological features such as surface streams. The weathering crust is very variable, growing and decaying on the order of hours and days in response to changing weather conditions, with consequences for the surface albedo as well as meltwater storage and transport. The albedo is impacted both by the weathering crust structure and the presence of microbes and impurities (for example in the south-western Greenland ‘dark zone’). We have developed two mathematical models to investigate the evolution of the weathering crust and microbes over space and time: a one-dimensional model for the vertical structure, and a depth-integrated model to explore the lateral extent of the weathering crust and transport of meltwater. We present solutions generated by idealised forcings as well as observations from the field. This explains the observed response of the weathering crust to short-term changes in weather, and provides insight into the longer-term response of the weathering crust and algal blooms to climate change.

How to cite: Woods, T. and Hewitt, I.: Modelling the evolution of the weathering crust, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1052, https://doi.org/10.5194/egusphere-egu24-1052, 2024.

09:55–10:05
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EGU24-8038
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ECS
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On-site presentation
Ryan Strickland and Matthew Covington

Debris-covered glaciers develop complex, hummocky topography in their ablation zones. The development of hummocky topography coincides with the formation of supraglacial ponds and ice cliffs. Because the ponds and ice cliffs significantly increase melt rates, there is a need to understand how the hummocky topography evolves to better predict melt from debris-covered glaciers. Supraglacial ponds, and the ice cliffs that form along pond shorelines, develop within topographic depressions in the hummocky topography. Recent work (Strickland et al., 2023) showed that topographic depressions on the debris-covered Ngozumpa Glacier, Nepal, undergo positive feedback growth. The development of depressions is often attributed to contrasts in melt rates caused by contrasts in debris thickness. However, this hypothesis cannot explain positive feedback growth because it ignores the negative feedback caused by hillslope debris transport into the depression. Although not included in current models of surface evolution, meltwater drainage provides a potential mechanism for positive feedback depression growth. To better understand depression growth and the evolution of hummocky topography, we develop a two-dimensional topographic evolution model for debris-covered glaciers. Here, we explore how the emergence of englacial debris, hillslope transport of supraglacial debris, and meltwater drainage influence the development of topographic depressions. We first examine the topography that develops from a heterogeneous debris layer. Then, we add the influence of channel incision on topographic evolution. With these mechanisms included, the model only produces small, transient depressions. However, if we include englacial drainage points—locations where supraglacial meltwater and debris enters the subsurface drainage network— this spurs the growth of large, lasting depressions. These results suggest that englacial drainage is necessary to produce persistent depressions in hummocky topography.

How to cite: Strickland, R. and Covington, M.: Modeling the evolution of hummocky topography on debris-covered glaciers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8038, https://doi.org/10.5194/egusphere-egu24-8038, 2024.

10:05–10:15
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EGU24-18204
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On-site presentation
Eyjólfur Magnússon, Vincent Drouin, Finnur Pálsson, Krista Hannesdóttir, Joaquín M. C. Belart, Jan Wuite, Gunnar Sigurðsson, Bergur Einarsson, Tómas Jóhannesson, Benedikt G. Ófeigsson, Thomas Nagler, Magnús T. Gudmundsson, Thórdís Högnadóttir, and Etienne Berthier

We present a study on two jökulhlaups from the subglacial lake Grímsvötn, beneath Vatnajökull ice cap, SE-Iceland, giving new insights into the development of slowly rising jökulhlaups. In the first, spanning the period 14 November – 10 December, 2021, ~0.92 km3 of water was released, reaching peak discharge from the lake of ~3500 m3 s–1 from the lake on 4 December. In the latter, taking place 4­–22 October, 2022, the corresponding numbers were ~0.16 km3 and ~500 m3 s–1. Both jökulhlaups were captured by ICEYE X-band radar satellites, with daily repeated SAR images, allowing construction of 3D ice motion above the ~50-km long subglacial flood route, using InSAR and amplitude offset-tracking results. During both jökulhlaups, the outflow from the lake, derived from the lake level (with GNSS), was monitored, as well as the development of the flood near the glacier margin in the river Gígjukvísl. During the 2021 jökulhlaup, the ice motion above the flood path, deduced from the satellite data, was validated with data from a GNSS station operated ~30 km from the glacier margin. Surface elevation changes above the lake before, during and in between the jökulhaups were derived from Pléiades optical stereo images. Our data show that during the early phase of these jökulhaups, a flood wave propagates down glacier at pace of ~7 km d–1. The flood waves were most likely initiated at a bottleneck formed in a tunnel flow somewhere along the first 10 km of the flood path, while the discharge from the lake was still only few tens of m3 s–1. Five to seven days passed from the likely initiation of the flood wave until floodwater was detected in the river Gígjukvísl. The maximum observed horizontal ice motion above the flood path in 2021 was around 3 m d-–1 or ~5 times the maximum during normal winter conditions. At many locations, the horizontal velocity is increased by an order of magnitude. After the peak discharge from Grímsvötn was reached, the glacier almost immediately started slowing down, first rapidly or by ~50% over 1–2 days, but then gradually down to normal velocities in 4–5 days. In 2021, the observed rate of uplift was up to 0.5 m d1 during the rise of the jökulhlaup and the subsequent subsidence reached up 1.0 m d–1 during its decline. The study shows that ~0.3 km3 was stored beneath the glacier during the peak of the jökulhlaup, and it is therefore expected that the magnitude of the uplift/subsidence reached 2–3 m in some areas. The width of the flooded areas, observed from the subsidence during the early decline of the jökulhlaups, was typically 0.5–1 km the first 20 km of the flood path, while for the remaining 30 km, it was typically 2­–4 km. The effect of the floods on horizontal ice motion, presumably due to a disturbance in the subglacial water pressure, are, however, observed over a much larger area.

How to cite: Magnússon, E., Drouin, V., Pálsson, F., Hannesdóttir, K., Belart, J. M. C., Wuite, J., Sigurðsson, G., Einarsson, B., Jóhannesson, T., Ófeigsson, B. G., Nagler, T., Gudmundsson, M. T., Högnadóttir, T., and Berthier, E.: New insights into the development of slowly rising jökulhlaups from the Grímsvötn subglacial lake, Iceland, deduced from ICEYE SAR images and in-situ observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18204, https://doi.org/10.5194/egusphere-egu24-18204, 2024.

Coffee break
Chairpersons: Alison Banwell, Ian Hewitt
10:45–10:55
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EGU24-8950
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ECS
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On-site presentation
Sally Wilson, Anna Hogg, Richard Rigby, Thomas Slater, and Isabel Nias

Subglacial lakes beneath the Antarctic Ice Sheet were first identified using airborne radio-echo sounding (RES) surveys from the 1960s. In Antarctica, 20% of 675 currently identified subglacial lakes are “active,” exhibiting draining and filling behaviour as water flows through them. Clusters of active subglacial lakes often form in networks, connected by subglacial hydrological pathways which enable transfer of water between lakes themselves. Signals of this hydrological activity at the ice base can be detected in height changes at the ice sheet surface. Despite efforts to observe and understand this component of ice sheet mechanics, triggers of lake drainage events, in addition to drainage mechanisms and their variability are currently unresolved. An ongoing challenge lies in accurately identifying the location and extent of subglacial lakes.

We present a new dataset of locations and boundaries for over 100 newly identified subglacial lakes in Antarctica. Using 10 years of CryoSat-2 swath-processed altimetry data, from 2011-2021, we identify localised regions of ice surface uplift and subsidence associated with subglacial lake filling and draining cycles. We use a new method to manually delineate subglacial lake maximum extent boundaries for individual filling and drainage periods. These results provide insights into new areas of subglacial hydrological activity in Antarctica and their evolution over time, which are vital to resolve in order to understand their impacts on Antarctic Ice Sheet stability.

How to cite: Wilson, S., Hogg, A., Rigby, R., Slater, T., and Nias, I.: New Active Antarctic Subglacial Lakes using 10 years of CryoSat-2 Altimetry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8950, https://doi.org/10.5194/egusphere-egu24-8950, 2024.

10:55–11:05
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EGU24-1570
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ECS
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On-site presentation
Jennifer Arthur, Jelte van Oostveen, Calvin Shackleton, Geir Moholdt, and Kenichi Matsuoka

Subglacial lakes beneath the Antarctic Ice Sheet are known to influence ice-sheet dynamics and form part of an extensive active hydrological network. Ice surface elevation anomalies from repeat-track altimetry can be useful for detecting subglacial lakes and the evolution of subglacial water transport towards sub-ice-shelf cavities. Here, we analyse a 5-year time series of laser altimetry data from the ICESat-2 satellite to investigate potential subglacial lake activity in the coastal Dronning Maud Land region of East Antarctica. Our results reveal ice surface uplift and subsidence events which we interpret to reflect the active draining and filling of subglacial lakes over annual timescales. We find lake locations to be topographically-controlled and coincide spatially with predicted subglacial water routing pathways. Our results highlight subglacial lake activity as close as 10 km from the grounding line in a region of East Antarctica where no subglacial water has been observed in the coastal zone previously. These findings bring knowledge of the dynamics and evolution of subglacial meltwater in this region and provide new observational data to refine subglacial hydrological model estimates of water flux towards ice-shelf grounding zones.

How to cite: Arthur, J., van Oostveen, J., Shackleton, C., Moholdt, G., and Matsuoka, K.: Subglacial lake detection in Dronning Maud Land, East Antarctica using ICESat-2, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1570, https://doi.org/10.5194/egusphere-egu24-1570, 2024.

11:05–11:15
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EGU24-20653
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ECS
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Virtual presentation
Antarctic-wide subglacial hydrology modelling explores controls on ice velocity and ice shelf melt
(withdrawn)
Shivani Ehrenfeucht, Christine Dow, Koi McArthur, and Mathieu Morlighem
11:15–11:25
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EGU24-12569
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ECS
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On-site presentation
Thomas Gregov, Elise Kazmierczak, Violaine Coulon, and Frank Pattyn

Subglacial hydrology is a crucial element for understanding the dynamics of marine ice sheets. Indeed, the presence of subglacial water modulates the ice basal motion, resulting in a modified ice flow across the entire ice sheet. Nonetheless, the subglacial environment is difficult to reach, which makes it necessary to develop models. Many efforts have recently been made in the glaciological and hydrological communities to improve their accuracy and efficiency. Even so, the models currently being developed are typically fairly costly in terms of computing time. As a consequence, conducting numerical simulations over long time scales or running ensemble simulations remains particularly challenging.

Here, we propose a simplified approach for coupling subglacial hydrology with the motion of ice. First, we introduce a computationally efficient subglacial hydrology model that is suited for hard and soft bed types as well as efficient and inefficient drainage systems. Then, we show some numerical results based on our implementation of this model within the Kori-ULB ice-sheet code. We first study the impact of subglacial hydrology in the idealized MISMIP configuration. Subsequently, we show results of simulations conducted over Thwaites Glacier which suggest that the coupling of subglacial hydrology with ice flow could significantly increase the contribution of marine ice sheets to future sea-level rise.

How to cite: Gregov, T., Kazmierczak, E., Coulon, V., and Pattyn, F.: A new, fast and unified subglacial hydrological model applied to Thwaites Glacier, Antarctica, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12569, https://doi.org/10.5194/egusphere-egu24-12569, 2024.

11:25–11:35
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EGU24-10045
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ECS
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On-site presentation
Grounding line reconfiguration before and during lake drainage at Subglacial Lake Engelhardt, West Antarctica
(withdrawn)
Bryony Freer, Oliver J. Marsh, Helen Amanda Fricker, Anna E. Hogg, Dana Floricioiu, and Matthew R. Siegfried
11:35–11:40
11:40–11:50
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EGU24-2035
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ECS
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On-site presentation
Simon Jung, Mauro A. Werder, Anders Damsgaard, and Daniel Farinotti

Many of Antarctica’s ice streams reside on deformable beds. The description of their basal
conditions is a major source of uncertainty in modeling studies attempting to predict their
response to a changing climate. The mechanics at the glacier bed, often divided into glacier
sliding and deformation of the subglacial sediments (so-called till), depend on the subglacial
water pressure and thus on the subglacial drainage. To understand the drainage system at
the ice-till interface, past works modeled the stability of channels incised in the till (so-called
canals). Such canals open due to erosion by water flow and close due to till creep and fluvial
deposition. Till rheology is a central point of discussion in these models.
The original description by Walder and Fowler (1994) of canals assumed a viscous rheology of
the subglacial till. Lab and field experiments show the subglacial till to be better described by
a plastic rheology. A recent study by one of the co-authors of this contribution implemented a
plastic rheology and showed that this leads to plastic behaviour of the canals’ closure, such as
rapid canal collapse when their size is too large for prevailing effective pressure.
In this contribution, we extend this latter model to parameterize the effect of till deformation
induced by glacier sliding on canal dynamics. Our results show the glacier sliding to drive
canal closure at all effective pressures. We describe this process with a closure rate that scales
linearly with the basal sliding velocity and is increasing non-linearly with both the effective
pressure and the canals size.
By controlling the canals’ closure, basal sliding thus impacts the drainage capacity, and in
turn, the subglacial water pressure. Thus the positive relation between the basal sliding speed
and canal closure could potentially be a mechanism leading to high sliding speeds, such as
found in ice streams.

How to cite: Jung, S., Werder, M. A., Damsgaard, A., and Farinotti, D.: A parameterization for the closure rate of canals incised in subglacial till, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2035, https://doi.org/10.5194/egusphere-egu24-2035, 2024.

11:50–12:00
|
EGU24-9037
|
On-site presentation
Thomas Zwinger, Peter Råback, and Rupert Gladstone

Within the modelling framework of Elmer/Ice we have existing model components to compute the thermo-mechanical ice flow problem, using a full-stress approach as well as several model approaches for the bedrock hydrology, for instance the Glacier Drainage System model (GlaDS - Werder et al., 2013). Further, a thermodynamically consistent groundwater model including freezing (permafrost) and thawing of the pore-water  and the stress-induced deformation of the rock skeleton is implemented in Elmer. The real challenge lies within coupling those three components with mutual feedback, both, in mechanical and thermal aspects that mutually depend on each other, e.g. through a temperature and water-pressure dependent sliding law. The fact that all equations are implemented in the same Finite Element framework enables a consistent coupling of the equations solved on different domains (ice, water-sheet and sediment), in case of weakly coupling being able to use the residual to transfer loads. Along the lines of a synthetic glacier setup, we highlight the workflow of such a coupled simulation and point out the challenges of such a highly complex process model.

How to cite: Zwinger, T., Råback, P., and Gladstone, R.: A coupled model of glacier-ice dynamics, bed-hydrology and bedrock groundwater flow including heat-transfer, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9037, https://doi.org/10.5194/egusphere-egu24-9037, 2024.

12:00–12:10
|
EGU24-8364
|
On-site presentation
Coline Bouchayer, Ugo Nanni, Pierre-marie Lefeuvre, John Hulth, Louise steffensen Schmidt, Jack Kohler, Francois Renard, and Thomas vikhamar Schuler

Glacier flow variations are predominantly due to changes at the ice-bed interface, where basal slip and sediment deformation drive basal glacier motion. Determining subglacial conditions and their responses to hydraulic forcing remains challenging due to the difficulty of accessing the glacier bed. In this study, we analyze data series from instruments placed at the base of Kongsvegen glacier (Svalbard) thanks to a 350 m borehole.The borehole was instrumented witha pressure sensor, seismometers, and a ploughmeter to monitor the interplay between surface runoff and hydro-mechanical conditions. Covering the two ablation seasons of 2021 and 2022, , we measured point-scale subglacial water pressure and till strength, and we derived at a kilometre scale the subglacial hydraulic gradient and radius from seismic observations.. Across seasonal, multi-day, and diurnal time scales, we compared these measurements to characterize the variations in subglacial conditions caused by changes in surface runoff. We discuss our results in light of existing theories of subglacial hydrology and till mechanics. We find that during the short, low intensity melt season of 2021, the subglacial drainage system evolves to accommodate runoff variations, increasing its capacity as the melt season progressed. In contrast, during the long and high intensity melt season of 2022, the subglacial drainage system evolved transiently to respond to the abrupt and large water supply. We suggest that in this configuration, the drainage capacity of the hydraulically active part of the subglacial drainage system is exceeded, promoting the expansion of hydraulically connected regions and local weakening of ice-bed coupling, thus enhancing sliding. Our in-situ, multi-method approach provides a unique insight into conditions at the ice-bed interface.

How to cite: Bouchayer, C., Nanni, U., Lefeuvre, P., Hulth, J., Schmidt, L. S., Kohler, J., Renard, F., and Schuler, T. V.: Observed multi-scale variations of subglacial hydro-mechanical conditions at Kongsvegen, Svalbard., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8364, https://doi.org/10.5194/egusphere-egu24-8364, 2024.

12:10–12:20
|
EGU24-12711
|
On-site presentation
Samuel Doyle, Stephen Livingstone, Andrew Sole, Robert Storrar, Tun Jan Young, Ryan Ing, Neil Ross, Liz Bagshaw, Caroline Clason, Laura Edwards, Mike Prior-Jones, Gianluca Bianchi, Sammie Buzzard, Tifenn Le Bris, Guilhem Barruol, Florent Gimbert, Adrien Gilbert, Matthew Peacey, and Adam Booth

Hydrologically active subglacial lakes modulate subglacial hydrology, ice motion, microbial habitats, biogeochemical fluxes, and subglacial and proglacial geomorphic activity. The recent potential identification of active subglacial lakes beneath the ablation area of the Greenland Ice Sheet from repeat satellite altimetry data suggests that they are a significant yet poorly constrained component of the ice sheet hydrological system. These subglacial lakes, which are presumably fed by both supraglacial and subglacial water inputs, appear to be highly dynamic features that fill gradually (i.e. over years) but drain rapidly (i.e. hours to days), causing high discharge flood events observed in the proglacial area. While remote sensing observations constrain lake dynamics to a coarse temporal and spatial resolution the precise timing of lake filling and drainage and the detailed effect on ice dynamics can only be determined from field-based measurements. Here we present initial results from a comprehensive geophysical investigation of subglacial lake dynamics beginning in April 2023. We report measurements of horizontal and vertical ice surface motion together with horizontal strain rates from an array of 11 GNSS receivers installed across three juxtaposed subglacial lakes on Isunnguata Sermia — an ~6 km wide land-terminating outlet glacier in West Greenland. We combine these GNSS data with autonomous phase-sensitive radio echo sounding measurements of ice thickness and vertical strain to construct a time series of lake filling and drainage spanning the 2023 melt season. To investigate inter-relationships between subglacial lake hydrology and ice dynamics at both short (hourly) and seasonal timescales, we supplement these time series with data from an array of seismometers installed in between two of the lakes and at the glacier terminus, together with several kilometres of radio echo sounding measurements of ice thickness. 

How to cite: Doyle, S., Livingstone, S., Sole, A., Storrar, R., Young, T. J., Ing, R., Ross, N., Bagshaw, L., Clason, C., Edwards, L., Prior-Jones, M., Bianchi, G., Buzzard, S., Le Bris, T., Barruol, G., Gimbert, F., Gilbert, A., Peacey, M., and Booth, A.: Geophysical investigation of active subglacial lake dynamics in West Greenland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12711, https://doi.org/10.5194/egusphere-egu24-12711, 2024.

12:20–12:30
|
EGU24-6396
|
On-site presentation
Mark Behn, Wenyuan Fan, Nicholas Lau, Sarah Das, Jeffrey McGuire, Kirsten Arnell, Joshua Rines, and Erin Towns

The mass-loss rate of the Greenland Ice Sheet is accelerating due to increased surface melt and changes in ice-sheet dynamics; however, our understanding of how and when increased melt may lead to increased ice velocity is limited in part by the difficulty in characterizing the evolution of the basal meltwater system and its effects on ice sheet-bedrock coupling.  To monitor the evolution of the basal hydrologic system and its relationship to surface ice velocities, we conducted a field experiment from May to September 2022 near North Lake on the western margin of Greenland. We deployed seismic and geodetic instruments that captured the seasonal evolution of the basal hydrologic system, as well as the drainage of two nearby supraglacial lakes.  Our seismic network included three small-aperture dense arrays, which recorded continuous data generated by the evolving hydrologic systems. The seismic arrays are used to detect and locate seismic tremor sources at the ice-sheet bed, likely correlated with basal meltwater flow.  We locate tremor sources every 5 seconds and use their spatiotemporal distributions to monitor the evolution of the basal flow system over the melt season.  Our observations show tremor activity increases starting around day 175, preceding the increase in ice surface velocities relative to the winter velocity.  Tremor activity peaks in the days before the two rapid lake drainage events (day 195), likely associated with precursory surface-to-bed drainage through a moulin west of North Lake.  Immediately after lake drainage, tremor activity shuts down, though ice velocities remain elevated over winter velocities.  Finally, around day 213 tremor activity increases, becoming more episodic, while ice velocities decrease toward winter velocities.  These observations provide new constraints on the interconnected feedback processes between supraglacial and subglacial hydrologic systems and suggest that ice surface velocities may not be directly correlated to the activity of basal meltwater flow over the melt season. 

How to cite: Behn, M., Fan, W., Lau, N., Das, S., McGuire, J., Arnell, K., Rines, J., and Towns, E.: Combining seismic tremor and GPS observations to characterize the seasonal evolution of the Greenland basal hydrologic system and its relationship to ice dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6396, https://doi.org/10.5194/egusphere-egu24-6396, 2024.

Posters on site: Wed, 17 Apr, 16:15–18:00 | Hall X5

Display time: Wed, 17 Apr 14:00–Wed, 17 Apr 18:00
Chairpersons: Gabriela Clara Racz, Alison Banwell, Sophie de Roda Husman
X5.225
|
EGU24-1076
|
ECS
Jiao Chen, Rebecca Hodge, Stewart Jamieson, and Chris Stokes

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.

X5.226
|
EGU24-1655
|
ECS
|
Holly Wytiahlowsky, Chris Stokes, Rebecca Hodge, Caroline Clason, and Stewart Jamieson

Supraglacial channels are an increasingly common glaciological feature due to intensifying surface melt and form a key component of glacier hydrology and mass balance, transporting meltwater to englacial, subglacial, and peripheral positions. Whilst their occurrence is becoming increasingly well-documented on ice sheets, little is known about the distribution of channels on mountain glaciers, which often fall below the resolution of commercial satellites. Using high-resolution orthophoto imagery (~10 cm) and digital elevation models (~0.5 m), we provide the first inventory of supraglacial channels in an alpine environment, focusing on Valais Canton, Switzerland. We manually delineated 1890 channel segments on 85 glaciers, recording glacier characteristics across all 207 snow-free glaciers >0.1 km2 in Valais Canton, encompassing glaciers of differing debris-cover, altitude, and slope. We find that channel segments have a mean length of 212 m and a slope of 8°, with most channels exhibiting low sinuosity (mean: 1.1) and those with higher sinuosity (max: 3.8) only existing on very low surface slopes (<5°). Glaciers containing supraglacial streams have a mean area of 5.0 km2, with a mean drainage density of 1.0 km/km2 (max: 11.0 km/km2) and are likely to extend to lower elevations (mean: 2797 m.a.s.l). Conversely, glaciers without streams are smaller, with a mean area of 0.6 km2, and have a higher minimum elevation (mean: 2945 m.a.s.l). Our observations suggest that the highest drainage densities are found on glaciers characterised by low surface slopes, large ablation areas, low crevasse densities, and limited debris cover. Additionally, stream sinuosity and length appear to be controlled by glacier structure (i.e., crevasses and moulins), slope, and debris content. Our future work will expand on these results using field-based investigations to directly measure channel characteristics and improve estimates of the proportion of meltwater transported as supraglacial run-off versus that entering en- and sub-glacial pathways.

How to cite: Wytiahlowsky, H., Stokes, C., Hodge, R., Clason, C., and Jamieson, S.: Assessing the distribution and characteristics of supraglacial channels in an Alpine setting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1655, https://doi.org/10.5194/egusphere-egu24-1655, 2024.

X5.227
|
EGU24-2115
|
ECS
Katrina Lutz, Christian Sommer, Angelika Humbert, and Matthias Braun

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.

X5.228
|
EGU24-6661
|
ECS
Thomas Chudley, Thomas Winterbottom, Chris Stokes, and James Lea

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.

X5.229
|
EGU24-6955
|
ECS
Whyjay Zheng and Wesley Van Wychen

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.

X5.230
|
EGU24-7605
|
ECS
Pierre Zeiger, Ghislain Picard, Philippe Richaume, Nemesio Rodriguez Fernandez, and Arnaud Mialon

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.

X5.231
|
EGU24-8534
|
ECS
Xinyi Shang, Xiao Cheng, Lei Zheng, Qi Liang, and Teng Li

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.

X5.232
|
EGU24-10739
Jane Hart, Nathaniel Baurley, and Kirk Martinez

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.

X5.233
|
EGU24-11819
|
ECS
Neosha Narayanan, Aleah Sommers, Jakob Steiner, Winnie Chu, Muhammad Adnan Siddique, Colin Meyer, and Brent Minchew

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.

X5.234
|
EGU24-11852
Benjamin Männel, Angelika Humbert, Markus Ramatschi, and Daniel Steinhage

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.

X5.235
|
EGU24-12186
Ian Willis, Luke Donaldson, and Becky Dell

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.

X5.236
|
EGU24-12692
Louise Sandberg Sørensen, Sebastian Simonsen, Natalia Havelund Andersen, Rasmus Bahbah, Nanna Karlsson, Anne Solgaard, Amber Leeson, Jennifer Maddalena, Malcolm McMillan, Jade Bowling, Noel Gourmelen, Alex Horton, and Birgit Wessel

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.

X5.237
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EGU24-12972
Andreas Colliander, Alamgir Hossan, Joel Harper, Baptiste Vandecrux, Julie Miller, Nicole Schlegel, Shawn Marshall, and Craig Donlon

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.

X5.238
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EGU24-13358
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ECS
Alessandro Cotronei and Ulrike Feudel

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.

X5.239
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EGU24-14576
Valeria Di Biase, Peter Kuipers Munneke, Sophie de Roda Husman, Sanne Veldhuijsen, Michiel van den Broeke, Bert Wouters, and Brice Noël

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.

X5.240
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EGU24-16236
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ECS
Matthew Peacey, Stephen Livingstone, Samuel Doyle, Andrew Sole, Robert Storrar, Laura Edwards, Elizabeth Bagshaw, Thomas Chudley, Neil Ross, Sammie Buzzard, Adam Booth, Gianluca Bianchi, Ryan Ing, Caroline Clason, Tun Jan Young, Sian Thorpe, Florent Gimbert, Tifenn Le Bris, Guilhem Barruol, and Adrien Gilbert and the Cryoegg

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.

X5.241
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EGU24-16642
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ECS
James ONeill and Ed Gasson

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.

X5.242
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EGU24-18932
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ECS
Guillaume Timmermans and Xavier Fettweis

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.

X5.243
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EGU24-19042
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Rupert Gladstone, Chen Zhao, Thomas Zwinger, Samuel Cook, Yu Wang, David Gwyther, Mauro Werder, and John Moore
While the slow moving interior of the Antarctic Ice Sheet is not prone to rapid change, the fast flowing outlet glaciers may exhibit accelerations and unstable retreat in response to ocean induced melting of the ice shelves. This rapid motion is only possible due to sliding of ice over the bed, motion which is dependent on the presence, and pressure, of liquid water under the ice sheet.  This subglacial hydrologic system is fed by in-situ melting caused mainly by friction heat as ice slides over the bed, and its outflow feeds into ice shelf cavities across deep grounding lines.  Two-way interactions between ice dynamics and the hydrologic system may occur due to changing sliding speeds, subsequent meltwater generation, and the responding changes in basal water pressure, which in turn impact on sliding resistance.  The subglacial water system may also impact on ice shelf cavity circulation due to its very low density relative to ocean water, and this may also impact indirectly on ice dynamics due to the changing cavity circulation driving changing ice shelf melt rates, which affect ice shelf thickness and therefore backstress.
 
The current generation of ice sheet models used in sea level prediction do not represent the evolution of the subglacial hydrologic system.  A typical approach is to spatially tune a sliding parameter in which all aspects of basal physics relating to sliding and hydrology are implicitly hidden.  We will outline a modelling approach to incorporate the GLAcier Drainage System (GlaDS) model into a coupled system in which the hydrologic system can interact with both ice dynamics and cavity circulation. Ice dynamic model Elmer/Ice and the Regional Ocean Modelling System (ROMS) will be used, coupled through the Framework for Ice Sheet - Ocean Coupling (FISOC).  GlaDS represents the subglacial hydrologic system as two interacting components: a distributed network of linked cavities and a network of channels.  We will show preliminary simulations of these linked cavities and channels from Antarctic simulations. We will outline a plan for moving towards fully coupling GlaDS to the ice dynamics and ice shelf cavities, along with an "accelerated forcing" approach to handle asynchronicities.

How to cite: Gladstone, R., Zhao, C., Zwinger, T., Cook, S., Wang, Y., Gwyther, D., Werder, M., and Moore, J.: Simulating the impact of Antarctic subglacial hydrology on ice sheet evolution, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19042, https://doi.org/10.5194/egusphere-egu24-19042, 2024.

X5.244
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EGU24-19875
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ECS
Jeremie Schmiedel, Angelika Humbert, Thomas Kleiner, and Roiy Sayag

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.

Posters virtual: Wed, 17 Apr, 14:00–15:45 | vHall X5

Display time: Wed, 17 Apr 08:30–Wed, 17 Apr 18:00
Chairperson: Ian Hewitt
vX5.24
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EGU24-21477
Analysis of UAV-based multi-spectral data over southwest Greenland for machine learning applications 
(withdrawn after no-show)
Marco Tedesco, Rafael Antwerpen, Samuel Fields, Hugo Ginoux, Braden Huffman, Sushant Prabhu, and Devan Samant