CR2.1 | Modelling ice sheets and glaciers
EDI
Modelling ice sheets and glaciers
Convener: Sainan Sun | Co-conveners: Fabien Gillet-Chaulet, Mauro Werder, Rabea SondershausECSECS
Orals
| Mon, 15 Apr, 14:00–15:40 (CEST), 16:15–17:55 (CEST)
 
Room 1.61/62
Posters on site
| Attendance Tue, 16 Apr, 10:45–12:30 (CEST) | Display Tue, 16 Apr, 08:30–12:30
 
Hall X5
Orals |
Mon, 14:00
Tue, 10:45
This session is intended to attract a broad range of ice-sheet and glacier modelling contributions, welcoming applied and theoretical contributions. Theoretical topics that are encouraged are higher-order mechanical models, data inversion and assimilation, representation of other earth sub-systems in ice-sheet models, and the incorporation of basal processes and novel constitutive relationships in these models.
Applications of newer modelling themes to ice-sheets and glaciers past and present are particularly encouraged, in particular those considering ice streams, rapid change, grounding line motion and ice-sheet model intercomparisons.

Orals: Mon, 15 Apr | Room 1.61/62

Chairpersons: Sainan Sun, Rabea Sondershaus, Mauro Werder
14:00–14:10
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EGU24-15275
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ECS
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On-site presentation
Tim van den Akker, William H. Lipscomb, Gunter R. Leguy, Willem Jan van de Berg, and Roderik S.W. van de Wal

The basal friction parameterization is often mentioned as key source of uncertainty when using ice sheet models to project future evolution of the ice sheet. Previous work suggests that parameterizations with an exponential relationship between friction and basal velocity (power laws) predict lower sea level rise than ‘Coulomb-style’ friction laws. For Coulomb laws, the basal friction asymptotes for high velocities and is effectively independent of velocity for fast-flowing ice. We use the Community Ice Sheet Model (CISM) for two kinds of simulations: one with present-day climate forcing, including sub-shelf ocean temperatures kept constant and one with 1-degree ocean warming in the Ross Sea, both matching the current rate of ice thickness changes. In the constant scenario, Thwaites Glacier and Pine Island Glacier collapse, creating a huge, laterally bounded ice shelf. In the scenario with Ross Sea warming, a large part of the Ross Ice Shelf disappears, allowing Siple Coast glaciers to flow freely into the ocean. For Thwaites and Pine Island Glaciers, there are competing processes causing increases or decreases in ice flux across the grounding line, ice shelf thickness, buttressing, and ice velocities, once the glaciers are collapsing. These processes work in the opposite direction of the differences caused by choosing different basal friction parameterizations. Therefore, in our model runs, the choice of basal friction parameterization has little effect on the collapse of Thwaites and Pine Island glacier. In the unbuttressed Siple Coast case, we confirm earlier results: Coulomb friction leads to more ice mass loss and sea level rise. We conclude that unbuttressed glaciers are more sensitive to the choice of basal friction parameterizations than are heavily buttressed glaciers, and that the presence of a large buttressing ice shelf decreases the sensitivity of glacier dynamics to different basal friction parameterizations. 

How to cite: van den Akker, T., Lipscomb, W. H., Leguy, G. R., van de Berg, W. J., and van de Wal, R. S. W.: Modelled ice sheet sensitivity to basal friction parameterizations is controlled by the amount of buttressing, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15275, https://doi.org/10.5194/egusphere-egu24-15275, 2024.

14:10–14:20
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EGU24-14499
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ECS
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On-site presentation
Chen Zhao, Rupert Gladstone, Thomas Zwinger, Fabien Gillet-Chaulet, Yu Wang, Justine Caillet, Pierre Mathiot, Leopekka Saraste, Ben Galton-Fenzi, Poul Christoffersen, and Matt King

Subglaical hydrology significantly influences the basal sliding that controls how fast ice sheets transport ice from land to oceans. The absence of hydrologic systems in ice sheet models is therefore a notable source of uncertainty in projected ice-mass loss and its subsequent impact on sea-level rise. Specifically, the uncertainty associated with the representation of effective pressure (the difference between subglacial water pressure and ice overburden pressure) in basal sliding lacks comprehensive investigation in Antarctic sea-level rise projections. Here we use Elmer/Ice ice-sheet model setups to examine how different approaches to determining effective pressure in the regularised Coulomb sliding law impact the projected ice mass loss pre-2300 under both continental and basin scales. Our results reveal basin-specific responses to the representation of effective pressure in basal sliding, significantly influencing projected ice-mass loss and the timing of the passing of tipping points. We find that the ongoing interactions between ice dynamics and the hydrologic system render the grounding line much more mobile than in models with no such interaction. Notably, for the entire Antarctic Ice Sheet, grounding line flux is more than doubled by 2300 when employing a smoothly decreasing effective pressure near the grounding line, compared to constant pressure. Remarkably, Thwaites Glacier shows a tenfold increase in its grounding line flux by 2300. These findings underscore the critical need to better understand the interactions between ice dynamic evolution and the subglacial hydrologic system. Explicitly modelling the hydrologic system in a coupled ice sheet-subglacial hydrology models is crucial to make more robust predictions of Antarctica's future ice-mass loss, thereby reducing uncertainty in sea-level rise projections. 

How to cite: Zhao, C., Gladstone, R., Zwinger, T., Gillet-Chaulet, F., Wang, Y., Caillet, J., Mathiot, P., Saraste, L., Galton-Fenzi, B., Christoffersen, P., and King, M.: Subglacial Water Pressure Reshapes projected Antarctic Sea-Level Rise, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14499, https://doi.org/10.5194/egusphere-egu24-14499, 2024.

14:20–14:30
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EGU24-11319
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On-site presentation
Carlos Martin and Mark Hehlen

The force balance of an ice steam determines its velocity, and along with cross sectional area, influences total flux of glacial ice to the ocean. Satellite datasets provide us strong time series velocity data, while radar, seismics, and geophysical inversion methods yield width and depth estimates within an ice column. However, should an ice stream widen or narrow, the flux of ice to the ocean could change perceptibly. 
Thwaites Glacier’s eastern shear margin is not topographically bounded, but rather arcs across a shallow subglacial rise of intermittent hills and valleys. To determine the stability of the margin it is imperative to understand the force balance and total energy of the glacier system along the shear zone. Driving forces are balanced by normal and shear stresses along the bed, and longitudinal shearing in the margin. The resistance (or lack thereof) creates deformational (frictional-sliding) heating which add energy to the system altering rate factor and meltwater generation, which in turn alter the viscosity and slip factors, making a complex feedback system.
To analyze this system, we develop a 3D full-Stokes flow model in the Elmer/ICE finite element software. The model resolves at 500 m horizontally over realistic surface and bed topography from BedMachinev3. Model domains cover key data acquisition sites from the International Thwaites Glacier Collaboration, Thwaites Interdisciplinary shear Margin Evolution (ITGC TIME) seismic and radar field studies. To determine energy balance, we employ the enthalpy field equations which efficiently solve the thermal field, solve for water content generation, and couple nicely with variable rate factors. Models are initialized by a suite of 1D thermal profiles, converted to enthalpy values, derived from quartile statistics of RACMO2.3p1 surface specific mass balance data, and then advected to steady state flow. 
These models are then run with a flow-coupled glacier drainage system (GlaDS) and enthalpy relation to determine temperate ice distribution, and basal water production. Non-linear Coulomb and Weertman sliding laws are tested between scenarios of natural melt generation, through full drainage piracy of the upper Pine Island catchment, which will determine the effect of spatiotemporal variation in effective pressure (N) on shear margin stability.
Through the suite of spin up models and scenarios, we aim to determine the stability of Thwaites Glacier’s eastern shear margin from perturbations in enthalpy from both sliding friction, and viscous heating from temperate ice generation over non-idealized bed topography and within the shear margin itself. Results will help inform catchment scale transient flow models which aid in determining sea level contribution and West Antarctic Ice Sheet stability.  

How to cite: Martin, C. and Hehlen, M.: An Enthalpy-Hydrology Coupled 3D full-Stokes Flow Model of Thwaites’ Eastern Shear Margin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11319, https://doi.org/10.5194/egusphere-egu24-11319, 2024.

14:30–14:40
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EGU24-3996
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ECS
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On-site presentation
Matt Trevers, Anthony Payne, Stephen Cornford, and Ed Gasson

The drainage catchments of the neighbouring Thwaites and Pine Island Glaciers, situated in the Amundson Sea Embayment, West Antarctica, contain sufficient ice to raise global mean sea level by a meter. In recent years, significant scientific attention has been given to the potential for sustained retreat of these glaciers as a possible pathway towards widespread deglaciation of the marine-based West Antarctic Ice Sheet. Some recent studies have demonstrated that the Thwaites Ice Shelf provides only limited buttressing to the upstream grounded ice, suggesting limited sensitivity to the melt-driven loss of the ice shelf.

We use the BISICLES ice sheet model to perform a series of 1000-year model experiments on the Amundson Sea domain. A synthetic sub-shelf melt rate is selectively applied to the Pine Island, Thwaites and Crosson/Dotson basins or combinations of those basins. We find that over millennial timescales, Thwaites is relatively insensitive to melt-driven thinning of its ice shelf, with its grounding line rapidly restabilising ~60km upstream of its current location. The same melt forcing applied to Pine Island Glacier leads to widespread deglaciation of the Pine Island catchment and significant retreat in the neighbouring Thwaites catchment despite the lack of melting there. Applying melting simultaneously in the Thwaites and Crosson/Dotson basins leads to widespread deglaciation that is much greater than the sum of its parts. This retreat is driven by a feedback between the ice fluxes crossing the basin boundary.

We also conduct further experiments to determine the melt rates or additional processes required to trigger retreat of Thwaites Glacier in isolation. The results of our experiments support the suggestion that the Thwaites ice shelf provides limited buttressing, while also demonstrating that Thwaites is still vulnerable to retreat via other pathways.

How to cite: Trevers, M., Payne, A., Cornford, S., and Gasson, E.: Retreat of Thwaites Glacier, West Antarctica, triggered by its neighbours., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3996, https://doi.org/10.5194/egusphere-egu24-3996, 2024.

14:40–14:50
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EGU24-4001
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ECS
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On-site presentation
Brad Reed, Mattias Green, Adrian Jenkins, and Hilmar Gudmundsson

In recent decades glaciers in the Amundsen Sea Embayment in West Antarctica have undergone substantial changes, including widespread retreat and acceleration. The subsequent mass loss caused the largest contribution to sea level rise from the entire Antarctic Ice Sheet. These changes have led to concerns about the stability of the region and the implications of future climate change. Recent modelling results show that one of the largest and fastest flowing of these glaciers, Pine Island Glacier (PIG), has already undergone an unstable and irreversible retreat in its recent history, when it detached from a subglacial ridge between the 1940s and 1970s.

Here we use the ice-flow model Úa to study the sensitivity of this retreat to changes in basal melting. We show that an intermittent increase in basal melting would have been sufficient to force PIG into a retreat from its stable position on the ridge. Once high melting begins upstream of the ridge, only near-zero melt rates can stop the retreat. Our results suggest that unstable and irreversible responses to warm anomalies are possible, and this can lead to substantial changes in ice flux over relatively short periods of only a few decades.

How to cite: Reed, B., Green, M., Jenkins, A., and Gudmundsson, H.: Melt sensitivity of irreversible retreat of Pine Island Glacier, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4001, https://doi.org/10.5194/egusphere-egu24-4001, 2024.

14:50–15:00
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EGU24-15478
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ECS
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On-site presentation
Javier Blasco, Yanjun Li, Violaine Coulon, and Frank Pattyn

The Antarctic Ice Sheet (AIS) is the largest ice sheet and hence the potentially largest contributor to future sea-level rise. However, the AIS represents also the largest source of uncertainty regarding future projections. One of the main sources for this uncertainty are the floating ice shelves. While these ice shelves do not directly contribute to sea-level rise, they play a major role in the dynamics of the AIS. By transmitting resistive stress to the grounding line, they are capable of slowing down inland ice. If ice shelves disintegrate, this buttressing effect disappears, promoting the flow of inland ice into the ocean. Thus, the assessment of ice shelf stability in future scenarios becomes crucial for accurate predictions.

One key element which is often overlooked is the formation of ice fractures. Satellite images display increased crevasse formation on Antarctic ice shelves and grounded ice near the grounding line over the past decade. These fractures, referred to as damage, impact the ice flow by reducing its viscosity. Reduced viscosity enhances ice flow, leading to higher strain rates which further promotes more damage formation. However, despite its known effect, its application has been only done on idealized domains so far.

Here we will assess the damage sensitivity of a three-dimensional ice-sheet-shelf model in a simplified, symmetric case (MISMIP+ domain) and a complex real-world scenario such as the Amundsen-Sea Embayment (ASE). For this we will test three different damage formulations from literature which account for explicit crevasse formation. In addition, we will also test a new regularization approximation in our viscosity formulation. This approximation ensures that if no damage is applied, then the effective yield strength of our model cannot exceed the failure strength of ice.

Our findings reveal that incorporating damage or viscosity regularization into future projections of the ASE results in higher sea-level contribution and faster grounding-line migration. This underscores the critical need to enhance our understanding of damage and its implications for future sea-level rise, since current projections do not account for this process.

How to cite: Blasco, J., Li, Y., Coulon, V., and Pattyn, F.: The effect of ice damage on future Antarctic projections, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15478, https://doi.org/10.5194/egusphere-egu24-15478, 2024.

15:00–15:10
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EGU24-12685
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ECS
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On-site presentation
Jowan Barnes, G. Hilmar Gudmundsson, Daniel Goldberg, and Sainan Sun

Calving is a key process in the dynamics of marine-terminating glaciers with large ice shelves, such as those in West Antarctica. However, this process is currently not included in most predictive models, due to its difficulty to implement in a general form which can reliably reproduce rates of calving over a range of scenarios. We set out to investigate how important it is to develop such representation of calving for future modelling.

In this study, we quantify the sensitivity of modelled future mass loss to ice front retreat in the Amundsen Sea Embayment, including Pine Island and Thwaites Glaciers. We find that prescribing constant frontal retreat rates from 0.1 to 1 km a­­-1 progressively increases the contribution to sea level rise when compared to experiments with a fixed ice front. The result is up to 80% more loss of ice by 2100, and more than triple the ice loss in projections beyond 2200 with the higher rates of retreat. The spatial pattern of ice loss is non-uniformly distributed, with some regions thinning and others thickening as an initial response to the calving front retreat. We identify specific thresholds in the geometry of the system, which have clear effects on the ice flow and are reached at different times depending on the retreat rate.

We compare variability in the range of our results using different retreat rates to that in the range of ISMIP6 ocean forcing products, as ocean-induced melt is known to be a major factor in determining the future evolution of the Antarctic ice sheet. We find that the variability due to these two factors is initially similar, and that variability due to ice front retreat becomes comparatively greater over time. Our results demonstrate the high importance of accurately representing calving processes in models, showing that they are at least as important as ocean forcing and deserve a similar amount of attention in future model development work.

How to cite: Barnes, J., Gudmundsson, G. H., Goldberg, D., and Sun, S.: The importance of calving in ice sheet models: A sensitivity study of ice front retreat in the Amundsen Sea Embayment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12685, https://doi.org/10.5194/egusphere-egu24-12685, 2024.

15:10–15:20
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EGU24-8114
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On-site presentation
C. Rosie Williams, Pierre Thodoroff, Robert J. Arthern, James Byrne, J. Scott Hosking, Markus Kaiser, Neil D. Lawrence, and Ieva Kazlauskaite

The West Antarctic Ice Sheet (WAIS) is losing ice and its annual contribution to sea level is increasing. The future behaviour of WAIS will impact societies worldwide, yet deep uncertainty remains in the expected rate of ice loss. High impact low likelihood scenarios of sea level rise are needed by risk-averse stakeholders but are particularly difficult to constrain. Here we combine traditional model simulations of the Amundsen Sea sector of WAIS with Gaussian process emulation to show that ice-sheet models capable of resolving kilometre-scale basal topography will be needed to assess the probability of extreme scenarios of sea level rise. This resolution exceeds many state-of-the-art continent-scale simulations. Our model simulations show that lower resolutions tend to overestimate future sea level contribution and inflate the tails of the distribution. We therefore caution against relying purely upon low resolution simulations when assessing the potential for societally important high impact sea level rise.

How to cite: Williams, C. R., Thodoroff, P., Arthern, R. J., Byrne, J., Hosking, J. S., Kaiser, M., Lawrence, N. D., and Kazlauskaite, I.: Calculating exposure to extreme sea level risk will require high resolution ice sheet models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8114, https://doi.org/10.5194/egusphere-egu24-8114, 2024.

15:20–15:30
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EGU24-10305
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Virtual presentation
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Daniel Goldberg and Morlighem Mathieu

It is important that modellers be able to make reasonable projections of ice-sheet loss over the next 50-100 years so that costal planners can make informed decisions. Despite many innovations in modelling and satellite observing, several recent studies show that the agreement between models and the observational record remains poor -- raising concerns about their ability to predict responses to changes in climate on decadal to centennial time scales. A common means to address model-data misfit is via assimilation of satellite data, in which poorly constrained parameters are chosen in a way to minimize this misfit. Data assimilation has been employed extensively, including by many of the models participating in the ISMIP6 intercomparison. However, they are limited to observations at a single point in time (a "snapshot"). Such inversions do not take advantage of the time series of velocity and altimetry observations currently available -- largely due to the complexity and computational expense. The use of Automatic Differentiation makes such approaches possible. The method -- termed "transient assimilation" or "transient calibration" -- provides a physically consistent, time-dependent model which agrees with time-resolved observations.

But with such a development, questions arise: how does transient calibration impact future modelled behaviour? Which types of observations most strongly constrain models? Are results consistent across different models? Here we apply transient calibration to the Amundsen Sea Embayment using two independent models, the Ice-sheet and Sea-level System Model (ISSM) and the MITgcm STREAMICE model, using time-resolved velocities and surface altimetry from 2004 to 2017. We assess the performance of transient compared to snapshot calibrations in terms of capturing past and current trends in speed change, thinning, and grounded ice loss; and we additionally run 50-year projections using the calibrated models. While overall 50-year mass loss is not strongly dependent on assimilation strategy, the rates of mass loss vary greatly, suggesting greater differences on the century time scale or longer. Moreover, we see that the runs calibrated with altimetry: (i) agree best with recent mass loss rates; (ii) show the greatest conformity between models; and (iii) show the largest mass loss rates at the end of the 50-year runs. The results likely have implications for optimal data needs and assimilation strategies in the next generation of ice-sheet models.

How to cite: Goldberg, D. and Mathieu, M.: Transient calibration of the Amundsen Sea Embayment: a model and methodology comparison, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10305, https://doi.org/10.5194/egusphere-egu24-10305, 2024.

15:30–15:40
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EGU24-12813
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ECS
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On-site presentation
Richard Parsons, Sainan Sun, and Hilmar Gudmundsson

Antarctic sea ice extent reached a record minimum in 2023. Whilst the buttressing resistance provided by ice shelves has been quantified through past numerical studies, the degree to which sea ice can buttress and regulate upstream ice flow is not known. If significant, a future decline in sea ice extent would lead to increased ice discharge rates and a higher global mean sea level.

The January 2022 disintegration of landfast sea ice in the Larsen B embayment was closely followed by a significant increase in ice flow velocities and retreat rates of numerous outlet glaciers in the region. Notably, Crane glacier saw an initial ~8km retreat over six weeks, during which time a 5% increase in velocity was observed. Afterwards, the full evacuation of ambient sea ice between October and November was accompanied by the most significant monthly increase in velocities.

We use the numerical ice flow model, Ua, to investigate the buttressing effect of sea ice to Crane glacier. The ice-sheet model was initialised with sea ice included and constrained with observational velocity and geometry data sets. We conducted perturbation experiments on sea ice properties to explore its impact on the glacier. The results suggest that sea ice provided significant buttressing to the glacier before its collapse.

How to cite: Parsons, R., Sun, S., and Gudmundsson, H.: Quantifying the Buttressing Contribution of Sea Ice to Crane Glacier, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12813, https://doi.org/10.5194/egusphere-egu24-12813, 2024.

Coffee break
Chairpersons: Mauro Werder, Rabea Sondershaus, Sainan Sun
16:15–16:25
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EGU24-14128
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ECS
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Virtual presentation
Samar Minallah, William Lipscomb, Sean Swenson, and Gunter Leguy

Simulating mass changes and ice dynamics for mountain glaciers using Earth System Models (ESMs) is challenging due to their small size, sheer number, and spatial discontinuities in the ground ice coverage. This has resulted in a knowledge and representational gap in ESMs. However, there is a need for scaling ESMs from global to regional domains for comprehensive glacio-hydrological and hydroclimatic assessments.

We introduce new developments for simulating the mass balance and dynamic evolution of mountain glaciers within the Community Earth System Model (CESM). We provide an overview of this work across two spatiotemporal scales related to: (1) the dynamic evolution of the Central European glaciers under the GlacierMIP3 protocol using the Community Ice Sheet Model (CISM) and (2) the energy and water balance of the Upper Indus glaciated basins at daily-monthly timescales using the Hillslope Hydrology configuration of the Community Land Model (CLM).

How to cite: Minallah, S., Lipscomb, W., Swenson, S., and Leguy, G.: Simulating Mass Balance and Dynamics of Mountain Glaciers within an Earth System Modeling Framework, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14128, https://doi.org/10.5194/egusphere-egu24-14128, 2024.

16:25–16:35
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EGU24-11836
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On-site presentation
Anuar Togaibekov, Florent Gimbert, Adrien Gilbert, and Andrea Walpersdorf

Basal shear stress on hard-bedded glaciers results from normal stress against bed roughness, which depends on basal water pressure and cavity size. These quantities are related in a steady state but are expected to behave differently under rapid changes in water input, which may lead to a transient frictional response not captured by existing friction laws. Here, we investigate transient friction using GPS vertical displacement and horizontal velocity observations, basal water pressure measurements, and cavitation model predictions during rain-induced speed-up events at Glacier d'Argentière, French Alps. We observe up to a threefold increase in horizontal surface velocity, spatially migrating at rates consistent with subglacial flow drainage, and associated with surface uplift and increased water pressure. We show that frictional changes are mainly driven by changes in water pressure at nearly constant cavity size. We propose a generalized friction law capable of capturing observations in both the transient and steady-state regimes.

How to cite: Togaibekov, A., Gimbert, F., Gilbert, A., and Walpersdorf, A.: Observing and modeling short-term changes in basal friction during rain-induced speed-ups on an Alpine glacier, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11836, https://doi.org/10.5194/egusphere-egu24-11836, 2024.

16:35–16:45
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EGU24-8997
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On-site presentation
Guillaume Jouvet, Guillaume Cordonnier, Fabien Maussion, Samuel Cook, Brandon Finley, Andreas Henz, Oskar Herrmann, Sarah Kamleitner, Tancrede Leger, Kejdi Lleshi, Jürgen Mey, Dirk Scherler, and Ethan Welty

We present the concepts and capabilities of IGM (https://github.com/jouvetg/igm), a fast and accessible Python model that simulates the evolution of glaciers at any scale by coupling ice thermomechanics, surface mass balance, and mass conservation. IGM models the ice flow by physics-informed deep learning. Specifically, we use a convolutional neural network, which is trained to minimise the energy associated with high-order ice flow physics. Based on the Tensorflow library, IGM performs a suite of fast, vectorised, and differentiable operations, which can be accelerated with a graphics processing unit (GPU). In turn, this allows fully-parallelised implementations of key model components in glacier modelling applications such as the positive degree day surface mass balance scheme, the enthalpy scheme for modelling the thermal regime of ice, or the integration of a large amount of particle trajectories for modelling debris transportation. As a result, IGM combines coding simplicity and modularity, high computational efficiency, state-of-the-art thermomechanical modelling, and efficient data assimilation thanks to underlying automatic differentiation tools. We demonstrate the capability of IGM for two different applications. First, we present a complete workflow (including OGGM-based data preprocessing, inverse and forward modelling, rendering of results) that allows us to model any mountain glacier in the world within a few minutes requiring only its Randolph Glacier Inventory (RGI) ID. Second, we present an application in paleo glacier modelling by simulating the entire European Alpine ice field (about 800 km long) in high resolution (200 m) during the Last Glacial Maximum.

How to cite: Jouvet, G., Cordonnier, G., Maussion, F., Cook, S., Finley, B., Henz, A., Herrmann, O., Kamleitner, S., Leger, T., Lleshi, K., Mey, J., Scherler, D., and Welty, E.: Capabilities of IGM, a thermo-mechanical glacier evolution model accelerated by deep-learning and GPU, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8997, https://doi.org/10.5194/egusphere-egu24-8997, 2024.

16:45–16:55
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EGU24-10934
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On-site presentation
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Ian Hewitt and Emilie Herpain

Marine ice sheets terminate in the ocean where they form floating ice shelves or calve icebergs.  They can significantly influence sea level because of the potential for rapid transfer of grounded ice (with thickness greater than floatation) to floating ice shelves or icebergs.  Most models of marine ice sheet evolution assume that the bed elevation stays constant, or responds isostatically to the weight of the ice sheet.  However, it is known that there is sediment deformation beneath the ice sheet (which is in part what enables the ice to move), and that deposition of this sediment in the vicinity of the grounding line can result in the formation of a grounding-zone wedge.  Although it is widely recognised that such a wedge can influence the evolution of the grounding line (where the ice becomes afloat), there is incomplete knowledge about the interaction of the ice and sediment/bed dynamics.

In this study, we build on idealised two-dimensional (flow-line) models of a marine ice sheet to investigate the influence of a deforming sediment layer at the bed.  We examine how different conditions lead to the development of a grounding zone wedge, and how this impacts the possible steady states of the model under given climate forcing, and under different assumptions about the sediment dynamics.  We then examine how the sediment dynamics, and the presence of the grounding-zone wedge, influence the stability of the system.

How to cite: Hewitt, I. and Herpain, E.: Evolution of marine ice sheets with bed sedimentation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10934, https://doi.org/10.5194/egusphere-egu24-10934, 2024.

16:55–17:05
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EGU24-5370
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On-site presentation
Jim Jordan

The representation of ice shelf calving in numerical ice models is a new and emerging field in cryospheric modelling. As yet, there has been no systematic, in-depth study of how this process is implemented and whether the results can be trusted. Calving MIP is an ongoing model intercomparison project that seeks to address this issue by providing a common framework for model simulations of ice shelf calving, so that results between different models and approaches can be compared. We find it helpful to distinguish between a calving algorithm, the numerical implementation in a model of how ice is removed due to calving, and a calving law, a law with some physical basis that determines how much ice needs to be removed due to calving. The first phase of Calving MIP experiments are primarily interested in comparing different calving algorithms, whilst future experiments are planned to investigate different calving laws as well as compare simulated results with real world observations.

We present here results from across the cryospheric modelling community from the first phase of Calving MIP experiments investigating calving algorithms as well as future plans for further experiments.

How to cite: Jordan, J.: Calving MIP: Results and conclusions from the first phase of a model intercomparison project into ice shelf calving, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5370, https://doi.org/10.5194/egusphere-egu24-5370, 2024.

17:05–17:15
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EGU24-13290
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ECS
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On-site presentation
Daniel Moreno-Parada, Alexander Robinson, Marisa Montoya, and Jorge Alvarez-Solas

We present a physical description of the ice-sheet model Nix v1.0, an open-source project intended for collaborative development. Nix is a 2D thermomechanical model written in C/C++ that simultaneously solves for the momentum balance equations, mass conservation and temperature evolution. Nix's velocity solver includes a hierarchy of Stokes approximations: Blatter-Pattyn, depth-integrated higher order, shallow-shelf and shallow-ice. The grounding-line position is explicitly solved by a moving coordinate system that avoids further interpolations. The model can be easily forced with any external boundary conditions, including those of stochastic nature. Nix has been verified for standard test problems. Here we show results for a number of benchmark tests from standard intercomparison projects and assess grounding-line migration with an overdeepened bed geometry. Lastly, we further exploit the thermomechanical coupling by designing a suite of experiments where the forcing is a physical variable, unlike previously idealised forcing scenarios where ice temperatures are implicitly fixed via an ice rate factor. Namely, we use atmospheric temperatures and oceanic temperature anomalies to assess model hysteresis behaviour with active thermodynamics. Our results show that hysteresis in an overdeepened bed geometry is similar for atmospheric and oceanic forcings. We find that not only the particular sub-shelf melting parametrisation determines the temperature anomaly at which the ice sheet retreats, but also the particular value of calibrated heat exchange velocities. Notably, the classical hysteresis loop is narrowed for both forcing scenarios (i.e., atmospheric and oceanic) if the ice sheet is thermomechanically active as a results of the internal feedback among ice temperature, stress balance and viscosity. In summary, Nix combines rapid computational capabilities with a Blatter-Pattyn stress balance fully coupled to a thermomechanical solver, not only validating against established benchmarks but also offering a powerful tool for advancing our insight on ice dynamics and grounding line stability.

How to cite: Moreno-Parada, D., Robinson, A., Montoya, M., and Alvarez-Solas, J.: Description and validation of the ice sheet model Nix v1.0, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13290, https://doi.org/10.5194/egusphere-egu24-13290, 2024.

17:15–17:25
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EGU24-19141
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ECS
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On-site presentation
Jan Swierczek-Jereczek, Marisa Montoya, Konstantin Latychev, Alexander Robinson, Jorge Alvarez-Solas, and Jerry Mitrovica

The vast majority of ice-sheet modelling studies rely on simplified representations of the Glacial Isostatic Adjustment (GIA), which, among other limitations, do not account for lateral variations of the lithospheric thickness and upper-mantle viscosity. In studies using 3D GIA models, this has however been shown to have major impacts on the dynamics of marine-based sectors of Antarctica, which are likely to be the greatest contributors to sea-level rise in the coming centuries. This gap in comprehensiveness is explained by the fact that 3D GIA models are computationally expensive, seldomly open-source and require the implementation of an iterative coupling scheme to converge with the history of the ice-sheet model. To close this gap between "best" and "tractable" GIA models, we here propose FastIsostasy, a regional GIA model capturing lateral variations of the lithospheric thickness and mantle viscosity. By means of Fast-Fourier transforms and a hybrid collocation scheme to solve its underlying partial differential equation, FastIsostasy can simulate 100,000 years of high-resolution bedrock displacement in only minutes of single-CPU computation, including the changes in sea-surface height due to mass redistribution. Despite its 2D grid, FastIsostasy parametrises the depth-dependent viscosity in a physically meaningful way and therefore represents the depth dimension to a certain extent. FastIsostasy is here benchmarked against analytical, 1D and 3D GIA solutions and shows very good agreement with them. It is fully open-source, documented with many examples and provides a straight-forward interface for coupling to an ice-sheet model. The model is benchmarked here based on its implementation in Julia, while a Fortran version is also provided to allow for compatibility with most existing ice-sheet models. The Julia version provides additional features, including a vast library of time-stepping methods and GPU support.

How to cite: Swierczek-Jereczek, J., Montoya, M., Latychev, K., Robinson, A., Alvarez-Solas, J., and Mitrovica, J.: FastIsostasy - An accelerated regional GIA model for coupled ice-sheet/solid-Earth simulations with laterally-variable solid-Earth structures, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19141, https://doi.org/10.5194/egusphere-egu24-19141, 2024.

17:25–17:35
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EGU24-11040
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ECS
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On-site presentation
Tancrède Leger, Jeremy Ely, Christopher Clark, Sarah Bradley, Rose Archer, and Jiang Zhu

Ice sheets have a memory that is stored within both the geometry and thermal properties of the ice. The current Greenland Ice Sheet is thus not in equilibrium with present-day climate, but is in fact affected by a complex product of past changes that occurred over millennial timescales. Therefore, simulating the late-Pleistocene evolution of the Greenland Ice Sheet accurately is important when running future projections using paleo model initialization procedures. Using a novel model-data comparison procedure, we ran an experiment that aimed to produce numerical model simulations that fit available empirical data on the extent and timing of the grounded margin evolution of the Greenland Ice Sheet from the global LGM (24 kyr BP) to 1850 AD. Given the numerous uncertain parameters and boundary conditions required by numerical ice sheet models, finding simulations which adequately replicate empirical data on past grounded ice extent is a challenging task. In an attempt to address this challenge, we ran a perturbed parameter ensemble of 100 ice-sheet-wide simulations at 5 km spatial resolution using the Parallel Ice Sheet Model. Our simulations are forced by the latest transient paleo-climate and ocean simulations of the isotope-enabled Community Earth System Model (iCESM 1.2 and 1.3). Using quantitative model-data comparison tools and the newly developed, Greenland-wide PaleoGrIS 1.0 isochrone reconstruction of former ice extent, each ensemble simulation’s fit with empirical data was assessed quantitatively across both space and time. Using our best-scoring simulations, we here present new insights into the former Greenland Ice Sheet’s likely response to transitional climatic phases throughout the last deglaciation. Secondly, our results suggest ice temperature, geometry, and glacial isostatic adjustment-induced mechanisms of centennial to millennial-scale inertia in ice-extent response to past climatic forcing, with potential implications for the future evolution of the ice sheet. Thirdly, our results show that different parameter combinations produce a better model-data fit during different time periods and for different regions of the ice sheet – i.e. parameter values that work well at one place or time, produce worse fit at others. We hypothesise that better paleo model initializations may be achieved using time- and space-dependent parameter configurations. Finally, after extending several past ensemble simulations to the end of the 21st century under CMIP6-derived forcing, we find that accounting for the past modifies projections of the future. Using a steady-state contemporary ice sheet as an initial state leads to vastly different projected sea level contributions when compared to simulations that perform well at recreating past glacial history.

How to cite: Leger, T., Ely, J., Clark, C., Bradley, S., Archer, R., and Zhu, J.: Insights into the LGM-to-present evolution of the Greenland Ice Sheet from a data evaluated ensemble of numerical model simulations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11040, https://doi.org/10.5194/egusphere-egu24-11040, 2024.

17:35–17:45
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EGU24-4155
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ECS
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On-site presentation
Jessica Badgeley, Helene Seroussi, and Mathieu Morlighem

State-of-the-art ice sheet model simulations used in the Ice Sheet Model Intercomparison Project (ISMIP) show a mismatch with recent observations of dynamic ice sheet change. In particular, the difference between the modeled and observed cumulative mass balance trend over the last several decades calls into question the accuracy of current projections of ice sheet contribution to sea level rise. Here, we use one of these models, the Ice-sheet and Sea-level System Model, to investigate how transient calibration may improve model hindcasts of ice dynamics and impact projections. Transient calibration is a relatively new capability in ice flow models; it uses a time series of observations to invert for uncertain model parameters, such as basal friction and ice rheology. With more observational constraints than the common snapshot inversion method, transient calibration has been shown to better capture trends and to have the ability to estimate how parameters evolve through time. We apply this method to Northwest Greenland, a region undergoing rapid changes that also has high-resolution, high-accuracy data for bed topography, ice surface velocity, and ice front positions. We find that transient calibration brings hindcast simulations of cumulative mass balance to within observational error. We also find that, when the basal friction parameter is allowed to vary, transient calibration can help mimic the impacts of subglacial hydrology and reproduce observations of seasonal velocity variability. Future simulations to 2100 using the ISMIP6 protocols show that the use of transient calibration leads to greater mass loss and, in the near term out to 2050, has a greater impact on mass balance than the choice of climate forcing scenario.

How to cite: Badgeley, J., Seroussi, H., and Morlighem, M.: Improving modeled ice dynamics in Northwest Greenland with transient calibration: From multi-decadal trends to seasonal cycles, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4155, https://doi.org/10.5194/egusphere-egu24-4155, 2024.

17:45–17:55
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EGU24-13210
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ECS
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On-site presentation
Daniel Richards, Elisa Mantelli, Samuel Pegler, and Sandra Piazolo

Ice fabrics – the alignment of crystal orientations - can cause the ice viscosity to vary by an order of magnitude, consequently having a strong impact on the large-scale flow of ice sheets and glaciers. Because of this, there is a need for fabric models which are computationally efficient enough to be included in large-scale ice sheet models. We examine a range of existing models in this class and show they can be combined into a common equation which is a function of 2-3 parameters. By comparing with observations from the Greenland ice sheet, we get the best model predictions by assuming the ice deforms close to the Sachs hypothesis – that all grains experience the same stress. As these fabric predictions also depend on the flow law used, we provide a test of competing anisotropic flow laws for the first time, making a step towards reliably incorporating the effect of fabric and viscous anisotropy in ice sheet flow models.

How to cite: Richards, D., Mantelli, E., Pegler, S., and Piazolo, S.: Unifying and comparing different models of viscous anisotropy to be included in ice sheet models., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13210, https://doi.org/10.5194/egusphere-egu24-13210, 2024.

Posters on site: Tue, 16 Apr, 10:45–12:30 | Hall X5

Display time: Tue, 16 Apr 08:30–Tue, 16 Apr 12:30
Chairpersons: Rabea Sondershaus, Fabien Gillet-Chaulet
X5.204
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EGU24-2585
Yu Zhu, Shiyin Liu, Ben W. Brock, Fuming Xie, and Ying Yi

The influence of supraglacial debris cover on glacier dynamics in the Karakoram is noteworthy. However, the investigation of how debris cover affects the seasonal and long-term variations in glacier mass balance through alterations in the glacier's energy budget is scarce. The present study applied an energy-mass balance model coupling heat conduction within debris layers on Batura Glacier in Hunza valley, renowned as the most representative debris-covered glacier in the Karakoram, to demonstrate the influence of debris cover on glacial surface energy and mass exchanges. The mass balance of Batura Glacier is estimated to be -0.262 ± 0.561 m w.e. yr-1, with debris cover accounting for 45% of the mass balance variation. Due to the presence of debris cover, a significant portion of the energy income is utilized for heat conduction within the debris layer, reducing the melt latent heat at the glacier surface. We found that the mass balance reveals a pronounced arch-shaped structure along the elevation gradient, which primarily attributes to the distribution of debris thickness and the impact of debris cover on the energy structure within various elevation zones. Through a comprehensive analysis of the energy transfer within each debris layer, we have demonstrated that the primary impact of debris cover lies in its ability to modify the energy reaching the surface of the glacier. Thicker debris cover results in a smaller decrease in temperature between debris layers and the ice-contact zone, consequently reducing heat conduction. Over the past two decades, Batura Glacier has maintained a relatively small negative mass balance, owing to the protective effect of debris cover. The glacier exhibits a tendency towards a smaller negative mass balance, with diminishing dominance of ablation at the glacier terminus on glacier mass changes. 

How to cite: Zhu, Y., Liu, S., Brock, B. W., Xie, F., and Yi, Y.: Controls on the relatively slow thinning rate of a debris-covered glacier in the Karakoram over the past 20 years: evidence from mass and energy budget modelling of Batura Glacier, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2585, https://doi.org/10.5194/egusphere-egu24-2585, 2024.

X5.205
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EGU24-4943
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ECS
Florian Hardmeier, James C. Ferguson, and Andreas Vieli

Debris-covered glaciers are found in most glaciated areas in the world and often represent an important water resource for downstream areas. The dynamics of coupled debris and glacier interactions are not fully understood, which is why there has been an increasing effort in recent years to use numerical modelling to gain a better understanding thereof.

As process understanding is quite limited, implementations of the debris-glacier system vary widely. Here we model the glacier in the along-flow dimension and set the focus on debris transport and tracking debris within and on the ice. We examine feasible implementations of involved processes and their coupled effects on glacier dynamics in a transient climate and that allows to vary the location and rate of debris input into the system.

We perform a sensitivity analysis on this model and conduct experiments of increasing complexity, varying both climate forcing and debris deposition and on both simple synthetic and realistic bedrock topographies. Our modelling corroborates the earlier finding from earlier simpler models (without internal debris tracking) of strongly delayed retreat that only sets in after stagnation of the tongue. Our results show beyond that after retreat following warming, debris covered glaciers show a long-term re-advance effect, even when the absolute debris entrainment rate stays the same. We explain this by the increase of the debris-ice ratio in the debris deposition zone. Interestingly, results also show that – when accompanied with a permanent, regular supply of debris input– single large deposition events can have a sustainable growth effect on the glacier, even after the debris from that event has exited the system. In experiments with below century scale fluctuations in climate and/or debris input the glacier length does not really respond. We conclude that this insensitivity and the response of debris covered glacier in general is not only influenced by debris insulation on the tongue, but is also affected by the long time-scale (centuries) involved in transporting the debris through the glacier system.

How to cite: Hardmeier, F., Ferguson, J. C., and Vieli, A.: Modelling the complex response of debris covered glaciers on variations in climate and debris input , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4943, https://doi.org/10.5194/egusphere-egu24-4943, 2024.

X5.206
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EGU24-13830
Gunter Leguy, William Lipscomb, and Samar Minallah

We have implemented a new framework for simulating the dynamic evolution of mountain glaciers in the Community Ice Sheet Model (CISM), a 3D, higher-order ice sheet model that serves as the ice dynamics component of the Community Earth System Model. We have used CISM to simulate all the glaciers of the European Alps at a resolution of 100 m. We describe the modeling framework and present results for the third phase of the GlacierMIP project (GlacierMIP3), which aims to determine the equilibrium area and volume of all glaciers outside the ice sheets, if global mean temperatures were to stabilize at present-day or various warmer levels. Compared to other glacier models, CISM is relatively sensitive to warming. We project that Alpine glaciers will lose a majority of their area and volume under present-day temperatures, with nearly complete ice loss under warmer scenarios. We are extending this framework to other glacier regions and will show preliminary result.

How to cite: Leguy, G., Lipscomb, W., and Minallah, S.: Simulating glacier evolution with a 3D ice sheet model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13830, https://doi.org/10.5194/egusphere-egu24-13830, 2024.

X5.207
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EGU24-12564
Mamta K C, Harald Köstler, and Johannes Fürst

Deep learning-based surrogate models have emerged as computationally inexpensive tools for simulating glacier dynamic systems defined by complex, nonlinear partial differential equations. Despite the potential, the application of physics-informed neural networks  (PINNS) in glacier modelling is sparse. Thus, this study explores the potential of  NVIDIA Modulus-Sym, a PyTorch-based framework, in simulating glacier velocities. The framework NVIDIA Modulus-Sym provides ground for building, training and fine-tuning physics-based surrogate models targeting computational fluid problems. This study presents the pipeline to generate glacier velocities using the physics-constraint approach that incorporates the physics regularisation term within the loss function to enhance generalisation performance. The study further emphasises the challenges and limitations of tools in glaciological research. 

Keywords: Deep learning, Surrogate Models, Glacier Dynamics,  Glaciology

How to cite: K C, M., Köstler, H., and Fürst, J.: Exploring physics-informed neural networks for glacier flow., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12564, https://doi.org/10.5194/egusphere-egu24-12564, 2024.

X5.208
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EGU24-2403
Liyun Zhao, Yan Huang, Michael Wolovick, Liliang Ma, and John Moore

Geothermal heat flow (GHF) is the dominant factor affecting the basal thermal regime of ice sheet dynamics. But it is poorly defined for the Antarctic ice sheet. We compare basal thermal state of the Totten Glacier catchment as simulated by eight different GHF datasets. We use a basal energy and water flow model coupled with a 3D full-Stokes ice dynamics model to estimate the basal temperature, basal friction heat and basal melting rate. In addition to the location of subglacial lakes, we use specularity content of the airborne radar returns as a two-sided constraint to discriminate between local wet or dry basal conditions and compare them with the basal state simulations with different GHF. Two medium magnitude GHF distribution maps derived from seismic modelling rank well at simulating both cold and warm bed regions, the GHFs from Shen et al. (2020) and Shapiro and Ritzwoller (2004). The best-fit simulated result shows that most of the inland bed area is frozen. Only the central inland subglacial canyon, co-located with high specularity content, reaches pressure-melting point consistently in all the eight GHFs. Modelled basal melting rates in the slow-flowing region are generally 0-5 mm yr-1 but with local maxima of 10 mm yr-1 at the central inland subglacial canyon. The fast-flowing grounded glaciers close to Totten ice shelf are lubricating their bases with melt water at rates of 10-400 mm yr-1.

How to cite: Zhao, L., Huang, Y., Wolovick, M., Ma, L., and Moore, J.: Using specularity content to evaluate eight geothermal heat flow maps of Totten Glacier, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2403, https://doi.org/10.5194/egusphere-egu24-2403, 2024.

X5.209
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EGU24-8524
Johannes Feldmann, Ronja Reese, and Ricarda Winkelmann

The observed rapid thinning, speed-up and retreat of the ice in West Antarctica’s Amundsen Sea Embayment might indicate an early stage of a marine ice sheet instability (MISI), potentially leading to the disintegration of the West Antarctic Ice Sheet (WAIS). In general, the stability of a marine ice sheet is strongly linked to the dynamics of its buttressing ice shelves which act as a regulator of the ice discharge into the ocean. Existing numerical modeling studies usually simulated MISI-type WAIS retreat either under prescribed fixed present-day calving front positions (associated with very strong ice-shelf buttressing) or in the absence of ice shelves (neglecting ice-shelf buttressing). These approaches represent extreme cases of realizing ice-shelf buttressing in simulations of a WAIS retreat and comparison between the study results are difficult due to the use of different numerical models and experimental designs. Here we aim to investigate the influence of time-evolving calving fronts and associated buttressing changes in the course of an unfolding WAIS disintegration, based on simulations with the Parallel Ice Sheet Model (PISM). One focus will be on how ice-shelf calving affects MISI retreat rates and the extent of a potential WAIS collapse, i.e., the time evolution and magnitude of the associated sea-level contribution.

How to cite: Feldmann, J., Reese, R., and Winkelmann, R.: Simulated influence of ice-shelf calving on the evolution of a potential West Antarctic Ice Sheet instability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8524, https://doi.org/10.5194/egusphere-egu24-8524, 2024.

X5.210
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EGU24-17606
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ECS
Simon Schöll, Ann Kristin Klose, Ronja Reese, Nicolas Jourdain, and Ricarda Winkelmann

Projections for Antarctica's contribution to global sea-level rise until 2100 range from a positive contribution due to increased ice loss, caused by an increase in surface melt and in dynamic loss of grounded ice, to a negative contribution due to increased snowfall. The high uncertainties in projections can be attributed to different sources, including emission trajectories, climate forcings from Global Circulation Models (GCMs) and Regional Climate Models (RCMs), as well as inter- and intra-ice-model differences.
Here, we present an ensemble of future projections based on simulations with the Parallel Ice Sheet Model (PISM), driven by multiple climate forcings. These are based on several initial states and ice-sheet trajectories over the historical period, consistent with observations.
We assess the influence of the initial states on the spread in projected sea-level change and compare these to the uncertainties arising from climatic forcings, to compare the sources of uncertainty in future sea-level projections until 2100 and beyond.

How to cite: Schöll, S., Klose, A. K., Reese, R., Jourdain, N., and Winkelmann, R.: Effect of initial states on the uncertainty in sea-level rise projections until 2100 and beyond, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17606, https://doi.org/10.5194/egusphere-egu24-17606, 2024.

X5.211
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EGU24-17095
Cyrille Mosbeux, Gael Durand, Nicolas Jourdain, Fabien Gillet-Chaulet, Justine Caillet, Violaine Coulon, Frank Pattyn, Simon Schoell, Ann Kristin Klose, Ricarda Winkelman, Stephen Cornford, Suzanne Bevan, Tijn Berends, Roderik van de Wal, Heiko Goelzer, Tamsin Edwards, Fiona Turner, Charles Amory, Christoph Kittel, and Michiel van den Broeke and the PROTECT

Mass loss from the Antarctic Ice Sheet is increasing, accelerating its contribution to global sea level rise. Projecting the future evolution of the Antarctic Ice Sheet but also better understanding the processes at play is therefore of major importance for the mitigation/adaptation of/to sea level rise.  

Despite considerable advancements in the initialization of ice sheet models over the last decade, challenges persist in reproducing the observed trend in global Antarctic mass loss. This discrepancy between models and reality reflects in the large range of sea level projections in the recent Ice Sheet Model Intercomparison Project (ISMIP6). As part of the European H2020 project, PROTECT, we conducted Antarctic Ice Sheet simulations with six European ice-sheet models until 2150, focusing on the ability of the model to reproduce observations. These simulations were driven by a range of ocean and atmospheric forcings derived from Earth System models or downscaled by regional climate models under various Shared Socioeconomic Pathways (SSPs). Our experimental design enables us  to sample climate forcing as well as model and parametric uncertainties, ensuring a comprehensive exploration of the future evolution of the Antarctic System and its contribution to sea level rise

Our simulations confirm that, regardless of the model used, the Amundsen sector is the region that will most likely dominate mass loss in the decades to come. In high emission scenarios (SSP5-8.5), a large increase in surface mass balance is also expected to temporarily overshadow acceleration in mass loss caused by ice-shelf basal melting. All the models show an acceleration in mass loss from the middle of the 22th century, following the significant increase in surface melting from the end of the 21st century for the SSP5-8.5 scenario. This emphasizes the pivotal role of surface melt in the long-term evolution of the Antarctic ice sheet and its contribution to sea level rise.

 

How to cite: Mosbeux, C., Durand, G., Jourdain, N., Gillet-Chaulet, F., Caillet, J., Coulon, V., Pattyn, F., Schoell, S., Klose, A. K., Winkelman, R., Cornford, S., Bevan, S., Berends, T., van de Wal, R., Goelzer, H., Edwards, T., Turner, F., Amory, C., Kittel, C., and van den Broeke, M. and the PROTECT: Assessing Antarctic Ice Sheet Dynamics and Sea Level Rise: Insights from PROTECT Model Intercomparison, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17095, https://doi.org/10.5194/egusphere-egu24-17095, 2024.

X5.212
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EGU24-9861
Trystan Surawy-Stepney, Stephen L. Cornford, and Anna E. Hogg

Many numerical models used to simulate ice streams require the specification of control fields representing the slipperiness of the ice/bed interface and local deviations in the assumed rheological properties of the ice. These poorly constrained components of the system are often found by solving an inverse problem given observations of model state variables - typically ice flow speed. However, these inverse problems are generally ill-posed, resulting in degenerate or error-dominated solutions. The clearest way to improve this is to take advantage of additional prior information regarding the control fields. 

In this study, we investigate two ways of using maps of surface fracture, derived from Sentinel-1 satellite imagery, to provide prior information to the inverse problem. We first consider a prior that assumes values of effective viscosity significantly different from Glen's flow law are, for the most part, due to observable fractures. Using Pine Island Glacier as a case study, we investigate the solutions and conditioning of this data-informed inverse problem and compare with a typical heuristic regularisation technique. We find that the inclusion of fracture data results in softness fields that resemble fracture features on floating ice. On grounded ice, despite the prevalence of surface crevassing, the softness fields look no more plausible when fracture data is included - suggesting that the presence of surface fracture is not the largest contribution to our uncertainty in the ice rheology. We go on to investigate the use of timeseries of fracture maps to constrain the evolution of the softness field on ice shelves through time, making the assumption that changes to ice rheology occurring on annual timescales are dominated by the fracturing of ice. We show that this method can result in softness fields that visually mimic fracture patterns on floating ice without significantly affecting the quality of the misfit. Such softness fields could be used to constrain evolution equations in isotropic damage models.

How to cite: Surawy-Stepney, T., Cornford, S. L., and Hogg, A. E.: Using observations of surface fracture to address ill-posed ice softness estimation over Pine Island Glacier, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9861, https://doi.org/10.5194/egusphere-egu24-9861, 2024.

X5.213
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EGU24-10845
Sainan Sun and G. Hilmar Gudmundsson

High-end estimates of sea-level change from Antarctica have been derived from simulations using upper-end forcing scenarios and ice-cliff height dependent calving laws. Those have been hypothesised to cause collapse of glaciers in West Antarctica through marine ice cliff instability (MICI). However, some previously published high-end estimate are based on results from a limited number of ice-sheet models, or even only a single ice-flow modelling study. There is, furthermore, low agreement on the implications of some of those calving laws for the West Antarctic Ice Sheet, and limited evidence of MICI having occurred in the past. Here we investigate the dynamic response of West Antarctic glaciers to high-end calving laws using the Úa ice-sheet model. Specifically, we conduct ice-shelf collapse experiments as defined in ABUMIP (Sun et al., 2020) with and without cliff failure mechanism in transient simulations conduced over centennial time scales. We find that the ice-cliff height dependent calving laws can cause glaciers to retreat and collapse from both fast and slow flowing regions. Furthermore, we find that the results are sensitive to numerical resolution near the grounding line. We suggest therefore that ice-sheet modellers always conduct convergence studies when implementing high-end calving laws.

How to cite: Sun, S. and Gudmundsson, G. H.: Revisiting the implications of cliff-height dependent calving law on West Antarctic glaciers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10845, https://doi.org/10.5194/egusphere-egu24-10845, 2024.

X5.214
|
EGU24-16256
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ECS
Annegret Pohle, Ivan Utkin, Ludovic Räss, and Mauro Werder

The Subglacial Drainage System model (GlaDS) is one of the most widely used advanced glacier drainage models, with implementations in several ice sheet models. Here we present a new version of this model capable of execution on graphics processing units (GPUs) programmed in Julia. The aim is for the model to run on meshes larger than 10,000² grid points, which would allow, for instance, to simulate Antarctica at 500m resolution. Unlike the original GlaDS implementation, this is based on a finite difference scheme on a structured grid. Together with a matrix-free solver, this allows us to leverage the full performance capabilities of GPUs. We present model runs of the SHMIP test cases, show the model's scalability and provide an outlook towards higher-resolution continental-scale applications and inversion schemes.

How to cite: Pohle, A., Utkin, I., Räss, L., and Werder, M.: Modelling subglacial drainage with GlaDS on GPUs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16256, https://doi.org/10.5194/egusphere-egu24-16256, 2024.

X5.215
|
EGU24-19220
Darrel Swift, Carlos Martin, and Jeremy Ely

We present detailed modelling of ice flow over a synthetic topography using the full-Stokes ice flow model ELMER-ICE. Our results indicate that landforms/obstacles under 1000 m wavelength contribute importantly to basal drag, implying that predictive ice sheet models that are initialised using static parameterisations of basal drag will greatly underestimate the possible mediating effects of bedrock topography. We conducted numerous simulations using a 10 m resolution, 40 x 22 km model domain with a uniform ice thickness of 1000 m and with sliding restricted to a 20 km-wide central corridor to negate ice leaving the lateral margins. Basal slipperiness (i.e. skin drag) in all simulations used the value obtained during an initial simulation using an entirely flat bed and an imposed surface velocity of 150 m a-1. Subsequent simulations used a synthetic bed with wavelength 5 km, amplitude 200 m, and randomised superimposed smaller-scale roughness. Because ice sheet beds are bumpy at a range of scales - from landforms reflective of km-scale patterns of glacial bedrock erosion down to m-scale obstacles characteristic of bedrock structure – roughness was introduced gradually into the simulations by stepwise reduction of the degree of smoothing applied to the synthetic topography using a band-pass filter. Our results demonstrated that around two-thirds of observed surface velocity was by sliding, and that mean sliding velocity (and thus surface velocity) declined rapidly when introducing roughness with length scale smaller than 1000 m. Further, the observed decline appeared broadly exponential in relation to obstacle size as smaller roughness length scales were added, down to the smallest length scale (10 m) permitted by present model resolution. The results therefore highlight the potential importance of form drag provided by sub-km scale bed roughness in stabilising ice flow, including flow in grounding line locations that are critical to marine ice sheet stability. The results also have implications for predictive ice sheet models, which typically use static fields of basal drag derived from inversions of present-day surface observations, and do not distinguish between form and skin drag. As such, current models could imprecisely predict ice discharge and grounding line behaviour in regions of evolving bedrock or sedimentary landforms, which are ubiquitous to ice sheet beds.

How to cite: Swift, D., Martin, C., and Ely, J.: The importance of bed roughness on ice sheet flow investigated using a full-Stokes ice flow model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19220, https://doi.org/10.5194/egusphere-egu24-19220, 2024.

X5.216
|
EGU24-10817
Yilu Chen, Ivan Utkin, Ludovic Räss, and Mauro Werder

There are many uncertainties associated with natural processes governing the evolution of glaciers and ice sheets. Unknown parameters, such as basal drag or surface mass balance, can be estimated through data assimilation workflows coupled with physics-based models of ice flow. The multi-scale nature of ice dynamics and significant spatial and temporal variations in physical properties challenges accurate estimations of distributed fields of unknown parameters. High-performance computing and modern computational architectures such as graphics processing units (GPUs) enable efficient and scalable solvers for the ice flow.

In this work, we introduce a novel GPU-accelerated inversion framework to enable a point-wise reconstruction of unknown parameter fields at high resolution. The inversion framework is based on the adjoint sensitivity method combined to a gradient-based optimisation. The derivation of the adjoint problem often represents a tedious task which limits the applicability of adjoint-based inversions to simplified ice flow models and hinders fast development. To address these limitations we use differentiable programming and the Julia language which permit automatic differentiation (AD) of arbitrary GPU code. Our GPU-based inversion procedure combines an automatically generated adjoint solver by the Enzyme.jl package using AD and a forward solver to retrieve the point-wise gradient we further use to minimise a cost-function.

We demonstrate the capabilities of our inversion framework by developing a forward solver, based on shallow ice approximation (SIA), and several inverse models, utilising different assumptions about the ice flow. One inversion model assumes that the glacier is in a steady-state, which requires iterative solution of SIA equations. The inversion procedure estimates distributions of sliding coefficient, matching the observed ice thickness, glacier outline, and surface velocities. Another inversion model is based on a "snapshot" approach, in which the surface elevation is fixed from observations, and the sliding coefficient is solved to only match observed surface velocities. These two models represent two end members of the spectrum of data assimilation approaches, which will serve as building blocks for more complex workflows, such as transient evolution of glaciers.

The feasibility of our inversion algorithms is validated through extensive testing on synthetic glaciers. Then we consider the application of our inversion approach to glaciers in the European Alps using remote sensing data. A map of sliding coefficients is reconstructed by matching the observed ice surface velocity and elevation. The successful application to real glaciers confirms that our inversion models are well suited for large scale and high-resolution simulations. We also present the performance testing results demonstrating close-to-optimal performance of forward and inverse models on NVIDIA GPUs.

How to cite: Chen, Y., Utkin, I., Räss, L., and Werder, M.: Constraining the basal sliding of alpine glaciers using adjoint-based inversions and automatic differentiation on GPUs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10817, https://doi.org/10.5194/egusphere-egu24-10817, 2024.

X5.217
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EGU24-16675
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ECS
Ivan Utkin, Ludovic Räss, Filippo Quarenghi, and Mauro Werder

Efficient modeling of ice sheets involves considering multiple coupled physical processes, including thermomechanical interactions. While using a Full-Stokes model for ice flow in Greenland and Antarctica provides most accurate results, it is can be extremely costly on a large scale with existing software, justifying the use of various reduced models.

Some important features of ice sheets, such as ice streams, are inherently three-dimensional. Accurate stress distribution, particularly around topography features comparable to ice thickness and near a grounding line, can only be achieved with a full stress tensor. In addition, a reference Full-Stokes solver for regional to ice sheet scale simulations can be a valuable tool for calibrating reduced models.

We introduce FastIce, a novel ice flow model for massively parallel architectures, written in Julia. Leveraging GPUs (Nvidia, AMD) and supporting distributed computing, FastIce includes a thermo-mechanically coupled Full-Stokes ice flow model and a novel conservative energy formulation for describing thermal effects. FastIce is written to be easily extensible, and its core is fully differentiable, enabling data assimilation pipelines using adjoint sensitivities and automatic differentiation (AD).

We validate FastIce through ISMIP-HOM benchmark tests and assess the coupled thermomechanical solver using the method of manufactured solutions. Our results showcase the thermo-mechanical instability arising from the non-linear interaction between temperature-dependent viscosity of ice and shear heating, reproducing existing analytical results. We present the performance testing of FastIce in single-node and distributed scaling benchmarks on LUMI, the largest European supercomputer.

How to cite: Utkin, I., Räss, L., Quarenghi, F., and Werder, M.: Benchmarking FastIce, a new massively parallel thermomechanical ice flow solver, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16675, https://doi.org/10.5194/egusphere-egu24-16675, 2024.

X5.218
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EGU24-17427
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ECS
Janosch Beer, Mylène Jacquemart, Ivan Utkin, Matthias Huss, Andreas Vieli, and Daniel Farinotti

Despite constituting 80% of the total number of glaciers in mid- to low-mountain range catchments, the attention paid to very small glaciers (< 0.5 km2) in glacier research remains relatively low. However, glaciers of this size category are expected to undergo dramatic changes. Within Switzerland, more than half are predicted to disappear within the next two decades. As these glaciers shrink, they lose their firn cover, a crucial latent heat source through refreezing meltwater. Simultaneously, reduced glacier dynamics result in less ice deformation and decreased frictional heating at the base. Various studies suggest that such conditions can promote cooling, possibly enabling a transition from temperate to polythermal or cold states. Polythermal glaciers, especially those with partly frozen glacier beds, have been found to accumulate excessive meltwater, significantly increasing their hazard potential. In this study we present a new enthalpy-based englacial temperature model (IceT) to investigate the potential transition of very small Swiss glaciers from temperate to polythermal or cold conditions. The study focuses on identifying key parameters influencing glacier thermal transitions through a sensitivity analysis. Furthermore, we apply the model on a subset of 20 very small Swiss glaciers and compare our findings against previously generated model results of the Glacier Evolution Runoff Model (GERM). Our results indicate that mass balance and the liquid water content are the most significant factors for predicting glacier thermal states. The influence of mass balance works in two ways: (1) Highly negative mass balances hinder the development of a polythermal structure by allowing surface melt to surpass the propagation of the cold-temperate transition surface (CTS). (2) Less negative mass balances combined with limited snowfall, induce a transition to polythermal conditions by enabling the CTS propagation to outpace surface melt. Ultimately, the liquid water content (φ) appears as the most critical parameter in predicting ice temperatures. A mere increase of φ by 1% could reduce the maximum CTS depth by 165.07 m and lower the annual CTS propagation rate by 13.85 m a-1. Significant differences emerge between GERM and IceT findings. GERM suggests that the majority of all very small Swiss glaciers exhibit polythermal conditions, while in the subset of 20 glaciers modeled with IceT, only 15% show indications of a polythermal regime. However, the considerable impact of liquid water on predicting ice temperatures, coupled with the incomplete knowledge regarding its distribution within glaciers, leads to substantial uncertainties in the presented model outcomes.

How to cite: Beer, J., Jacquemart, M., Utkin, I., Huss, M., Vieli, A., and Farinotti, D.: Determining the englacial temperature evolution of very small glaciers in the Swiss Alps: An enthalpy-based modelling approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17427, https://doi.org/10.5194/egusphere-egu24-17427, 2024.

X5.219
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EGU24-16922
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ECS
Recent and future variability of the ice-sheet catchment of Jakobshavn Isbræ, Greenland
(withdrawn after no-show)
Anja Løkkegaard, William Colgan, Andy Aschwanden, and Shfaqat Abbas Khan