The Antarctic and Greenland Ice Sheets (AIS and GrIS) play a critical role in shaping future sea-level rise (SLR), but their contributions and human greenhouse gas emissions remain the largest sources of uncertainty in SLR projections (Edwards et al., 2021). This uncertainty, along with the risk of potential tipping points leading to rapid ice loss, arises from a limited understanding of key processes that govern ice-sheet behaviour (Fox-Kemper et al., 2021). In the Ice Sheet Model Intercomparison for CMIP6 (ISMIP6), 55% of AIS and 15 to 35% of GrIS future mass loss uncertainty is due to ice-sheet models’ uncertainty (Seroussi et al., 2023; Jager et al., 2024; Goelzer et al., 2020). While modeling the AIS’s and GrIS’s complex interactions with the climate is difficult (Seroussi et al., 2023), one other uncertain process is basal sliding over bedrock. Because this process is not directly observed due to the large thickness, its representation in current models remains rudimentary. The primary goals of Combining Coupled Modelling and Machine Learning to Constrain Antarctica’s Uncertain Future (ICEMAP) project include (i) better quantification of uncertainties related to basal sliding, (ii) comparison of these uncertainties to other sources of uncertainty, and (iii) exploration of how satellite data can help reduce these uncertainties.
To achieve these goals, we employ the Shallow Shelf Approximation (SSA) implemented in the Elmer/Ice model, an open source finite element software for ice sheets, glaciers and ice flow modelling, which was one of the participants in ISMIP6 (Gagliardini et al., 2013; Seroussi et al., 2023). It uses inverse methods to calibrate the many unknown parameters related to rheology and friction. Here, we take into account various physical and numerical uncertainties to perform multiple calibrations using remote-sensing velocity data to compute basal sliding and basal shear stress. Subsequently, these values and their spatial variations can be compared with the diverse existing theories that have been developed from small-scale physical and numerical experiments (Gagliardini et al., 2007; Zoet and Iverson, 2020).
Our analysis demonstrates that the principal characteristics of these parameterisations, derived from small-scale experiments, are observable at a large scale. However, the values may deviate from expected norms, particularly with regard to the exponent of the Weertman friction law. This investigation enables the quantification of both the parameter values and their associated uncertainties within the friction parameterisations governing the AIS and the GrIS. Furthermore, it highlights the critical influence of basal water presence, which appears to play a pivotal role in the variability of basal sliding. Incorporating this factor into models, whether through varying levels of model complexity or the use of proxies, is deemed essential for accurately capturing the temporal variations in basal sliding.
How to cite: Jager, E., Gladstone, R., Zwinger, T., Uotila, P., and Moore, J.: Friction: what’s going on underneath the Antarctic and Greenland ice sheets?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6813, https://doi.org/10.5194/egusphere-egu25-6813, 2025.
The response of the Antarctic ice sheet to climate change and its contribution to sea level under different emission scenarios are subject to large uncertainties. A key uncertainty is the slipperiness at the ice sheet base and how it is parameterized in glaciological projections. Alternative formulations of the sliding law exist, but very limited access to the ice base makes it difficult to select among them. Here, we use satellite observations of ice flow, inverse methods, and a theory of acoustic propagation in granular material to relate the effective pressure, which is a key control of basal sliding, to seismic observations recovered from Antarctica. Together with independent estimates of grain diameter and porosity from sediment cores, this enables a comparison of basal sliding laws within a Bayesian framework. The presented direct link between seismic observations and sliding law parameters can be readily applied to any acoustic impedance data collected in a glacial environment. For rapidly sliding tributaries of Pine Island Glacier, these calculations provide support for a Coulomb sliding law and widespread low effective pressures.
How to cite: Hank, K., Arthern, R. J., Williams, C. R., Brisbourne, A. M., Smith, A. M., Smith, J., Wåhlin, A., and Anandakrishnan, S.: The Antarctic Ice Sheet sliding law inferred from seismic observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3221, https://doi.org/10.5194/egusphere-egu25-3221, 2025.
Understanding the physical laws governing glacier and ice sheet basal sliding speed is crucial for accurately predicting their dynamics and contribution to sea-level rise. However, basal sliding is controlled by complex processes linked to subglacial hydrology, which remains difficult to constrain. Previous studies based on Argentière glacier (France) suggest a simplification of the law describing the long-term evolution of sliding velocity, by proposing that long-term subglacial water pressure of hard-bedded glaciers is determined by the basal shear stress condition. The applicability of these findings to other glaciers and over long timescales has not been fully explored yet. In this study, we analyze multidecadal timeseries of surface velocities and elevations from various locations on seven Alpine glaciers, spanning from the early 20th century to the present. Using the Elmer/Ice finite element model, we solve for the full-Stokes equations to derive realistic estimates of basal sliding velocities and shear stresses from observed surface velocity and topography. Our analysis of these datasets reveals distinct basal friction behaviors both among glaciers and within different profiles of the same glacier. We identify three types of friction laws governing glacier dynamics. Most sites follow a Lliboutry-type law, where significant variations in sliding velocity occur under minor changes in shear stress. This behavior can be explained by the formation of water-filled cavities that grow as a function of sliding velocity under constant effective pressure. Other sites exhibit a Weertman-type law, characterized by a power-law scaling between shear stress and sliding velocity, implying constant cavity size through time. Finally, only Gébroulaz glacier follows a Coulomb-type law typical of sedimentary beds, where basal velocities increase dramatically beyond a critical shear stress threshold. For each measurement site, we derive a value of maximum shear stress CN and friction coefficient As and find that hard-bedded glaciers in the Weertman and Lliboutry regimes align along a unified friction law with similar values for the friction exponent m and the bed-shape exponent q. Our results show that the basal friction at all sites can be explained by a single friction law where the effective pressure either remains constant through time or scales with the basal shear stress. Further exploration of correlation between these friction laws and glacier geometric parameters, such as surface slope and bedrock roughness, may provide insights into the underlying mechanisms regulating the long-term effective pressure.
How to cite: Zeller, M., Gilbert, A., and Gimbert, F.: Investigating the basal friction law of Alpine glaciers from multi-decadal up to centennial observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16821, https://doi.org/10.5194/egusphere-egu25-16821, 2025.
In fast-flowing regions of the Antarctic and Greenland ice sheets, most motion occurs through slip at the boundary between ice and its substrate. Glaciologists have developed “slip laws” that describe basal motion as a function of resistive stress (e.g. basal drag) and effective pressure. When implemented in ice sheet models, the choice of slip law affects predictions of grounding-line migration and sea-level rise. Slip laws implemented in ice sheet models assume that the base of the glacier is “clean” (without rock debris) and separated from the bed by a thin frictionless water film, implying that the only source of basal drag is viscous flow and regelation around bed obstacles. However, observations of basal ice indicate that it is “dirty” (debris or sediment-rich) in most glacial environments, suggesting an additional source of drag due to friction between debris-laden basal ice and the bed. Incorporating debris-bed friction into a slip law may lead to significantly different predictions of the magnitude of basal drag and alter the functional form of the slip law.
Here, we report results of laboratory experiments using a geomechanical apparatus (cryogenic ring shear) to slide ice over a rigid bed composed of inclined marble steps at realistic glaciological conditions (e.g. slip velocity, effective pressure, temperature). We conduct a control experiment by sliding clean ice at a range of velocities and recording the resistance to basal motion. We then slide debris-laden basal ice to determine how debris affects the magnitude and functional form of the basal slip law. Our results suggest that slip in clean ice conditions is well described by the commonly used regularized Coulomb slip law. However, debris-bed friction is a significant source of basal drag, raising measured shear stress by ~50-75% despite a sparse areal debris concentration of ~5%. We derive a slip law incorporating debris-bed friction that fits our experimental data within measurement uncertainty with two tuning parameters. The debris-bed friction slip law is composed of three terms: a clean ice term (equivalent to regularized Coulomb), a pressure-dependent debris friction term, and a velocity-dependent debris-friction term. We further validate this slip law for realistic 3-D bed topographies using a finite-element ice flow model (Elmer/Ice). Finally, we implement a parameterized form of the slip law in an ice sheet model (MPAS-Albany Land Ice) and assess the sensitivity of grounding-line migration and ice-mass loss to the choice of slip law.
How to cite: Brooks, J., Zoet, L., Hansen, D., Helanow, C., Hillebrand, T., Hoffman, M., Morgan-Witts, N., and Perego, M.: A glacier slip law incorporating debris-bed friction, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-737, https://doi.org/10.5194/egusphere-egu25-737, 2025.
Basal sliding is a key process that controls the ice discharge of ice into the ocean. Understanding this process is essential for improving the reliability of future projections of ice sheet evolution and sea level rise. The basal sliding law, which governs ice-bed interactions, remains a critical yet poorly understood process in ice sheet models. Recent advances in transient calibration techniques, which incorporate time series of observed surface velocity and elevation, have enhanced the ability of ice numerical models to infer basal conditions. However, relying on the same type of observational datasets for both model calibration and validation limits the ability to independently evaluate model performance, particularly for future projections. In this study, we introduce an independent observational dataset: measurements from the Global Navigation Satellite Systems (GNSS) collected by Greenland GNSS Network (GNET) stations located along Greenland's coastline. By comparing observed uplift signals with modeled mass change, we can validate model behavior and identify sliding laws most consistent with GNSS data. Here, we illustrate this approach by modeling Helheim and Jakobshavn Glaciers from 2007 to 2022 using three different sliding laws. While all sliding laws produce similar surface velocity patterns consistent with InSAR-derived velocity observations, the patterns of mass change, which control bed uplift, differ significantly. Our analysis reveals that all three sliding laws can reproduce uplift signals consistent with GNSS measurements in terms of inter-annual variability. However, only coulomb-limited sliding laws generate uplift signals consistent with GNSS measurements in multi-annual trends. These results highlight the importance of incorporating multiple independent observational data, such as GNSS, into ice sheet models to refine our understanding of basal sliding laws and reduce uncertainties in predicting future sea level rise.
How to cite: Cheng, G., Barletta, V. R., Khan, S. A., Morlighem, M., Seroussi, H., and Berg, D.: Identifying the Basal Sliding Law Using Numerical Modeling and GNSS Observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10180, https://doi.org/10.5194/egusphere-egu25-10180, 2025.
Basal sliding and other processes affecting ice flow are challenging to constrain due to limited direct observations. Inversion methods, which typically fit an ice flow model to observed surface velocities, enable the reconstruction of basal properties from readily available data. We present a numerical inversion framework for reconstructing the glacier basal sliding coefficient, applied to both synthetic and real-world alpine glacier scenarios. The framework employs automatic differentiation to generate adjoint code and runs in parallel on graphics processing units (GPUs).
We explore two inversion workflows using the shallow ice approximation (SIA) as the forward model: a time-independent approach fitting to a single snapshot of annual ice velocity and a time-dependent inversion accounting for both ice velocity and changes in geometry. We find that the time-dependent inversion yields more robust and accurate velocity fields than the snapshot inversion. However, it does not significantly improve the problematic initial transients often encountered in forward model runs that employ sliding fields from snapshot inversions. This is likely due to the limitations of the forward model. This methodology is transferable to more complex forward models and can be readily implemented in languages supporting automatic differentiation.
How to cite: Utkin, I., Chen, Y., Räss, L., and Werder, M.: Snapshot and time-dependent inversions of basal sliding using automatic generation of adjoint code on graphics processing units, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18791, https://doi.org/10.5194/egusphere-egu25-18791, 2025.
Mountain glaciers provide an irreplaceable water resource in High Mountain Asia, with a significant proportion of water input to rivers coming from glacial meltwater. However, the volume of water held in these glaciers and the predicted evolution of the glaciers over the coming decades is subject to great uncertainty.
Previous global ice thickness inversion studies have used low-order models (such as the shallow ice approximation, which is known to be locally unreliable on mountain glaciers) to describe the relationship between ice velocity and thickness. Furthermore, the reliability of the resulting thickness products in High Mountain Asia is severely limited, since at the time they were produced, only an extremely small dataset of measured thicknesses in that region was available for constraint and validation. Lastly, time-dependent ice thickness simulation runs often show an initial ‘shock’ in modelling a glacier’s evolution, due to the lack of consistency between the ice flow physics and existing thickness products, leading to unreliable results.
To construct more accurate thickness maps for selected glaciers, we use the Instructed Glacier Model, a novel deep-learning-based high-order ice flow model with the capability to invert observed glacier surface velocity for ice thickness. This inversion method, which utilises gradient-based optimization techniques, additionally allows for the inclusion of observed thicknesses to constrain the thickness field.
A new airborne radar method for measuring ice thickness has been deployed in the Himalayas near Mount Everest, unlocking new possibilities for thickness inversion in this region, which has historically not been well covered by in-situ observations. Here, we use the data from this aerial survey to constrain the thickness inversion of the Instructed Glacier Model.
After showing that contemporary ice thickness products are generally inaccurate on High Mountain Asia glaciers, we present new inverted thickness maps for the 13 glaciers which have observations in this new dataset. We assess the accuracy of the results using a subset of the available data as validation, and demonstrate that our results show significant improvement over earlier thickness products.
How to cite: Smith, G., Goldberg, D., Jouvet, G., Maddison, J., and Pritchard, H.: Inverting glacier thickness in High Mountain Asia with a deep-learning-based ice flow model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-357, https://doi.org/10.5194/egusphere-egu25-357, 2025.
The thermal regime of glaciers plays a critical role in their dynamics and potential hazards. In particular, impermeable cold ice can trap and store liquid water leading to the formation of intraglacial water pockets, as in the Tête Rousse Glacier (France), where the sudden drainage of over 100,000 m³ of water in 1892 caused 175 fatalities and significant damage to the village of Saint-Gervais.
The objective of this work is to produce a detailed thermal regime map of Alpine glaciers to identify those most susceptible to host this type of thermic water pockets. To achieve this, we use a thermo-mechanical ice flow model based on the Elmer/Ice code to simulate the thermal structure of synthetic 2D glacier profiles. The model is based on the enthalpy formulation, where the surface boundary conditions are computed by a subgrid model solving for meltwater percolation and refreezing in the firn. The synthetic 2D profiles are chosen to be representative of the morphological and climatic diversity of the Alps with various length, slope, bedrock shape, elevation range, aspect, and snow accumulation distribution.
The outputs of these simulations form a large database of glacier thermal structures, which will serve as the training dataset for a machine learning emulator currently under development. This emulator will provide a tool to infer thermal regimes to the scale of the entire Alpine region, predicting basal temperatures based on glacier morphology.
The results from the 2D simulations suggest that snow accumulation patterns play a dominant role in shaping glacier thermal regimes: (i) upstream over-accumulation promotes percolation and refreezing of liquid water, releasing latent heat and warming the glacier locally, while (ii) exposed ice downstream acts as an impermeable thermal barrier, creating favorable conditions for water storage.
This integrated approach, combining detailed physical modeling with machine learning techniques, provides a way to build a tool that can be easily applied at a large scale while accounting for the complex interactions that determine the thermal regime of glaciers. In the longer term, it seeks to deliver a comprehensive thermal regime map of Alpine glaciers, providing a valuable resource for identifying glaciers most at risk of hosting intraglacial water pockets and improving the prevention and management of glacier-related hazards.
How to cite: Bonnet, J., Gilbert, A., Ozenda, O., and Gagliardini, O.: Regional scale thermal regime mapping of Alpine glaciers inferred from 2D thermo-mechanical modeling, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6245, https://doi.org/10.5194/egusphere-egu25-6245, 2025.
The acquisition of 1.5 Myr ice cores is a major objective of Antarctic exploration, aiming to enhance our understanding of the causes behind the Mid-Pleistocene Transition. Here, we combine radar observations and ice-flow modeling to investigate the age, basal thermal state and temperature of the ice sheet in the Dome Fuji region, Antarctica, to provide significant information for selecting the drill site.
We use a 3-D ice-flow model to couple the mechanical, thermal and hydrological processes in the ice sheet. Radar internal stratigraphy and the previously identified subglacial waterbodies are incorporated as constraints in the inverse modelling to improve the reliability of the model results. The modelled basal temperature reaches the pressure melting point in most of the study area, while there is a lower modelled basal temperature near the New Dome Fuji (NDF, 77.789° S, 39.053° E) and southeast of the old Dome Fuji drill site (DF, 77.317° S，39.703° E). The relative basal reflectivity, derived from radar bed return power and modelled 3-D ice temperature, is relatively low in these areas as well. This suggests a lower possibility of basal melting, and thus suggests that a longer climate record might be preserved in the ice. The modelled age of of the ice near the base reaches 1.5 Myr near NDF and south of DF. These modelled results enhance the understanding of ice dynamics, age distribution and thermal structure in the Dome Fuji region.
How to cite: Wang, Z., Wolovick, M., Steinhage, D., Dong, S., and Eisen, O.: 3-D thermal structure and age modelling of the ice sheet in the Dome Fuji region, Antarctica, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17432, https://doi.org/10.5194/egusphere-egu25-17432, 2025.
In the accumulation regions of the Greenland Ice Sheet (GrIS), not all surface meltwater contributes to runoff. A significant portion is retained through refreezing within the underlying firn layer, a process that critically moderates the overall mass loss from the GrIS. The refreezing of percolating meltwater at shallow depths leads to densification of the near-surface and the formation of ice layers. The extent of meltwater refreezing is influenced by firn density and temperature, which together govern the permeability of the near-surface ice layers. The presence of shallow, thick ice layers (> 1m thick, also known as "ice slab") restricts the deeper percolation of meltwater, thereby promoting its conversion into runoff. For example, the formation of ice slab in GrIS has resulted in nearly a 30% increase in the area contributing to runoff generation since 2001. Therefore, modelling ice slab is essential for understanding the total mass loss of the GrIS, both in recent years and in future projections.
In this study, we present a high vertical resolution, physically distributed model that simulates surface mass balance, refreezing, ice layer formation, and runoff. A novel temperature-dependent criterion for ice layer permeability is incorporated that has been rigorously validated against field measurements from the Devon Ice Cap in the Canadian Arctic, where it demonstrates a strong agreement with point-scale observations of surface mass balance and vertical density profiles. We applied the model to the GrIS from 1999 to 2022, using a horizontal spatial resolution of 0.25° × 0.25°, a vertical resolution of 1 cm, and a temporal resolution of 15 minutes. The model simulations are calibrated using the SUMup archive of surface mass balance observations and validated against shallow core measurements of vertical density profiles. The high vertical resolution of the model provides insights into the process of ice slab evolution and impacts on runoff magnitudes and spatial distribution from the accumulation area of the GrIS. We analyze the model results to examine the relationship between the formation of ice slab and the runoff limit across the GrIS exploring sensitivities to changing climate.
How to cite: Laha, S. and W. F. Mair, D.: Modelling evolution of Greenland Ice Sheet near-surface ice slab and its impact on runoff , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1342, https://doi.org/10.5194/egusphere-egu25-1342, 2025.
Mountain glaciers are a major source of sea-level rise and also represent an important freshwater resource in many mountainous regions. Thus, accurate estimations of their thickness and, therefore, the total ice volume are important both in predicting and mitigating the global and local effects of climate change. However, to date, only 2% of the world’s glaciers outside the ice sheets have any thickness observations, due to the logistical difficulties of obtaining such measurements, creating a large and policy-relevant scientific gap.
The recent development of a global-scale ice-velocity dataset, however, provides an ideal opportunity to fill this gap and determine ice thickness across the 98% of glaciers for which no thickness data is available. This can be done by inverting an ice-dynamics model to solve for ice thickness. For accurate thickness results, this needs to be a higher-order model, but such a model is far too computationally cumbersome to apply on a global scale, and simpler, quicker methods usually based on the shallow ice approximation (SIA) are unsuitable, particularly where sliding dominates glacier motion. The only attempt that has been made to leverage the global velocity dataset to retrieve ice thickness has, though, used the SIA, simply because higher-order approaches are not computationally realistic at this scale. Consequently, most of the widely-used global glacier models have made no systematic attempt to invert global ice thickness, owing to these limitations. Allied to this is that, once an inversion is done, subsequent forward modelling is rarely physically consistent with the physics used in the inversion, leading to model inconsistencies that affect the accuracy of simulations.
As a solution to these problems, we apply the deep-learning-driven ice-flow model, the Instructed Glacier Model (IGM), that emulates the performance of state-of-the-art higher-order models at a thousandth of the computational cost. This model, by solving a multi-variable optimisation problem, can fully use and assimilate all available input datasets (surface velocity and topography, ice thickness, etc.) as components of its cost function to invert ice thickness. This approach also gives us the possibility of using consistent ice-flow physics for inversion and forward modelling, reducing the magnitude of the shock inherent in traditional modelling approaches. Our previous work focused on the European Alps; here we update the method for a global scale and present results. We show that our volumetric estimates at a regional scale are generally consistent with previous global thickness-modelling studies, and provide preliminary forward-modelling results showing the committed ice loss globally at the 2050 horizon.
How to cite: Cook, S., Jouvet, G., Millan, R., Rabatel, A., Maussion, F., Zekollari, H., and Dussaillant, I.: Global ice thickness and committed loss to 2050, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2800, https://doi.org/10.5194/egusphere-egu25-2800, 2025.
Iceberg calving due to fracture accounts for around half of the ice lost annually from Antarctica, but physically based models representing this process are not currently included in ice sheet models. By using a phase-field viscoelastic model for fracture we can model both slow deformation of ice and the distribution and evolution of cracks leading to calving. The model solves equations for non-linear viscous flow, elastic displacement and a phase-field variable which allows cracks to nucleate and propagate in response to the evolving stress field. Without making any assumptions about the type of calving, we apply this model to a simulate fracture of an iceberg and an ice shelf, giving both insights into parameterisations and a pathway to including fracture directly in ice sheet models.
How to cite: Richards, D., Arthern, R., Marsh, O., and Williams, R.: A viscoelastic phase-field model for calving and fracture in ice, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17134, https://doi.org/10.5194/egusphere-egu25-17134, 2025.
The material behaviour of ice is complex: At short time scales it behaves as a brittle solid in extension, or a plastic material under compression/shear, whereas at longer time scales the visco-elastic behaviour dominates in all deformation modes. Furthermore, as the temperature of ice is close to its melting point, material properties are strongly impacted by small temperature changes (e.g. those induced via plastic dissipation). All these phenomena are also interlinked with fracture propagation: At lower confining pressure cracks form in a purely brittle manner as a response to sudden stress changes, whereas viscous creep will prevent cracks from forming during slower loading. Instead, at higher pressures (e.g. near the base of ice sheets), cracks develop based on the energy dissipated by plastic work.
Here, a modelling framework able to capture these different regimes will be presented, using the phase-field fracture paradigm to allow for complex fracture patterns. Application will be shown to both small-scale tri-axial compression tests, demonstrating the accuracy of the model and its ability to replicate experimental observations, as well as large-scale cliff failure to showcase the impact of using this material model on predictions of ice-cliff failure.
How to cite: Hageman, T. and Martínez-Pañeda, E.: An ice-specific phase-field fracture model for predicting brittle and ductile failure, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2472, https://doi.org/10.5194/egusphere-egu25-2472, 2025.
Debris cover on glaciers is expanding worldwide as glaciers are retreating. While the impact of debris cover on local mass balance is relatively well-established, the long-term dynamics of these glaciers are more complex and not fully understood. The dynamics are a key factor when trying to establish relationships between erosion rates, debris fluxes, and debris cover thicknesses while all of these properties are either completely unknown or only known locally in space and time.
Numerical modelling can help us better understand the data scarce debris-covered glacier system. While most recent approaches model englacial debris as an advected concentration, we establish a novel approach that exploits Lagrangian particle tracking in the Instructed Glacier Model (IGM). IGM uses deep learning to solve ice flow equations, greatly reducing computation times and enabling long-term model runs with large amounts of particles. In our implementation, a single particle represents a unit volume of debris and can be assigned any other property. The user can define a particle seeding area through either manual mapping or automatic classification based on conditions. Once particles emerge at the glacier surface in the ablation area, they are evaluated to compute debris cover thickness, which is then tied back to surface mass balance through a user-defined function.
As examples to showcase the capabilities of the model we use Zmuttgletscher, Switzerland, and Satopanth Glacier, India. We explore the sensitivities of the model to the use of different seeding strategies, changes in debris input amounts, mass balance functions, and model parameters such as grid size and seeding frequency.
How to cite: Hardmeier, F., Muñoz-Hermosilla, J. M., Miles, E., Jouvet, G., and Vieli, A.: Exploiting Lagrangian particle tracking in the Instructed Glacier Model (IGM) to model coupled debris-covered glacier dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6707, https://doi.org/10.5194/egusphere-egu25-6707, 2025.
Both the Greenland and Antarctic ice sheets are experiencing increased levels of melt, contributing to potentially devastating sea level rise. Quantifying their future changes is imperative in order to understand and mitigate the risks associated with their demise. Projections of future ice sheet change due to climate change are highly uncertain. Palaeo-ice sheets left behind a wealth of information on past ice extents, timing and flow directions. By looking to the past and using such data to validate and constrain numerical ice sheet model simulations, the formulation of model approaches can be improved, and the uncertainty within projections of ice mass loss and sea level rise can be reduced.
Here we simulate the last Eurasian Ice Sheet complex (EISC) between 40 and 5 thousand years ago, to find a model input parameter space that is optimised to fit the available flow geometry as revealed by observations of former ice flow direction such as from drumlins. We present a new Bayesian framework that takes an initial perturbed parameter ensemble for the EISC, compares each ensemble member to past observed flow directions and identifies an updated parameter sampling routine on a reduced parameter space to improve the overall model-data match of further simulations. To quantitatively compare and score observed flow geometry from glacial landforms with model simulations in a statistically rigorous way, a new model-data comparison tool is utilised: the Likelihood of Accordant Lineations Analysis (LALA) tool. This work could not only be used further to develop a robust simulation of the EISC, as well as other palaeo-ice sheets, optimised to flow geometry, but also to simulate data-driven spin-ups for use in future ice sheet projections.
How to cite: Archer, R., Ely, J., Johnson, J., Oakley, J., Clark, C., Butcher, F., Dulfer, H., Hughes, A., Boyes, B., and Reese, R.: Statistically optimising the input parameter space of a numerical ice sheet model to improve the model fit to observations of palaeo-ice flow direction , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19449, https://doi.org/10.5194/egusphere-egu25-19449, 2025.
The grounding line marks the boundary between grounded and floating ice, and is a critical region for ice-sheet stability and sea-level projections. The complex ice-flow at the grounding line, where the stress regime moves from vertical shear to horizontal extension over a relatively short distance, is prone to numerical instability in transient full-Stokes simulations. Furthermore, boundary conditions change at the grounding line, switching from a friction law in grounded ice to an ocean pressure force at the ice-ocean interface. Grounding-line full-Stokes problems have been successfully stabilised by the sea spring stabilisation scheme in Elmer/Ice (Durand et al., 2009) which mimicks an implicit time-stepping scheme by predicting the surface elevation and corresponding ocean pressure corrections in the next time step. We extend on this stabilisation approach by introducing the Free-Surface Stabilisation Approximation (FSSA) to the ice-ocean interface. FSSA has been proven successful in allowing larger stable time steps in grounded problems with an evolving ice-atmosphere interface (Löfgren et al., 2022; Löfgren et al., 2024). This stabilisation approach incorporates a boundary condition term into the weak-form of the Stokes equations representing the predicted stress adjustment between the current and next time step. Using a synthetic MISMIP set up (Pattyn et al., 2012), we investigate the applicability of FSSA to the ice-ocean interface.
G. Durand, O. Gagliardini, B. de Fleurian, T. Zwinger, and E. Le Meur. Marine ice sheet dynamics: Hysteresis and neutral equilibrium. Journal of Geophysical Research, 114(F3):F03009, 2009. doi: 10.1029/2008JF001170.
A. Löfgren, T. Zwinger, P. Råback, C. Helanow, and J. Ahlkrona. Increasing numerical stability of mountain valley glacier simulations: implementation and testing of free-surface stabilization in Elmer/Ice. The Cryosphere, 18(8):3453–3470, 2024. doi: 10.5194/tc-18-3453-2024.
A. Löfgren, J. Ahlkrona, and C. Helanow. Increasing stable time-step sizes of the free-surface problem arising in ice-sheet simulations. Journal of Computational Physics: X, 16:100114, 2022. doi: 10.1016/j.jcpx.2022.100114.
F. Pattyn, C. Schoof, L. Perichon, R. C. A. Hindmarsh, E. Bueler, B. de Fleurian, G. Durand, O. Gagliardini, R. Gladstone, D. Goldberg, G. H. Gudmundsson, P. Huybrechts, V. Lee, F. M. Nick, A. J. Payne, D. Pollard, O. Rybak, F. Saito, and A. Vieli. Results of the Marine Ice Sheet Model Intercomparison Project, MISMIP. The Cryosphere, 6(3):573–588, 2012. doi: 10.5194/tc-6-573-2012.
How to cite: Henry, C., Zwinger, T., and Ahlkrona, J.: Numerical stabilisation of grounding line dynamics in Stokes problems, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11161, https://doi.org/10.5194/egusphere-egu25-11161, 2025.
In a warming climate, the potential collapse of the West-Antarctic Ice Sheet is a threat for coastal livelihood as it implies a multimeter sea level rise with unprecedented rate. It is a high-dimensional process, since it involves a number of spatio-temporal variables that interact with each other (e.g. the ocean temperature, the ice thickness and the bedrock elevation). To obtain a better understanding of what initiates a collapse, we propose to apply model reduction techniques to simulations of the Antarctic Ice Sheet under warming scenarios and rely therefore on modern machine learning concepts. Based on this reduced-order representation, we propose an early warning signal that predicts the onset of the marine ice sheet instability in the Thwaites region with a lead time of several decades. This is of key importance to develop meaningful adaptation strategies, which can save lives and critical infrastructure. Most importantly, the early warning signal can be projected back onto the full dimensionality of the problem, thus giving insights into the physics underlying the collapse. This implies that the present work can even serve for developing efficient monitoring systems and mitigation strategies.
How to cite: Swierczek-Jereczek, J., Hill, A., Robinson, A., Alvarez-Solas, J., and Montoya, M.: A reduced-order representation of the West Antarctic Ice Sheet, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10371, https://doi.org/10.5194/egusphere-egu25-10371, 2025.
The loss of Thwaites Glacier is the most important factor in determining the future stability of the West Antarctic Ice Sheet (WAIS), which contains enough ice to raise global mean sea level by up to 3.4 m. All ice that will terminally calve from a glacier can be shows as a flux, that is a velocity through a cross-sectional area. This flux is partly controlled by the distance between the two lateral shear margins that bound an ice stream. For glaciers unconstrained by topography, margin migration can significantly influence ice discharge to the ocean. This is well illustrated in the case of the eastern shear margin (ESM) of Thwaites.
The initiation of basal slip is determined according to a sliding law. Although regularized Coulomb-style sliding laws can resolve slip over both hard and soft bedded glaciers, they depend on knowledge of the effective pressure (ice overburden minus water pressure) of the ice. Most modeling studies that examine Coulomb style slip laws limit themselves to a constant floatation percentage, a constant melt rate based on thickness, or other hard parametrizations, while inverting for friction coefficient values. Instead, I look to find the effect of the variation of basal hydrology with a constant friction coefficient, and quantify the change in slip initiation under differing upstream water flux scenarios.
To examine hydrological shear margin controls, I implemented two models. First, a regional hydrology model which couples the Glacier Drainage system model (GlaDS) with a shallow shelf flow approximation (SSA) forced by an ITS_LIVE annual velocity mosaic. This model yields a high resolution, near-steady state, regional-trending hydrologic system across the Amundsen Sea Sector of West Antarctica which informs boundary conditions for a finer scale model. The second model is local to the Thwaites ESM. It is a hydro-thermomechanical 3D flow model which melt in the basal elements of the domain from enthalpy. In the local model, I couple this melt and hydrology to slip through a regularized Coulomb-style sliding law to calculate the spatial slip distribution over the shear margin.
This work finds good agreement between flow solutions and current velocity observations at the local model scale. Additional upstream water sources divert excess water to the Thwaites catchment rather than to neighboring Pine Island Glacier, and these increased fluxes drive a widening of Thwaites’ main trunk (a margin drift outwards). Future work should expand this local model to regional and WAIS-wide domains to resolve many ice stream dynamics in prognostic ice flow models to more accurately predict sea level rise contributions.
How to cite: Hehlen, M. and Martin, C.: Modeling Thwaites Glacier shear margin stability by slip initiation due to variation of effective pressure, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12934, https://doi.org/10.5194/egusphere-egu25-12934, 2025.
The Pine Island and Thwaites glaciers in the Amundsen Sea Embayment are losing mass faster than any others in Antarctica, and are crucial for the stability of the West Antarctic Ice Sheet. Here we examine their sensitivity to the treatment of basal effective pressure and sub-ice shelf melting over millennial timescales, using the BISICLES ice sheet model. We carry out 1000-year simulations with melting applied selectively to either the Pine Island or Thwaites catchments. To examine the sensitivity to effective pressure, we apply an explicit bed weakening scheme below a critical height-above-flotation which has been used in previous studies. We apply a simple depth power law parameterisation foe sub-ice shelf melt and vary a melt coefficient to test the melt sensitivity.
We find that mass loss rates generally increase with the critical height-above-flotation. The sensitivity is greatest for small values of the critical height-above-flotation. However, we also find that for both Pine Island and Thwaites glaciers, increasing the critical height-above-flotation and the high end of the range actually delays the onset of rapid retreat. We also find that Pine Island glacier is highly sensitive to the sub-shelf melt rate, and projections of future mass loss depend more upon enhanced ocean melting than on the effective pressure. By comparison, Thwaites glacier was relatively insensitive to increases in ocean melting, and the value of the critical height-above-flotation was more important in controlling rates of mass loss compared to Pine Island glacier.
These results are in line with other recent studies, and support the finding that the Pine Island ice shelf provides significant buttressing strength while the Thwaites ice shelf has minimal buttressing strength. They also demonstrate the importance of accounting for effective pressure in ice sheet model-based experiments. We will present and discuss these results.
How to cite: Trevers, M., Cornford, S., and Payne, T.: Millenial-scale sensitivity of Pine Island and Thwaites glaciers to the treatment of effective pressure and melt forcing, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18635, https://doi.org/10.5194/egusphere-egu25-18635, 2025.
Thwaites and Pine Island glaciers, West Antarctica, are some of the most dynamical areas of the Antarctic Ice sheet and both currently are discharging more ice into the ocean than is replenished through surface snow accumulation. While the current imbalance does not represent a large contribution to global sea level rise, as compared to the Greenland Ice Sheet an Alpine Glaciers, both Thwaites and Pine Island glaciers have rightly received considerable attention by the glaciological community. This interest is related to the suggestion that these glaciers either have already, or are likely to become, dynamically unstable. Here we review the history of ice-dynamical studies of those systems and show how, in recent years, a more detailed picture of the contemporary dynamics of those systems has emerged. Our new model-based consensus confirms some previously suggested dynamical behaviour, but also points towards a new understanding of the stability regime of those glaciers. The stability regime of marine-type ice sheet cannot be determined based on local geometry alone. In particular, the slope of the bed with respect to flow direction does not determine the stability of grounding lines. Neither Pine Island nor Thwaites glaciers are currently in a dynamically unstable state. However, Pine Island Glacier did go through a phase of unstable retreat during the 1970s. This unstable phase has now come to a halt. Thwaites glacier similarly appears currently to be responding to some past external forcing, which has yet to be fully identified. However, all studies published do indicate that Thwaites will enter a large-scale unstable and irreversible retreat once, or if, the grounding lines retreats about 75 km upstream of its current location. This recent progress can be described using the well-known IPCC confidence levels, as a shift in the confidence in the potential of near-future collapse of Thwaites from low agreement and low evidence to high agreement and medium evidence. The biggest unknown is now no longer whether Thwaites glacier can in principle become unstable, but when and if this instability will arise.
How to cite: Gudmundsson, G. H., Morlighem, M., Goldberg, D., Rydt, J. D., Getraer, B., Barnes, J., Sun, S., and Rosier, S.: The stability regimes of Thwaites and Pine Island Glaciers, West Antarctica., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11774, https://doi.org/10.5194/egusphere-egu25-11774, 2025.
Time-averaged or snapshot observations of contemporary ice sheet geometry and surface velocity are commonly used in numerical ice-sheet simulations to infer information about ice viscosity and basal sliding. The solution generally depends on the form of the basal sliding law, ice rheology and some form of regularization. On the other hand, close relationships between observed changes in ice sheet geometry and surface velocity are not systematically examined, yet they contain valuable information about the laws that govern ice-sheet dynamics. For example, it can be shown that the functional relationship between perturbations in ice thickness and ice speed depends on the sliding law exponent in a monotonic way. Hence, by harnessing the information contained in successive measurements of ice-sheet geometry and velocity, one can plausibly derive constraints on the form of the sliding law. Here we use a high-resolution numerical setup of the modern-day West Antarctic Ice Sheet to simulate the response of ice speed to contemporary changes in geometry (ice front location and ice thickness between 2000 and 2020). The simulated changes in ice speed are compared to observations over the same period and used in a Bayesian framework to derive constraints on the form of the basal sliding law, ice rheology, and regularization parameters. The a-posteriori distribution of model parameters is used to construct an ensemble of initial states for the whole of the Antarctic Ice Sheet in the year 2000. The ensemble serves as a starting point for hindcast and forecast simulations, with quantified uncertainties for key model parameters.
How to cite: De Rydt, J.: Calibration of an Antarctic Ice Sheet model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1718, https://doi.org/10.5194/egusphere-egu25-1718, 2025.
Rapid global warming has resulted in substantial mass loss from the Antarctic Ice Sheet, contributing to global sea level rise. This study aims to delineate the future evolution of the Lambert Glacier-Amery lce Shelf system, the largest drainage system in East Antarctica, under the contrasting emission scenarios in Phase 6 of the Coupled Model Intercomparison Project (CMlP6), specifically SSP5-8.5 and RCP8.5. Employing the ice flow model Úa coupled with the basal melt model PlCO, we analyzed the dynamics of the Amery lce Shelf from 2000 to 2100. The ice shelf's thickness and velocity changes are predominantly driven by the distribution of basal melting. Despite thinning across most simulations, the grounding line showed minimal retreat, with the most sianificant retreat occurring only about 20 km downstream in the eastern sector. By the end of the 21st century, while a marked oceanic warming is evident, it is the Surface Mass Balance (SMB) that predominantly dictates the system's response.The coupled model based on Úa and PICO successfully revealed the increasing trend of the potential contribution of the Lambert-Amery basin to the sea level rise. It was found that even under strong basal melting conditions (5 m/a), the grounding line finds it difficult to cross the shallow sills, highlighting the key impact of bedrock topography on the stability and dynamics of the ice shelf.
How to cite: Wang, Q., Cheng, X., and Li, T.: Projections of the Lambert Glacier–Amery Ice Shelf system's change, East Antarctica, from 2000 to 2100, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2127, https://doi.org/10.5194/egusphere-egu25-2127, 2025.
Rapid ice sheet sliding requires warm basal temperatures and lubricating basal meltwater. However, ice sheet models often constrain sliding by inverting surface velocity observations with the vertical structure of temperature and rheology held constant. If the inversion is allowed to freely vary sliding, then this approach can lead to inconsistencies between the basal temperature and sliding fields. In this study, we propose a new method to quantify the inconsistency between a modelled ice temperature field and the ice velocity field obtained when that temperature field is used to constrain an inversion. This method can be used to evaluate the quality of a modelled temperature field without requiring any englacial or subglacial measurements. We use the method to evaluate simulation results for Totten Glacier using an isotropic 3D ice sheet model with eight geothermal heat flux (GHF) datasets and compare our results with inferences on basal thermal state from radar specularity. The rankings of GHF datasets based on internal inconsistency aligns closely with those using independent specularity content data. Moreover, the spatial distribution of overcooling inconsistency for all datasets shows insufficient GHF at the western boundary of Totten Glacier between 70°S-73°S, which is characterized by a bedrock canyon with fast basal ice velocity. The overheating inconsistency reveals that poorly performing GHF datasets tend to overestimate GHF in central Totten Glacier. Our approach opens a new avenue for assessing the reliability of ice sheet model results and GHF datasets, which may be widely applicable.
How to cite: Wang, J., Zhao, L., Wolovick, M., and Moore, J. C.: Using temperature-sliding inconsistency to evaluate eight geothermal heat flux maps for Totten Glacier, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2721, https://doi.org/10.5194/egusphere-egu25-2721, 2025.
Totten Glacier in East Antarctica holds a sea level potential of 3.85 m and is mostly grounded below sea level. It has the third highest annual ice discharge, 71.4±2.6 Gt yr-1, among East Antarctic outlet glaciers and has been losing mass over recent decades. Recent thinning of the Totten ice shelf is likely to be due to high basal melt rates driven by increasing intrusion of warm Circumpolar Deep Water. Here we simulate the evolution of the Totten Glacier subregion using a full-Stokes model with different basal sliding parameterizations (linear Weertman, nonlinear Weertman, and regularised Coulomb) as well as sub-shelf melt rates to quantify their effect on the projections. The modelled grounding line retreat and decline in ice volume above floatation using the linear Weertman and the regularised Coulomb sliding parameterizations are close, and both larger than that using the nonlinear Weertman sliding parameterization. The simulated grounding line retreats mainly on the eastern and southern grounding zone of Totten Glacier. The change of sub-shelf cavity thickness is dominated by sub-shelf melt rates, yielding strong volume above floatation dependence on melting through the mechanism of reduced buttressing.
How to cite: Zhao, L., Ma, Y., Gladstone, R., Zwinger, T., Wolovick, M., and Moore, J.: Sensitivity of Totten Glacier dynamics to basal sliding parameterizations and ice shelf basal melt rates, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2782, https://doi.org/10.5194/egusphere-egu25-2782, 2025.
The West Antarctic Ice Sheet (WAIS) is losing ice and its annual contribution to sea level is increasing. The biggest changes are found in the Amundsen Sea sector of WAIS, which contains two of the most rapidly thinning ice streams, Pine Island Glacier (PIG) and Thwaites Glacier (TG). The future behaviour of these glaciers will impact societies worldwide, yet deep uncertainty remains in the expected rate of ice loss. One prominent question is whether the retreat in this region has already passed a tipping point. In ice-sheet projections using the WAVI model, Thwaites Glacier continues to retreat even in an unrealistic scenario of zero oceanic melting, implying that a tipping point has already been passed. Here, we investigate the robustness of this conclusion to the choices made during the ice sheet model initialisation. In particular, we explore the effects of internal ice temperature, ice shelf extent and initial ice damage on forward runs of the WAVI model under the zero-melt scenario (with no evolving damage). We repeat these experiments for initialisations at different time points within the last ~30 years to assess whether the ice damage in this region passed a tipping point within this timeframe.
How to cite: Williams, C. R., Bett, D., Arthern, R., Holland, P., Bradley, A., and Slater, T.: Effect of model initialisation on committed sea level contribution from the Amundsen Sea Sector, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4095, https://doi.org/10.5194/egusphere-egu25-4095, 2025.
When modelling ice flows there are a number of properties of the ice which are poorly constrained by observations, in particular the ice rheology and basal slipperiness at the ice bed. Inversion methods are frequently used to estimate the distribution of these 'hidden' fields in computational ice flow models. These methods use surface measurement data in combination with a forward model of the ice dynamics that relate the hidden fields to the surface fields. In this study we use first-order linear perturbation theory to gain insights into our ability to extract information about the ice viscosity at the same time as basal slipperiness, and understand the theoretical limitations of this approach. We frame the typical inversion problem in terms of a Gaussian maximum a-posteriori estimation with explicitly stated priors for the hidden fields. We illustrate the inversion behaviour with perturbations applied to flow down a laterally confined channel, where both viscosity and slipperiness play a significant role in the ice sheet dynamics. Our results indicate that it is possible to extract information about the viscosity field at the same time as estimating the basal slipperiness, and that explicitly recognising uncertainty in the viscosity field is important.
How to cite: Schelpe, C. and Gudmundsson, G. H.: On the theoretical aspects of joint inversion for basal slipperiness and viscosity in ice-flow models, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8757, https://doi.org/10.5194/egusphere-egu25-8757, 2025.
Many processes that influence the dynamic behaviour of the Antarctic ice sheet, such as basal sliding, ice rheology, and subglacial meltwater production, largely depend on the thermal state and how it evolves. However, significant uncertainties remain regarding the factors influencing basal and englacial temperatures, hindering the predictions of ice sheet models. These uncertainties pertain to geothermal heat flow, past and present surface climatic conditions, and the inherent complexity of ice flow models. In this study, we provide new estimates of englacial and basal thermal conditions and conduct an ensemble of simulations to quantify the impact of these factors on the basal thermal regime and assess their contributions to model uncertainty. We use observational constraints, including deep borehole measurements, englacial temperatures derived from SMOS satellite observations, and the presence of subglacial lakes, to evaluate the ensemble results and determine the most likely simulations. Although we find that geothermal heat flow remains the largest source of uncertainty, recently published heat flow data seem to better fit the observational constraints. Nevertheless, since the englacial temperature field is sensitive to the past climate history, accounting for variations in surface temperatures and accumulation rates over the last glacial-interglacial cycle results in colder temperature profiles and basal thermal conditions, which points to possible overestimation of thermal conditions based on present-day boundary conditions.
How to cite: Raspoet, O. and Pattyn, F.: Assessing uncertainties in modelling the thermal state of the Antarctic Ice Sheet, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9928, https://doi.org/10.5194/egusphere-egu25-9928, 2025.
Ice-sheet modelling studies of the Amundsen Sea Embayment (ASE) in West Antarctica have provided estimates of its future impacts on sea level rise. However, many of these have not considered the impacts of ice front movement due to calving, a key process in the dynamics of marine-terminating glaciers. Sensitivity to calving front retreat is not well understood, so we set out to investigate it in a systematic manner using the recently implemented level set method in the ice-sheet model Úa. Here, we quantify the sensitivity of modelled future mass loss to ice front retreat in the ASE, including Pine Island and Thwaites Glaciers. We find that prescribing constant frontal retreat rates from 0.1 to 1 km/yr progressively increases the contribution to sea level rise when compared to experiments with a fixed ice front. The result with our highest rate of retreat is up to 21.4mm additional sea level contribution by 2100, and 239mm by 2300. We identify specific buttressing thresholds where loss of contact with bedrock features causes changes in the ice dynamics. These are reached at different times depending on the retreat rate, and are the main cause of sensitivity to movement of the ice front. 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 similar. We also find that the additional loss of ice due to a prescribed retreat rate is not heavily dependent on ocean forcing, so can be quantified independently of the ocean-induced melt. Our results demonstrate the importance of accurately representing calving processes in models, showing that they can be as important as ocean forcing and therefore deserve a similar amount of attention in future model development work.
How to cite: Barnes, J., Gudmundsson, H., Goldberg, D., and Sun, S.: Modelling the sensitivity of ice loss to calving front retreat in the Amundsen Sea Embayment, West Antarctica, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10964, https://doi.org/10.5194/egusphere-egu25-10964, 2025.
In the last decades, Pine Island Glacier (PIG) and Thwaites Glacier (TG) are observed to be losing ice with increasing rates, contributing to sea-level rise. To estimate their potential sea-level contribution in the future, it’s essential to understand the mechanisms driving the dynamical changes at present. Various processes have been suggested to influence the dynamics of PIG and TG, including ocean driven sub-ice-shelf melting, iceberg calving, basal sliding and ice fracturing/damage. However, the relative importance of these physical processes for past and future changes of the glaciers remains uncertain. In this study, we use the abundant remote-sensing observations acquired in the recent decades (1996-2023) to quantitatively constrain and perturb an ice-sheet model. By simulating the ice discharge and spatial changes in ice thickness of the glaciers through sensitivity experiments, we quantify the relative impact of the above mentioned processes on the dynamics of PIG and TG.
How to cite: Sun, S.: Contribution of ice-shelf melt, calving and damage to the evolution of Pine Island and Thwaites glaciers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10973, https://doi.org/10.5194/egusphere-egu25-10973, 2025.
Numerical models simulating the evolution of the Antarctic Ice Sheet still contain considerable uncertainty.The dynamic instability of the Antarctic ice sheet is one of the most uncertain factors affecting global mean sea level rise. Among the various factors, ice shelf damage is a major challenge and a key focus in current research on the dynamic changes of the Antarctic ice sheet. In this study, we apply a newly developed three-dimensional thermomechanically coupled higher-order ice flow model PoLaRIS (Polar Land Ice Simulator) to simulate the Antarctic Ice Sheet. First, we conducted initialization simulations of the Antarctic Ice Sheet, which are crucial for future projection studies. We used the Robin inversion algorithm for initialization, constraining and inverting the basal friction coefficient based on the observed surface velocity. The simulation results closely match the observations. Based on the initial conditions we have simulated, we are now focusing on the numerical simulation of pan-Antarctic ice shelf damage. We use different methods to simulate the present state of ice shelf damage, validate the model results with the satellite imagery, and compare these methods to identify the best schemes for damage simulation. In the future, we will continue predicting the evolution of the Antarctic Ice Sheet by incorporating the ice shelf damage process into the ice sheet model, studying its dynamic instability and its impact on global mean sea level rise.
How to cite: Long, Q. and Zhang, T.: A Comparison of Different Ice Shelf Damage Modeling Schemes in Antarctica, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21070, https://doi.org/10.5194/egusphere-egu25-21070, 2025.
Global sea-level rise is significantly influenced by glacier melting and retreat palpable all around the world. Of particular interest are marine- and lake-terminating (MALT) glaciers, which, despite their small number, store a substantial portion of the global glacier ice volume. One key component of the glacier mass budget in MALT glaciers is frontal ablation, which involves mass loss at calving fronts through calving, subaerial melting and sublimation, and subaqueous melting. In order to estimate the impact of frontal ablation on the evolution of MALT glaciers, ice-flow models need to exhibit a calving criterion as well as a tracking algorithm for frontal migration. Most of the regionally or globally applicable glacier evolution models (GEM) either lack explicit tracking of ice fronts or, if at all, rely on simple empiric calving parametrization. Here we equip a regionally applicable GEM with a state-of-the-art calving module with the aim to lift the confidence of projecting MALT glacier evolution under climate changes.
In this calving module, an implicit level-set tracking scheme is implemented. The level set function (LSF) evolves based on the frontal ice velocity, melting and calving rate. While subaerial melting is ignored, the ice velocity is determined from the Instructed Glacier Model (IGM). The model is applied to an idealized synthetic glacier geometry featuring undulating bed topography in a 2-D space is used. These synthetic experiments enabled to test the sanity of the implementation, mass and shape conservations as well as numerical stability. Furthermore, the implementation allows for appropriate ice front advance and retreat.
The second part of calving algorithm involves estimation of the calving rate using Eigen calving. It assumes calving rates to be proportional to along and transversal strain rates. The calving algorithm is integrated with the Instructed Glacier Model and applied to selected glaciers of the Kongsfjorden region, Svalbard. Abundant calibration data is available from remote sensing in form of multi-temporal ice-front positions. This approach provides a robust framework for incorporating calving dynamics into regional glacier evolution models. It addresses key gaps in existing methodologies and enhances the ability to better predict glacier front propagation.
How to cite: Prasad, V., Groos, A., Tabone, I., Hermann, O., Jouvet, G., Jordan, J. R., and Fürst, J. J.: Equipping an ice-flow model with calving and ice-front migration, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19571, https://doi.org/10.5194/egusphere-egu25-19571, 2025.
Traditional numerical solvers for simulating glacier dynamics are computationally demanding, particularly for large-scale and long-period projections. Recent use of neural networks(NNs) based surrogate models, including data-driven and physics-informed convolutional neural networks (CNNs), have shown considerable success in accelerating simulation while maintaining adequate accuracy. However, conventional NN-based surrogate models typically map finite-dimensional Euclidean spaces, making them confined to particular discretization or resolution. As a result, these models often exhibit limited generalization capabilities and require frequent retraining when applied to new geometries or solution scenarios outside their training domain. Neural operators (NOs) offer a promising alternative. Unlike classical NNs, NOs learn the mapping between functions in infinite-dimensional spaces, making predictions more invariant with regard to resolution. They learn the parametric dependence of solutions across entire families of partial differential equations, making them better at generalization. Despite these advantages, limited existing literature uses neural operators for glacier flow simulation.
This study presents different versions of a NO-based surrogate model to predict glacier velocity. These implementations will be evaluated against classical NN-based approaches, focusing on their computational efficiency, accuracy, and generalization across varying resolutions. Additionally, the study will explore key hyperparameters that influence the stability and performance of NO models and perform sensitivity analysis to identify the most effective configurations. The first results are promising and give insight into the performance and potential of NO-based surrogate models for ice-flow simulations.
How to cite: K C, M., Köstler, H., and Fürst, J. J.: Predicting Glacier Dynamics with Neural Operator-Based Surrogate Models., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16232, https://doi.org/10.5194/egusphere-egu25-16232, 2025.
Marine ice sheets are essential components of the climate system, with dynamics strongly influenced by interactions with the atmosphere and the ocean. The grounding line, which separates the grounded region of the ice sheet from the floating region, plays a key role in the evolution of marine ice sheets. While numerous studies have focused on grounding-line migration and its sensitivity to physical processes, the influence of localized bedrock features, known as pinning points, remains less well understood. These pinning points can locally ground the floating ice, thereby altering ice flow by providing additional resistance.
Here, we investigate the impact of pinning points on marine ice-sheet dynamics using numerical simulations. The discontinuity in the momentum balance at the grounding line results in a component of the Jacobian matrix for the linearized problem becoming unbounded near pinning points. This behavior is intrinsic to the system and persists regardless of numerical discretization, even over smooth bedrock geometries and with friction laws that vanish at the grounding line. This suggests adopting a regularized approach that ensures a smooth transition between the grounded and floating regions. Based on numerical experiments in idealized setups, we show that a regularized formulation produces results that are qualitatively different from those of the original, unregularized formulation. Hence, the regularization appears a singular perturbation to the equations. This raises interesting questions about the treatment of grounding lines in marine ice-sheet models. Finally, we discuss potential approaches to mitigate this singular behavior and improve the modeling of marine ice sheets and of their grounding lines.
How to cite: Gregov, T., Pattyn, F., and Arnst, M.: Sensitivity of grounding-line migration to ice-shelf pinning, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11628, https://doi.org/10.5194/egusphere-egu25-11628, 2025.
Glaciers in the European Alps play an important role, e.g. for water storage, water supply and the ecosystem. Here, we model the future evolution of two valley glaciers in the European Alps over the course of the 21st century. The Great Aletsch Glacier is located in the Western Alps (Switzerland), while the Hintereisferner is in the Eastern Alps (Austria). The two different glacier locations allow us to compare glacier development in the Western and Eastern Alps in a changing climate. We use a three-dimensional model that combines the full Stokes ice dynamics and basal friction inversion on a 25m horizontal grid. The coupled energy balance model computes the surface mass balance based on high-resolution regional RCP8.5 and RCP2.6 climate model (RCM) data from the EURO-CORDEX ensemble (a total of 62 different GCM-RCM combinations). In addition, SSP5-8.5 and SSP1-2.6 of the newer CMIP6 generation have been calculated based on the ISIMIP3b ensembles (10 different GCMs in total). All simulations show a dramatic volume loss, with the GAG disappearing in 2100 under the high-emission scenarios (RCP8.5 and SPP5-8.5) and the HEF already disappearing in around 2060. A special feature is that the HEF shows a similar volume loss under SSP5-8.5 and SSP1-2.6. The GAG has the ability to stabilize under SSP1-2.6.
How to cite: Rückamp, M., Gutjahr, K., Möller, M., and Mayer, C.: Future retreat of Great Aletsch Glacier and Hintereisferner – an East-West comparison, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15050, https://doi.org/10.5194/egusphere-egu25-15050, 2025.
Subtemperate sliding is key to ice stream formation. It has been shown that models without any approximations to the Stokes equations are necessary to capture temporal instabilities at an ice-sheet scale. In this project we analyze the temporal stability of subtemperate regions using a Stokes flow-line model of an ice stream thermodynamically coupled to a continuous water sheet at the bed using Elmer/Ice. We use Newtonian rheology with suitably chosen physical parameters. Subtemperate sliding was modeled through a temperature dependent sliding with strong sensitivity to temperature changes which introduces an additional thermo-frictional feedback. We perform transient perturbation experiments with small variations of the sliding coefficient. We explore the cases of strong and weak temperature dependence of sliding and the effects of a Weertman and a regularized Coulomb sliding law in the temperate region.
How to cite: Brass, S., Mantelli, E., and Zwinger, T.: Temporal stability of subtemperate regions in an ice-sheet scale flow-line model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17306, https://doi.org/10.5194/egusphere-egu25-17306, 2025.
Debris-covered glaciers play an important role in alpine hydrology and surface debris substantially alters glacier processes and evolution. Yet the processes governing the transport and distribution of debris remain poorly understood, and thus poorly included in models of glacier evolution. To address this gap, we are developing a numerical model of debris transport within the framework of the Instructed Glacier Model (IGM), leveraging a newly implemented Lagrangian particle tracking module to simulate the movement of debris across the glacier.
This study focuses on the Oberaletsch Glacier in Switzerland, where we explore different seeding strategies for the debris particles, which involve defining how and where debris particles are introduced into the model to simulate their transport and distribution. These strategies aim to reproduce the spatial and temporal evolution of debris coverage, starting from a debris-free glacier geometry at the end of the Little Ice Age. This negligible-debris known geometry allows us to spin up the model without debris for our initial condition. To reach this pseudo-steady-state, we calibrate the mass-balance model with historic measurements at the nearby Grosseraletschgletscher. We then focus on the debris seeding: by adjusting the debris seeding locations and rates to reproduce the historic changes in debris extent, we assess the influence of initial particle placement and quantity on the debris distribution.
Preliminary results highlight the sensitivity of debris coverage to changes in the seeding strategies. Our simulations also reveal that certain characteristics of the glacier-surface debris coverage —the location and extent of medial moraines— are linked to glacier morphology and arise from the interaction between ice flow dynamics and the structure of the glacier bed, which collectively dictate where debris is transported and deposited on the glacier surface, irrespective of debris seeding strategy.
This study highlights the potential of integrating Lagrangian particle tracking into glacier models as a robust tool for advancing our understanding of debris-covered glaciers. This approach also provides new insights into the coupling of glacier dynamics and debris transport processes, and offers a framework to understand and characterize the debris inputs to these systems. It is the first step towards developing fully operational models for predictions of glacier evolution in debris-covered glacier systems under changing climatic conditions.
How to cite: Muñoz-Hermosilla, J. M., Miles, E., McCarthy, M., Hardmeier, F., Melo Velasco, V., Jouvet, G., and Pellicciotti, F.: Towards Reconstructing Debris Supply to Reproduce the Historic Changes in Debris Extent at a Swiss Glacier, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17446, https://doi.org/10.5194/egusphere-egu25-17446, 2025.
The aerial extent of supraglacial debris cover is increasing on mountain glaciers as a result of recent climatic warming. A thicker debris cover tends to shield the glacier surface from melting, with important consequences for glacier dynamics and evolution. However, only a few studies have tried to model the impact of a changing supraglacial debris cover on glacier evolution at a regional scale. For nearly all of the existing models, it is difficult to calibrate the individual unknown model parameters, such as the degree-day factors, temperature and precipitation biases, debris supply rate and englacial debris concentration, because of the strong interdependencies between mass balance, ice-flow and debris cover and thickness evolution. In the case of regional scale modelling of glacier evolution, almost all of these unknown model parameters are tuned with respect to a small set of selected glaciers. As a result, the level of uncertainty in the calculated model outputs varies for those glaciers that are outside the set of glaciers that were used during calibration. On top of that, due to process-based complexities, many of these models have parameterised the evolution of spatial distribution of debris thickness rather than using process-based models. Therefore, we propose using Bayesian inference to calibrate the coupled ice-flow and debris evolution model. Bayesian inference presents a unique way to calibrate the model parameters while taking into account the uncertainty in the observed data. The stochastic calibration of model parameters through Bayesian inference enables a robust uncertainty analysis of the model results. Using Bayesian inference, helps decouple the intertwined complex process that renders model calibration easy.
To demonstrate the above, as a first step, we present a strategy to effectively decouple and separately calibrate the mass-balance and debris cover evolution modules. We first calibrate the unknown parameters of the mass balance model, namely the degree day factor and the temperature and precipitation biases. We use Bayesian inference for calibrating the mass balance model against geodetic mass balance and satellite-derived, maximum annual snowline altitude. Next, we calibrate a debris cover evolution model using the calibrated mass balance model. We first test this approach at the Oberaletsch Glacier in the Swiss Alps. The mass balance model is forced by reanalysis temperature and precipitation, using a degree-day model modified for debris melt effects. Using our strategy, we simulate the 20-year averaged glacier-wide mass balance within 10% uncertainty as compared to existing geodetic mass balance data. In addition, we simulate the evolution of supraglacial debris-cover for every 10 m elevation band within a mean uncertainty of ~11% as compared to satellite-derived debris cover data. In the future, in addition to the mass balance and debris evolution, we also aim to use this strategy to calibrate the ice-flow module. Once calibrated, the coupled model will be used to estimate the future evolution of glaciers located in the Swiss Alps.
How to cite: Gantayat, P., Miles, E., McCarthy, M., Jouberton, A., Melo Velasco, V., and Pellicciotti, F.: A robust strategy to calibrate a coupled ice-flow, mass balance and debris cover evolution model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18027, https://doi.org/10.5194/egusphere-egu25-18027, 2025.
The implementation of ice shelf calving in numerical ice models is a recent development in the field of cryospheric modelling. As roughly half of Antarctica's ice mass loss is due to calving a thorough understanding of the process is required to make accurate predictions of the future Antarctic mass balance. As yet, there has been no comprehensive investigation into the capabilities and robustness of these models for simulating the complicated physical process that is ice shelf calving.
CalvingMIP is an ongoing model intercomparison project that seeks to address this with a series of experiments and tests of increasing complexity, starting from simplified, idealised simulations before expanding to real world predictions. We make a clear distinction between calving algorithms (how a model numerically represents the physical process of ice calving) and calving laws (how much ice should calve at a given time). The recently completed phase one of CalvingMIP focussed on calving laws with the next phase investigating calving laws. Results from phase one are shown from ten different modelling groups across the cryospheric community.
How to cite: Jordan, J. and the The CalvingMIP Team: Results from phase one of CalvingMIP: , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2866, https://doi.org/10.5194/egusphere-egu25-2866, 2025.
Corridors of fast ice flow, ice streams, dominate the mass discharge of contemporary ice sheets. Ice streams are points of vulnerability for ice sheet instabilities, and so to understand past and future ice sheet change we need to understand ice stream behaviour. Computer simulations can replicate the position and magnitude of palaeo and contemporary ice streams with some skill, but for accurate future projections of ice mass change we need confidence that simulated ice streams will evolve and adjust to a retreating ice sheet in a realistic manner. This is much harder to constrain with empirical evidence, and there is still considerable uncertainty regarding ice stream response to changes in wider ice sheet geometry.
To explore the behaviour of simulated ice streams on a fundamental level, we run simulations of a circular ice sheet on a flat bed using the BISICLES numerical ice sheet model. We simulate a series of idealised circular ice sheets of various radii, finding that plausible ice stream spacing and magnitude is simulated even on a flat bed, and that ice stream size and frequency scales with ice volume. We apply the idealised model to the bed of the Last Glacial Maximum Icelandic Ice Sheet, resulting in a simulation with less frequent ice streams, each with a greater size than would be expected based on the idealised case. The realistic topography makes ice stream position broadly insensitive to changes in topographic roughness and geothermal heat flux. These simulations provide increased confidence in the ability of ice sheet models to simulate dynamic ice stream change and could act as a starting point for more realistic simulations of the advance and retreat of the last Icelandic Ice Sheet.
How to cite: Gandy, N., Veness, R., Ely, J., and Storrar, R.: Simulations of Ice Stream Size and Frequency Scaling with Ice Sheet Radius, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6479, https://doi.org/10.5194/egusphere-egu25-6479, 2025.
