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: Tue, 5 May, 14:00–08:35 | Room L3
Ice sheets can undergo self-sustained retreat (or regrowth), with important impacts on sea-level, climate and consequently life on Earth. For instance, the collapse of the ice saddle between the Cordilleran and the Laurentide Ice Sheet during the last deglaciation has been suggested to contribute to the rapid sea-level rise that characterized Meltwater Pulse 1A, which led to significant changes in atmospheric circulation thereafter. Conversely, saddle mergers have been shown to drive self-sustained ice growth, potentially playing a key role in the large-scale inception of the Laurentide and British Isles Ice Sheet. In the present work, we simulate a similar behaviour for the Antarctic Ice Sheet, which additionally presents a larger hysteresis and more bifurcation points than previously simulated. We generalise the idea of saddle merger/collapse under the concept of perimeter feedback, which applies well beyond this specific case and refers to the fact that an ice sheet typically increases its mass balance when decreasing the ratio of perimeter to surface area. This is largely conditioned by the bedrock roughness and the coastline irregularity, and results from the interplay between thermo-mechanics, ice-ocean-atmosphere interactions and geometry. In particular, we show that the perimeter feedback plays a key role in the collapse of the West-Antarctic Ice Sheet simulated under global warming, as well as in abrupt regrowth of the East-Antarctic Subglacial Basins under global cooling. The analysis performed here does not introduce new physics but provides a key tool to better understand a ubiquitous mechanism underlying the instabilities simulated by ice-sheet models.
How to cite: Swierczek-Jereczek, J., Alvarez-Solas, J., Robinson, A., Gutiérrez-González, L., and Montoya, M.: The perimeter feedback: a cornerstone of ice-sheet stability, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3526, https://doi.org/10.5194/egusphere-egu26-3526, 2026.
In the classical marine ice sheet instability, a grounding line of an unbuttressed ice sheet on a retrograde bedslope (that is, upwards sloping in the direction of ice flow) is theoretically unstable. However, these theories assume that the forcing on the ice sheet changes slowly, compared to the timescale on which the ice sheet responds to climate perturbations. In a world where climate forcing is ramping up very quickly, this assumption probably doesn’t hold. This is particularly pertinent in the context of climate overshoots — temporary detours above the 1.5C Paris Agreement target — which look increasingly likely if we are to ultimately limit warming to 1.5C. For how long, and how far, can we overshoot 1.5C, while avoiding passing a tipping point, even if that tipping point is around 1.5C of warming? We probe these questions using a simple model of grounding line dynamics, in conjunction with few, more detailed simulations of the retreat of the Pine Island Glacier over the 20th century following its passing a tipping point. We demonstrate that temporary overshoots above tipping points are possible, provided that climate forcing is ramped down sufficiently quickly. However, the likelihood of extreme ice loss is very sensitive to how high the overshoot goes, demonstrating the need to limit overshoots to prevent significant, long timescale ice loss from the Antarctic Ice Sheet.
How to cite: Bradley, A. and McCormack, F.: What does marine ice sheet (in)stability mean in the context of climate overshoot?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1602, https://doi.org/10.5194/egusphere-egu26-1602, 2026.
Thwaites Glacier, the West Antarctic marine giant at the center of the fastest-retreating sector of the ice sheet, has been a top priority for projections of future sea level rise since observations of its ongoing mass loss were first recognized in the mid-2000’s. The observed retreat at Thwaites Glacier is thought to be strongly influenced by the intrusion of warm circumpolar deep water (CDW) onto the continental shelf, where CDW temperature, thermocline depth, and circulation control the delivery of heat to the ice shelf and drive basal melting. This hypothesized control on retreat has led to a push to improve the source of melt rate data used in forward simulations of Thwaites, ranging from advances in observations of melt to the development of fully coupled ice–ocean models which allow for realistically responsive ocean circulation. After over a decade into the effort to couple ice sheet models and general circulation models, we ask: Is Coupled Ice–Ocean Modeling Needed to Improve Projections of Thwaites Glacier?
We present new experimental results from a coupling of the Ice-sheet and Sea-level System Model (ISSM) and the Massachusetts Institute of Technology general circulation model (MITgcm), examining the evolution of Thwaites over the 21st century. We test the response of ice loss and grounding line retreat to future climate scenarios, thermocline depth, and periodic variability in thermocline depth on inter-annual to decadal timescales, in one of the largest sensitivity testing experiments to date. Our results show that for periods of at least decadal signals, capturing realistic variability in melt rates does not have a significant impact on the current trajectory of Thwaites’ ice loss. While error in melt rates over longer timescales, due to error or uncaptured trends in thermocline depth and resulting heat flux, can impart substantive bias into the projections of mass loss, in our model these accumulate to a relative bias of less than 10% by 2100—an absolute bias on the order of 1 to 2 mm. Significantly, the overall trends of mass loss and patterns of grounding line retreat over this time period are broadly similar in our model to uncoupled schemes. Integrating these results with past work, we argue that coupled modeling, while a powerful tool with utility in other problems, should not be prioritized as an area of research necessary to improve current projections of mass loss from Thwaites Glacier.
How to cite: Getraer, B., Morlighem, M., and Goldberg, D.: Is Coupled Ice–Ocean Modeling Needed to Improve Projections of Thwaites Glacier?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21985, https://doi.org/10.5194/egusphere-egu26-21985, 2026.
Thwaites Glacier is rapidly evolving and could make large sea-level contributions in the coming centuries, making it essential to understand the drivers of the ongoing ice loss. Sediment core analysis suggests that Thwaites Glacier was in a relatively quasi-steady state for millennia before its western pinning point ungrounded in the 1940s. We use the MITgcm-WAVI coupled ocean-ice sheet model to create example quasi-steady pre-1940s configurations for Thwaites Glacier, including a most plausible pre-1940s state, finding that healing the damaged ice shelf is necessary to achieve this. Next, we trigger ice retreat and highlight key processes as the model evolves into the present-day configuration, including ice damage, pinning-point ungrounding driven by ocean melting, and ice piracy between eastern and western Thwaites Glacier. By conducting reversibility experiments during the retreat, we find that multiple quasi-steady ice-sheet states are possible under the same ocean forcing, demonstrating the importance of feedbacks and possible tipping points in the system. Either ice damage or increased ocean forcing can eliminate these quasi-steady states, prompting retreat, as observed today.
How to cite: Bett, D., Bradley, A., Miles, B., Williams, C. R., Holland, P., and Arthern, R.: Modelling the evolution of Thwaites Glacier over the 20th century, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9750, https://doi.org/10.5194/egusphere-egu26-9750, 2026.
The future evolution of Greenland’s remaining ice shelves is generally not considered a major contributor to the ice sheet’s overall mass loss. However, their role in buttressing the present-day ice sheet has not yet been quantified through a systematic analysis. Here we perform a series of experiments with the ice-sheet model Úa. Results from a control simulation with present-day ice shelf extents and atmospheric conditions are contrasted to RCP8.5 climate change scenario with 1) intact ice-shelves, and 2) the catastrophic and irreversible loss of all floating ice. Immediately following ice shelf collapse, ice flux across the grounding line doubles, leading to a sustained more than 4-fold increase in solid ice discharge, with implications for how freshwater flux influences local ocean circulation. By the end of the century, these end-member scenarios demonstrate a response of ~2.5 mm additional sea level rise due to ice shelf loss.
How to cite: Zanker, J. and De Rydt, J.: Assessing the Importance of Greenland's Ice Shelves for Future Sea Level Rise Predictions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5790, https://doi.org/10.5194/egusphere-egu26-5790, 2026.
Uncertainty in the future contribution of the ice sheets to sea level rise associated with different climate forcings has been well studied in the most recent Ice Sheet Model Intercomparison Project for CMIP6 (ISMIP6). Similarly, the uncertainty due to differences in basal sliding laws or calving laws has also been thoroughly investigated. However, the uncertainty due to the bed topography has not yet been rigorously quantified. The majority of the models within the ISMIP6 ensemble use a single bed topography map, BedMachine Greenland, thereby hindering our ability to better understand how uncertainties in the bed topography affect the overall uncertainty in future projections of sea level rise. To address this, we follow the methodology from Castleman et al. (2022) and create an ensemble of 32 bed topography maps with realistic bed roughness by perturbing the BedMachine bed topography using discrete wavelet decomposition techniques. We update the initial bed topography in ice sheet models from Choi et al., (2021), which provide Greenland-wide, high-resolution, data constrained projections that include calving dynamics, and run projections out to 2300. Though we expect northwest and central west Greenland glaciers to contribute more to sea level rise than other glaciers, we find that models initialized with BedMachine bed topographies tend to overestimate mass loss in these regions. We also find that the addition of bed roughness reduces the future contribution of the ice sheet to sea level rise over the 21st century, but to a lesser extent than the deep, wide subglacial basins of Antarctica. Lastly, we also determine that the uncertainty in the future contribution of the Greenland Ice Sheet due to different climate forcings and the uncertainty due to the bed topography are comparable at the end of this century, however the uncertainty due to climate forcings dominates in the long run.
How to cite: Krishna, M., Morlighem, M., Mangini, D., and Choi, Y.: Quantifying the uncertainty in Greenland’s contribution to sea level rise due to the bed topography, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5996, https://doi.org/10.5194/egusphere-egu26-5996, 2026.
Outlet glaciers of the Greenland Ice Sheet typically undergo a seasonal cycle in ice flow, yet the magnitude and timing of peak annual velocities vary substantially among glacier systems, across years, and with distance away from the terminus. At tidewater glaciers, this variability reflects mainly the competing influences of surface meltwater-driven basal lubrication and flexural perturbations associated with calving-front dynamics. Because observations alone cannot readily separate these processes, we develop a physics-based framework that integrates ice-flow simulations with high-resolution surface velocity observations to decompose seasonal ice motion into basal and frontal components.
We apply this approach to 61 tidewater glacier basins in western Greenland and show that seasonal velocity variations are primarily controlled by evolving basal hydrologic conditions. Frontal perturbations nonetheless exert a secondary but persistent influence on seasonal ice flow. Near glacier termini, mixed basal–frontal control occurs 49.6–62.3% of the time, and although the influence of frontal forcing generally diminishes inland, it can extend to elevations of up to 2000 metres above sea level at fast-flowing glaciers such as Sermeq Kujalleq (Jakobshavn Isbræ). Our method further isolates signals that are subdued in raw velocity observations and closer aligned with expected patterns of seasonal basal drainage development. Importantly, results from three independent transient model configurations demonstrate that our conclusions are robust to the choice of sliding law, with consistent identification of the dominant controlling process in 97.1% of cases. We therefore propose that this framework provides a reliable basis for process-level interpretation of seasonal ice-flow variability across Greenland.
How to cite: Oniszk, K., Badgeley, J., Cheng, G., Colgan, W., and Khan, S. A.: Decomposing Seasonal Ice-flow Variability in Western Greenland using Modelling and Observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10708, https://doi.org/10.5194/egusphere-egu26-10708, 2026.
Numerical age models are useful tools for investigating the age of the ice in an ice sheet. They can be used to date ice cores or to interpret isochronal horizons which are observed by radar instruments. Here, we present a new numerical age model for a flow line of an ice sheet. The assumption here is that the geometry of the flow line and the velocity shape functions are steady (i.e. constant in time). A time-varying factor can only be applied to the surface accumulation rates and basal melting rates. Our model uses an innovative logarithmic flux coordinate system (π , θ ), previously published, which is suitable for solving transport equations because it tracks ice trajectories. Using this coordinate system, solving the age equation is simple, fast and accurate, because the trajectories of ice particles pass exactly through the nodes of the grid. Our numerical scheme, called Eulerian-Lagrangian, therefore combines the advantages of Eulerian and Lagrangian schemes. We present an application of this model to the flow line going from Dome C to the Beyond EPICA Little Dome C drill site and show that horizontal flow is a non-negligible factor which should be considered when modelling the age-depth relationship of the Beyond EPICA ice core. The code we developed for age modelling along a flow tube is named age_flow_line-1.0 and is freely available under an open-source license.
How to cite: Parrenin, F., Chung, A., and Martín, C.: age_flow_line-1.0: a fast and accurate numerical age model for a pseudo-steady flow tube of an ice sheet, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7367, https://doi.org/10.5194/egusphere-egu26-7367, 2026.
Fast-flowing ice streams drain most of the inland ice from the Antarctic and Greenland ice sheets (GrIS). The Northeast Greenland Ice Stream (NEGIS), for example, extends for more than 500 km from the central GrIS ice divide to its outlets, with flow velocities up to ten times higher than in the surrounding ice. Despite extensive research, the mechanisms responsible for ice stream formation remain poorly understood. NEGIS, as a representative case of ice streams that are not topographically confined, has recently also been found to lack an area of elevated geothermal heat flux below. However, no model has so far been able to test whether ice stream initiation can solely result from the evolving internal properties of the ice itself, without relying on external forcing, given that slow-moving ice may be frozen to the bed before ice-stream formation.
Ice is strongly anisotropic because it deforms more easily parallel to its crystallographic basal plane than perpendicular to it along the crystal's c-axis. During deformation, this difference leads to a preferred alignment of the crystal lattice orientations. This anisotropy has significant implications for ice flow. We present a three-dimensional full-Stokes model of an analogue to NEGIS. In our modelling, ice first shows convergent flow towards the outlet gate. During flow, c-axis rotations calculated by our model cause the directional alignment of the easy-glide crystallographic basal planes parallel to the vertical shear plane, which make the ice effectively softer. Shear zones usually form in pairs due to the localized shearing, known as shear margins that bound the ice stream that can now flow much faster and extend further inland. Our results show that a fully developed, fast-flowing ice stream can form in only 1000–2000 years solely due to the evolving ice anisotropy. We perform several model runs up to 4000 years to explore the effect of varying boundary conditions, which result in different geometries of an ice-stream system. Ice streams in the system can potentially initiate and evolve by the formation and movement of shear margins in relation to the location of outlet gates within the drainage basin. This work stresses the importance of evolving ice anisotropy on ice-sheet mass balance and sea-level rise during global climate change.
How to cite: Zhang, Y., Bons, P. D., Franke, S., Sachau, T., Yang, H., Király, Á., and Weikusat, I.: Mechanical anisotropy as a driver of shear margin and ice stream formation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4960, https://doi.org/10.5194/egusphere-egu26-4960, 2026.
Ice crystal fabrics can exert significant rheological control on ice sheets and ice shelves, potentially softening or hardening anisotropic ice by several orders of magnitude compared to isotropic ice. We introduce an anisotropic extension of the Shallow Shelf Approximation (SSA), allowing for fabric-induced viscous anisotropy to affect the flow of ice shelves in coupled, transient simulations. We show that the viscous anisotropy of synthetic ice shelves can be parameterized using an isotropic flow enhancement factor, suggesting that existing SSA flow models could, with little effort, approximate the effect of fabric on flow. Next, we propose a new way to directly solve for SSA fabric fields using satellite-derived velocities, assuming velocities are approximately steady and that fabric evolution is dominated by lattice rotation with or without discontinuous dynamic recrystallization. We apply our method to the Ross and Pine Island ice shelves, Antarctica, suggesting that these regions might experience significant fabric-induced hardening and softening depending on the relative strength of lattice rotation and recrystallization. Our results emphasize the icedynamical relevance of needing to better constrain the strength of fabric processes. This calls for more widespread fabric and temperature measurements from the field, since measurements are currently too sparse for model validation.
How to cite: Rathmann, N., A. Lilien, D., H. Richards, D., S. McCormack, F., and Montagnat, M.: Rheological control of crystal fabrics on Antarctic ice shelves, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14739, https://doi.org/10.5194/egusphere-egu26-14739, 2026.
Large-scale continuum ice sheet models solve a set of conservation-of-momentum equations to calculate ice speed given the ice sheet geometry and, often, some a priori unknown parameters. To facilitate the initialisation of projections, many such models allow one to calcuate gradients of model outputs with respect to those unknown input paramters. In some models, this is done with the help of algorithmic differentiation (AD), while in others it is done using hand-derived PDE-level adjoint rules. Increasingly, there is interest in computing higher-order derivatives, for example, to facilitate the use of different optimisation algorithms or perform uncertainty quantification. In this work, we derive and implement a second-order adjoint (SOA) model for the shallow stream equations, implementable in any 2D ice sheet model. We implement this in a finite volume code written in a numerical computation library for Python called JAX. We conduct comparisons between the computation of Hessians using this SOA model and using the AD tools provided by JAX. The SOA model makes the assumption of linear rheology, as many first-order adjoint models do. We find that this causes a rapid departure in the directions of the principal components of the Hessian from those founding using AD. Hence, we consider AD to be the more suitable choice for many applications.
How to cite: Surawy-Stepney, T. and Cornford, S.: Comparing methods of computing second order derivatives in numerical ice sheet models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11418, https://doi.org/10.5194/egusphere-egu26-11418, 2026.
Long-term models for ice-sheets and glaciers are in general modeled as very slow, viscous fluids, which allows for large time steps on the order of years. However, over the past few decades, observations and theoretical studies have shown that ice streams exhibit short-term responses when it comes to external forcing due to ocean tides, which induce for example non-linear velocity variations.
Short-term models typically apply viscous-elastic ice rheologies to capture these effects. However, resolving tidal dynamics requires very small time steps on the order of minutes, making long-term simulations computationally challenging.
To address this, we propose a temporal averaging approach to include short-term tidal effects into efficient, long-term simulations. We present initial results based on a two-component modeling framework. The long-term component models the ice sheet as a viscous fluid governed by the p-Stokes equations with free surfaces. The short-term component describes the elastic response of the ice to tidal forcing, modeled by an elasticity problem driven by variations in hydro-static pressure due to ocean tides. This leads to a variational inequality of Signorini type, reflecting intermittent contact between the ice and the bedrock.
As the tidal cycle causes the ice–bedrock contact zone to evolve in time, the basal boundary condition alternates between frictional contact and floating due to ocean-pressure. By exploiting the periodic nature of the tidal forcing, we derive effective, tidally averaged basal traction coefficients based on the varying grounding line position. These effective coefficients can be incorporated into the basal friction law of the viscous, long-term ice-flow model. The averaged friction coefficients are updated after a time step in the long-term model to take the geometric deformation of the ice sheet into account.
This approach allows for efficient simulations that capture the influence of short-term tidal dynamics on ice-streams effectively, and relies on a clear separation between the short tidal time scale and the long-term viscous dynamics of the ice sheet.
How to cite: Reddig, C. and Richter, T.: Incorporating Tidal Forcing into Long-Term Ice-Sheet Dynamics via Temporal Averaging, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11796, https://doi.org/10.5194/egusphere-egu26-11796, 2026.
Ice-flow modelling continues to be challenging due to the need to balance computational efficiency with physical complexity, a choice that directly affects the accuracy of sea-level projections. Several studies have successfully introduced numerical stabilisation schemes to Stokes models that reduce the stiffness of the system of equations by predicting the ice geometry at the next time step, allowing for larger time-step sizes without loss of accuracy (Durand et al., 2009, Löfgren et al., 2022, Henry et al., 2025). However, the high physical complexity of Stokes models nonetheless renders them infeasible in large-scale simulations, in part due to memory restrictions.
To address this, we introduce the Thickness Stabilisation Scheme (TSS) for the Shallow Shelf Approximation (SSA). This numerical stabilisation scheme is constructed by modifying the momentum equations with terms that predict the ice thickness at the next time step, thereby also reducing the stiffness of the problem. In order to investigate the accuracy and efficiency of TSS, we perform numerical experiments of idealised ice shelves. The results show that the inclusion of the TSS allows for a significantly larger time-step size. The improved efficiency of SSA simulations through the inclusion of the TSS enables the reallocation of computational resources towards increased spatial resolution and greater physical complexity.
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.
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.
A.C.J. Henry, T. Zwinger, and J. Ahlkrona. Grounding-line dynamics in a Stokes ice-flow model: Improved numerical stability allows larger time steps. EGUsphere, 2025.
How to cite: Henry, A. C., Westling Dolling, T., and Ahlkrona, J.: A numerical stabilisation scheme for the Shallow Shelf Approximation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19218, https://doi.org/10.5194/egusphere-egu26-19218, 2026.
How to cite: Ahlkrona, J., Henry, C., and Löfgren, A.: A second-order implicit time-stepping scheme for full-Stokes ice-sheet models, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22583, https://doi.org/10.5194/egusphere-egu26-22583, 2026.
Recently, a very efficient numerical scheme for the shallow ice approximation (SIA) was proposed. It technically even allows for 0.25 year time increments at spatial resolutions of 25 m, which would make it a very interesting tool for simulating alpine glaciers. However, the SIA in its simplest form neglects all horizontal stress components, which leads to severe limitations in alpine valleys, where the ice thickness is typically not sufficiently small compared to the valley width. The question of whether there is a chance to extend the new numerical scheme to more complex flow models remained open.
Here, preliminary tests of an approach that somehow builds a new house from the roof are presented. The idea is not to include the additional terms of existing extensions of the SIA (e.g., second-order terms or a combination with the shallow shelf approximation) in the numerical scheme, but to develop a new approximation to the Stokes equations that already harmonizes well with the new numerical scheme. As a key point, the basic structure of the SIA is kept in the sense that ice flow still follows the steepest decline of the ice surface (hydrostatic approximation). In turn, the diffusivity term of the SIA is no longer parameterized directly by the ice thickness and the slope, but described by an additional differential equation. This differential equation is developed explicitly for taking into account the transverse shear stresses, which contribute much to the deficiencies of the SIA in narrow alpine valleys.
The first results, obtained from 2-D simulations of valley cross sections, are very promising. The additional differential equation can be parameterized in such a way that the error in total ice flux is only a few percent for various valley shapes even down to aspect ratios of 2:1. The across-valley profile of the surface velocity is also reproduced quite well as long as sliding is not too strong. As a main limitation, however, longitudinal stress components cannot be included easily.
How to cite: Hergarten, S.: A novel approximation for the flow of ice in narrow valleys, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3787, https://doi.org/10.5194/egusphere-egu26-3787, 2026.
Marine sectors of ice sheets and marine-terminating glaciers are pivotal to cryospheric mass loss. Despite their limited areal extent, marine regions strongly regulate ice discharge across the grounding line. Moreover, although most glaciers are not marine-terminating, those that are represent a large share of total glacier ice volume and, among glaciers, dominate the potential glacier contribution to future sea-level rise. Accurately representing marine regions in ice-flow models is thus essential.
Here, we present current progress towards extending IGM to account for marine regions. IGM is a model that uses physics-informed machine learning to simulate ice-flow dynamics (Jouvet and Cordonnier, 2023). In IGM, the mapping between glacier configuration (e.g., geometry) and ice velocity can be obtained either with classical numerical approaches or by learning a neural-network surrogate through the optimization of its weights. The model is implemented in Python with a modular design, which facilitates the implementation and modification of individual physical components, and enables the use of high-performance libraries such as TensorFlow for GPU computing. IGM has demonstrated orders-of-magnitude speedups over classical solvers and has enabled continental-scale, long-term simulations of mountain glaciers (e.g., Leger et al., 2025).
However, IGM was not originally developed for marine settings. Extending it to such regions is challenging because (i) the stress balance differs from that of grounded ice, with negligible basal friction, (ii) the resulting dynamics are markedly more nonlocal due to the stronger influence of membrane stresses (the elliptic terms in the stress balance), and (iii) the transition from grounded to floating ice occurs over short spatial scales, on the order of a few hundred meters. We describe the progress made to address these challenges, including a multiscale strategy that locally decouples distinct flow regimes. We will present results on idealized test cases, with particular attention to numerical accuracy and computational efficiency.
How to cite: Gregov, T., Rosier, S., Finley, B., Vieli, A., and Jouvet, G.: Simulating the ice flow of marine ice sheets and outlet glaciers with IGM, a physics-informed deep-learning model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8003, https://doi.org/10.5194/egusphere-egu26-8003, 2026.
Knowledge of glacier ice volumes is crucial for constraining future sea level rise, evaluating freshwater resources, and assessing impacts on societies, from regional to global. Yet, significant uncertainties persist in both regional estimates of total glacier ice volume and in distributed ice thickness for individual glaciers. Here, we present the results from IceBoost v2.0, a machine learning system able to model the ice thickness of individual glaciers, trained on 7 million ice thickness measurements and informed by physical and geometrical predictors. Globally, we find a total glacier volume of (149 ± 38) × 103 km3 and sea level equivalent of 323 ± 91 mm, both well within existing estimates. We examine major glaciated regions and compare the results with other models. Confidence in our solution is highest at higher latitudes, where abundant training data adequately sample the feature space. Over steep and mountainous terrain, small glaciers, and under-represented lower-latitude regions, confidence is lower. IceBoost v2.0 demonstrates strong generalization at ice sheet margins. On the Geikie Plateau, East Greenland, we find nearly twice as much ice compared to BedMachine v3, highlighting the method's potential to refine the bed topography in parts of the ice sheets. The quality of the modeled ice thickness depends on the accuracy of the training data, the digital elevation model, ice velocity fields, and glacier geometries, including nunataks. We present the released dataset of ice thickness and associated uncertainty for all glaciers within the Randolph Glacier Inventory version 6 and 7, totaling half a million maps. This may be useful for modeling glacier dynamics, future evolution and sea-level rise, informing the design of glaciological surveys, field campaigns, as well as guiding policies on freshwater management.
How to cite: Maffezzoli, N., Rignot, E., Barbante, C., Morlighem, M., Petersen, T., and Vascon, S.: Machine-learned global glacier ice volumes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2036, https://doi.org/10.5194/egusphere-egu26-2036, 2026.
Among components of the cryosphere, the Greenland Ice Sheet (GrIS) is currently the largest contributor to global mean sea-level rise, driven by both enhanced surface melt and dynamic ice loss to the ocean. Evidence from the Holocene suggests that the GrIS can undergo substantial deglaciation under climatic conditions only slightly warmer than at present day. However, projections of its future evolution remain highly uncertain, largely due to the heterogeneous response of individual outlet glaciers to ocean forcing, particularly in the relatively understudied and sparsely sampled northern GrIS.
In this project, we investigate the present-day state and future evolution of the northern GrIS, with a specific focus on CH Ostenfeld Glacier. This glacier lost its floating extension completely decades ago, which could be a precursor of the fate of the nearby Ryder and Petermann glacier. We use the Ice-sheet and Sea-level System Model (ISSM) for this purpose. We integrate new ice-penetrating radar observations of the subglacial topography in the grounding zone of Ostenfeld Glacier, collected during the GEOEO 2024 North of Greenland Expedition aboard the ice breaker Oden. Together with existing subglacial topography datasets these data are used to assess the sensitivity of modelled glacier behaviour to variations in subglacial topography. Using the updated subglacial topography dataset, we furthermore investigate the subglacial hydrological network. Modelled freshwater fluxes from this network will be used to investigate the interaction between the marine-terminating ice sheet and fjord circulation, in collaboration with researchers from the Tracing How Atlantic Water Influences Northern Greenland (THAWING) project. This coupling governs the delivery of warm Atlantic Water to the glacier grounding zone and, consequently, the magnitude of frontal melt at CH Ostenfeld Glacier. The freshwater released from the CH Ostenfeld glacier through this frontal melting or from the subglacial hydrological network, will influence the fjord circulation and thereby the availability of Atlantic Water at the front of the glacier.
How to cite: van den Akker, T., Wang, Z., and Kirchner, N.: Modelling of the present-day state and future evolution of CH Ostenfeld glacier, northern Greenland, using new subglacial topography observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7655, https://doi.org/10.5194/egusphere-egu26-7655, 2026.
Geothermal heat plays an important role in basal ice sheet processes, potentially influencing the stability of Antarctica’s interior ice sheets. Modelled geothermal heat flow can yield discrepancies due to methodological choices and limited data. Recent advances in multivariate analysis and empirical methods have resolved many of these inconsistencies, yielding more consistent outputs that now serve as valuable inputs to ice sheet simulations. Nevertheless, substantial uncertainties remain, particularly in regions with sparse observational coverage. A key factor in addressing these challenges is the spatial resolution of heat flow maps, which governs how basal melt is represented in ice sheet dynamics.
We introduce two new geothermal heat flow models designed for glaciated regions: Aq2, developed for continental Antarctica, and Kq2, developed for Greenland. Both models utilise a common framework and employ a multivariate, empirical similarity approach that integrates 18 of the most recent and highest quality observables with the latest reference geothermal heat database, to which we apply weighting and pre-processing to improve representation. Compared to previous empirical models, Aq2 and Kq2 offer reduced uncertainty, greater robustness, and refined spatial resolution. Geothermal heat flow is mapped onto a 0.5 × 0.5 km grid using a forward redistribution approach, which enables higher spatial resolution by leveraging refined observations where available.
The models are openly shared in interoperable formats, complete with uncertainty estimates and reproducible code.
How to cite: Stål, T., McCormack, F. S., Reading, A. M., and Al-Aghbary, M. and the Aq2 Interdisciplinary Research Collaboration: Aq2 and Kq2, refined geothermal heat flow models from multivariate observables for application to ice sheet modelling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6138, https://doi.org/10.5194/egusphere-egu26-6138, 2026.
Geothermal Heat Flow (GHF) is an important and poorly constrained boundary condition on the grounded parts of the Antarctic ice sheet. Almost all existing estimates of Antarctic GHF are based on solid-earth observables such as magnetic anomalies or the seismic structure of the upper mantle. However, many glaciological observations are sensitive to the thermal structure of the ice sheet, such as subglacial lakes identified through both ice-penetrating radar and satellite altimetry, radar reflectivity and specularity, basal freeze-on, borehole temperature measurements, and more. Here, I present the first preliminary results from a project that aims to solve for Antarctic GHF by inverting an ice sheet thermal model to fit glaciological observations. This model is a 3D steady-state enthalpy-conserving advection-diffusion model for ice temperature, coupled to a balance-flux model of subglacial hydrology capable of producing both melt and basal freeze-on, along with a 3D balance ice flow and rheology model constrained by surface gradients and the observed flow direction. Forward model runs forced by a geophysically-informed GHF prior reveal a wealth of detail on the Antarctic thermal structure. In this model, West Antarctica is almost completely warm-based because of the high GHF prior there, while East Antarctica has a mixed thermal state. Fast-flowing ice streams are almost completely warm-based because of the influence of strain heating, suggesting they will have relatively limited sensitivity to GHF. Thick temperate layers (i.e., temperate ice above the basal plane) are rare overall but are present in roughly 25% by area of the fast-flowing ice streams, suggesting that they may play an important role in regulating the resistance to flow in dynamically important regions. To prepare for the inversion, I compile a wide range of glaciological observations, including assembling and leveling radar reflectivity data from many disparate campaigns and sources. I define a multi-part cost function using a variety of glaciological observations, rheological constraints, a geophysical prior, and a regularization term. I then derive a formulation for the adjoint of the 3D model that can be computed using the same solver as the forward model, allowing rapid computation of down-gradient step direction during the inversion. The computed adjoint reveals how information from observational constraints is transported upstream in both ice and water flow to constrain boundary conditions in the catchment above the observations. I test the computed adjoint using finite difference perturbations at a selection of representative regions and find good agreement, giving me confidence that it can be used to guide an inversion. I conclude by running a first test inversion, showing that the computed adjoint can indeed be used to tune GHF to fit observational constraints. The next steps include filling out the remaining observational constraints, especially with additional basal freeze-on data, and L-curve analysis to guide selection of the (currently arbitrary) regularization term.
How to cite: Wolovick, M.: 3D Thermal Modeling of Antarctica in Preparation for Heat Flow Inversion, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9531, https://doi.org/10.5194/egusphere-egu26-9531, 2026.
The importance of calving losses from marine-terminating ice margins in a warming world has highlighted the need for reliable representation of calving in predictive ice-sheet models. However, there is currently no consensus regarding the most appropriate form for calving functions (so-called 'calving laws'), and the calving problem remains open. We advocate an integrated approach, in which observations, theory and high-fidelity modelling are used to develop and calibrate optimal, general calving functions for continuum ice-sheet models. Our work has demonstrated that calving is a stochastic process that gives rise to self-organising behaviour at a range of scales, including calving-size distributions, waiting times, and ice-front fluctuations. Individual calving events occur in response to critical and/or sub-critical crack propagation under tensile, shear or mixed stress regimes. We have used these insights to develop a position-based stochastic calving function, in which calving probabilities are scaled to the state of stress in the ice. When implemented in the full-stress continuum model Elmer/Ice, the calving function exhibits a wide range of realistic self-organising behaviour, and successfully reproduces observed ice-front fluctuations of Jakobshavn Isbrae and Store Glacier without the need for site-specific tuning. A calving algorithm suitable for vertically integrated ice-sheet models is in development.
How to cite: Benn, D., Wheel, I., Åström, J., Luckman, A., Cook, S., Christoffersen, P., Spicer, W., and Nick, F.: Progress in understanding and modelling calving, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4251, https://doi.org/10.5194/egusphere-egu26-4251, 2026.
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. We explore how the calving rate is influenced by changing a range of parameters, and find it is particularly sensitive to the water level inside the cracks.
How to cite: Richards, D., Arthern, R., and Marsh, O.: A viscoelastic phase-field model for calving and fracture in ice , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1931, https://doi.org/10.5194/egusphere-egu26-1931, 2026.
Iceberg calving from tidewater glaciers has contributed more than half of the total mass loss of the Greenland Ice Sheet over the past four decades, and observations have shown that episodes of increased iceberg discharge have coincided with rising air temperatures and/or the occurrence of warmer coastal waters into fjords within which they discharge. Despite significant advances in understanding over the last two decades, major uncertainties still remain in understanding how sensitive iceberg calving rates are to climate-induced exchanges of heat and freshwater around marine terminating ice sheet margins. This is partly because we do not know the long-term, multi-decadal to centuries historical context of the ice-ocean system that links our understanding of contemporary process with longer term glacier response to climate.
In this study, we use the Ice-sheet and Sea-level System Model (ISSM) to simulate the advance and retreat of a fast-flowing tidewater glacier in southwest Greenland, Kangiata Nunata Sermia, over the last 1000 years to indentify the drivers of advance and retreat and evaluate calving-parameter choices against observed long-term ice-margin variability. While models have successfully reproduced observed recent retreat, their parameters are rarely tested against centennial- to millennial-scale records of advance. We explore the parameter space governing calving-front advance, focusing on submarine melt rates and von Mises calving-law stress thresholds for grounded and floating ice and validate model ensembles against a well-constrained millennial-scale record of advance and retreat. Using Latin Hypercube Sampling, we assess two criteria: whether the calving front advances at all, and whether it can reach the reconstructed Little Ice Age (LIA) position.
We find that advance can occur across the full tested range of submarine melt rates, up to 1.5 m d⁻¹. However, successful advance to the LIA position is more tightly constrained by the von Mises stress thresholds. In several simulations, the calving front advances only as far as a widening in the fjord, unless the calving rate is reduced by setting a sufficiently high stress thresholds. Our results highlight a strong interaction between calving physics and fjord geometry in controlling long-term advance. This project contributes to improving confidence in multi-decadal to centennial projections of ice sheet behaviour through validating model performance over similar timescales including prolonged episodes of both glacier advance and retreat.
How to cite: Jones, D., Mair, D., Nias, I., Lea, J., and Morlighem, M.: Modelling the advance and retreat of major Greenlandic tidewater glacier over the last 1000 years reveals high sensitivity to calving front forcing criteria, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3545, https://doi.org/10.5194/egusphere-egu26-3545, 2026.
Marine-terminating glaciers play a significant role he loss of ice mass from Greenland. Iceberg calvings are thought to account for about half of Greenland ice mass loss. These events produce seismic waves (glacial earthquakes) recorded by global seismic networks and contain information such as the iceberg volume and the forces acting during the event. Previous work showed that seismic inversion, coupled to numerical modeling, can be used to decipher the glacial earthquake signal [Sergeant 2019]. However, the lack of consideration for the hydrodynamic forces applied onto the glacier leads to large uncertainties in the iceberg volume estimations. Therefore, based on previous work, a Computational Fluid Dynamics (CFD) model is employed to model the complex fluid/structure interaction between a capsizing iceberg and the ocean. The simulations match results from laboratory experiments with great accuracy (rotation kinematics, effect of calving type, hydrodynamic pressure, etc.) [De Pinho Dias 2025].
In this presentation, we will show how the forces applied onto a simple model of Helheim glacier during an iceberg calving depend on geometrical parameters (iceberg height, aspect ratio, water depth, iceberg drop height). The pressure force exerted onto the glacier front has a significant magnitude of more than 50 % of the iceberg/glacier contact force which acts in the opposite direction.
The forces are then converted into seismic signals and show a very good match with the signal recorded at 8 stations in Greenland.
In addition, we will show the path of particle tracers advected by calving-induced water currents.
Sergeant, A. et al. (2019) ‘Monitoring Greenland ice sheet buoyancy-driven calving discharge using glacial earthquakes’, Annals of Glaciology, 60(79), pp. 75–95. doi:10.1017/aog.2019.7.
De Pinho Dias, N., Leroyer, A., Mangeney, A. and Castelnau, O., 2025. Fluid-structure modeling of iceberg capsize. Ocean Engineering, 336, p.121765. doi:10.1016/j.oceaneng.2025.121765
How to cite: De Pinho Dias, N., Leroyer, A., Burton, J. C., Ngugi, W., Dideriksen, A. K., Ruiz-Castillo, E., Harcourt, W. D., Kerby, J. T., Rysgaard, S., Castelnau, O., and Mangeney, A.: Unravelling the importance of iceberg-calving-induced hydrodynamic forces to monitor Greenland ice mass loss with seismic inversion of glacial earthquakes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6643, https://doi.org/10.5194/egusphere-egu26-6643, 2026.
Surface mass balance (SMB) estimates of glaciers in Svalbard have a relatively high degree of uncertainty despite decades of modeling and observations for the region (van Pelt et al., 2019). This is in part because the surges of marine terminating surging glaciers are complicating estimates of the mass flux towards the ocean (Schuler et al., 2020). Approximately 52% of the glaciers in Svalbard are likely or confirmed surging glaciers (Harcourt et al., 2025), making this complication to estimating the SMB common on Svalbard. The climate in Svalbard changes more rapidly than global averages (Maturilli et al., 2013; Nordli et al., 2014; Isaksen et al., 2016) but it is still unclear to what degree this affects the glaciers in Svalbard as the surge mechanics are still not well understood (Schuler et al., 2020). It does seem that the surges are increasing in frequency over the last years (Farnsworth et al., 2016). Therefore, it is hard to give projections into the future on how glaciers in Svalbard will evolve over the next 50 to a 100 years.
In our study we have looked at Tunabreen, a marine terminating surging glacier that has surge twice in the last 25 years. We use Sentinal-1-based velocity data and digital elevation models (ArticDEMs) to analyze the last surge of Tunabreen. These data show that the surge starts at the terminus and moves up in several distinct phases.
This knowledge is used to fit a calving flowline SSA model to replicate Tunabreen behavior over the last 25 years. The SSA model is based on the model from (Nick et al., 2010) with an adaptable mesh to accommodate a moving terminus as a consequence of calving. Furthermore, the model is adapted from its original form to incorporate the boundary conditions for a grounded marine terminating glacier. The calving law is based on the observed relation between water temperature and terminus retreat (Luckman et al., 2015). To force the model, we used model data of the last 25 years from ERA5-LAND for the air temperature and water temperature.
As such our model is able to replicate the evolution of Tunabreen over the last 25 years to provide insight in the possible surging mechanisms. It shows that a combination from calving, that initiated the surging, as well as subsurface hydrology sustaining the surge, leads to the typical behavior observed at Tunabreen. Using the fitted model, we can estimate how Tunabreen will evolve in the next few decades and what the effect of different climate forecast models or possible pinning points in the bedrock may have on it.
How to cite: Blank, B., Nick, F., Oerlemans, J., and Luckman, A.: Exploration of Tunabreen surge mechanics through a fitted calving SSA model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20608, https://doi.org/10.5194/egusphere-egu26-20608, 2026.
Ice streams are fast-flowing “rivers” of ice within an ice sheet, and are responsible for the majority of mass loss from continental ice sheets. The onset region of these ice streams is especially interesting, as that is where ice transitions from slow interior flow to fast, sliding-dominated ice-stream flow. Subtemperate sliding, i.e., sliding below the melting point, is thought to be important in enabling this transition. Previous theoretical work has shown that the subtemperate region is subject to a host of temporal instabilities. Yet, the role of these instabilities in driving the temporal dynamics of ice streams remains unclear. In this work, we use a thermomechanically-coupled Stokes flow model of an idealised, 2D ice-sheet flowline in Elmer/Ice to investigate how these temporal linear instabilities play out in the full nonlinear evolution of the ice sheet. Using a combination of numerical simulations and theory allows us to investigate the physical mechanisms behind sliding onset, and to gain insight into what controls the observed switching “on and off” of ice streams over time. We also explore details of a thermodynamically consistent numerical implementation in Elmer/Ice of frozen-temperate boundaries at the bed.
How to cite: Woods, T., Mantelli, E., Zwinger, T., and Schoof, C.: Temporal ice-stream dynamics resulting from subtemperate sliding instabilities, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1137, https://doi.org/10.5194/egusphere-egu26-1137, 2026.
Basal sliding is a key component of ice motion that is implemented in ice flow models via the use of a friction law, a relation between the basal shear stress, basal sliding velocity, and the effective pressure. Recent studies have performed two-way coupling between two-dimensional subglacial hydrology models with inefficient and efficient drainage components, and ice flow models via the effective pressure in the friction law. However, to date, there has not been an investigation of the impact of the friction law on two-way coupled ice flow/subglacial hydrology modeling. Here, we examine the effect of the Budd friction law, the Schoof friction law, and two regularized-Coulomb friction laws that we develop, on coupled modeling in the Siple Coast of West Antarctica. We found that when using the Budd friction law, the basal shear stress failed to respond to changes in both ice speed and effective pressure in a fashion that was consistent with the state of the subglacial hydrologic system, and the Schoof friction law did not accurately estimate the state of the subglacial hydrologic system. Consequently, using the Budd and Schoof friction laws led to instabilities in ice motion and flooding of the subglacial hydrologic system due to dynamic thinning of ice. The new friction laws we developed ensured an accurate estimation of the state of the subglacial hydrologic system, and no such instabilities arose in the corresponding simulations.
How to cite: McArthur, K., Dow, C., and Ehrenfeucht, S.: The impact of the friction law on coupled ice flow/subglacial hydrology modeling, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12663, https://doi.org/10.5194/egusphere-egu26-12663, 2026.
Glaciers interact with adjacent proglacial lakes through a range of thermomechanical processes. These interactions occur in addition to climate-driven ablation but are capable of amplifying or modifying climatic effects through various feedback mechanisms. In particular, the connection between lake water-level and the subglacial hydrological system can reduce basal friction, which in turn leads to increased glacier flow and dynamic thinning. This creates a positive feedback loop in which decreased effective pressure, also driven potentially by negative surface mass balance, enhances flow velocity, in line with similar processes observed at marine-terminating glaciers.
Our aim in this study is to develop a simple model that can be used to understand the critical controls on the dynamic behaviour of glaciers as they transition from land- to lake-terminating systems. Here, we investigate the behaviour of Skaftafellsjökull in Iceland, which has undergone such a transition over the past twenty-five years. More specifically, we use the Shallow Shelf Approximation (SSA) in Elmer Ice to model ice dynamics, incorporating a water pressure-dependant friction law to model basal sliding with a simple parameterization of basal water pressure.
The model successfully reproduces the observed velocity patterns, capturing the shift from deceleration near the front in 2010 to pronounced acceleration in 2018–2020, reflecting the growing influence of the proglacial lake. We find a threshold behaviour between basal water pressure and ice velocity, whereby small increases in water pressure beyond a critical value led to strong acceleration, consistent with previous empirical observations. Furthermore, our results imply that surface thinning exerts a stronger control on the near terminus acceleration than the observed terminus retreat. Our results suggest that the modelling framework developed provides a valuable tool for simulating these complex interactions in a computationally efficient manner.
How to cite: Otero, J., Goldberg, D., Nienow, P., and Wang, Y.: Modelling the transition in ice-dynamics from land- to lake-terminating glaciers: a case study in Iceland , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14757, https://doi.org/10.5194/egusphere-egu26-14757, 2026.
Ice dynamics plays a primary role in rapid sea level rise, and our approach to ice dynamic modeling therefore determines our ability to assess future ice mass changes and resulting global implications. Over the last several years, the coupling of subglacial hydrology and ice dynamics models has allowed an enhanced analysis of the impact of basal boundary conditions and drainage networks on ice flux. Here, we discuss the progress to date of hydrology-ice dynamics coupling within the Ice-sheet and Sea-level System Model (ISSM), the impacts from coupling on hydrology and ice dynamic development, and the challenges that remain to better represent the ice-bed system in both catchment and continent-scale simulations. We also examine the role of projected surface melt in Antarctica and how that may affect subglacial hydrology development, basal sliding, and ocean melt under floating ice shelves. We outline the next steps for the field of hydrology-ice dynamics coupling and how this can benefit the wider glaciological community.
How to cite: Dow, C., Ehrenfeucht, S., McArthur, K., Morlighem, M., and McCormack, F.: The current and future state of subglacial hydrology and ice dynamics model coupling., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-15140, https://doi.org/10.5194/egusphere-egu26-15140, 2026.
Numerical models of subglacial drainage have evolved to combine both distributed and channelized drainage in two dimensions, and have enabled many studies of subglacial hydrology and of its link to ice flow in glaciers and ice sheets. However, a key limitation in these models has been the inability to incorporate bounded subglacial water pressures, preventing the representation of the physical regimes of ice uplift and free-surface flow. We present a new subglacial drainage model, which extends the Glacier Drainage System (GlaDS) model to include subglacial water pressures that are bounded between atmospheric and ice overburden values. The new model includes a physics-based representation of pressurized subglacial flow, ice uplift, and free-surface flow and automatically handles the transitions between each regime domain. We demonstrate this model’s capabilities through the simulation of a rapid drainage of a supraglacial lake in Greenland, during which we observe the formation of a traveling subglacial water blister inducing ice uplift, and the partial emptying of the subglacial space at the glacier terminus near the end of the drainage.
How to cite: Wells, S., Utkin, I., and Werder, M.: Modeling subglacial drainage including ice uplift and free-surface flow in 2D, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20081, https://doi.org/10.5194/egusphere-egu26-20081, 2026.
In past decades, substantial advances on understanding ocean–ice-shelf interactions have been made, and a number of parameterisations that provide sub-shelf melting for ice sheet modelling studies have been developed. Through ISMIP6, it was found that the choice of parameter values in melt parameterisations can influence the order of magnitude of melt rate changes in projections. Moreover, it has been shown that constraining those parameters with present-day observations is not sufficient to constrain melt rate changes under future warming. For ISMIP7, we hence propose a “come-as-you-are” approach for the choice of the sub-shelf melt parameterisation, but suggest a protocol for calibrating parameters using ocean model simulations and observations that show large changes in cavity temperatures as additional constraints. This is embedded into an updated and revised protocol for processing CMIP model data for the ISMIP7 Antarctic ice-ocean forcing protocol.
Come to the presentation if you are interested to learn (more) about the protocol, discuss your testing experiences, or provide feedback.
How to cite: Reese, R., Jourdain, N., Asay-Davis, X., Lambert, E., Burgard, C., Nakayama, Y., Hattermann, T., Zhou, Q., Zhou, S., Holland, P., Dutrieux, P., and Nowicki, S.: Discussions on the ISMIP7 Antarctic ice-ocean forcing protocol, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16669, https://doi.org/10.5194/egusphere-egu26-16669, 2026.
How to cite: Rhee, D., Sun, S., and Gudmundsson, H.: Under what conditions will the Wilkes Subglacial Basin exhibit large scale retreat?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12144, https://doi.org/10.5194/egusphere-egu26-12144, 2026.
How to cite: Gudmundsson, G. H., De Rydt, J., Goldberg, D., Morlighem, M., and Getraer, B.: How sensitive is Thwaites glacier to ocean conditions?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13628, https://doi.org/10.5194/egusphere-egu26-13628, 2026.
The stability of the Antarctic Ice Sheet is a key control on global sea-level rise, with ice shelves acting as critical regulators of glacier discharge into the ocean. Understanding the processes governing ice-shelf stability and glacier dynamics is therefore essential for improving projections of future sea-level change. Pine Island Glacier is among the most rapidly changing glaciers on Earth and plays a major role in Antarctic mass loss, currently ranking as the largest single contributor to Antarctic-driven global mean sea-level rise. Between 1992 and 2011, the Pine Island grounding line retreated by approximately 31 km, leading to a substantial increase in ice discharge. This dynamic evolution has been accompanied by weakening of shear margins and increased ice damage, expressed by the proliferation of crevasses and rifts, which reduces the glacier's ability to transmit resistive stresses. In this study, we simulate the evolution of damage in the Pine Island Ice Shelf using the Elmer/Ice finite-element model. We invert for ice viscosity and the related ice damage under the shallow shelf approximation. We investigate the sensitivity of modeled damage to different ice-thickness datasets derived from radar and laser altimetry as well as satellite photogrammetry, all constrained by the same surface velocity observations. We further assess the impact of dataset spatial resolution on the inferred damage fields and compare the results with fracture maps derived using deep learning on satellite imagery. To evaluate temporal changes, we perform a serie of inversions spanning 1992–2022, using time-evolving observations of surface velocity and ice-shelf thickness. Finally, we compare the evolution of ice-shelf damage with changes in the ice-shelf buttressing index to assess the overall influence of damage on the stability of Pine Island Glacier over the past decades. This study was funded as part of the ERC-research project IceDaM.
How to cite: Millan, R., Bacchin, L., Mosbeux, C., Gimenes, L., and Shahateet, K.: Evolution of ice-shelf damage at Pine Island Ice Shelf using Elmer/ice and multiple satellite derived observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12979, https://doi.org/10.5194/egusphere-egu26-12979, 2026.
The accelerating rate of global sea-level rise underscores the growing importance of
understanding how ice sheets respond to climate forcing and how this response is
represented in models. The Antarctic Ice Sheet (AIS) represents one of the largest potential
contributors to future sea-level rise, yet its projected contribution remains highly uncertain,
reflecting limitations in our understanding and representation of key dynamical processes.
Improving confidence in future projections therefore requires a clearer assessment of ice-
sheet model behaviour and of the mechanisms that control ice discharge, particularly in
dynamically active regions. To this end, we analyse ensemble simulations from ISMIP6,
which provide a unique framework to explore the diversity and consistency of ice-sheet
model responses under common climate forcings. Unlike most analyses, which evaluate
model evolution over time, here we focus on the Amundsen Sea sector and compare the
local response of models when a grid point corresponds to the grounding line. This
grounding-line-centred diagnostic allows us to assess how ice flux, thickness, and velocity
vary as the grounding line migrates, and to explore the consistency of these relationships
across models. By focusing on local dynamical behaviour rather than time-integrated
evolution, this approach aims to improve our understanding of how grounding-line
processes control ice discharge in a region that dominates Antarctic mass loss.
How to cite: de Coatpont, M., Mosbeux, C., and Durand, G.: Grounding-Line-Centred Diagnostics of Ice Discharge in the Amundsen Sea Sector, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17396, https://doi.org/10.5194/egusphere-egu26-17396, 2026.
Pine Island (PIG) and Thwaites (TG) glaciers currently dominate Antarctica's sea-level contribution. These glaciers began a synchronous retreat in the mid twentieth century when PIG ungrounded from a submarine ridge and Thwaites from its Western pinning point. The historical ice loss in this sector is ultimately caused by changes in ocean melting. However, it remains unclear the extent to which the ongoing ice loss is driven by anomalously warm present-day ocean conditions, potentially caused by anthropogenic climate change, or is an ongoing response to a natural climate anomaly in the 1940s, to which the ice sheet is still adjusting. Here, we probe these drivers of ice loss by completely removing the ocean forcing. We use three state-of-the-art ice sheet models to simulate the response of PIG and TG in an extreme hypothetical scenario of zero ocean melting, maintained over a policy-relevant timescale (150 years). We find that PIG thickens and re-advances to the prominent sea-bed ridge on which it was grounded prior to the 1940s. In contrast, Thwaites continues to lose ice (at a decreasing rate) over the next 150 years, despite the absence of sub-ice shelf melt. This tells us two things. Firstly, since all the forcing is removed in these experiments, the ice loss from Thwaites must have a substantial component that is an ongoing transient response to historical forcing. Secondly, the historical retreat of Thwaites has led to a present-day state that cannot re-advance under any ocean cooling measures. Thus, Thwaites is now in a dynamically different state to its 1940s configuration. While this does not imply commitment to irreversible future retreat, the historical mass loss from Thwaites is now built-in and cannot be reversed through reductions in ocean forcing alone. This further suggests that some future sea-level contribution is unavoidable on centennial timescales, even under strong policy interventions that result in ocean cooling.
How to cite: Williams, C. R., Trevers, M., Sun, S., Holland, P., Bett, D., Arthern, R., and Bradley, A.: Thwaites Glacier loses ice even without ocean melting , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13396, https://doi.org/10.5194/egusphere-egu26-13396, 2026.
We present a 2.5D pseudo-steady state inverse model applied to the flow line from Dome Fuji (DF) to the EPICA Dronning Maud Land (EDML) ice core drill site. The model is constrained by radar horizons dated from 4-132 ka using the DF ice core chronology. We interpolate and extrapolate the age field using these horizons. The simplicity of our 2.5D numerical integration scheme results in an efficient computation time allowing us to use inverse methods to determine poorly known parameters such as surface accumulation rate, velocity profile and basal conditions.
We find that the amount of basal melting along the DF-EDML flowline generally correlates with higher ice thickness. We also look at the spatial origin of particles now at the EDML drill site, as this is an important consideration for corrections in measurements of the ice core itself. We compare to a Huybrechts et al. 2007 who used a more complex model on the same area. Finally, we look at areas along the flowline where ice >1Ma could potentially be found.
How to cite: Chung, A., Parrenin, F., Eisen, O., and Steinhage, D.: Age field and particle trajectories using a 2.5D inverse model along a flowline from DF to EDML, Antarctica , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9372, https://doi.org/10.5194/egusphere-egu26-9372, 2026.
The sensitivity of ice sheet dynamics to grounding line processes remains a primary source of uncertainty in sea-level rise projections. In current numerical models based on the Stokes equations, the grounding line is treated as a free boundary solved through an explicit dynamic contact formulation. This approach is highly sensitive to mesh resolution, often requiring grid spacing finer than ~200 m to ensure numerical convergence, making Stokes-based grounding line calculations computationally prohibitive for continental-scale simulations.
We present an alternative formulation for modelling the grounding line position based on the mass conservation of ice and sea water. This framework provides a physically consistent description of the ice sheet and ice shelf systems without requiring high mesh resolutions. We compare our results against existing test case suggested by Schoof (2007), show the resolutions necessary for mesh convergence and demonstrate the computational efficiency of the method.
References
1. Schoof, C. (2007). Ice sheet grounding line dynamics: Steady states, stability, and hysteresis. Journal of Geophysical Research: Earth Surface, 112(F3).
How to cite: Utkin, I., Wells, S., Humbel, C., and Werder, M.: A new approach to model the grounding line based on mass conservation principles, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20196, https://doi.org/10.5194/egusphere-egu26-20196, 2026.
Accurate partitioning of present-day Greenland Ice Sheet (GrIS) mass change is essential for closing the sea-level budget and constraining future projections. Vertical bedrock motion from the Greenland GNSS Network (GNET) has recently been used as a virtual instrument for GrIS mass change, but interpretations diverge. At Jakobshavn Isbræ, GNSS uplift has been linked both to dynamic thinning that leads changes in ice discharge by about 0.87 years, implying predictive power for future ice flux, and to seasonal uplift peaks that precede ice-mass loss by 4.5–9 weeks, interpreted as evidence for substantial transient meltwater storage within the ice sheet. Here we reconcile these seemingly contradictory results by jointly analysing GNET observations, mass-balance products, and a numerical ice-sheet model of Greenland’s major outlet glaciers. We show that there is neither a phase shift between bedrock uplift and ice mass-change signals nor any substantial seasonal missing mass. Instead, we find that the two earlier results stem from an incorrect physical interpretation of the GNSS signal. From our analysis, the variability in bedrock uplift is primarily driven by the advance and retreat of the ice front within roughly 10 kilometres of the glacier termini, a zone that is often poorly captured by input–output methods and coarse-resolution mass-balance products. Our results clarify the physical origin and timing of vertical bedrock shifts in Greenland and provide tighter constraints on the contemporary GrIS mass budget.
How to cite: Cheng, G., Barletta, V. R., Berg, D., Morlighem, M., Khan, S. A., and Seroussi, H.: When the Ground and the Glacier Disagree: The Timing Mystery of Bedrock Uplift and Ice Discharge Peaks, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4612, https://doi.org/10.5194/egusphere-egu26-4612, 2026.
The future contribution of the Antarctic Ice Sheet to sea-level rise remains highly uncertain, partly due to limited knowledge of subglacial bedrock topography. Although Bedmap3 represents a major improvement over earlier compilations, substantial uncertainty persists, particularly in deep troughs beneath fast-flowing outlet glaciers.
Here, we assess how uncertainty in Antarctic bedrock topography propagates into ice-sheet projections by systematically perturbing the Bedmap3 bed within its mapped 1σ uncertainty range. Using the Parallel Ice Sheet Model (PISM), we perform transient simulations from 1950 to 3000 under constant present-day climate forcing, applying uniform and spatially correlated bed perturbations consistent with Bedmap3 uncertainty.
Bedrock uncertainty within the Bedmap3 1σ range produces an Antarctic-wide spread of approximately 0.5 m sea-level equivalent by model year 3000, highlighting bed topography as a major source of long-term projection uncertainty.
How to cite: Meijers, D., Spezia, E., Sutter, J., Bodart, J., and van de Wal, R.: Antarctic Bedrock Uncertainty, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20577, https://doi.org/10.5194/egusphere-egu26-20577, 2026.
Recent studies show that critical thresholds, tipping points, likely exist for the Antarctic Ice Sheet, and potentially individual drainage basins within Antarctica. Surpassing these critical thresholds for key glacier drainage basins can have significant impacts on the long-term sea-level contribution of the ice sheet, which may be irreversible. The marine ice sheet instability (MISI) is considered to be one of the key feedback mechanisms capable of triggering tipping dynamics in ice sheets, wherein grounding line retreat past a stable position along the bed can trigger further rapid and extensive retreat due to the internal dynamics of ice flow. Model simulations that exhibit this instability tend to project much higher degrees of sea-level rise than those where MISI is not initiated. As such, it is important to understand what factors determine if MISI takes effect and the timing of its onset. The sliding velocity of a glacier is a fundamental variable in calculating overall ice flow, and how the sliding velocity evolves in time is a critical factor in determining if MISI is triggered or not during model simulations projecting future glacier dynamics. While it is well understood that the sliding velocity is highly dependent upon the basal environment, much remains unknown regarding its specific characteristics including where sediment accumulates and how much is present, how meltwater flows through the basal environment, and how to best represent basal friction felt by the glacier. Uncertainties associated with both the physical processes governing ice sheet responses to climate warming, and the parameter choices associated with those physical processes make the analysis of potential ice sheet tipping points particularly difficult. Here, we aim to better understand the influence that the basal environment has on the tipping behavior of the Antarctic Ice Sheet. We use the Parallel Ice Sheet Model (PISM) to identify critical temperature thresholds that will lead to irreversible ice sheet mass loss and quantify the associated long-term sea-level commitment from Antarctica. Climate forcings will be dictated according to the TIPMIP protocols, following stylized warming scenarios and exploring the ice sheet equilibrium response to constant climates at different global warming levels. We analyze model results for differences in tipping behavior obtained by using various different representations of hydrology in the basal environment and ranging values for associated parameters. Here, we present the initial results of these experiments and discuss the relative importance of subglacial hydrology in determining if and when critical tipping points are exceeded for the Antarctic Ice Sheet.
How to cite: Ehrenfeucht, S., Albrecht, T., Klose, A. K., Dennis, D., and Winkelmann, R.: Basal environment uncertainty and the triggering of Antarctic Ice Sheet tipping points, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18793, https://doi.org/10.5194/egusphere-egu26-18793, 2026.
On the Greenland Ice Sheet, drainage of supraglacial lakes via hydrofracture can transport substantial volumes of meltwater into the subglacial drainage system within hours, generating subglacial “blisters” that transiently accelerate adjacent ice flow. The blisters subsequently dissipate, with their thickness diminishing as water spreads laterally, propagates, and leaks into adjacent components of the subglacial drainage system. Although field observations reveal surface-elevation and velocity anomalies associated with blisters, existing subglacial hydrology models—typically comprised of linked cavities and channels—do not include the physics of elastic ice uplift, and therefore cannot reproduce the observed flood propagation or ice-flow anomalies.
We present a modelling framework that integrates elastic ice uplift with an established subglacial hydrology model of linked cavities and channels to model subglacial blisters and their interactions with the surrounding hydrological network. We further couple this framework to a depth-integrated ice-flow model, and simulate the resulting, transient surface-uplift and velocity anomalies following lake drainages. This unified model provides a new tool for interpreting remote-sensing and in situ observations of drainage events on short timescales, and for assessing how lake-drainage processes influence ice dynamics and the long-term mass balance of the Greenland Ice Sheet.
How to cite: Zhang, H., Stevens, L., Hewitt, I., and Stuart, H.: Modelling Subglacial Blisters and Transient Ice-Flow Anomalies Following Supraglacial Lake Drainage, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3127, https://doi.org/10.5194/egusphere-egu26-3127, 2026.
Geothermal heat flow (GHF) plays a fundamental role in regulating basal thermal conditions of ice sheets, influencing basal sliding, internal deformation, and lithospheric rheology. Despite its importance, GHF in polar regions remains poorly constrained due to the scarcity of borehole measurements and substantial divergence among existing geophysical and glaciological estimates. These discrepancies stem from differences in methodology, data availability, and underlying assumptions, leading many ice sheet models to rely on spatially uniform values, ensemble means, or legacy products that inadequately represent spatial variability. We review all available continent-wide GHF fields, analysing their methodologies and data sources, and provide recommendations on their use. GHF fields generally fall into three categories: (1) outdated due to improved data availability, (2) overly simplified parametrization, and (3) preferred fields. To further assess applicability, we conducted an online expert elicitation survey to identify the most suitable fields for ice sheet modeling, particularly for ISMIP7. For preferred fields, we discuss uncertainty and data dependency to guide their use in different applications.
In Antarctica, all fields agree on the broad division between low heat flow in East and higher heat flow in West Antarctica, though spatial patterns vary. Preferred fields serve as a baseline for local studies, which can incorporate additional datasets like magnetic depth estimates or regional geological constraints. In Greenland, uncertainty is particularly high at NGRIP, where estimation and observations are difficult to reconcile. Local heterogeneity impacts heat flow observations in ways that regional fields cannot yet fully address. Nonetheless, recent estimates suggest low to moderate heat flow under the Greenland ice sheet, indicating that the Iceland hot spot has a limited impact, while subglacial geology plays a dominant role in controlling local variations.
Results from the expert survey indicate broad support for multivariate, data-driven approaches that integrate geological and geophysical constraints, including recent fields by Stål et al. (2021), Lösing & Ebbing (2021), and Colgan et al. (2022). These methods are generally regarded as better equipped to use all existing information, represent spatial heterogeneity, provide uncertainty information, and remain consistent with inferred basal conditions. Importantly, the survey captures, as objectively as possible, the reasons why a given GHF field is a good choice as a representation to be used for ice sheet modelling, and hence, model intercomparisons.
Continued progress in GHF estimation will require both methodological innovation and improved data coverage. Integrating machine learning with physics-based models, fostering cross-disciplinary data integration, and increasing spatial resolution are key priorities. In the context of ISMIP7, we recommend moving beyond outdated or purely interpolated GHF products and adopting modern, data-driven fields that better reflect current understanding.
How to cite: Lösing, M., Colgan, W., Seroussi, H., Stål, T., Zhang, T., McCormack, F., Ebbing, J., Stearns, L., Gravsholt Busck, A., Fahrner, D., Høyer Svendsen, S., and Reading, A.: Geothermal heat flow fields for ISMIP7 – Community recommendations for Antarctica & Greenland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11622, https://doi.org/10.5194/egusphere-egu26-11622, 2026.
A wide range of calving functions is currently available but there is no consensus on the best approach. Current assessments of calving functions are often crudely done by fitting functions to observed terminus positions, neglecting the physical processes that drive changes in calving dynamics. Here, we use 3D simulations of synthetic tidewater glacier domains in Elmer/Ice, to determine whether natural behaviours emerge from the crevasse-depth and von Mises calving functions, and to provide a basis for more robust assessments of the potential capabilities of calving functions. Both functions are derived from the full 3D Cauchy stress tensor and are simple functions that can be exported to ice sheet models. The crevasse-depth calving function is shown to be able to simulate both serac and full thickness calving events and simulates how their relative proportion is altered by changing the ice freeboard or submarine melting. A clear distinction between rate- and position-based calving is shown with the von Mises calving function unable to respond to imposed changes in topography or glacier geometry. Importantly, any feedback between glacier dynamics and the von Mises calving function is through an unphysical velocity feedback loop.
Through these simple experiments we show both steady state and transient behaviour can modelled using a position-based calving function while rate-based functions can only capture an imposed state. It is clear we must look beyond just terminus positions when assessing the suitability of a calving function. Manual tuning can mask unphysical calving behaviour and restrict behaviour to that of the tuned period. Furthermore, we show that a robust calving function does not require site or timeframe specific tuning using the crevasse-depth calving function at Store Glacier (Sermeq Kujalleq) and Jakobshavn Isbrae (Sermeq Kujalleq).
By comparing the two calving functions, it is apparent that full-depth calving is irrefutably position-based. Consequently, future projections must not be made using rate-based calving functions. Using a position function, calving rates vary with time and glacier state, so cannot be assumed to be a constant function of stress.
How to cite: Wheel, I., Benn, D., Crawford, A., and Cook, S.: Evaluating calving functions: emergent dynamics from a position-based calving function and the limits of rate-based calving functions. , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1854, https://doi.org/10.5194/egusphere-egu26-1854, 2026.
In recent years, a number of calving parametrisations have been derived and evaluated in simulations on the scale of individual glaciers. However, these new calving parametrisations have not yet been systematically tested in a continental-scale simulation of an ice sheet. We consider four rate-based calving parametrisations of which two match current observations from calving glaciers in Alaska (Mercenier et al. 2018) and the Antarctic Peninsula (Parsons et al. 2025), while the other two are designed as cliff calving parametrisations (Schlemm & Levermann 2019, Crawford et al. 2021) and give non-zero calving rates only for cliff heights larger than currently observed in calving glaciers.
We evaluate these calving parametrisations in an ice-sheet dynamical simulation of the Antarctic ice sheet using the Parallel Ice Sheet Model (PISM). Starting from an ISMIP6 present-day initial state at 8 km resolution, we apply each parametrisation under SSP5-8.5 forcing.
Already at the beginning of the simulation, when forcing is still similar to present day, parametrisations that match observations from current calving glaciers in Alaska and the Antarctic Peninsula produce spurious terminus retreat at locations where no retreat is observed so far. This is due to high initial cliff heights (>100m) along the coast in the ISMIP6 initial state.
In contrast, cliff calving laws, which include a critical cliff height threshold (below which no calving occurs) and produce smaller calving rates, are more conservative and better suited for continental-scale applications, despite not matching observations from current glaciers. However, even these more conservative laws can produce calving in locations where it's not expected. Better results are achieved, when calving of grounded ice is restricted to the Amundsen, Amery, Ross and Ronne-Filchner basins.
How to cite: Schlemm, T., Klose, A. K., and Albrecht, T.: Systematic comparison of calving rate parametrisations in an ice-sheet dynamical simulation of the Antarctic Ice Sheet, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13787, https://doi.org/10.5194/egusphere-egu26-13787, 2026.
How to cite: Prasad, V., Herrmann, O., K. c, M., R. Groos, A., and J. Fürst, J.: Till calving do us apart: Systematising data assimilation of frontal ice retreat for glacier evolution modelling of marine- and lake-terminating glaciers, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18806, https://doi.org/10.5194/egusphere-egu26-18806, 2026.
Calving of ice shelves and tidewater glaciers plays a critical role in controlling glacier and ice-sheet mass loss, yet its physical representation in numerical models remains challenging due to the strong coupling between continuum deformation, fracture initiation, and discrete separation processes. Direct observations of calving are limited by field accessibility and satellite temporal resolution, highlighting the need for numerical models to investigate calving mass loss and its mechanisms, and to explore future scenarios and sensitivity experiments. In this study, we present the preliminary development of a numerical framework for the analysis of calving-related mechanical processes based on a Particle Discretization Scheme Finite Element Method (PDS-FEM).
PDS-FEM is a numerical approach originally developed for quasi-static and dynamic fracture problems in solid mechanics, including fracture propagation in residual stress fields. The method provides a particle description to the solid continuum with a mathematically consistent finite element formulation. This particle discretization scheme enables precise evaluation of deformation, stress localization, and crack initiation without prescribing explicit crack paths or tuning parameters. In this initial phase, we focus on formulating the governing equations, implementing the numerical scheme, and examining its basic mechanical behavior under simplified conditions relevant to calving.
We investigate simplified three-dimensional configurations to examine the basic mechanical behavior of ice under tensile and bending stresses which are commonly associated with calving processes near ice fronts. Constitutive laws and boundary conditions are intentionally simplified, and therefore the results are qualitative and intended to demonstrate feasibility rather than provide quantitative predictions.
While the present results are preliminary, this work demonstrates the potential of PDS-FEM as a framework for analyzing calving which includes continuum ice dynamics and fracture-related processes. Future work will focus on model validation, applications to more realistic glacier and ice-shelf geometries, and exploring more complex constitutive laws for ice deformation.
How to cite: Hirobe, S., Sato, Y., and Oguni, K.: Towards a particle-based finite element framework for ice calving simulation, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9524, https://doi.org/10.5194/egusphere-egu26-9524, 2026.
Over the past decade, Greenland’s major outlet glaciers have more than doubled their contribution to global sea-level rise. Among these, Jakobshavn Isbræ, located in West Greenland, is the largest outlet glacier by drainage area, accounting for approximately 6.5% of the Greenland Ice Sheet. The pronounced acceleration of Jakobshavn Isbræ around 2000 has been widely attributed to the collapse of a substantial portion of its floating ice tongue and the retreat of its terminus. This collapse is thought to be linked to enhanced basal melting beneath the ice shelf, driven by the intrusion of warm ocean waters, as well as the increased calving activity associated with a reduction in sea ice within the fjord. Estimates of the rate of retreat and mass loss from 1950 to 2000 remain very uncertain due to the sparsity of data throughout that timeframe.
In this study, we develop a new high-resolution model of the region that is constrained by available observations to reconstruct the retreat, acceleration, and thinning of the glacier during this time period. We use Ice-sheet and Sea-level System Model (ISSM) to simulate Jakobshavn Isbræ from 1958 to 2025. Our analysis integrates a comprehensive set of observational data, including ice front positions derived from Landsat imagery, ice velocity variations, and surface elevation changes. The simulations are performed on an unstructured, adaptively refined mesh with a model resolution reaching 100 m within the first few kilometers around the terminus position. The resulting transient simulations document the temporal evolution of glacier mass balance from 1958 to the present. Model performance is evaluated by comparing simulated ice volume changes with independent volume estimates derived from CryoSat-2, Envisat, ICESat, ICESat-2, and NASA’s Operation IceBridge Airborne Topographic Mapper, as well as digital elevation models from 1964 and 1985, providing a robust reconstruction of Jakobshavn's recent history.
How to cite: Felten, S. M., Cheng, G., Khan, S. A., and Morlighem, M.: Reconstructing Jakobshavn Isbræ's evolution from 1958 to 2025 with ISSM constrained by multi-mission observations, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14559, https://doi.org/10.5194/egusphere-egu26-14559, 2026.
Future projections of ice loss from the Greenland ice sheet are subject to large and often poorly quantified uncertainties. These arise both from uncertainties in climate forcing projections and poorly constrained processes in ice sheet models. Ice-sheet model initialisation, in particular, is a major contributor to projection uncertainty. Here, we aim to calibrate a Greenland-wide ice sheet model configuration that replicates the recent trend (1996--2022) in observed changes in ice speed and thickness. First, we generate an ensemble of simulations using the ice-sheet model Úa, each forced with datasets of surface mass balance and ice front positions, and input parameter values sampled from prior probability distributions. This ensemble is then used to train a surrogate model, designed to emulate the temporal- and spatially integrated combined misfit between observed and modelled changes in ice speed and thickness. We then use this emulator for Bayesian inference to determine the posterior model parameter distributions needed to minimise the misfit between observed and modelled quantities of interest and ultimately best replicate the observed trend in Greenland ice sheet mass loss. By calibrating the model in such a way, we can reduce the uncertainties in forward-projections and have confidence in the predictive capabilities of our model.
How to cite: Hill, E., Gudmundsson, G. H., and Wake, L.: Calibrating a Greenland ice sheet model using historical simulations between 1996-2022, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19142, https://doi.org/10.5194/egusphere-egu26-19142, 2026.
Alpine glaciers provide an accessible window into the dynamics of Antarctic ice streams, providing key insights into the processes controlling ice flow. Grenzgletscher, a polythermal glacier in the Swiss Alps, has cold-bedded ice in the accumulation zone and temperate-bedded ice downstream. The location of the transition between these basal regimes remains poorly constrained. We build a full-Stokes ice flow model with Elmer/Ice to reproduce observed surface velocities under varying basal conditions. Three scenarios are tested: (1) a frozen bed (no slip); (2) sliding with spatially variable basal friction; and (3) inclusion of borehole-derived temperature profiles to evaluate the influence of thermal structure on flow. The study provides constraints for geophysical investigations where surface velocities are not matched and informs a borehole campaign planned for next summer targeting the cold-temperate transition. These simulations aim to clarify how basal thermal state and sliding jointly shape glacier dynamics.
How to cite: Gerli, C., Mantelli, E., and Zwinger, T.: Modelling the influence of thermal state and sliding on the dynamics of Grenzgletscher, Swiss Alps, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-878, https://doi.org/10.5194/egusphere-egu26-878, 2026.
The Karkonosze Mountains are one of the few ranges within the Bohemian Massif that preserve evidence of Pleistocene glaciations. They also constitute an area where some of the earliest investigations into mountain glaciation and the processes now referred to as periglacial were undertaken. Despite the relatively good geomorphological understanding of the Karkonosze, the abundance of environmental studies, and the broad availability of digital datasets, a clear synthesis remains lacking, not only regarding the age of the former glaciers, but also their extent and thickness. Changes in the altitudinal zones in which periglacial processes operated during the Pleistocene and Holocene have likewise not been examined. In this study, we re-evaluate the existing literature and available rock- and sediment-dating data. We conduct a detailed analysis of a high-resolution Digital Terrain Model (DTM) using GIS-based methods. The results enable a partial reconstruction of the extent of the Karkonosze glaciers and allow us to determine the spatial range and duration of the periglacial zone. The landforms shaped by these processes are fundamental to the distinctive character of the Polish and Czech national parks in the region, and knowledge of their origin should be communicated effectively to a broader audience.
How to cite: Sadkiewicz, M. and Kasprzak, M.: Modelling glacial and periglacial processes in the Karkonosze Mountains, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1647, https://doi.org/10.5194/egusphere-egu26-1647, 2026.
Svalbard is among the fastest warming regions on Earth, with mean air temperatures rising several times faster than the global average. Approximately 57% of the archipelago remains glacierized, and most of these glaciers are polythermal, containing both cold and temperate ice layers. Understanding their response to ongoing and future climate change requires physically-based thermomechanical modelling capable of capturing the evolution of internal ice temperatures and cold–temperate transitions.
In this study, we apply the Instructed Glacier Model (IGM), an open-source, Python-based glacier model that integrates climate-driven surface mass balance, ice-flow and heat transfer processes. IGM further employs physics-informed machine learning and GPU acceleration to efficiently resolve high-order ice-flow dynamics, enabling large-scale simulations at high spatial resolution.
Svalbard benefits from extensive ground-penetrating radar (GPR) datasets, providing rare observational constraints on the cold–temperate transition surface (CTS). We exploit multi-epoch GPR observations to evaluate the ability of IGM thermodynamics to reproduce the observed CTS evolution. As a first step in a broader PhD project aiming to simulate the evolution of all land-terminating Svalbard glaciers under different greenhouse gas emission scenarios, we focus on Werenskioldbreen, a well-instrumented glacier with repeated GPR surveys (1998, 2008, 2016, 2024) and long-term mass-balance records. This work provides a crucial benchmark for improving thermomechanical modelling of polythermal glaciers and contributes to reducing uncertainties in projections of Svalbard glacier change.
How to cite: Bacchin, L. and Navarro, F.: Modelling the evolution of the hydrothermal structure of polythermal glaciers in Svalbard, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7880, https://doi.org/10.5194/egusphere-egu26-7880, 2026.
The Vernagferner in the Ötztal Alps has a history of several surges since 1599. The occurrence was periodic, with a short active advance and a much longer retreat; the whole cycle lasted, on average, 82 years. The mode of ice flow typically changed, i.e., the surge speed increased by more than one order of magnitude with heavy crevassing. The dimensions of advance and retreat were much larger than those known from other glaciers in the area (Hoinkes 1969).
In general, the understanding of surging glaciers is limited due to the sheer diversity of surge-type glaciers. Consequently, numerous mechanisms have been proposed to explain glacier surging. Here, we follow the approach by Benn et al. (2019), which includes both temperate and polythermal glacier surges, based on a coupled ice-flow and enthalpy description. The theory parameterizes key thermodynamic and hydrological processes, including surface-to-bed drainage and distributed and channelized drainage systems. The lumped-element model is extended to realistic 3D geometries and implemented within the existing enthalpy framework of the Ice-sheet and Sea-level System Model. We illustrate the surging behaviour on a simplified 3D glacier geometry and present preliminary results of the Vernagtferner.
REFERENCES
Hoinkes, H. C. (1969): Surges of the Vernagtferner in the Ötztal Alps since 1599, Canadian Journal of Earth Sciences, Vol. 6, No. 4, p. 853-861
Benn, D. I., Fowler, A. C., Hewitt, I., Sevestre, H. (2019): A general theory of glacier surges, Journal of Glaciology, Vol. 65, No. 253, p. 701-716
How to cite: Rückamp, M. and Mayer, C.: Modelling the surges of Vernagtferner (Ötztal Alps) since 1599, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9268, https://doi.org/10.5194/egusphere-egu26-9268, 2026.
The representation of glacier ice flow dynamics in glacier models in response to climate change, such as basal sliding or rheology, remains a critical challenge, particularly in integrating mechanistic models based on differential equations with the growing availability of observational data. Here, we present ODINN.jl, an open-source, modular framework for hybrid glacier modelling that combines scientific machine learning (SciML) with physical process-based approaches based on partial differential equations (PDEs). The framework is designed to facilitate both forward and inverse simulations of glacier evolution, enabling the assimilation of diverse datasets—such as ice thickness, surface velocities, and climate reanalyses—into a unified modelling ecosystem.
We have recently released ODINN.jl v1.0 after almost 5 years of work, providing a new architecture and stable API structured as an interconnected suite of Julia packages, each addressing specific tasks: Sleipnir.jl for data management, Muninn.jl for surface mass balance, Huginn.jl for ice flow dynamics, and ODINN.jl itself as the SciML interface for differentiation, optimisation, and hybrid modelling. This architecture allows users to easily customise model components, swap physical parametrisations, and integrate data-driven models (e.g., neural networks) to represent sub-grid processes or empirical laws. A key feature of this framework is its capacity to leverage automatic differentiation and adjoint methods to optimise model parameters, initial conditions, and statistical regressors. Parallelization is available for both forward simulations and advanced inverse methods, such as universal differential equations (UDEs), to explore poorly understood processes like basal sliding or calving. An early prototype of the model showed its potential to learn hidden laws in a noisy synthetic dataset, and with this new stable release we are now moving to large-scale applications using regional remote sensing and field observations such as high-resolution ice surface velocities and ice thickness.
ODINN.jl is compatible with the Open Global Glacier Model (OGGM) ecosystem, enabling simulations for virtually any glacier worldwide using preprocessed datasets (e.g., RGI outlines, DEMs, climate reanalyses). This new modelling framework offers a reproducible, open-source solution to bridge the gap between physical understanding and data-driven discovery. Through modularity, scalability, and open-source collaborative approaches, ODINN.jl aims to explore both methodological advancements and large-scale applied modelling in glaciology.
How to cite: Bolibar, J., Sapienza, F., Gossard, A., le Séac'h, M., Gimenes, L., Gajadhar, V., Maussion, F., Lai, C.-Y., Wouters, B., and Pérez, F.: ODINN.jl: A new modular, hybrid, differentiable glacier model , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10260, https://doi.org/10.5194/egusphere-egu26-10260, 2026.
High Mountain Asia (HMA) glaciers are critical for downstream water resources and are an increasing contributor to global sea level rise. Yet, their 21st century evolution remains uncertain because of complex topography, heterogeneous climate forcing, and limited observational constraints. Ongoing glacier mass loss reflects a shift in their buffering capacity, with consequences for the timing and reliability of downstream meltwater supply, as well as for the stability of glacierized landscapes. Quantifying this glacier response requires physically based projections of glacier evolution that adequately capture ice flow and surface processes. Existing regional projections rely on simplified flow-line, shallow-ice flow models approximating ice-dynamic processes. In this study, we simulate the glacier mass change across HMA until the end of 2100 using the Ice-sheet and Sea-level System Model (ISSM). We use a MOno-Layer Higher-Order (MOLHO) ice flow approximation on a non-uniform triangular finite-element mesh at high spatial resolution (30–500 m), locally refined based on present-day observed ice velocities. Basal friction coefficients are inferred through inverse modeling by minimizing the misfit between observed and modeled surface velocities, with independent calibration performed for each HMA subregion using observations from 2022. We use a temperature index method for surface mass balance (SMB) that explicitly accounts for the spatial distribution of supraglacial debris cover. SMB is calibrated using geodetic estimates based on stereo-imagery for the period of 2000 to 2020. We project the glaciers evolution under SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 climate scenarios, using bias corrected climate forcing from five CMIP6 global climate models referenced to ERA5-Land. Our results show that all regions experience mass loss by 2100, but hightlight pronounced spatial heterogeneity in glacier mass change across High Mountain Asia, with strongly varying magnitudes across subregions and climate scenarios. Under the low-emission scenario, projected mass loss remains between 11–40% compared to the glacier mass during 2000, whereas high-emission scenarios lead to substantial ice loss across most regions, ranging between 42–74% in regions such as Nyainqentanglha, Pamir, and eastern Hindu Kush. These results provide improved projections of HMA glacier change and offer valuable insights for assessing future water availability and supporting sustainable water-resource management in High Mountain Asia.
How to cite: Hassan, J., Cheng, G., Seroussi, H., Morlighem, M., and Khan, S. A.: Projected Glacier Mass Change in High Mountain Asia Through 2100 Using the Ice-sheet and Sea-level System Model, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19880, https://doi.org/10.5194/egusphere-egu26-19880, 2026.
