West Antarctic outlet glaciers are in a stage of rapid retreat, modulated by wind-driven exposure to warm Circumpolar Deep Water (CDW). Retreat likely began in the mid-20th century, and is often attributed to increased CDW volume near the ice shelves forced by strengthening westerly winds over the continental shelf break. This westerly wind trend is a feature of some historical climate simulations but is not supported by proxy observations. Here, we present an ensemble of regional ocean simulations and proxy-constrained climate reconstructions, and show that shelf-break westerlies are a poor indicator of ocean conditions near the ice shelves. Instead, cumulative northerly wind anomalies close coastal polynyas, driving anomalous warming and freshening near the ice shelves, increasing ice-shelf melting. The increased meltwater leads to strengthening of the undercurrent that supplies CDW, further enhancing ice-shelf melting. Our results highlight the importance of local northerly winds and associated sea ice changes on ice-shelf melting in West Antarctica. Proxy reconstructions show a significant historical northerly wind trend in this region (an extension of Amundsen Sea Low deepening), providing the atmospheric forcing that can explain the initiation of West Antarctic glacier retreat during the mid-20th century.
How to cite: O'Connor, G., Nakayama, Y., Steig, E., Armour, K., Thompson, L., Hyogo, S., Berdahl, M., and Shimada, T.: Enhanced West Antarctic ice loss triggered by polynya response to meridional winds, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13728, https://doi.org/10.5194/egusphere-egu25-13728, 2025.
While East Antarctica ice shelf cavities are currently filled with cold surface water and experience low basal melting, West Antarctica ice shelf cavities are filled with warm Circumpolar Deep Water (CDW) and experience high basal melting. Recent modeling studies have shown that cavities currently filled with cold water may suddenly transition to warm water conditions under climate change scenarios. However, the dynamical drivers of such regime changes are poorly understood, such that the likelihoods of ocean cavities tipping from cold to warm conditions on sea levels and global ocean circulation are still uncertain.
Recent studies have used conceptual box models to propose a mechanistic explanation for the transition from a low melt rate regime (due to cold, saline surface water filling the cavity) to a high melt rate regime (driven by CDW intrusions) in specific ice shelf cavities [1,2]. Here, we extend an existing conceptual model to study these regime shifts. This new model takes into account polynya convection thanks to a sea surface box at the front of the ice-shelf, but also ice shelf/ocean interactions as in the Potsdam Ice-shelf Cavity model (PICO) [3] to generically study various Antarctic ice shelves. We find that numerous ice shelf ocean cavities are in a bistable regime and check that the results are robust against changes in model parameterizations. The surface box enables a representation of the impact of polynyas on dense water formation, which we demonstrate plays a key role in the bistable dynamics of under-ice-shelf seas. Our results suggest that the melt rate of ice shelves might vary abruptly under weak atmospheric changes.
[1] J. E. Hazel, A. L. Stewart, Bistability of the Filchner-Ronne Ice Shelf Cavity Circulation and Basal Melt. J. Geophys. Res. Ocean. 125, 1-21 (2020).
[2] R. Moorman, A. F. Thompson, E. A. Wilson, Coastal polynyas enable transitions between high and low West Antarctic ice shelf melt rates. Geophysical Research Letters. 50, 16 (2023).
[3] R. Reese, T. Albrecht, M. Mengel, X. Asay-Davis, R. Winkelmann, Antarctic sub-shelf melt rates via PICO. The Cryosphere. 12(6), 1969-1985 (2018).
How to cite: Saddier, L., Herbert, C., Bull, C. Y. S., and Couston, L.-A.: Bistable Dynamics of Ocean Circulation under Antarctic Ice Shelves: Insights from a Low-Dimensional Model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4369, https://doi.org/10.5194/egusphere-egu25-4369, 2025.
Ice shelf ocean cavities are among the least observed regions of the oceans. While we know that eddying motions are ubiquitous in the oceans, there are few observations of such processes in ice shelf cavities. Here, we describe multi-year hydrographic mooring from central Ross Ice Shelf to understand baroclinic eddy properties and their potential effect on cavity circulation and basal ice melting. As the data are limited, some assumptions need to be made to estimate the eddying motion and separate it from the background circulation. Here we resolve the kinematic structures of the selected eddy signals. The analysis suggests the eddies are around 22 km in diameter with a velocity scale of between 0.8 and 1.8 cm/s. The thermohaline structure of the selected baroclinic eddies suggests that baroclinic eddies can entrain High Salinity Shelf Water from the benthic water column to the mid-water column. However, in the instance of the central Ross Ice Shelf cavity region, there are cold-water intrusions in the mid-water column that serve to partially isolate the ice from many of the ocean cavity conditions.
How to cite: Xiahou, Y., Stewart, C., Bowen, M., Brewer, M., Hulbe, C., and Stevens, C.: Eddies observed in the Ross Ice Shelf ocean cavity, and the implications for circulations and melting, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5261, https://doi.org/10.5194/egusphere-egu25-5261, 2025.
Melange and multi-year fast ice is known to be able to suppress calving and dampen long-period ocean swells at the termini of marine-terminating glaciers. Currently, the effectiveness of fast ice at suppressing calving and/or providing direct buttressing to grounded ice remains controversial. Here we show that the interaction between tidewater glaciers and persistent fast ice can support the early stages of ice-shelf formation, as evidenced by localized areas of the northern Antarctic Peninsula that have undergone decadal cooling. We find that during persistent fast ice occupation, calving almost completely ceased, and a floating glacier tongue formed. As the glacier tongue advances it interacts with the fjord walls, increasing the resistive lateral stress on the lower glacier. This is similar to the well-known formation process of Arctic-style ice shelves in Ellesmere Island and Northern Greenland, for example, the recently collapsed Hunt Fjord Ice Shelf.
We have identified several ice shelf or glacier tongue areas in Antarctica that have both highly persistent fast ice and thicker glacier ice advancing into these fast ice protected areas. These regions include the Larsen B embayment (2011-2022), Land Glacier and Nickerson Ice shelf (~1960s-present), Shackleton and West ice shelves, and the Lützow-Holm Bay region (past few decades). For these case study regions, we present preliminary data of ice shelf and upstream glacier velocity change, grounded glacier thickness change, and a synthesis of climate data to confirm a locally cooling climate in these areas. Our analysis will offer essential quantifiable evidence on the extent to which fast ice enhances the stability of upstream glacier ice, and will seek to test several components of the overall ice tongue/ice shelf advance process.
How to cite: Ochwat, N., Scambos, T., and Banwell, A.: Persistent landfast sea ice supports early stages of ice shelf formation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-1810, https://doi.org/10.5194/egusphere-egu25-1810, 2025.
Classical treatments of ice-shelf bending suggest that shelf fronts should bend downwards, due to the distribution of hydrostatic water pressure at the front. However, there are several observed instances in lidar data of upward-bending ice-shelf fronts. While this phenomenon has often been attributed to a buoyant force created by a submerged ice bench, recent work suggests that vertical variations in viscosity within the ice shelf, caused by a temperature gradient, can induce an internal bending moment that causes the shelf front to bend upwards, even in the absence of a bench.
To investigate this novel bending mechanism, we present the first two-dimensional, viscoelastic models of ice-shelf-front bending assuming a standard dependence of ice rheology on temperature and depth. Our results confirm the thin-plate analytic prediction that an ice-shelf front can bend upwards with a sufficiently cold surface temperature and a sufficiently high ratio of activation energy to flow-law exponent. The results also demonstrate that the temporal evolution of the flexural wavelength and the relationship between the edge deflection amplitude and the flexural wavelength are consistent with thin-plate analytic predictions, though modeled uplift starts to gradually outpace analytic predictions over time. These deviations are attributed to two distinct forms of two-dimensional flow effects that we term “bulge” and “flare”.
Model results also demonstrate that the internal moment mechanism produces uplift with a shorter flexural wavelength than the submerged bench mechanism. This difference can be leveraged to discern between causal mechanisms of the upward bending seen in lidar data, which we illustrate with an example from the Ross Ice Shelf front. We also illustrate how comparing model results with data offers a way to constrain the parameters describing ice rheology.
How to cite: Glazer, E. and Buck, W. R.: Impacts of Temperature- and Stress-Dependent Rheology on Ice-Shelf Front Bending, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11769, https://doi.org/10.5194/egusphere-egu25-11769, 2025.
The crevasse-depth approach to calving remains promising but in its classic form struggles to produce calving without including additional stresses, such as from meltwater in surface crevasses, which may not be realistic. Here, we present new analytical results that account for stress concentration under crevassing, following recent work by Buck (2023). Focusing on grounded tidewater glaciers, we further consider non-zero ice tensile strength and the potential influence of basal friction. This results in a revised version of the crevasse-depth law that produces plausible calving regimes without needing to invoke added external stresses. The revised law has an ice thickness threshold of approximately 400 m, below which the ice tensile strength is able to resist full-thickness calving, suggesting that glaciers with thicknesses above or below this threshold should have differing dominant calving style. We discuss strong observational support for this finding, and consider the role of the revised formulation in the search for an overall calving law.
How to cite: Wagner, T. and Slater, D.: Differences in calving styles at tidewater glaciers explained by horizontal stress balance, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12957, https://doi.org/10.5194/egusphere-egu25-12957, 2025.
Predicting calving in glacier models is challenging, as observations of diverse calving styles appear to contradict a universal calving law. Here, we generalize and apply the analytical Horizontal Force Balance (HFB) fracture model from ice shelves to land- and marine-terminating glaciers. We consider different combinations of "crack configurations" including dry or meltwater surface crevasses above saltwater- or meltwater-filled basal crevasses. Our generalized model analytically reveals that, in the absence of meltwater, calving criteria depends on two dimensionless variables: buttressing B and dimensionless water level λ. Using a calving regime diagram, we quantitatively demonstrate that glaciers are generally more prone to calving with reduced buttressing B and lower water level λ. For a specified set of B, λ and crack configuration, an analytical calving law can be derived. For example, the calving law for an ice shelf, land-, or marine-terminating glacier with a dry surface crevasse above a saltwater basal crevasse reduces to a state with no buttressing (B = 0). With climate warming, glaciers are expected to become more vulnerable to calving due to meltwater-driven surface and basal crevassing. Our findings provide a framework to understand diverse calving styles.
How to cite: Coffey, N. and Lai, C.-Y.: Horizontal Force Balance Calving Laws: Ice Shelves, Marine- and Land-Terminating Glaciers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12550, https://doi.org/10.5194/egusphere-egu25-12550, 2025.
The North-East Greenland Ice Stream is the largest ice stream of the Greenland Ice Sheet and drains an area of some 200,000 km2, which equates to ~12% of the ice sheet, and the entire catchment holds sufficient water to impact eustatic sea level (~1.1 m). It appeared relatively resilient to atmospheric warming until the mid-2000s, since when two of the outlets, 79N and Zachariæ Isstrøm, have started to thin and accelerate. Zachariæ Isstrøm experience rapid retreat followed by loss of the ice shelf by 2010. This work focuses on the ~80 km long ice shelf fronting 79N, which has previously been shown to have thinned significantly since 1994. The main structural components of the ice shelf are identified and mapped, at approximately 5 yearly intervals, from Landsat imagery, spanning 1985 to 2024. Retreat of the grounding line is approximated by the migration of supraglacial meltwater ponds which migrate upflow over the timeseries. The location of lateral grounding lines are tracked using their topographic expression (Midgardsormen), along the margins of the ice shelf. Taking the surface elevation of the ice shelf from the Arctic DEM and the bed topography/bathymetry from BedMachine and assuming the floating part of the ice shelf is in hydrostatic equilibrium, a time series of ice shelf reconstructions are generated by tracking the migration of the Midgardsormen towards the fjord margins. Evolution of the grounding lines and the structure of the 79N ice shelf are assessed in relation to air and ocean temperature records across the timeseries.
How to cite: Rea, B., Roberts, D., Bentley, M., Darvill, C., Humbert, A., Jamieson, S., Lane, T., and Smith, J.: Evolution of the 79N ice shelf, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11447, https://doi.org/10.5194/egusphere-egu25-11447, 2025.
Mass loss from marine terminating glaciers in Greenland is often simulated using physically-based models driven by multiple parameters such as atmospheric forcing, submarine melt, fjord topography and iceberg calving, each of which carry their own uncertainties. While these models may perform well, they are time intensive to set up, calibrate and validate, and the development of simpler though potentially informative observationally-based models has received less attention.
In this study, we develop a simple observationally derived approach to hindcast and project the future behaviour of Narsap Sermia, a marine-terminating glacier in Nuuk Fjord, south-west Greenland. This glacier has experienced significant retreat (~3.5km) between 2014 and 2024 and is approaching a significant overdeepening located ~7.5km from its current terminus position. Once it reaches this overdeepening, it has the potential to rapidly destabilise, with the next likely stable topographic configuration located ~21km further up-glacier. This will have implications for the safety of local and tourist activities and the operation of Greenland’s largest port at nearby Nuuk.
To achieve this, we have constrained terminus behaviour under different fjord conditions through analysis of terminus positions from satellite imagery. The link between terminus migration and fjord conditions has been compared with varying potential drivers (e.g. runoff, fjord surface temperature and air temperature), and is found to be most closely linked to the presence or absence of a proglacial ice mélange which in turn is linked to cumulative positive and negative degree days. Using calculated degree day thresholds, the model estimates dates of mélange formation and break-up, driving changes in the pattern of terminus migration by switching between observationally derived values of terminus change for rigid mélange and open water conditions. The model reproduces terminus migration at Narsap Sermia over the 2014-2024 period, achieving a mean absolute deviation of 243m for the entire period of observed retreat. Assuming current calving behaviour continues, we are able to project future mélange behaviour and terminus migration using bias corrected CMIP6 2m air temperature data for three climate scenarios. We use this approach to explore a range of scenarios projecting when Narsap Sermia will reach the overdeepening.
How to cite: White, G., Lea, J., and Brough, S.: Projecting the retreat of Narsap Sermia using a minimum observational inputs approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18682, https://doi.org/10.5194/egusphere-egu25-18682, 2025.
A reduction in sea ice extent and increasing temperatures have been linked to enhancement and shallowing of warm Atlantic Water (AW) advection into Isfjorden, a fjord on the west coast of Svalbard (Skogseth et al., 2020). With warming AW (Walczowski et al., 2017), there is an increased interest in how this affects the stability of marine-terminating glaciers (MTGs) (Skogseth et al., 2020), as an increase in water temperatures could lead to enhancing melt rates and therefore a destabilisation of MTGs (Luckman et al., 2015). Usually, sills protect the MTGs by blocking the pathway of AW into the fjord, however, with a shallowing of AW it can enter the fjord more easily. A better understanding of the circulation in fjords with MTGs is crucial in quantifying the effect of enhancement and shallowing of AW on MTGs.
In June 2023, data were collected aboard the RV Hanna Resvoll to measure temperature, salinity, turbulent kinetic energy dissipation, and velocities across the glacier front. High-resolution data were obtained using a Microstructure Profiler and a vessel-mounted Acoustic Doppler Current Profiler (ADCP). Two moorings were deployed to capture flow across the fjord sill.
A general-purpose hydrodynamic model (MITgcm) is used to investigate sensitivity of glacial melt to varying combinations of the inflowing water temperature, the depth of maximum temperature, tidal flows and sub-glacial discharge rate. The model was configured using realistic bathymetry from multibeam surveys on a 50m x 50m horizontal grid with 2m resolution in the vertical. Realistic tides were forced at the seaward boundary, the "iceplume" package (Cowton et al., 2015) was used to simulate glacial melt and sub-glacial discharge at the glacial terminus. The model is initialised and validated with the independent observational data set as described above. Additionally, simulations explore the combined impact of a deepening and warming AW layer, along with increased subglacial discharge plume.
These results provide critical insights into the future stability of MTGs in a warming climate and offer a more comprehensive understanding of how shifts in fjord circulation could enhance melt rates and further destabilize glacier fronts.
How to cite: Riehn, L., Skogseth, R., Frank, N., and Inall, M.: Impact of Atlantic Water and Subglacial Discharge on Marine-Terminating Glaciers: Insights from Field Observations and Numerical Modeling in Tempelfjorden, Svalbard, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18299, https://doi.org/10.5194/egusphere-egu25-18299, 2025.
Land-terminating glacier surges begin at the upstream region, followed by the flow acceleration propagating downward. However, marine-terminating glacier surges in Svalbard may be triggered by frontal thinning and retreat, indicating different driving factors of surge initiation from land-terminating glaciers. Here, we present detailed observations of glacier surface elevations for two marine-terminating glaciers, Wahlenbergbreen and Negribreen, and characterize the evolution from frontal thinning to glacier-wide surges. Wahlenbergbreen and Negribreen entered an active surge phase in 2016 and 2017, respectively, with a surface elevation drop of ~60 m at their thinning centers. Interestingly, our analysis using the ArcticDEM strip data reveals that the intensive frontal thinning took place three years before the active surge phase. The centers of frontal thinning then gradually shifted upstream at a rate of 2-3 km/yr during the following three years until the glacier-wide surges occurred. Based on these observations, we propose a physical framework for surge initiation due to ocean-induced thinning. This thinning signal can kinematically propagate inland, increase the surface slope and driving stress until a certain threshold is achieved, and finally accelerate the entire glacier with an inefficient subglacial drainage system. This proposed mechanism can contribute to surge initiation with other driving factors, such as excessive meltwater supply to the bed. A region-wide survey for this surge precursor (inland thinning propagation at the glacier front) is now being planned to answer whether all marine-terminating glacier surges in Svalbard have a terminus origin and whether these surge events are fundamentally different from land-terminating glacier surges driven by thickened upstream bulges.
How to cite: Zheng, W.: Upward thinning propagation as a surge precursor of marine-terminating glaciers in Svalbard, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14750, https://doi.org/10.5194/egusphere-egu25-14750, 2025.
During the GEOEO North of Greenland expedition with Swedish Icebreaker Oden in the summer of 2024, radio-echo sounding (RES) campaigns were undertaken at CH Ostenfeld, Ryder and Petermann glaciers. The CH Ostenfeld RES survey focused on the ice trunk upstream of the current calving front, which has been the glacier’s terminus since the collapse of CH Ostenfeld’s floating tongue in 2002/2003. At Ryder and Petermann glaciers, less extensive RES surveys were focused on the grounding zones areas, covering both the grounded ice and the floating ice tongues. Ryder Glacier’s grounding line has recently retreated across the fjord unevenly, with observed retreat of c. 8 km in the north-eastern part and less than 2 km in the south-western section (Millan et al., 2023). Millan et al. (2023) also report cumulative mass loss at Ryder Glacier during 2000-2021 as c. 55 Gt, dominated by basal melt (c. 46 Gt) likely driven by the presence of warm Atlantic water, followed by surface melt, runoff and calving (Box et al., 2022; Slater and Straneo, 2022).
Here, we present an overview of the data acquisition campaign at Ryder Glacier, as well as radargrams from the survey lines. The radargrams show evidence of a sub-ice shelf structure interpreted to represent a sub-ice shelf melt channel. Evidence for it is visible in the radargrams at four instances (across various survey lines) along a 22 km quasi-flowline of Ryder Glacier’s tongue. Between the farthest upstream and farthest downstream location, the channel width increases from c. 500 m to c. 2 km, while channel depth ranges between c. 100 and 400 m. At the farthest downstream location, the sub-ice shelf melt channel seems moreover to be co-located with a supraglacial melt channel clearly identifiable from satellite imagery. The suspected sub-ice shelf melt channel is also coincident with the region of largest grounding line retreat. At present, the most recent mapped grounding line of Ryder Glacier is from 2020, but work is ongoing to retrieve the 2024 grounding line to enable evaluation of the significance of the new RES observations. Better understanding of the spatio-temporality of basal melt and its implications for grounding line retreat and ice dynamics is important for assessing the future behaviour of Ryder Glacier.
References:
Box, J. E., Hubbard, A., Bahr, D. B., Colgan, W. T., Fettweis, X., Mankoff, K. D., Wehrlé, A., Noël, B., van den Broeke, M. R., Wouters, B., Bjørk, A. A., and Fausto, R. S. 2022. Greenland ice sheet climate disequilibrium and committed sea-level rise, Nature Climate Change, 12, doi.org/10.1038/s41558-022-01441-2;
Millan, R., Jager, E., Mouginot, J. et al. 2023. Rapid disintegration and weakening of ice shelves in North Greenland. Nat Commun 14, 6914. doi.org/10.1038/s41467-023-42198-2
Slater, D. A. and Straneo, F. 2022. Submarine melting of glaciers in Greenland amplified by atmospheric warming, Nature Geoscience, 15, doi.org/10.1038/s41561-022-01035-9
How to cite: Kirchner, N., Wang, Z., Jakobsson, M., and Ross, N.: Recent rapid grounding line retreat at Ryder Glacier focused around a sub-ice shelf melt channel: first indications from airborne radio-echo sounding, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16192, https://doi.org/10.5194/egusphere-egu25-16192, 2025.
Mass loss from the Greenland Ice Sheet is a major contributor to sea level rise, driven primarily by increased surface melting and dynamic mass loss. Tidewater glaciers, which extend from the ice sheet to terminate in fjords, drive dynamic mass loss through frontal ablation at their termini by calving and oceanic melt. Calving rates and style vary substantially over time and between individual glaciers, making general parameterizations difficult. Capturing spatially and temporally high-resolution observations of calving is particularly challenging due to the harsh and remote environment. This limits our understanding of this critical process and reduces our ability to accurately predict the future evolution of the Greenland Ice Sheet.
Here, we present a unique in-situ dataset comprising terrestrial radar interferometry (TRI) acquisitions, time-lapse imagery, seismic measurements, infrasound recordings, wave height data, fiber-optic cable measurements and manual observations. While each technique has its own temporal or spatial limitations, their integration offers a comprehensive perspective on the calving process at the tidewater glacier Eqalorutsit Kangilliit Sermiat (EKaS) in South Greenland. The simultaneous recording, co-detection and subsequent synthesis of these diverse multi-week to annual datasets overcome current observational constraints, providing crucial insights into calving dynamics. These novel observations are critical for understanding and predicting the role of calving in the mass loss of the Greenland Ice Sheet.
How to cite: Kneib-Walter, A., Dachauer, A., Gräff, D., Salamin, A., Rosier, S. H. R., Marchetti, E., Welty, E., Liposky, B., Walter, F., and Vieli, A.: Disentangling temporal and spatial calving dynamics using a multisensor approach, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15857, https://doi.org/10.5194/egusphere-egu25-15857, 2025.
Ice mélange, a mixture of icebergs and sea ice located in front of tidewater glaciers usually terminating in relatively narrow fjords, is believed to impact the calving dynamics of said glaciers through buttressing force and to alter the fjord circulation through freshwater fluxes. Still, given its potential impact on sea level rise, research concerned with the influence of the mélange is scarce. This study seeks to clarify its’ effect on calving dynamics based on remote sensing data for the two fast flowing Greenland outlets Helheim Gletsjer (East Greenland) and Nunatakassaap Sermia (Alison Glacier, West Greenland).
To achieve this Sentinel-1 radar and Sentinel-2 optical images are combined to retrieve an intra-seasonal timeseries of ice mélange dynamics before the relationship between a shrinking/growing ice mélange and calving dynamics is analyzed. To further aid the interpretation of ice mélange composition, the radar images with mélange matrix are studied based on their statistical variations in pixel intensity. The detection of calving events’ and upper bounds for their respective size is based on the dataset of outlet glacier terminus position traces AutoTerm (Zhang et al., 2023) as well as near-terminus velocity mosaics from the ITS_LIVE dataset (Gardner et al., 2018). Finally, to investigate the impact of the mélange and of related driving mechanisms on calving dynamics for Helheim Gletsjer and Nunatakassaap Sermia, the resulting timeseries of mélange dynamics and calving event characterization are combined with datasets of sea surface temperature, surface temperature, glacier ice velocity, etc.
How to cite: Socher, T., Bjørk, A., Andersen, J., and Solgaard, A.: The impact of ice mélange dynamics on the calving of two major Greenland tidewater glaciers, Helheim and Nunatakassaap Sermia, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15533, https://doi.org/10.5194/egusphere-egu25-15533, 2025.
Uncertainty in the rate and extent of ice lost from Antarctica and Greenland is the largest source of uncertainty in predicting global sea-level rise, largely due to a poor understanding of the mechanisms governing iceberg calving. Ice-shelf fracture models are typically estimated using a linear elastic model for ice. However, ice exhibits both elastic and viscous behavior in response to a load. This is evidenced by the observation that fractures within glaciers reduce their ability to support a load, resulting in accelerated ice flow downstream.
To examine the coupling between the flow response of ice and crevasse growth, we use a phase-field description of ice fracture to compare crevasse propagation rates. We examine fracture rates amongst a linearly elastic, Maxwell, and Kelvin-Voigt model of ice during deformation. We impose Robin boundary conditions for a fixed ice-shelf with constant rates of strain downstream and further compare two domains, in which the ice-shelf is either being longitudinally stretched from upstream flow or vertically bent due to tidal forcing. From these numerical experiments, we find that both a Maxwell and Kelvin-Voigt model for ice reduce the rate of crevasse propagation as compared to a linearly elastic model. This implies that crystal plastic processes relax stress around crevasses and therefore controls the rate of crack growth in ice-shelves. The results of crevasse evolution, as governed by elastic and viscoelastic end-member cases, indicate that the viscous response of ice plays a significant role in crack propagation—highlighting the importance of incorporating descriptions of crystal plasticity in predictions of crevasse development.
How to cite: Houdyshell, K., Hansen, L., and Ranganathan, M.: A phase-field description of crevasse growth: comparison of elastic, Maxwell, and Kelvin-Voigt models for ice, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15490, https://doi.org/10.5194/egusphere-egu25-15490, 2025.
Antarctica’s ice shelves play a crucial role in the stability of the ice sheet and the rate at which it contributes to sea-level rise. While large, tabular iceberg calving accounts for most of the ice discharged from Antarctic ice shelves, less attention has been given to smaller-scale frontal ablation processes that also contribute to ice-shelf area and mass changes. This can be caused by: (1) the collision of large- to medium-sized (>100 km2) tabular icebergs with the coastline, (2) undercutting of ice-shelf fronts by ocean waves, causing edge wasting, and (3) the absence of protective landfast sea ice that can expose calving fronts to damaging ocean swell.
Here, we analyse calving front dynamics and frontal ablation through observed ice-shelf advance and retreat rates in the coastal Dronning Maud Land region of East Antarctica since 2015. Using time series derived from semi-automated classification of Sentinel-1 radar imagery, we quantify ice-shelf frontal ablation and mass change rates. Our results reveal complex seasonal and interannual patterns in calving front dynamics, demonstrating the importance of multiple ice-shelf frontal ablation processes. Iceberg collisions triggered a cascade of regional calving in 2021, as well as damage to several fronts that did not calve. These cascading calving events were initiated by collisions with iceberg D28 from the Amery Ice Shelf, which released further icebergs that drifted and collided with other parts of the coast. Observations of small-scale ice-shelf frontal retreat during periods of unusually absent landfast sea ice and dense pack ice suggests frontal ablation is partially linked to the persistence of protective sea ice. Altogether, these findings provide improved knowledge of calving front dynamics and its drivers in East Antarctica, needed for refining calving parameterizations to more accurately predict ice-shelf evolution and stability.
How to cite: Arthur, J., Moholdt, G., Wendt, L., and Cristea, A.: Calving front dynamics in coastal Dronning Maud Land, East Antarctica, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9697, https://doi.org/10.5194/egusphere-egu25-9697, 2025.
Outlet glaciers play a crucial role in transporting ice from the interior of the Antarctic Ice Sheet to the coast, where they transition into floating ice shelves at the grounding line. Shear margins, which separate these fast-moving glaciers from relatively stationary ice, are regions of intense lateral shearing that generate side drag—a resistive force that counteracts glacier driving stress and mitigates sea-level rise. The nature of this side drag depends largely on bulk ice stiffness, a property which is poorly understood due to the numerous challenges in accessing and measuring these most dynamic regions. Here, we use the vertical displacement of floating ice under tidal loading as a natural experiment to constrain bulk ice stiffness within shear margins. Using a GAMMA Portable Radar Interferometer (GPRI), we monitored the tidal flexure zone of Priestley Glacier, which flows into the Nansen Ice Shelf, over a full spring-neap tidal cycle in December 2024. Preliminary results suggest shear-zone weakening, supported by in-situ GPS measurements capturing the corresponding horizontal ice dynamics and ApRES observations of internal strain within the bending ice column. These findings enhance our understanding of the mechanisms driving ice discharge and provide critical observational constraints for simulations of ice-sheet dynamics, ultimately refining estimates of Antarctica’s contribution to sea-level rise.
How to cite: Wild, C. T., Rosier, S. H., Jung, J., Na, J. S., Lee, W. S., Lee, C. K., Floricioiu, D., and Drews, R.: Turning the Tide on Antarctic Shear Zones, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13517, https://doi.org/10.5194/egusphere-egu25-13517, 2025.
Basal terraces are characteristic stepped features with steep, near-vertical walls which are interspersed by smooth horizontal sections. They occur beneath many Antarctic ice shelves and their genesis has been linked to stable ocean stratification beneath the horizontal sections which ceases near the walls where ocean-induced melt rates intensify. However, how terraces initially form and how they evolve over time is poorly observed and understood. Here, we present temporal changes in basal topography from densely spaced GPR profiles imaging the 3D structure of a basal terrace field on Ekström ice shelf in East in 2021/22 and 2022/23. Many features can be traced coherently across time and the majority of the structures advected with ice flow, with the exception of some local modifications near some walls. A concurrent year-long time series of an ApRES situated above one of those terraces shows moderate melt rates comparable to the ice-shelf wide magnitudes, confirming previous assertions that melt rates at the terraces are low. Imaging of the 3D structure of the basal terraces now enables us to identify off-angle reflections in the ApRES time series and thus quantify if localized horizontal melting at the walls can be detected.
How to cite: Drews, R., Schlegel, R., Eisen, O., Falk, O., Koch, I., Ershadi, R., Noll, J., and Köppe, S.: Yearly evolution of Basal Terraces at Ekström Ice Shelf (East Antarctica), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18654, https://doi.org/10.5194/egusphere-egu25-18654, 2025.
The grounding line defines the boundary of grounded ice of marine ice sheets in Greenland and Antarctica. The speed and extent of grounding line retreat indicate ice sheet stability, making tracking and quantifying grounding line migration imperative. Although satellite observations of several key glaciers and ice streams in these regions have enabled spatially dense grounding line mappings, the revisit frequency of current missions is inadequate to capture the tide-induced grounding line migration. Moreover, limited tide information due to insufficient observations and the coarse resolution of tide models near the grounding line makes it challenging to correlate tide levels to the grounding line position.
Here, we focus on observing and quantifying solely the grounding line movement at the different time scales without using tide models and taking advantage of the dense time series of Sentinel-1 SAR data acquisitions of the Antarctic Ice Sheet margins. We generated double difference interferograms with all available and coherent 6-day Sentinel-1 triplets in 2015-2024. The interferograms were generated with the custom processing chain developed at the Remote Sensing Technology Institute of the German Aerospace Center (Muir, 2020). The grounding lines were automatically delineated in the DInSAR phase using our deep neural network-based delineation pipeline, as detailed in Ramanath Tarekere et al., 2024. The Getz Ice Shelf is coherently captured in most Sentinel-1 acquisitions, making it an ideal region to test our algorithm. We will develop a statistical method to measure the spatial variation of the lines and identify stationary and non-stationary regions. Additionally, in the non-stationary regions, we will decompose the time series into seasonal and trend components, possibly discriminating long-term climate-induced grounding line retreat and variations in grounding line positions caused by different ocean tide levels.
References
version 1.0. https://climate.esa.int/media/documents/ST-UL-ESA-AISCCI-SSD-001-v1.1.pdf
delineation in DInSAR interferograms [Preprint]. EGUsphere, 2024, 1–35. https://doi.org/10.5194/egusphere-2024-223
How to cite: Ramanath, S., Krieger, L., and Floricioiu, D.: Tracking the grounding line migration at Getz Ice Shelf using Sentinel-1 A/B observations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6003, https://doi.org/10.5194/egusphere-egu25-6003, 2025.
Ice shelves play a crucial role in buttressing the ice flux from the ice sheet. It is therefore critical to monitor their evolution and weakening. Changes in basal melting rates, driven by enhanced advection of circumpolar deep water, are one of the primary drivers of ice shelf weakening in Antarctica. In the Amundsen Sea Embayment, basal melting rates are the highest in Antarctica, exceeding 100 m/yr at the grounding line of Pine Island Glacier (PIG), which has discharged more than 130 Gt/yr of ice into the ocean since 2008 (Mouginot et al., 2013; Rignot et al., 2019). Previous studies of basal melting below PIG (Adusumili et al., 2022) were limited by low spatial resolution, showing significant differences from local high-resolution estimates (Shean et al., 2019), and temporal discrepancies when compared to in-situ ocean observations, highlighting the limitations of existing products (Dutrieux et al., 2014; Jenkins et al., 2018). Biases may arise from the challenge of performing remote sensing in Antarctica (fast changing ice bodies), with sensor-specific complexities (e.g., radar altimetry, laser, stereo-photogrammetry) and reliance on model outputs (SMB, firn). In this study, we revisit the estimation of melting rates on PIG using high-resolution multi-sensor optical imagery from 2000s onward. Leveraging modern geospatial formats like GeoParquet, coupled with DuckDB and high-level tools such as Xarray/Dask, we develop a high-performance pipeline to process heterogeneous elevation datasets. Data from GeoEye/WorldView (Maxar) as well as from ASTER (NASA/METI) were used, regenerated and aligned to a combination of measurements with a centimetric precision from the LVIS and ATM instruments aboard NASA's Operation IceBridge, and the ICESat missions. Dozens of millions of data points are uniformly filtered, advected, and corrected for tides, atmospheric pressure, geoid, and mean dynamic topography throughout the entire observation period with dynamically evolving ice shelf geometry from updated grounding lines and ice front positions. We estimate basal melting on summer mosaics, within a consistent Lagrangian framework by calculating changes in thickness, SMB, firn, and rapid ice advection (Shean et al., 2019; Millan et al., 2023). We quantify the error in melting rates using error propagation and supplement this analysis using different firn and SMB products (RACMO, FDM, CFM). We compare the spatial and temporal variability of our melting rate estimates with previous satellite data on PIG as well as in-situ measurements (Dutrieux et al., 2014). The methodology we propose here is based on state-of-the-art tools in geospatial analysis and offers new perspectives for mapping the evolution of basal melting at high resolution on a regular basis over the past two decades. It provides a coherent framework, with the most precise spatio-temporal measurements, limiting sensor-specific biases, which will be extended to all Antarctic ice shelves. We also provide a more conservative uncertainty estimates based on measurement errors as well as an ensemble-based approach for firn and SMB, which are significant sources of uncertainty. This data will be of direct interest for reanalyzing the stability of ice shelves and for constraining ocean models to better resolve basal melting variability.
How to cite: Gimenes, L., Millan, R., Barré, J. B., and Dehecq, A.: Analyzing two decades of basal melting rates below Pine Island Ice Shelf using multi-sensors remote sensing data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-2835, https://doi.org/10.5194/egusphere-egu25-2835, 2025.
In Antarctica, changes in ice dynamics dominate the ice sheet’s contribution to global sea-level rise. Changes to the continent’s ice shelves play a key role in this dynamic evolution through the buttressing that they provide to the upstream grounded ice. One striking and well observed example of the importance of ice shelves is Pine Island Glacier Ice Shelf, which has undergone dramatic changes in the modern observational period. This includes major periods of grounding line retreat and ice-shelf thinning due to influxes of warm ocean water, combined with large calving events and the disintegration of its southern shear margin. Overall, these changes have reduced the buttressing support provided by the ice shelf, leading to increased ice discharge and dynamic thinning on the inland portion of the glacier.
Concurrent with the erosion of Pine Island Glacier Ice Shelf, ice-shelf thickness anomalies originating at the glacier grounding line, known as ice keels, have regularly bumped along the bedrock underneath the ice shelf. This has caused small regions ephemeral grounding, which occur irregularly in the central shelf. While known, these events remain largely unstudied, and the effects of this ephemeral grounding on stresses within the ice shelf and the evolution of ice-shelf dynamics remain poorly understood.
Here we use a combination of satellite observations and ice sheet modelling to study the movement of a prominent ice keel over a bathymetric ridge during the period 2014-2021 and analyse the effects this had on the dynamics of the ice shelf.
To observe the grounding of the ice keel, we use the differential range offset tracking technique applied to synthetic-aperture radar (SAR) data from the European Space Agency and European Commission Copernicus' Sentinel-1 satellites to produce a dense timeseries of ice keel grounding without the need for interferometric coherence. With this dataset we track the motion of the ice keel in the last decade, showing that at times up to 10 km2 of the central ice shelf was grounded. Alongside these observations, we use the BISICLES ice sheet model to analyse the impacts of this ephemeral grounding on the dynamics and stress regime of the ice shelf. Finally, we discuss our results in terms of re-grounding as a mechanism which may stabilise the retreat of marine ice sheets.
How to cite: Wallis, B., Surawy-Stepney, T., and Hogg, A.: Ephemeral grounding of ice-keels on Pine Island Glacier Ice Shelf: observations, modelling, and dynamic impacts., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7146, https://doi.org/10.5194/egusphere-egu25-7146, 2025.
More than 80% of the grounded ice of the Antarctic ice sheet drains into the ocean through ice shelves. It is estimated that roughly half of the ice shelves’ mass is eventually lost through melting from the underside, where the ice gets in contact with warmer ocean waters. Loss of these ice shelves could cause an increase of the discharge of grounded ice which would lead to additional sea-level rise. It is thus important to accurately quantify the rate at which ice shelves are melting if we wish to estimate future sea-level rise. Here, we present a novel methodology for estimating basal melt rates, by assimilating remotely derived estimates of surface velocities, ice sheet thickness, surface elevation changes and modelled surface mass balance using an ice sheet model (Ua). This methodology allows for a less noisy, physically consistent estimate of the ice mass divergence, and considers the uncertainty associated with each data product. The resulting estimates of the melt rate pattern at almost every Antarctic ice shelf is compared with previous remotely derived estimates.
How to cite: Brils, M. and Gudmundsson, H.: Using data inversion to infer basal melt rates underneath ice shelves, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12249, https://doi.org/10.5194/egusphere-egu25-12249, 2025.
The Antarctic Ice Sheet (AIS) exerts a critical influence on global sea level rise (SLR). Accelerating mass loss, particularly in West Antarctica, is projected to significantly enhance its contribution in the coming centuries. Approximately half of the surface mass gain is offset by ocean-induced basal melting, highlighting the critical role of ice-ocean interactions (Depoorter et al., 2013; Paolo et al., 2023). Despite advances in AIS modelling, significant uncertainties persist, largely arising from the representation of basal melt processes, which are influenced by varying parameterizations, parameter choices and sparsely sampled oceanic forcing datasets. These uncertainties, coupled with divergent future climate forcing scenarios, lead to a large spread in future ice-sheet trajectories and their contribution to SLR by 2300 (Seroussi et al 2024).
To enable robust estimates of future mass fluxes from the AIS, this study uses a circum-Antarctic high-resolution configuration of the Úa ice-sheet model (Gudmundsson, 2020, 2024) to conduct a series of transient simulations spanning 2000-2020. These simulations are used to quantify uncertainties and sensitivities in modelled ice-shelf melt. We apply multiple basal melting parameterizations and a plausible range of parameter choices, including the Local Quadratic Melting (Jourdain et al., 2020), PICO (Reese et al., 2018), and Plume Models (Jenkins, 1991; Lazeroms et al., 2019; Rosier et al., 2024), forced by two different observational oceanic datasets. By varying initial ice-sheet conditions, basal melting schemes, and external forcing, a large ensemble of hindcast simulations was generated and validated against observed changes in ice velocity, thickness, and grounding line position, providing robust insights into model behaviour and ice-ocean interactions.
This initial work, funded by the Horizion Europe project OCEAN ICE, forms a robust foundation for the next phase of forecast transient simulations, enabling long-term projections of AIS contributions to SLR for an ensemble of observationally-constrained model parameters. Our work aims to quantify the complex interplay between basal melting, ice dynamics, and oceanic forcing, while delivering key insights for enhancing the predictive capability of coupled ice-sheet-ocean models in a rapidly changing climate.
How to cite: Qin, Q., De Rydt, J., Coulon, V., and Pattyn, F.: Ice-Sheet Model Calibration and Parametric Uncertainty Analysis for 2000-2020, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4568, https://doi.org/10.5194/egusphere-egu25-4568, 2025.
