Differential synthetic aperture radar interferometry (DInSAR) of COSMO-SkyMed (CSK) SAR 1-day tandem pairs was used to map the 2020-2021 grounding line (GL) of the Cook Ice Shelf, East Antarctica, and to assess the observed retreat relative to the 1996 GL and 2018 grounding zone (GZ). To interpret the dynamics of the retreat, we combined annual ice velocities, ice-thickness change rates, and bed topography. Agreement between tidal predictions and DInSAR-derived vertical displacements within the hydrostatic-equilibrium zone indicates that the GL mapping is robust. The CSK-DInSAR GL shows inland retreat of ~ 5.8km relative to the 2018 upstream GZ boundary in the western Cook East Ice Shelf and ~ 8.8km relative to the 1996 GL across Cook West Ice Shelf, while other sectors remain stationary. In the retreating sector of western Cook East Ice Shelf, ice flow slowed in 2017-2018 and then increased by ~ 60m/yr in 2018-2019, returning to prior speeds with no further acceleration. The retreat occurred where the 2018 upstream GZ already lay on a retrograde bed. The 2020-2021 GL occupies either a local prograde bed or a retrograde segment immediately seaward of a prograde transition, suggesting threshold-like retreat controlled by bed geometry.

The Bratina Island meltwater ponds (McMurdo Ice Shelf, Antarctica) host complex microbial communities in the form of benthic microbial mats. These ponds are long-lasting but can experience significant alterations in physicochemistry on an annual or decadal basis, with additional alterations expected due to climate change. Here, we explored the impact of two potential future climate scenarios on the 16S rRNA gene sequence-based microbial community composition of three meltwater pond mats: desiccation (due to decreased precipitation and/or increased evaporation) and shading (due to increased precipitation resulting in increased ice cover). In a multi-year manipulation experiment, we found that the mat bacterial community composition shifted substantially with desiccation in all ponds studied. Desiccation reduced overall diversity, with cyanobacteria mostly being lost and members of the Bacteroidota phylum increasing in abundance. Halotolerance was indicated as a potential trait allowing for survival upon desiccation. We found that the community composition of the mats was resilient to shading (in the form of 75% light reduction), with no significant changes in composition observed. Instead, we observed a strong coloration change in the mats in response to shading, which could be due to positive phototaxis of Oscillatoria trichomes in the shaded mats. These results help inform how the prokaryotic communities in these highly productive mats may respond to future climate scenarios.

The stability of Antarctic ice shelves, which regulate the flow of grounded ice into the ocean, depends critically on ocean-driven basal melting. Basal channels, widespread features beneath many ice shelves, modulate ice-shelf basal melt rates and influence ice-shelf stability, yet their oceanic drivers remain poorly understood. Using high-resolution simulations of a cold-water ice shelf cavity, we show that interactions between circulation and channelized topography generate localized overturning that traps intruding warm Circumpolar Deep Water (CDW) beneath the ice, amplifying melt rates by an order of magnitude within channels. This ocean-driven process significantly enhances the sensitivity of the ice shelf basal mass loss to ocean warming, and the resulting differential melting promotes channel growth, with the potential to undermine the structural stability of the deeper part of the ice shelf. Our results reveal a key mechanism for basal channel evolution and indicate that even modest CDW intrusions could have important implications for the stability of cold Antarctic ice shelves.

Extracting Antarctic ice shelf fracture depths using the linear cloth simulation filtering algorithm

Understanding the long-term deformation behavior of glacier ice at the calving front is a crucial point for the derivation of calving criteria regarding ice mass loss. To some extent, linear models are sufficient to capture the elastic as well as viscous response of the motion of ice. However, finite deformation models are inevitable, especially for simulations taking into account deformations over decades. Following this, a finite viscoelastic Maxwell model is employed to capture the elastic and short-term response, which is denoted by e.g. changing loading conditions, as well as the long-term and viscous response by the creep behavior of the ice flow. A further extension of the standard Maxwell model is given by including Glen’s flow law, resulting in nonlinear stress-dependent viscosities and thus, nonlinear viscous flow. The model here presented utilizes a multiplicative split of the deformation gradient into an elastic and viscous part, followed by the derivation of the evolution equation based on a Lie derivative. An essential part is the application of an exponential map as the integrator for the update of the internal viscous variables in time, ensuring an isochoric viscous flow throughout the whole simulation. The performance of the model is demonstrated on two numerical examples, illustrating the enforcement of the incompressible viscous flow and numerical stability as well as an ice shelf benchmark that serves as a comparative study for the monitoring of occurring stresses and displacements assuming a constant as well as stress-dependent viscosity using Glen’s flow law.

Major shift in mesozooplankton community structure after spring bloom in the Ross Sea Region Marine Protected Area

The interactions among ice, ocean, and seafloor in Antarctic grounding zones hold major implications for global sea level rise over the coming century and beyond. Meltwater buoyancy means that grounding zone conditions influence basal boundary layer throughout the entire cavity. Because of the difficulty of direct access, grounding zone ocean environments have been sampled only a handful of times and then usually only as a brief data snapshot. Here, we present ocean data from the Kamb Ice Stream grounding zone of the Ross Ice Shelf that reveal a consistently stratified 30-meter-thick water column beneath nearly 600meters of ice and snow. Warmer inflowing seawater is vertically separated from an overlying colder outflowing mixture of seawater and glacial meltwater. The 10-month long timeseries of stratification reveals that this layering is resilient but variable, with internal wave activity resulting in frequent mixing between the two layers that suggests a mechanistic underpinning for the grounding zone as a distinct region within the cavity.

As new airborne surveys of the Antarctic ice sheet are completed, the ever-enlarging survey dataset provides an opportunity for generating new 'Bedmaps' of ice thickness, surface and bed topography. These surveys are fundamental to improving our ability to predict the future of Antarctica, but other data-analysis challenges emerge because surveys often do not agree, large data gaps remain, the ice thickness changes or interpolation works well for one landscape but not another. Similar problems afflict other key Bedmap components: the coastline, the grounding line, rock outcrops, the ice shelves and the bathymetry. The process of merging the interpolated ice sheets and shelves and the grounded bed with the sea floor can also inject spurious cliffs and bumps in the grounding zone-exactly where ice-sheet models are most sensitive to flaws in their boundary conditions. In each case, unintended errors and artefacts that arise in the Bedmap grids require careful checking, correction and sometimes bespoke, local approaches to interpolation, slowing the process further. Here, I highlight the key challenges to overcome and address the question of how future Bedmaps can be automated to speed up the supply of new datasets demanded by the ice-sheet modelling community. This article is part of the Theo Murphy meeting issue 'Next generation ice-sheet bed measurements'.

Grounding zones have long been recognized as critical for understanding the past, present and future evolution of ice sheets. The ice mass flux through the grounding line contributes to global sea-level rise, and the freshwater flux impacts ocean salinity. This narrow zone-where the grounded ice sheet transitions into a floating shelf-is challenging to observe and model because of the remoteness of ice sheet beds and ice shelf cavities and is thus poorly understood. However, our understanding of grounding zones has changed as we collect new observations, which are revealing a far more complex system than previously thought. These observations serve as the foundation for mathematical and numerical models of ice sheets. Models have progressed from simply representing the grounding line as hydrostatic equilibrium and treating ice flow as a viscous fluid to solving visco-elastic problems, including coupled ice sheet-subglacial hydrological models and complex grounding zones. What all these models, however, have in common is the need to know the shape of the bedrock and basal conditions beneath the grounded ice, making a targeted observational campaign of bedrock in current and future possible grounding zones key to fully understanding the Antarctic ice sheet. This article is part of the Theo Murphy meeting issue 'Next generation ice-sheet bed measurements'.

The Western Antarctic Peninsula (WAP) is one of the fastest warming regions on Earth, with increasing freshwater input from melting glaciers and ice shelves. Although surface-layer freshening is well documented, the extent to which glacial meltwater influences subsurface waters remains poorly constrained. Here, we investigated the vertical distribution and origin of freshwater anomalies using hydrographic, isotopic (δ ¹⁸ O, δ ² H), and major-ion data from three sites along the WAP: Cierva Cove, Petermann Island, and Paradise Bay. The data show consistent freshening below 50 m depth. Chloride dilution and isotope depletion define conservative mixing between local seawater and a strongly δ ¹⁸ O-depleted glacial meltwater endmember, with this signal extending to depths greater than 90 m in the more enclosed embayments. Estimated meltwater fractions at these depths are approximately 0.5 to 2%. Major-ion and halogen ratios also vary conservatively, supporting mixing between seawater and glacial meltwater rather than addition of a chemically distinct subsurface fluid. Despite limited vertical sampling, the deepest samples at each site remain consistent with the inferred surface-to-depth mixing relationships. These findings indicate that glacial meltwater can be stored well below the surface layer along parts of the WAP, likely through plume-driven neutral-buoyancy intrusions, lateral advection, and mixing. Recognising this subsurface meltwater reservoir is important for understanding local stratification and for improving representation of freshwater input in ocean models of the region.

Abstract. Constraining the dynamic evolution of past ice sheets is critical for unravelling their responses to external forcing and feedbacks over long timescales. This is particularly true in the context of marine ice sheet collapse, as this is one of the largest sources of uncertainty for future sea-level rise projections. The Iceland Ice Sheet (IIS) provides an empirically constrained case study for investigating such an instability, having retreated from a predominantly marine-based ice sheet to isolated mountain ice caps during the last deglaciation. However, previous reconstructions of the IIS have been limited by either sparse data or a restricted exploration of model parameter space, lacking a robust quantification of uncertainties. Here, we address this gap by performing a truncated history matching of the last glacial cycle of the IIS. We use the Glacial Systems Model (GSM) constrained by a curated set of geochronological data to generate an envelope of not-ruled-out-yet(NROY) ice sheet histories. Our results indicate that numerous asynchronous ice streams effectively drain ice from the interior to the margins, resulting in an extensive yet relatively thin ice sheet. During its local Last Glacial Maximum (23.6–20.9 ka), the IIS reaches the continental shelf edge in most sectors with a total volume of 0.41 to 0.76 metres equivalent sea level (m e.s.l.). In the most extreme NROY glaciation scenarios, our model reveals an ice bridge connecting the Iceland and Greenland ice over Denmark Strait. We find that accelerated ice discharge (at the grounding line) dominates mass loss during deglaciation. This acceleration is primarily driven by atmospheric warming through a cascade of mechanisms: surface meltwater induces hydrofracturing, leading to both ice shelf disintegration and tidewater calving, which in turn reduces buttressing and triggers rapid ice stream acceleration. The critical role of hydrofracturing in enabling model capture of deglacial data constraints is shown by explicit sensitivity experiments. This thereby supports inclusion of hydrofracturing for modelling of ongoing ice sheet response to climate change.

Abstract. Ocean-driven basal melting of Antarctic ice shelves plays an important role in the mass loss of the Antarctic Ice Sheet. Ice shelf cavity-resolving ocean models are a valuable tool for understanding ice shelf-ocean interactions and for simulating projections of ice shelf and ocean states under future climate. Designed to assess the current state of ice shelf–ocean modelling, the second Ice Shelf–Ocean Model Intercomparison Project, ISOMIP+, consists of 12 ocean model configurations submitted with a common, idealised experimental setup. Here, we focus on the experiments Ocean0–2 (Asay-Davis et al., 2016), which are ocean models with idealised, static ice shelf geometries, but where the ocean reaches a balance with prescribed far-field ocean conditions. Different thermal transfer coefficient values (ranging from 0.011 to 0.2) are used for each model in the melting parameterisation to achieve a common, tuned melt rate since the models cover a range of types of vertical coordinates, ice–ocean boundary layer treatments, and numerical schemes. These model differences lead to spread in the resultant ocean properties, circulation, boundary-layer structure and spatial distribution of melting. We also highlight similarities between models, such as a shared linear relationship across most models between melt rate and overturning and barotropic streamfunctions during the spin-up and spin-down, demonstrating a robust relationship between melt and circulation across models and forcing conditions. The ISOMIP+ results provide a systematic comparison of ice shelf cavity-capable ocean models. However, we also demonstrate the need for realistic ice shelf–ocean model intercomparison projects (some already underway) to assess model biases and inter-model variation against sparse observations. Further research is needed to understand the differences between models and further improve our modelled representations of the ice–ocean boundary layer and ice shelf cavity circulation.

Recent decades have seen record-high temperatures on the Antarctic Peninsula (AP) due to combined atmospheric rivers (ARs) and föhn warming. While ARs frequently enhance föhn, not all events cause surface warming over the entire Larsen C Ice Shelf (LCIS). Using high-resolution Polar WRF simulations, we examine the relationship between ARs and föhn over the AP during austral summers and identify four distinct AR shapes associated with föhn-induced surface warming over the LCIS: zonal-perpendicular, zonal-like, convex, and concave. Zonal-like ARs associated with coupled low-high-pressure systems and convex ARs linked to blocking highs produce strong föhn warming across the entire LCIS, primarily affecting its northern and southern sectors, respectively. In contrast, zonal-perpendicular and concave ARs generate moderate-to-weak warming, owing to either weaker AR intensity or AR curvature. Although downward shortwave radiation dominates surface warming, enhanced moisture suppresses its increase from föhn-induced cloud clearance while enhancing downward longwave radiation near mountain gaps. Sensible heat flux also contributes substantially along the mountain foothills. As ARs intensify under climate change, their interaction with föhn over the AP can critically influence the future stability of coastal ice shelves.

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Violent ice fracture events often trigger rapid climatic or geomorphic changes, including Antarctic ice shelf collapse, glacial outbursts, and frost quakes. Existing models of sequential crack propagation inadequately explain the sudden, explosive nature observed in natural events. Here, we uncover a previously unidentified eruptive fracture of ice adhered to solid surfaces upon quasistatic cooling, which can even cause the underlying substrate fragmentation. This explosive ice instability depends on the threshold internal grain size of the ice. Above this threshold, fracture proceeds in a progressive, energy-dominated mode, whereas below it the ice undergoes an abrupt, strain-dominated fracture. We found that the apparent tensile strength of adhered ice ranges from 39 to 58 megapascals, over an order of magnitude higher than the typical value of ice (0.7 to 3.1 megapascals). This work provides a mechanistic framework for understanding and predicting abrupt cryospheric fracture events and points toward rational strategies for designing self-actuating deicing systems that exploit thermomechanical instabilities.

Climate models show that Antarctic surface melt will increase through the current century. Surface melting changes ice sheet albedo, the availability of liquid water for endemic and invasive species, and may even accelerate ice shelf collapse and global sea level rise. Here we show, using 1 km downscaled projections of potential Antarctic surface melt, that the total area experiencing surface melt will expand by more than 10% by 2100 under a Shared Socio-economic Pathway 3-7.0 scenario, with increased potential melt totals likely to threaten the viability of ice shelves mostly in the West Antarctic Peninsula and Amundsen Sea Embayment, through an elevated risk of hydrofracture. By calculating the latitudinal rate of melt migration we also find that Shared Socio-economic Pathway 1-2.6 is the only emissions scenario under which the rate of future Antarctic surface melt expansion will stabilize at present levels.

Abstract The spatial distribution and dynamics of glacial meltwater (MW) influence ocean circulation off and basal melt rate below Antarctic ice shelves. While previous studies described the MW distribution in Pine Island Bay off Pine Island Ice Shelf (PIIS), quantitative constraints on the spatial heterogeneity of the spread of MW associated with lateral mixing remain unknown. In this study, the distribution and spreading mechanisms of MW were investigated based on in situ observations using conductivity‐temperature‐depth and lowered acoustic Doppler current profiler measurements at 68 stations off PIIS and Thwaites Ice Shelf in summer 2020 (January–February). The composite tracer method was used to calculate the MW fraction using the properties of Winter Water, modified Circumpolar Deep Water, and MW. The results showed that the high‐MW fractions were primarily distributed along two separate isopycnals (27.38 σ θ and 27.48 σ θ ) near PIIS and along a deep isopycnal (27.48 σ θ ) near TIS. Exponentially fitted line of MW fractions along the deeper (27.48 σ θ ) isopycnal showed a much larger curvature and steeper slope near TIS than near PIIS. Based on the 1‐dimensional advection–diffusion model, the results indicated stronger mixing off PIIS than TIS along 27.48 σ θ , and stronger mixing along 27.48 σ θ than 27.38 σ θ off PIIS. This study suggests that along‐isopycnal MW mixing varies between ice shelves and between MW‐rich isopycnals, improving our understanding of MW distribution and spreading patterns and the implications of these patterns for regional circulation.

ABSTRACTAntarctic marginal seas are crucial for the global climate, but direct observations, especially of mesoscale ocean eddies, remain scarce. Here, by analyzing the unprecedented high-resolution sea surface height data provided by the recently launched Surface Water and Ocean Topography (SWOT) satellite, we reveal a widespread presence of mesoscale eddies across the Antarctic continental shelf. The geographic distributions of the observed eddies, along with eddy-resolving model simulations, support the hypothesis that ice shelf basal melting and dense shelf water formation are key processes driving the prevalent eddy activity. Our findings highlight the potential of innovative satellite measurements for monitoring critical Antarctic oceanic processes, and the need to resolve the abundant Antarctic ocean eddies in climate models.

Abstract Continued melting of Antarctic ice sheets and shelves adds freshwater to the Southern Ocean (SO), enhancing stratification and inducing surface cooling. This cooling influences tropical climate through coupled atmosphere–ocean interactions, though model responses vary. Using coordinated coupled model experiments with idealized Antarctic meltwater forcing, we assess the remote impacts of SO surface cooling. All 11 models simulate equatorial surface cooling and a northward Intertropical Convergence Zone shift, but show discrepant responses in the equatorial Pacific zonal temperature gradient and Atlantic meridional dipole. When normalized by SO cooling amplitude, these tropical metrics are positively correlated with shortwave cloud feedback strength. Surface energy budget analysis indicates that the previously proposed teleconnection mechanisms in the eastern Pacific are not robust across models. The timescale of tropical cooling and the relative roles of wind‐driven latent heat and shortwave fluxes differ across models and basins, highlighting the uncertainty in SO–tropics teleconnections.

Abstract. Knowledge of Antarctic glacier grounding lines, which mark the transition between grounded and floating ice, is a vital parameter in determining the stability of major ice shelves and hence the ice sheet. Rapid grounding line retreat and associated mass loss has been documented at numerous Antarctic glaciers, particularly in the Amundsen Sea Embayment. However, few comprehensive grounding line mappings exist, particularly from recent years. Here, we utilize a unique record of Sentinel-1 Synthetic Aperture Radar 1 d repeat-pass imagery to generate a comprehensive retrieval of grounding line location in the Amundsen Sea Embayment in 2025 and evaluate recent changes.