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Glaciologist Rob DeConto's research on polar climate change, specifically focusing on glaciers and ice sheets, is discussed in this article. DeConto explains the differences between Antarctica and Greenland and the challenges of understanding how the Antarctic ice sheet will behave in a warmer world. He also discusses the potential dangers of marine ice sheet instability and the impact of melting ice shelves on sea-level rise. The article emphasizes the uncertainties surrounding the rate of sea-level rise and the need for further research in this area. It highlights the term "deep uncertainty" used by the Intergovernmental Panel on Climate Change (IPCC) to describe the situation and the conservative nature of current projections. The author emphasizes the need for action to address the melting of ice sheets, as it poses a threat to infrastructure worldwide. [Extracted from the article]

An operational synoptic-scale sea ice forecasting system for the Southern Ocean, namely the Southern Ocean Ice Prediction System (SOIPS), has been developed to support ship navigation in the Antarctic sea ice zone. Practical application of the SOIPS forecasts had been implemented for the 38th Chinese National Antarctic Research Expedition for the first time. The SOIPS is configured on an Antarctic regional sea ice–ocean–ice shelf coupled model and an ensemble-based localized error subspace transform Kalman filter data assimilation model. Daily near-real-time satellite sea ice concentration observations are assimilated into the SOIPS to update sea ice concentration and thickness in the 12 ensemble members of the model state. By evaluating the SOIPS performance in forecasting sea ice metrics in a complete melt–freeze cycle from 1 October 2021 to 30 September 2022, this study shows that the SOIPS can provide reliable Antarctic sea ice forecasts. In comparison with non-assimilated EUMETSAT Ocean and Sea Ice Satellite Application Facility (OSI SAF) data, annual mean root mean square errors in the sea ice concentration forecasts at a lead time of up to 168 h are lower than 0.19, and the integrated ice edge errors in the sea ice forecasts in most freezing months at lead times of 24 and 72 h maintain around 0.5×106 km 2 and below 1.0×106 km 2 , respectively. With respect to the scarce Ice, Cloud, and land Elevation Satellite-2 (ICESat-2) observations, the mean absolute errors in the sea ice thickness forecasts at a lead time of 24 h are lower than 0.3 m, which is in the range of the ICESat-2 uncertainties. Specifically, the SOIPS has the ability to forecast sea ice drift, in both magnitude and direction. The derived sea ice convergence rate forecasts have great potential for supporting ship navigation on a fine local scale. The comparison between the persistence forecasts and the SOIPS forecasts with and without data assimilation further shows that both model physics and the data assimilation scheme play important roles in producing reliable sea ice forecasts in the Southern Ocean. [ABSTRACT FROM AUTHOR]

Projections of sea‐level rise from ice‐sheet shrinkage in a warming world have large uncertainties, linked to limited knowledge of changes at the ocean‐ice sheet interface. This interface most typically is modeled as a grounding line, across which still‐connected ice flows into the ocean to float as an ice shelf, or where icebergs calve from a cliff before the ice begins to float. But, extensive and rapidly increasing evidence shows that this is really a grounding zone, and that processes in this grounding zone omitted from many models could exert major controls on sea‐level rise. Plain Language Summary: Marine‐terminating glaciers flow into the ocean across extensive grounding zones. These kilometers‐long and glacier‐wide zones represent the last broad region of glacier contact with the rock and sediments below before the ice enters the ocean as a floating ice shelf or calved icebergs. Loss of this basal drag along with enhanced basal melting caused by tidally driven seawater intrusion leads to faster outflow and rapid thinning of the overlying ice. As a result of the local thinning, grounding zones retreat inland and sea level rises with more loss of previously grounded ice. Most ice‐sheet models used in sea‐level projections do not include grounding‐zone processes, but rather stop their ice‐ocean interactions at a grounding line. They are thereby omitting important dynamic feedbacks and underestimating future sea‐level contributions from the marine‐based sectors of the Greenland and Antarctic ice sheets. Key Points: Tidally modulated seawater intrusion leads to loss of ice‐bed contact as well as significant (maximal) basal melting within grounding zonesThe future dynamics of marine outlet glaciers are ultimately controlled by coupled processes operating within and through grounding zonesDespite the importance of grounding zones to ice‐sheet dynamics, most ice‐sheet models used in sea‐level projections do not include them [ABSTRACT FROM AUTHOR]

Understanding the drivers of iceberg calving from Antarctic ice shelves is important for future sea level rise projections. Ocean waves promote calving by imposing stresses and strains on the shelves. Previous modeling studies of ice shelf responses to ocean waves have focused on highly idealized geometries with uniform ice thickness and a flat seabed. This study leverages on a recently developed mathematical model that incorporates spatially varying geometries, combined with measured ice shelf thickness and seabed profiles, to conduct a statistical assessment of how 15 Antarctic ice shelves respond to ocean waves over a broad range of relevant wave periods, from swell to infragravity waves to very long period waves. The results show the most extreme responses at a given wave period are generated by features in the ice shelves and/or seabed geometries, depending on the wave regime. Relationships are determined between the median ice shelf response and the median shelf front thickness or the median water cavity depth. The findings provide further evidence of the role of ocean waves in large‐scale calving events for certain ice shelves (particularly the Wilkins) and indicate a possible role of ocean waves in calving events for other shelves (Larsen C and Conger). Further, the relationships determined provide a method to assess the potential for increased calving as ice shelves evolve with climate change, and, hence, contribute to assessments of future sea level rise. Plain Language Summary: Antarctic ice shelves are the floating extensions of the Antarctic Ice Sheet. They play a critical role in many Southern Ocean processes. In particular, they help maintain the stability of the Antarctic Ice Sheet by moderating the flow of grounded ice into the Southern Ocean. Climate change is causing them to thin and retreat, which is a major threat to global sea levels. Iceberg calving accounts for half of ice shelf loss, and ocean waves contribute to the calving process by rhythmically bending ice shelves. The influence of ocean waves on calving is expected to increase as the shelves and their surrounding sea ice barriers become weaker. Therefore, quantifying the responses of ice shelves to ocean waves is needed to project the future of the shelves and, hence, sea level rise. In this study, we use a recently developed mathematical model to analyze the responses of 15 Antarctic ice shelves to ocean waves, ranging from storm waves to tsunamis. We show how features in the geometry can create large responses that could drive calving events, and we derive simple relationships between the responses and the geometry to aid projections of future scenarios. Key Points: Crevasses and seabed protrusions create large ice shelf flexure in response to ocean wavesIce shelves that have experienced large scale calving events had much greater responses to swell than typical shelvesMedian ice shelf responses to swell are strongly correlated to median shelf front thicknesses [ABSTRACT FROM AUTHOR]

The Antarctic marginal ice zone, the regularly wave‐affected outer band of the sea ice covered Southern Ocean, typically contains an unconsolidated ice cover comprised of smaller, thinner floes than the inner ice pack. Thus, it is a highly dynamic region and susceptible to rapid expansion and contraction, making it a focal area for understanding and predicting the response of Antarctic sea ice to a changing climate. This novel study uses unsupervised statistical clustering of sea ice data simulated by a global sea ice model (standalone CICE6 combined with a wave propagation module and prescribed ocean) to address the outstanding challenge of separating the marginal ice zone from the inner ice pack in sea ice data sets. The method identifies a marginal ice zone with the desired characteristics and floe size is shown to be the key variable in the classification. Simulated marginal ice zone widths are similar to those derived from satellite observations of wave penetration distances, but contrast with those using the standard 15%–80% areal sea ice concentration proxy, particularly during austral winter. The simulated marginal ice zone is found to undergo a seasonal transition due to new ice formation in winter, increased drift in spring, and increased rates of wave‐induced breakup and melting in summer. The understanding gained from the study motivates incorporation of wave and floe‐scale processes in sea ice models, and the methods are available for application to outputs from high‐resolution and coupled sea ice–ocean–wave models for more detailed studies of the marginal ice zone (in both hemispheres). Plain Language Summary: The record‐setting responses of Antarctic sea ice extent to climate change over recent decades have generated intense research interest in the marginal ice zone at the outskirts of the ice cover. The presence of ocean waves in this region creates a granular ice cover composed of small floes, affecting heat fluxes between the atmosphere and ocean, whilst shielding inner‐pack ice, fast ice, and ice shelves from waves. Studies of the marginal ice zone are hindered by the lack of a pragmatic approach to extract the marginal ice zone from sea ice data, which aligns with its characterization as the regularly wave‐affected sea ice region. Most studies use a concentration‐based proxy, although it overlooks large wave‐affected areas. We develop new insights into the evolution of the marginal ice zone by applying a modern machine‐learning approach to model outputs, leveraging recent modeling advances. Our findings reveal a marginal ice zone composed of young, small floes during winter and older, fractured floes during summer. Simulated widths are consistent with wave‐penetration distance observations and provide evidence of the marginal ice zone's unique properties, including high melt rates. The proposed approach may provide the basis for future studies on its contribution to Antarctic sea ice variability. Key Points: A new method to identify the Antarctic marginal ice zone is proposed based on statistical clustering of sea ice propertiesSimulated marginal ice zone widths are similar to satellite observations of wave penetration distancesNew understanding gained of differences in ice melt rates and drift speeds between the marginal ice zone and the interior ice pack [ABSTRACT FROM AUTHOR]

The Ross Sea in the Southern Ocean is a key region for the formation of the Antarctic Bottom Water (AABW) that supplies the lower limb of the global overturning circulation, and contributes to 20–40 % of the total AABW production. AABW primarily originates from polynyas characterized by strong sea ice production and ocean convection that lead to the formation of Dense Shelf Water (DSW), the precursor of the AABW. The production and characteristics of DSW in the Ross Sea and AABW in the surrounding ocean are significantly affected by ice shelf meltwater transported from the nearby Amundsen Sea. The scarcity of long-term observations in the Ross Sea hinders the understanding of DSW and AABW variability, and numerical models are needed to explore the multi-scale variations of these water masses and the forcing mechanisms. In this work, a coupled high-resolution ocean-sea ice-ice shelf model is developed for the Ross Sea and Amundsen Sea, named RAISE (R oss- A mundsen Sea I ce- Se a Model). Detailed descriptions of the model configurations are provided. This study represents a first attempt to thoroughly evaluate the DSW properties and associated ocean-sea ice-ice shelf coupling processes among modelling studies in the Southern Ocean, using multiple datasets including satellite-based observations and hydrographic measurements from the World Ocean Database, Argo profilers and seal-tag sensors. In particular, the modelled temporal variations of DSW in polynyas and its key export passages are compared with long-term mooring observations, which are not seen in DSW studies before. RAISE demonstrates high skills in simulating the observed sea ice production rates in the Ross Sea polynyas, and the modelled spatial and temporal variability of DSW are significantly and strongly correlated with observations. RAISE can also effectively capture the observed long-term freshening trend of DSW prior to 2014 and the rebounding of DSW salinity after 2014. RAISE shows an overestimate of DSW density in the Ross Sea, which is associated with underestimate of ice shelf melting rates in the Amundsen Sea, missing ice shelf calving processes and subglacial discharge in the model. A sensitivity experiment simulating increased freshwater discharge from these processes can significantly improve the simulation of DSW properties. [ABSTRACT FROM AUTHOR]

Ice shelves in the Amundsen Sea have experienced the most rapid melting in the Antarctic and are expected to accelerate throughout this century under climate warming. In this study, a high‐resolution ocean‐sea ice‐ice shelf model is employed to conduct sensitivity experiments to explore the effects of increasing melt rates of the Amundsen Sea ice shelves on hydrography, sea ice and ice shelf in the Ross Sea. The results indicate that the substantial inflow of meltwater significantly freshens the Ross Sea, inhibiting the formation and export of the Dense Shelf Water, the volume of which is reduced by 19%–33% on the shelf. Temperatures in the eastern and western Ross Sea exhibit different responses to the enhanced meltwater input. The freshening of the western Ross Sea weakens the mesoscale eddy activities which are efficient in carrying warm Circumpolar Deep Water onto the shelf, leading to an average temperature decrease of 0.02–0.08°C. Conversely, in the eastern Ross Sea, there is a marked warming outside the shelf under increased meltwater, which results from zonal pressure gradients associated with the meltwater distributions. This consequently causes stronger on‐shelf heat transport and shows warming of 0.12–0.22°C on the eastern Ross Sea shelf. The narrow shelf in the eastern Ross Sea allows the warmer water to reach the Ross Ice Shelf (RIS) front, resulting in an about 6%–9% increase in the RIS melting. These results suggest a possible mechanism for acceleration in the RIS melting in the future that is associated with enhanced meltwater inflow. Plain Language Summary: Many studies suggest that the Amundsen Sea ice shelf will experience accelerated melting throughout this century, leading to the release of a substantial amount of freshwater, which will be transported westward and impact the Ross Sea downstream. In this study, a numerical model including ocean, ice shelves and sea ice is used to simulate the effects of increased melting rates of the Amundsen Sea ice shelves on the Ross Sea ocean and ice environments. The results indicate pronounced differences in temperature changes in the eastern and western Ross Sea under enhanced meltwater input. The freshening of the western Ross Sea weakens the warm water intrude onto the shelf, resulting in cooling of the western Ross Sea. In the eastern Ross Sea, there is warming associated with changes in large‐scale flows caused by the distributions of meltwater. More heat transport into the eastern Ross Sea shelf can reach the front of the Ross Ice Shelf (RIS) — the largest Antarctic ice shelf and promotes its melting. Our study proposes a mechanism for acceleration in the RIS melting in the future, highlighting the role of meltwater from the Amundsen Sea ice shelves. Key Points: Enhanced Amundsen Sea ice shelf melting causes marked freshening of the Ross Sea and inhibits the formation of Antarctic Bottom WaterThe increased meltwater inflow from the Amundsen Sea causes cooling of the western Ross Sea and warming of the eastern Ross SeaMore heat transport into the eastern Ross Sea shelf can reach the front of the Ross Ice Shelf and increase its melting rate [ABSTRACT FROM AUTHOR]

Autonomous underwater vehicles (AUVs) have been used in the polar regions for decades. The technical challenges are well understood, and since the mid 1990s, missions of several hundred kilometers under sea ice have been possible. However, there remains a large gap between the endurance achieved in practice and the 1000+ km needed for large-scale sea ice studies; multiple, parallel sections under West Antarctic ice shelves; or sections under the Filchner-Ronne Ice Shelf. This retrospective examines how the U.K. Autosub program's requirements for under ice observations were determined and how those requirements helped build a strategy for a decade of technical progression and scientific achievement. At times progress was faltering, vehicle reliability was inadequate and the approach to risk management was reactive rather than proactive. New analytical tools, some controversial, were developed to assess and manage risk and to drive improvements. While new satellite techniques arguably reduced the need for deployments under sea ice, they remain the only effective solution to fill data-gaps in bathymetry and ocean/ice interactions under ice shelves. The challenge for international collaboration is to accelerate the development of robust and reliable vehicles. The first task remains to survey the basic geometry of the key Antarctic ice shelf cavities. Taking a decadal view, AUV capability should expand to be capable of yearlong deployments under critical ice shelves. [ABSTRACT FROM AUTHOR]

The exchange of heat and freshwater between glaciers and the ocean is dictated by the circulation in glacial fjords and ice shelf cavities. Therefore, our ability to estimate and predict these fluxes depends on our understanding of the circulation mechanisms inside these polar estuaries. Here, we use an exceptionally long observational data set (8+ years) to develop and validate a high‐resolution realistic numerical model of Milne Fiord (Nunavut, Canada), a glacial fjord with an ice shelf at its mouth. Model results show the circulation inside Milne Fiord from 2011 to 2019 is highly three‐dimensional and unsteady. Three distinct circulation modes are identified (eddy, front, barotropic). The shifts between circulation modes are driven by density variations in the offshore coastal current, which restrict vertical stretching, allowing (or not) the coastal current to develop sufficient relative vorticity to enter the fjord. The unsteadiness of the system results in an overturning estuarine circulation with mean velocities ∼50 times smaller than the instantaneous field. Moreover, analysis of the model outputs suggest that at least 2 years of simulation are needed to yield reliable average heat flux estimates in this environment. This work highlights the value of combining long term (>1 year) observations with numerical modeling. This allowed us to uncover the spatial and temporal variability of the system, which impacts how heat and freshwater fluxes can be reliably estimated. Plain Language Summary: Fjords and bays where glaciers end their course in the ocean are common in the Arctic and in Antarctic. The circulation and the interactions between the ocean and glaciers in these polar estuaries has implications for ice loss and sea level rise. It is therefore important to understand the ocean dynamics in glacial fjords (a fjord with a marine terminating glacier) and ice shelf cavities (a water column overlain by the floating extension of a glacier or ice shelf) in order to quantify the impact of the ocean forcing on glaciers. In this study, we use a numerical model to reproduce the ocean conditions in Milne Fiord, a glacial fjord with an ice shelf on the north coast of Ellesmere Island, Nunavut, Canada. The model is validated with in situ observations. The results show that although the velocities are small in Milne Fiord (around 2 cm/s), the circulation is very dynamic. In fact, the circulation pattern is continually changing in response to offshore density variations (no steady‐state). This is problematic for estimating the heat exchange between the ocean and the glacier, because it means limited observations cannot be readily extrapolated in time and space. Key Points: A high‐resolution numerical model of a glacial fjord with an ice shelf (Milne Fiord) was run for 8.3 years and validated with observationsMilne Fiord circulation is highly variable across space and time and switches between three different circulation modes (no steady‐state)The variability of the circulation highlights the need for long term observational programs combined with (validated) numerical models [ABSTRACT FROM AUTHOR]

Antarctic ice shelves are losing mass at drastically different rates, primarily due to differing rates of oceanic heat supply to their bases. However, a generalized theory for the inflow of relatively warm water into ice shelf cavities is lacking. This study proposes such a theory based on a geostrophically constrained inflow, combined with a threshold bathymetric elevation, the Highest Unconnected isoBath (HUB), that obstructs warm water access to ice shelf grounding lines. This theory captures ∼ 90% of the variance in melt rates across a suite of idealized process‐oriented ocean/ice shelf simulations with quasi‐randomized geometries. Applied to observations of ice shelf geometries and offshore hydrography, the theory captures ∼80% of the variance in measured ice shelf melt rates. These findings provide a generalized theoretical framework for melt resulting from buoyancy‐driven warm water access to geometrically complex Antarctic ice shelf cavities. Plain Language Summary: The floating extensions of Antarctic glaciers ("ice shelves") are losing ice at drastically different rates. A large component of this ice loss is due to melting from below by relatively warm ocean waters, which typically lie hundreds of meters below the surface. Previous studies have attempted to predict ice shelf melt rates using knowledge of the interface between the ice and the ocean. However, these relationships struggle to capture the variations in melt rates around Antarctica, in part because they do not account for obstruction of warm water access by variations in the shae of the seafloor. In this study we introduce a theory for the rate at which warm waters access Antarctica's ice shelves, which indirectly predicts how much the ice shelf melts. This theory is grounded in the assumption that the ocean flow beneath cavities is dominated by the rotation of the earth, and utilizes a novel quantification of seafloor obstruction of warm water inflows. We show that this theory is successful at predicting melt in simulations of ice shelves of different shapes, and in observations of real ice shelves. This work provides a theoretical grounding for melt resulting from warm subsurface waters flowing underneath Antarctic ice shelves. Key Points: We introduce a new theoretical framework for inflow of warm water into ice shelf cavities based on geostrophically‐constrained circulationA new metric, the Highest Unconnected Isobath (HUB), quantifies bathymetric barriers to warm water access in complex geometriesOur HUB‐informed theoretical framework is able to accurately predict melt rates across a suite of idealized models and observational data [ABSTRACT FROM AUTHOR]

Introduction: This study focused on a Chinese Antarctic krill vessel utilising continuous pumping fishing technology. The resistance characteristics of Antarctic krill ships trawling in floating ice areas is of great significance for the navigation and fishing of krill ships in ice areas. Methods: Firstly, MATLAB programming using discrete elements combined with genetic algorithms was used to construct a normal distribution ice flow model. Secondly, a fluid-structure coupling interface is created through the contact between the fluid and the trawl grid, and the displacement and resistance of the trawl grid are evaluated on the shared interface. Finally, the effects of ice density and ship sailing speed on ice resistance were studied. Results and discussion: The results of the calculations results show that ice resistance is positively related to the concentration and speed of floating ice, moreover, there is a special speed point where ice resistance increases rapidly. As the speed increases, the proportion of trawl resistance to the total resistance continues to increase, while the proportion of ice resistance continues to decrease. This paper provides a reference for the navigation and fishing resistance assessment of Antarctic krill ships in floating ice areas. [ABSTRACT FROM AUTHOR]

The ice streams flowing into the Amundsen Sea, West Antarctica, are losing mass due to changes in oceanic basal melting of their floating ice shelves. Rapid ice‐shelf melting is sustained by the delivery of warm Circumpolar Deep Water to the ice‐shelf cavities, which is first supplied to the continental shelf by an undercurrent that flows eastward along the shelf break. Temporal variability of this undercurrent controls ice‐shelf basal melt variability. Recent work shows that on decadal timescales the undercurrent variability opposes surface wind variability. Using a regional model, we show that undercurrent variability is induced by sea‐ice freshwater fluxes, particularly those north of the shelf break, which affect the cross‐shelf break density gradient. This sea‐ice variability is linked to tropical Pacific variability impacting atmospheric conditions over the Amundsen Sea. Ice‐shelf melting also feeds back onto the undercurrent by affecting the on‐shelf density, thereby influencing shelf‐break density gradient anomalies. Plain Language Summary: The glaciers that flow toward the Amundsen Sea, West Antarctica, are losing ice faster than most others about the continent. Once these glaciers reach the coast, they extend out onto the ocean surface, forming ice shelves. The rapid loss of ice is caused by changes in melting by relatively warm ocean waters beneath the floating ice shelves. In the Amundsen Sea, a deep ocean current is responsible for delivering warm water from the deep ocean to the ice shelves. We present model results that show that this deep current varies on decadal timescales as a consequence of systematic sea‐ice melt and formation patterns. A faster current drives more rapid ice shelf melting which, via a feedback process, further accelerates the current. Climate variability originating in the tropical Pacific Ocean is responsible for the variability in the sea‐ice, and is therefore also responsible for the effects on melting of the ice shelves. Key Points: In the Amundsen Sea decadal variability of an undercurrent flowing along the shelf break drives decadal variability in ice‐shelf basal meltSea‐ice freshwater fluxes and positive feedbacks from ice‐shelf basal melt drive the undercurrent variabilityTropical Pacific teleconnections induce atmospheric anomalies over the Amundsen Sea which drive the sea‐ice freshwater flux variability [ABSTRACT FROM AUTHOR]

Present study focuses on the utilization of Earth observation satellite-04 (EOS-04) synthetic aperture radar (SAR) data for maintaining the continuity of the first Indian radar imaging satellite (RISAT)-1 SAR derived products along with exploring the potential of capability of the improved sensor over mountain and polar cryospheric region. Backscattering coefficient (σ0) of various snow and ice features over mountain and polar cryosphere have been analysed to understand the interaction mechanism using C-band SAR data. EOS-04 is able to pick up the spatio-temporal variability of SAR backscatters over accumulation and ablation zone of the glacier due to melt-freeze cycles, and observations were in accordance with variation in elevations over the glacier surface. When analysed for Drang-Drung glacier, wet snow zone was found to be prominently centered around 5500 m elevation zone, having sigmanaught backscatter lower than –10 dB in the ablation months, whereas percolation zone was observed at more than 6000 m elevation with higher sigma-naught backscatter of around –4 dB and above as winter started setting in. EOS-04 also showed the potential to classify various polar ice features based on backscattering signature using HH (H, horizontal) (σ0), HV (V, vertical) (σ0) and normalized difference polarization ratio index (NDPRI) respectively. EOS-04 data have been used to implement approaches to retrieve wet snow cover and set up of Weather Research and Forecasting Model Hydrological Modelling System (WRF hydro) model for snow melt runoff studies, interaction mechanism of snow and ice, snow/ice facies extraction, ice shelf monitoring, sea ice properties and sea ice advisory for Indian scientific expedition to Antarctica. Enrichment of EOS-04 data, suitable for cryosphere studies, will be employed to retrieve parameters such as snowpack properties, elevation, ice surface velocities over mountain and polar region, and to further improve comprehensive understanding on regional and global frozen ice dynamics. [ABSTRACT FROM AUTHOR]

The largest uncertainty in future sea-level rise is loss of ice from the Greenland and Antarctic Ice Sheets. Ice shelves, freely floating platforms of ice that fringe the ice sheets, play a crucial role in restraining discharge of grounded ice into the ocean through buttressing. However, since the 1990s, several ice shelves have thinned, retreated, and collapsed. If this pattern continues, it could expose thick cliffs that become structurally unstable and collapse in a process called marine ice cliff instability (MICI). However, the feedbacks between calving, retreat, and other forcings are not well understood. Here we review observed modes of calving from ice shelves and marine-terminating glaciers, and their relation to environmental forces. We show that the primary driver of calving is long-term internal glaciological stress, but as ice shelves thin they may become more vulnerable to environmental forcing. This vulnerability—and the potential for MICI—comes from a combination of the distribution of preexisting flaws within the ice and regions where the stress is large enough to initiate fracture. Although significant progress has been made modeling these processes, theories must now be tested against a wide range of environmental and glaciological conditions in both modern and paleo conditions. Ice shelves, floating platforms of ice fed by ice sheets, shed mass in a near-instantaneous fashion through iceberg calving. Most ice shelves exhibit a stable cycle of calving front advance and retreat that is insensitive to small changes in environmental conditions. Some ice shelves have retreated or collapsed completely, and in the future this could expose thick cliffs that could become structurally unstable called ice cliff instability. The potential for ice shelf and ice cliff instability is controlled by the presence and evolution of flaws or fractures within the ice. [ABSTRACT FROM AUTHOR]

Silt-rich meltwater plume deposits (MPDs) analyzed from marine sediment cores have elucidated relationships that are clearly connected, yet difficult to constrain, between subglacial hydrology, ice-marginal landforms, and grounding-zone retreat patterns for several glacial catchments. Few attempts have been made to infer details of subglacial hydrology, such as flow regime, geometry of drainage pathways, and mode(s) of sediment transport through time, from grain-scale characteristics of MPDs. Using sediment samples from MPD, till, and grounding-zone proximal diamicton collected offshore of six modern and relict glacial catchments in both hemispheres, we examine grain shape distributions and microtextures (collectively, grain micromorphology) of the silt fraction to explore whether grains are measurably altered from their subglacial sources via meltwater action. We find that 75 % of all imaged grains (n = 9400) can be described by 25 % of the full range of measured shape morphometrics, indicating grain shape homogenization through widespread and efficient abrasive processes in subglacial environments. Although silt grains from MPDs exhibit edge rounding more often than silt grains from tills, grain surface textures indicative of fluvial transport (e.g., v-shaped percussions) occur in only a modest number of grains. Furthermore, MPD grain surfaces retain several textures consistent with transport beneath glacial ice (e.g., straight or arcuate steps, (sub)linear fractures) in comparable abundances to till grains. Significant grain shape alteration in MPDs compared to their till sources is observed in sediments from glacial regions where (1) high-magnitude, potentially catastrophic meltwater drainage events are inferred from marine sediment records and (2) submarine landforms suggest supraglacial melt contributed to the subglacial hydrological budget. This implies that quantifiable grain shape alteration in MPDs could reflect a combination of high-energy flow of subglacial meltwater, persistent sediment entrainment, and/or long sediment transport distances through subglacial drainage pathways. Integrating grain micromorphology into analysis of MPDs in site-specific studies could therefore aid in distinguishing periods of persistent, well-connected subglacial discharge from periods of sluggish or disorganized drainage. In the wider context of deglacial marine sedimentary and bathymetric records, a grain micromorphological approach may bolster our ability to characterize ice response to subglacial meltwater transmission through time. This work additionally demonstrates that glacial and fluvial surface textures are retained on silt-sized quartz grains in adequate amounts for microtexture analysis, which has heretofore been conducted exclusively on the sand fraction. Therefore, grain microtextures can be examined on silt-rich glaciogenic deposits that contain little to no sand as a means to evaluate sediment transport processes. [ABSTRACT FROM AUTHOR]

The Northeast Water Polynya is a significant annually recurring summertime Arctic polynya, located off the coast of Northeast Greenland. It is important for marine wildlife and affects local atmospheric and oceanic processes. In this study, over 40 years of observational and reanalysis products (ERA5 and ORAS5) are analyzed to characterize the polynya's climatology and ascertain forcing mechanisms. The Northeast Water Polynya has high spatiotemporal variability; its location, size and structure vary interannually, and the period for which it is open is changing. We show this variability is largely driven by atmospheric forcing. The polynya extent is determined by the direction of the near‐surface flow regime, and the relative locations of high and low sea‐level pressure centers over the region. The surface conditions also impact the oceanic water column, which has a strong seasonal cycle in potential temperature and salinity, the amplitude of which decreases with depth. The ocean reanalyses also show a significant warming trend at all depths and a freshening near the surface consistent with greater ice melt, but salinification at lower depths (∼200 m). As the Arctic region changes due to anthropogenic forcing, the sea‐ice edge is migrating northwards and the Northeast Water Polynya is generally opening earlier and closing later in the year. This could have significant implications for both the atmosphere and ocean in this complex and rapidly changing environment. Plain Language Summary: Polynya's are areas of open water surrounded by sea ice. These features are important for marine wildlife and can impact how the atmosphere and ocean interact. The Northeast Water Polynya is one example from the Arctic. Each summer, it appears off the coast of Northeast Greenland. In this research we use data from the last 40 years to study this polynya. We find that its location, size and structure varies from year to year. The period for which it is open each year also changes. We conclude that these differences are due to changes in the wind direction near the surface. Winds that flow from south to north over the region are linked to a larger polynya. Winds that flow from north to south are linked to a smaller polynya. With climate change, the Northeast Water Polynya is opening earlier and closing later in the year. In the future, this polynya may no longer form as it does now, which will impact the local environment and wildlife. Key Points: A climatological study of the Northeast Water Polynya reveals spatial, interannual and decadal variabilityThe summertime polynya extent closely correlates to near‐surface winds, largely dictated by the orientation of the pressure gradient across Fram StraitBetween 1980 and 2022, the duration of the Northeast Water Polynya, and associated oceanic warming, increased [ABSTRACT FROM AUTHOR]

The article highlights a daring expedition to Antarctica's Canisteo Peninsula, where a team led by Peter Neff, a polar glaciologist, drills ice cores crucial for understanding the precarious state of the Pine Island and Thwaites glaciers. Topics include the urgent need for data on Antarctic coastal climate, the challenges of drilling in remote and stormy locations, and the significance of ice cores in unraveling past and future climate trends in the region.

Elevated ice shelf melt rates in West Antarctica have been attributed to transport of warm Circumpolar Deep Water (CDW) onto the continental shelf via bathymetric troughs. These inflows are supplied by an eastward, subsurface slope current (referred to as the Antarctic Slope Undercurrent) that opposes the westward momentum input from local winds and tides. Despite its importance to basal melt, the mechanism via which the undercurrent forms, and thus what controls the shoreward heat transport, remains unclear. In this study, the dynamics of the undercurrent are investigated using high-resolution process-oriented simulations with coupled ocean, sea ice, and ice shelf components. It is shown that the bathymetric steering of the undercurrent toward the ice shelf is driven by upwelling of meltwater within the ice shelf cavity. Increased basal melt therefore strengthens the undercurrent and enhances onshore CDW transport, which indicates a positive feedback that may accelerate future melt of ice shelves, potentially further destabilizing the West Antarctic Ice Sheet. [ABSTRACT FROM AUTHOR]

In recent decades, the Greenland ice sheet has been losing mass through glacier retreat and ice flow acceleration. This mass loss is linked with variations in submarine melt, yet existing ocean models are either coarse global simulations focused on decadal‐scale variability or fine‐scale simulations for process‐based investigations. Here, we unite these scales with a framework to downscale from a global state estimate (15 km) into a regional model (3 km) that resolves circulation on the continental shelf. We further downscale into a fjord‐scale model (500 m) that resolves circulation inside fjords and quantifies melt. We demonstrate this approach in Scoresby Sund, East Greenland, and find that interannual variations in submarine melt at Daugaard‐Jensen glacier induced by ocean temperature variability are consistent with the decadal changes in glacier ice dynamics. This study provides a framework by which coarse‐resolution models can be refined to quantify glacier submarine melt for future ice sheet projections. Plain Language Summary: Over the past several decades, the Greenland ice sheet has been losing ice and contributing to sea‐level rise. About half of this ice loss is induced by melt that occurs where glaciers meet the ocean. Using coarse‐scale ocean models that simulate circulation around the globe, previous studies have noted a strong link between ocean temperature and enhanced glacier ice loss. However, due to the small scale of Greenland's fjords, coarse models are unable to directly quantify circulation in these fjords and melt on submerged glaciers. In this study, we develop a new framework to "zoom in" on a fjord, using high‐resolution models driven by larger coarse‐resolution models. In this approach, we simulate melt on one of Greenland's biggest glaciers and find that periods of higher melt coincide with more ice loss as observed from satellites. Since this framework is adaptable to other regions, it could also be used to simulate melt on other glaciers and support estimates of future sea‐level rise. Key Points: Subsurface temperature variability is simulated in a narrow fjord network using regional models downscaled from a global state estimateModeled increases in ocean melt at Daugaard‐Jensen glacier coincide with the onset of acceleration in 2005 and retreat and thinning in 2011Model variations in shelf‐to‐fjord ocean properties match with observations, providing a basis to estimate ocean forcing in ice projections [ABSTRACT FROM AUTHOR]

Recent observations suggest that El Niño–Southern Oscillation (ENSO) impacts basal melting of West Antarctic ice shelves, yet sparse ocean observations limit our understanding of the associated processes. Here we investigate how ENSO events modulate subsurface West Antarctic shelf temperatures using high‐resolution global ocean‐sea ice model simulations. During El Niño, the subsurface shelf warming between 150 m and the shelf bottom can be up to 0.5°C in front of ice shelves. This warming arises from a weaker Amundsen Sea Low (ASL) and weaker coastal easterlies that reduce on‐shelf Ekman transport of cold surface waters, enabling enhanced transport of warm Circumpolar Deep Water (CDW) onto the shelf. A largely opposite response occurs during La Niña, with a stronger ASL and stronger Ekman transport that results in less cross‐shelf CDW transport and cooling in the subsurface. These findings have implications for interpreting basal melting on interannual to decadal time‐scales in West Antarctica. Plain Language Summary: El Niño‐Southern Oscillation (ENSO) is the Earth's dominant year‐to‐year climate variation. The impacts of its two phases, El Niño and La Niña, extend from the tropics to Antarctica through atmospheric waves. Past studies have suggested that West Antarctic ice shelves melt more during El Niño because of warmer ocean waters at the ice shelf bases. However, oceanic changes during El Niño lead to warming on the shelf near the ice which is difficult to isolate. That is because ENSO is only one of many drivers that impact shelf water temperatures. In this work, we simulate isolated ENSO events using an ocean circulation model. We show that during El Niño, the on‐shelf flow of cold surface waters in West Antarctica, driven by coastal easterly winds, is reduced because the winds weaken. To balance out this mass deficit at the surface, more warm CDW flows onto the continental shelf below. During La Niña, we see a largely opposite response. Stronger coastal easterlies increase the on‐shelf flow of cold surface waters and less CDW is flowing onto the shelf. Our results show the link between ENSO and mass loss of the West Antarctic ice shelves and ice sheet. Key Points: Ocean‐sea ice model simulations of El Niño and La Niña events illustrate how they modulate West Antarctic shelf temperaturesEl Niño weakens coastal easterlies, reduces on‐shelf Ekman flow of cold waters, increasing cross‐shelf flow of warm Circumpolar Deep Water (CDW)The La Niña shelf circulation response is largely opposite and reduces cross‐shelf transport of warm CDW [ABSTRACT FROM AUTHOR]

The 2023 Antarctic sea ice extent (SIE) maximum on 7 September was the lowest annual maximum in the satellite era (16.98 × 106 km2), with the largest contributions to the anomaly coming from the Ross (37.7%, −0.57 × 106 km2) and Weddell (32.9%, −0.49 × 106 km2) Seas. The SIE was low due to anomalously warm (>0.3°C) upper‐ocean temperatures combined with anomalously strong northerly winds impeding the ice advance during the fall and winter. Northerly winds of >12 ms−1 in the Weddell Sea occurred because of negative pressure anomalies over the Antarctic Peninsula, while those in the Ross Sea were associated with extreme blocking episodes off the Ross Ice Shelf. The Ross Sea experienced an unprecedented SIE decrease of −1.08 × 103 km2 d−1 from 1 June till the annual maximum. The passage of quasi‐stationary and explosive polar cyclones contributed to periods of southward ice‐edge shift in both sectors. Plain Language Summary: Sea ice provides a vital habitat for life in the Southern Ocean, and plays an important role in the ocean circulation, the dynamics of the Earth's climate, the biogeochemical cycle, and the regional ecosystem. Climatologically, Antarctic sea ice expands northwards from the continent each autumn and winter. However, in 2023 an unprecedented slow ice expansion occurred in the Southern Ocean ahead of the annual maximum on 7 September of 16.98 × 106 km2, which was 1.46 × 106 km2 below the long‐term average. In fact, the area covered by ice remained at a record low level every day from 21 April 2023 until 11 November 2023. Our findings suggest that an impact of upper‐ocean warming and changes in winds, combined with heat and moisture fluxes, extreme winds and high ocean waves associated with polar cyclones (storms), contributed to these record low ice conditions. In particular, cyclones caused episodes of exceptional slow ice expansion or even retreat, leading to negative ice anomalies. For instance, the ice‐edge in the Weddell Sea was moved southwards quickly in a few days (up to 256 km southward) with an ice area loss of ∼2.3 × 105 km2, equivalent to the size of United Kingdom. Key Points: The 2023 Antarctic sea ice extent maximum on 7 September (16.98 × 106 km2) was the lowest annual maximum in the satellite eraAnomalous upper‐ocean warming and strong northerly winds contributed to impeding the ice expansion in the Ross and Weddell SeasQuasi‐stationary and explosive polar cyclones contributed to periods of southward ice‐edge shift in both sectors [ABSTRACT FROM AUTHOR]

The rate at which the Antarctic Ice Sheet loses mass is to a large degree controlled by ice-ocean interactions underneath small ice shelves, with the most sensitive regions concentrated in even smaller areas near grounding lines and local pinning points. Sufficient horizontal resolution is key to resolving critical ice-ocean processes in these regions, but difficult to afford in large-scale models used to predict the coupled response of the entire Antarctic Ice Sheet and the global ocean to climate change. In this study we describe the implementation of a framework that couples the ice sheet flow model Úa with the Finite Element Sea Ice Ocean Model (FESOM-1.4) in a configuration using depth-dependent vertical coordinates. The novelty of this approach is the use of horizontally unstructured grids in both model components, allowing us to resolve critical processes directly, while keeping computational demands within the range of feasibility. We use the Marine Ice Sheet–Ocean Model Intercomparison Project framework to verify that ice retreat and readvance is reliably simulated, and inaccuracies in mass, heat and salt conservation are small compared to the forcing signal. Further, we demonstrate the capabilities of our approach for a global ocean/Antarctic Ice Sheet domain. In a 39-year hindcast simulation (1979–2018) we resolve retreat behaviour of Pine Island Glacier, a known challenge for coarser resolution models. We conclude that Úa-FESOM is well suited to improve predictions of the Antarctic Ice Sheet evolution over centennial time scales. [ABSTRACT FROM AUTHOR]

Melting icebergs provide nearly half of the total freshwater flux from ice shelves to the ocean, but the availability of accurate, data-constrained melting rate parametrisations limits the correct representation of this process in ocean models. Here, we investigate the melting of a vertical ice face in a warm, salt-stratified environment in a laboratory setting. Observations of the depth-dependent melting rates ${m}$ and boundary layer flow speed $U$ are reported for a range of initially uniform far-field ambient temperatures $T_a$ above ${10}\,^{\circ }{\rm C}$. Ice scallops are characteristic features observed in all experiments, with the width of the scallops consistent with the theory of double-diffusive layers. The morphology of the scallops changes from symmetric about the scallop centre in the colder experiments to asymmetric in the warmer experiments. Observed melting rates are consistent with a melting rate scaling of the form ${m}\propto U\,\Delta T_a$ proposed by previous work in less extreme parameter regimes, where $\Delta T_a$ is the magnitude of thermal driving between the ambient and ice–fluid interface. Our results indicate that ice scalloping is closely linked to the naturally convecting flow of the ambient fluid. Depth-averaged melting rates depend on the buoyancy frequency in the ambient fluid, and double-diffusive convection promotes a turbulent-flux regime distinct from that explained previously in an unstratified regime. These findings have implications for parametrising melting rates of icebergs and glaciers in numerical models or potential freshwater harvesting operations, and provide insights into the interplay between stratification and ice melting. [ABSTRACT FROM AUTHOR]

In late March 2011, landfast sea ice (hereafter, "fast ice") formed in the northern Larsen B embayment and persisted continuously as multi-year fast ice until January 2022. In the 11 years of fast-ice presence, the northern Larsen B glaciers slowed significantly, thickened in their lower reaches, and developed extensive mélange areas, leading to the formation of ice tongues that extended up to 16 km from the 2011 ice fronts. In situ measurements of ice speed on adjacent ice shelf areas spanning 2011 to 2017 show that the fast ice provided significant resistive stress to ice flow. Fast-ice breakout began in late January 2022 and was closely followed by retreat and breakup of both the fast-ice mélange and the glacier ice tongues. We investigate the probable triggers for the loss of fast ice and document the initial upstream glacier responses. The fast-ice breakup is linked to the arrival of a strong ocean swell event (>1.5 m amplitude; wave period waves >5 s) originating from the northeast. Wave propagation to the ice front was facilitated by a 12-year low in sea ice concentration in the northwestern Weddell Sea, creating a near-ice-free corridor to the open ocean. Remote sensing data in the months following the fast-ice breakout reveals an initial ice flow speed increase (>2 -fold), elevation loss (9 to 11 m), and rapid calving of floating and grounded ice for the three main embayment glaciers Crane (11 km), Hektoria (25 km), and Green (18 km). [ABSTRACT FROM AUTHOR]

The access of heat to the Antarctic ice shelf cavities is regulated by the Antarctic Slope Front, separating relatively warm offshore water masses from cold water masses on the continental slope and inside the cavity. Previous observational studies along the East Antarctic continental slope have identified the drivers and variability of the front and the associated current, but a complete description of their seasonal cycle is currently lacking. In this study, we utilize two years (2019–2020) of observations from two oceanographic moorings east of the prime meridian to further detail the slope front and current seasonality. In combination with climatological hydrography and satellite‐derived surface velocity, we identify processes that explain the hydrographic variability observed at the moorings. These processes include (a) an offshore spreading of seasonally formed Antarctic Surface Water, resulting in a lag in salinity and thermocline depth seasonality toward deeper isobaths, and (b) the crucial role of buoyancy fluxes from sea ice melt and formation for the baroclinic seasonal cycle. Finally, data from two sub‐ice‐shelf moorings below Fimbulisen show that flow at the main sill into the cavity seasonally coincides with a weaker slope current in spring/summer. The flow is directed out of the cavity in autumn/winter when the slope current is strongest. The refined description of the variability of the slope current and front contributes to a more complete understanding of processes important for ice‐shelf‐ ocean interactions in East Antarctica. [ABSTRACT FROM AUTHOR]

Ice shelves limit the flux of grounded ice into the ocean by buttressing the discharge of land-based ice upstream. Ice shelf weakening and collapse can lead to decreased buttressing and observations increasingly show that some ice shelves have experienced increased melt and increased calving, with recent hypotheses suggesting that increased melt leads to increased fracturing. However, the specific processes that control this correlation are not yet understood, with mechanisms other than melt affecting fracturing. Here we use the topography of the ice shelf base from BedMachine to investigate how basal melting and ice deformation contribute to crevasse and melt channel formation and evolution on the Pine Island Ice Shelf in West Antarctica. We find that high basal melt rates and high first principal strain rates lead to substantial roughening of the ice shelf through a collection of features, including melt channels and crevasses. Critically, melt channels and crevasses are the deepest in all directions at locations where the highest rates of melting and straining occur simultaneously. This suggests that the combination of melt rates and strain rates work in tandem to excavate and seed the deepest melt channels and crevasses on ice shelves. These features then may form lines of weakness that transform into rifts and, ultimately, the detachment boundary for calving events. This implies that melt and fracture play an important role in controlling the dynamics of ice shelves. Plain Language Summary Future sea level rise is tied to floating Antarctic ice shelves which limit the flow of ice from the continent. Ice shelf collapse could trigger an acceleration of land-based ice into the ocean due to the loss of support, leading to future sea level rise. It has been shown that ice shelves with a higher melt have more crevasses, are more fractured, and are rough. However, the specific processes driving the potential connection between melt and fracture are not well understood. Here we use ice shelf topography to study the relationship between roughness and the size and spacing of geometric features on the Pine Island Ice Shelf. We find that high melt rates and high strain rates result in deeper and wider features on the ice shelf. We also find that, in contrast to the results of previous studies, both melt and fracture contribute to the deepest features. This suggests that these processes contribute to enhancing the depth of features. We hypothesize that this amplifying interaction may then promote rifting and iceberg calving, hinting that it is the combination of melt and fracture that is important in controlling the dynamics of ice shelves. [ABSTRACT FROM AUTHOR]

Internal wave-driven mixing is an important factor in the balance of heat and salt fluxes in the polar regions of the ocean. Transformation of internal waves at the edge of the ice cover can enhance the mixing and melting of ice in the Arctic Ocean and Antarctica. In the polar oceans, internal solitary waves (ISWs) are generated by various sources, including tidal currents over bottom topography, the interaction of ice keels with tides, time-varying winds, vortices, and lee waves. In this study, a numerical investigation of the transformation of ISWs propagating from open water in the stratified sea under the edge of the ice cover is carried out to compare the depression ISW transformation and loss of energy on smooth ice surfaces, including those on the ice shelf and glacier outlets, with the processes beneath the ridged underside of the ice. They were carried out using a non-hydrostatic model that is based on the Reynolds-averaged Navier–Stokes equations in the Boussinesq approximation for a continuously stratified fluid. The Smagorinsky turbulence model extended for stratified fluid was used to describe the small-scale turbulent mixing explicitly. Two series of numerical experiments were carried out in an idealized 2D setup. The first series aimed to study the processes of the ISWs of depression transformation under an ice cover of constant submerged ice thickness. Energy loss was estimated based on a budget of depth-integrated pseudoenergy before and after the wave transformation. The transformation of ISWs of depressions is controlled by the blocking parameter β , which is the ratio of the minimum thickness of the upper layer under the ice cover to the incident wave amplitude. The energy loss was relatively small for large positive and large negative values of β. The maximal value of energy loss was about 38 %, and it was reached at β≈0 for ISWs. In the second series of experiments, a number of keels were located on the underside of the constant-thickness ice layer. The ISW transformation under ridged ice also depends on the blocking parameter β. For large keels (β<0), more than 40 % of energy is lost on the first keel, while for relatively small keels (β>0.3), the losses on the first keel are less than 6 %. Energy losses due to all keels depend on the distance between them, which is characterized by the parameter μ , i.e. the ratio of keel depth to the distance between keels. In turn, for a finite length of the ice layer, the distance between keels depends on the keel quantity. [ABSTRACT FROM AUTHOR]

Glacial fjords often contain ice mélange, a frozen conglomeration of icebergs, brash ice, and sea ice, that have been postulated to influence both glacier dynamics and fjord circulation through coupled mechanical and thermodynamic processes. Ice mélange meltwater can alter stratification of the water column by releasing cool, fresh water across a range of depths in the upper layer of the fjord. This meltwater input can subsequently modify the depth at which the subglacial discharge plume reaches neutral buoyancy and therefore the underlying buoyancy-driven fjord circulation and heat exchange with warm ocean shelf waters. Despite a spate of recent modelling studies exploring these proposed feedbacks, we lack in situ observations quantifying changes to the water column induced by ice mélange meltwater. Here we use a novel dataset collected before and after the melt, breakup, and down-fjord transport of an ephemeral ice mélange in front of Kangilliup Sermia (Rink Isbræ) to directly investigate the extent to which ice mélange meltwater can modify glacier-adjacent water properties. We find that even a short-lived ice mélange (4 days) can cause substantial cooling (0.18 °C) and freshening (0.25 g kg-1) of the water column that leads to stratification change down to the depth of the outflowing discharge plume. We compare our observations to an adjacent fjord, Kangerlussuup Sermia, where ice mélange seldom forms in the summertime, and show that the presence or absence of ice mélange melt creates fundamental differences in their upper layer hydrography. These observations provide critical constraints for recent modelling studies that have suggested ice mélange meltwater needs to be included in ocean circulation models for glaciers with deep grounding lines and high ice fluxes, which are precisely the glaciers exhibiting the largest magnitude terminus retreats at present. [ABSTRACT FROM AUTHOR]

Today, relatively warm Circumpolar Deep Water is melting Thwaites Glacier at the base of its ice shelf and at the grounding zone, contributing to significant ice retreat. Accelerating ice loss has been observed since the 1970s; however, it is unclear when this phase of significant melting initiated. We analyzed the marine sedimentary record to reconstruct Thwaites Glacier's history from the early Holocene to present. Marine geophysical surveys were carried out along the floating ice-shelf margin to identify core locations from various geomorphic settings. We use sedimentological data and physical properties to define sedimentary facies at seven core sites. Glaciomarine sediment deposits reveal that the grounded ice in the Amundsen Sea Embayment had already retreated to within ~45 km of the modern grounding zone prior to ca. 9,400 y ago. Sediments deposited within the past 100+ y record abrupt changes in environmental conditions. On seafloor highs, these shifts document ice-shelf thinning initiating at least as early as the 1940s. Sediments recovered from deep basins reflect a transition from ice proximal to slightly more distal conditions, suggesting ongoing grounding-zone retreat since the 1950s. The timing of ice-shelf unpinning from the seafloor for Thwaites Glacier coincides with similar records from neighboring Pine Island Glacier. Our work provides robust new evidence that glacier retreat in the Amundsen Sea was initiated in the mid-twentieth century, likely associated with climate variability. [ABSTRACT FROM AUTHOR]

We observe the evacuation of 11-year-old landfast sea ice in the Larsen B embayment on the East Antarctic Peninsula in January 2022, which was in part triggered by warm atmospheric conditions and strong offshore winds. This evacuation of sea ice was closely followed by major changes in the calving behaviour and dynamics of a subset of the ocean-terminating glaciers in the region. We show using satellite measurements that, following a decade of gradual slow-down, Hektoria, Green, and Crane glaciers sped up by approximately 20 %–50 % between February and the end of 2022, each increasing in speed by more than 100 ma-1. Circumstantially, this is attributable to their transition into tidewater glaciers following the loss of their ice shelves after the landfast sea ice evacuation. However, a question remains as to whether the landfast sea ice could have influenced the dynamics of these glaciers, or the stability of their ice shelves, through a buttressing effect akin to that of confined ice shelves on grounded ice streams. We show, with a series of diagnostic modelling experiments, that direct landfast sea ice buttressing had a negligible impact on the dynamics of the grounded ice streams. Furthermore, we suggest that the loss of landfast sea ice buttressing could have impacted the dynamics of the rheologically weak ice shelves, in turn diminishing their stability over time; however, the accompanying shifts in the distributions of resistive stress within the ice shelves would have been minor. This indicates that this loss of buttressing by landfast sea ice is likely to have been a secondary process in the ice shelf disaggregation compared to, for example, increased ocean swell or the drivers of the initial landfast sea ice disintegration. [ABSTRACT FROM AUTHOR]

Antarctic coastal polynyas are hotspots of biological production with intensive springtime phytoplankton blooms that strongly depend on meltwater‐induced restratification in the upper part of the water column. However, the fundamental physics that determine spatial inhomogeneity of the spring restratification remain unclear. Here, we investigate how different meltwaters affect springtime restratification and thus phytoplankton bloom in Antarctic coastal polynyas. A high‐resolution coupled ice‐shelf/sea‐ice/ocean model is used to simulate an idealized coastal polynya similar to the Terra Nova Bay Polynya, Ross Sea, Antarctica. To evaluate the contribution of various meltwater sources, we conduct sensitivity simulations altering physical factors such as alongshore winds, ice shelf basal melt, and surface freshwater runoff. Our findings indicate that sea ice meltwater from offshore is the primary buoyancy source of polynya near‐surface restratification, particularly in the outer‐polynya region where chlorophyll concentration tends to be high. Downwelling‐favorable alongshore winds can direct offshore sea ice away and prevent sea ice meltwater from entering the polynya region. Although the ice shelf basal meltwater can ascend to the polynya surface, much of it is mixed vertically over the water column and confined horizontally to a narrow coastal region, and thus does not contribute significantly to the polynya near‐surface restratification. Surface runoff from ice shelf surface melt could contribute greatly to the polynya near‐surface restratification. Nearby ice tongues and headlands strongly influence the restratification through modifying polynya circulation and meltwater transport pathways. Results of this study can help explain observed spatiotemporal variability in restratification and associated biological productivity in Antarctic coastal polynyas. Plain Language Summary: Antarctic coastal polynyas are key habitats of regional marine ecosystems. During spring, the upper part of the polynya water column restratifies and forms a near‐surface layer of low‐salinity water. This process is important for springtime phytoplankton blooms, as the stable surface layer keeps phytoplankton in the well‐lit region and enhances phytoplankton growth. Employing high‐resolution models of idealized coastal polynyas, this work unravels the spatial variation of restratification processes in a polynya and investigates the physical factors that affect them. It shows that sea ice meltwater from offshore regions is the foremost contributor to the near‐surface restratification in a polynya. Meanwhile, low‐salinity water from basal melt of a neighboring floating ice shelf contributes little to the near‐surface restratification in a polynya because much of the meltwater mixes vertically with ambient waters as it rises. This is in contrast to the sea ice meltwater being directly injected into the ocean surface. Freshwater runoff from the surface melt of an ice shelf is also directly injected into the polynya surface. However, due to earth rotation, it is often confined in a narrow coastal region next to the ice shelf and thus does not contribute to restratification in most of the polynya area. Key Points: Biologically‐important springtime near‐surface restratification in Antarctic coastal polynyas varies spatially within a polynyaSea ice meltwater from regions offshore of the polynya is the primary buoyancy source of polynya near‐surface restratificationIce shelf basal meltwater mixes over the water column during its ascent and contributes little to polynya near‐surface restratification [ABSTRACT FROM AUTHOR]

The ice shelves in the Bellingshausen Sea are melting and thinning rapidly due to modified Circumpolar Deep Water (mCDW) intrusions carrying heat toward ice‐shelf cavities. Observations are, however, sparse in time and space, and extensive model‐data comparisons have never been possible. Here, using a circulation model of the region and ship‐based observations, we show that the simulated water mass distributions in several troughs traversing mCDW inflows are in good agreement with observations, implying that our model has the skills to simulate hydrographic structures as well as on‐shelf ocean circulations. It takes 7.9 and 11.7 months for mCDW to travel to the George VI Ice Shelf cavities through the Belgica and Marguerite troughs, respectively. Ice‐shelf melting is mainly caused by mCDW intrusions along the Belgica and Marguerite troughs, with the heat transport through the former being ∼2.8 times larger than that through the latter. The mCDW intrusions toward the George VI Ice Shelf show little seasonal variability, while those toward the Venable Ice Shelf show seasonal variability, with higher velocities in summer likely caused by coastal trapped waves. We also conduct particle experiments tracking glacial meltwater. After 2 years of model integration, ∼33% of the released particles are located in the Amundsen Sea, supporting a linkage between Bellingshausen Sea ice‐shelf meltwater and Amundsen Sea upper ocean hydrography. Plain Language Summary: The Bellingshausen Sea Ice Shelves have been affected by high ice‐shelf melt and ice‐loss rates in Antarctica. The reason for the ice loss is the presence of warm modified Circumpolar Deep Water (mCDW) over the continental shelf, which intrudes into ice‐shelf cavities. Recently, studies combining observations and models have significantly advanced our understanding of Ice‐Ocean interactions around Antarctica. For example, in the Amundsen Sea, the region neighboring the Bellingshausen Sea and contributing the most to Antarctic glacial ice loss, such an approach has revealed the drivers and pathways of ocean heat intrusions as well as the impact of glacial meltwater on the Antarctic coastal circulation. We follow this approach and evaluate our ocean model by comparing it with ship‐based and satellite‐based observations. Using this model simulation, we show that the simulated mCDW intrudes from the continental shelf break toward ice‐shelf cavities mainly through two deep cross‐shelf troughs. The glacial meltwater is transported by the westward Antarctic Coastal Current (AACC) flowing into the Amundsen Sea. The mCDW inflow and AACC in the coastal area show seasonal variabilities with higher velocities in the summer, which are likely caused by coastal trapped waves. Key Points: The simulated hydrographic structures over the Bellingshausen Sea continental shelf region are in good agreement with observationsThe warm water intrusions toward the Venable Ice Shelf show peaks of higher velocities in summer, likely caused by coastal trapped wavesGlacial meltwater from about 33% of the area underneath the BS ice shelves flows into the Amundsen Sea within 2 years [ABSTRACT FROM AUTHOR]

Melting of ice shelves can energize a wide range of ocean currents, from three‐dimensional turbulence to relatively large‐scale boundary currents. Here, we conduct high‐resolution simulations of the western Amundsen Sea to show that submesoscale eddies are prevalent inside ice shelf cavities. The simulations indicate energetic submesoscale eddies at the top and bottom ocean boundary layers, regions with sharp topographic slopes and strong lateral buoyancy gradients. These eddies play a substantial role in the vertical and lateral (along‐isopycnal) heat advection toward the ice shelf base, enhancing the basal melting in all simulated cavities. In turn, the meltwater provides strong buoyancy gradients that energize the submesoscale variability, forming a positive loop that could affect the overall efficiency of heat exchange between the ocean and the ice shelf cavity. Our study implies that submesoscale‐induced enhancement of basal melting may be a ubiquitous process that needs to be parameterized in coarse‐resolution climate models. Plain Language Summary: Melting of ice shelves can energize a wide range of ocean currents, from three‐dimensional turbulence to relatively large‐scale boundary currents. Here, we conduct high‐resolution numerical simulations of the western Amundsen Sea to show that the basal melt of ice shelf cavities is affected by ocean eddies (vortices) that are large enough to be constrained by the Earth's rotation and ocean stratification. These eddies transport additional heat vertically toward the ice shelf base and enhance melting. In turn, the meltwater provides strong density gradients that energize the eddy variability. Our simulations imply that eddy‐induced enhancement of basal melting may be ubiquitous in ice shelf cavities. Key Points: High‐resolution ocean simulations of ice shelf cavities demonstrate the presence of strong submesoscale variabilitySubmesoscale eddies enhance the heat exchange between the ocean and the ice shelf by driving vertical and lateral heat fluxesCoupling between submesoscale variability and basal melting contributes to the efficiency of ice shelf heat exchange with the open ocean [ABSTRACT FROM AUTHOR]

The inflow of warm and salty Circumpolar Deep Water affects the melting of the ice shelf on the Amundsen Sea, a significant contributor to global sea level rise. Multi‐year mooring data (2014–2016 and 2018–2020) from the front of the Dotson Ice Shelf show the modified Circumpolar Deep Water layer was thicker during 2018–2020 than during 2014–2016. During 2014–2016, Ocean surface stress curl influenced the barotropic process and strengthened southward velocity, while during 2018–2020, it caused lift and downwelling of thermocline depth, increasing the impact of the baroclinic process in ocean circulation. The heat transport to the ice shelf during 2018–2020 (57.42 MW m−1) was half as much as it was during 2014–2016 (111.06 MW m−1) due to a weaker lower layer current. The difference in ocean circulation between two periods, caused by a difference in warm layer thickness, ultimately impacts the heat transport entering the ice shelf cavity. Plain Language Summary: Warm and salty water from the deep ocean flows into the ice shelf cavities in the West Antarctic, causing the ice to melt and contribute to global sea level rise. We measured the current and water properties in front of the Dotson Ice Shelf during 2014–2016 and 2018–2020 and found that the warm layer was thicker during the latter period. Unlike during 2014–2016 when ocean surface stress curl created a spatial imbalance in sea level and affected the southward current due to pressure gradients, during 2018–2020, ocean surface stress curl changed the density by causing upwelling and downwelling. This density change influenced the velocity variation toward the ice shelf. Although the mCDW layer was ticker, the heat influx to the ice shelf during 2018–2020 was half as much as it was during 2014–2016. The difference in ocean current during these two periods, due to differences in the warm layer thickness, ultimately affects how much heat is transported into the ice shelf cavity. Key Points: The modified circumpolar deep water layer was thicker in 2018–2020 than that during 2014–2016The baroclinic effect plays a more important role in the variability of the current entering the ice shelf during 2018–2020Differences in the seasonal cycle of the ocean surface stress curl can affect ocean circulation by changing ocean conditions [ABSTRACT FROM AUTHOR]

The Southern Ocean plays a major role in controlling the evolution of Antarctic glaciers and in turn their impact on sea level rise. We present the Southern Ocean high‐resolution (SOhi) simulation of the MITgcm ocean model to reproduce ice‐ocean interaction at 1/24° around Antarctica, including all ice shelf cavities and oceanic tides. We evaluate the model accuracy on the continental shelf using Marine Mammals Exploring the Oceans Pole to Pole data and compare the results with three other MITgcm ocean models (ECCO4, SOSE, and LLC4320) and the ISMIP6 temperature reconstruction. Below 400 m, all the models exhibit a warm bias on the continental shelf, but the bias is reduced in the high‐resolution simulations. We hypothesize some of the bias is due to an overestimation of sea ice cover, which reduces heat loss to the atmosphere. Both high‐resolution and accurate bathymetry are required to improve model accuracy around Antarctica. Plain Language Summary: Warm water from the Southern Ocean melts the glaciers and ice shelves around the Antarctic margin, leading to glacier de‐stabilization, and sea level rise. We present the Southern Ocean high‐resolution (SOhi) model to better represent ocean circulation and ice‐ocean interaction around Antarctica. We assess the accuracy of SOhi with in situ data from marine mammals and compare the results with three other ocean model simulations and to a baseline reference. All model results are slightly too warm on the continental shelf, but the higher‐resolution models yield colder waters in better agreement with observations. We attribute the warm bias to an overestimation of the sea ice cover in the ocean models. An improved bathymetry also significantly improves model accuracy in Antarctica. Key Points: High‐resolution ocean models with more complete physics are in better agreement with in situ ocean data than coarser resolution modelsAccurate bathymetry is essential to capture circulation pathways and warm water intrusions on the Antarctic continental shelfHigh‐resolution ocean models may remain too warm on the continental shelf because they over‐predict the sea ice cover [ABSTRACT FROM AUTHOR]

Identifying and quantifying irreducible and reducible uncertainties in the Antarctic Ice Sheet response to future climate change is essential for guiding mitigation and adaptation policy decision. However, the impact of the irreducible internal climate variability, resulting from processes intrinsic to the climate system, remains poorly understood and quantified. Here, we characterise both the atmospheric and oceanic internal climate variability in a selection of three CMIP6 models (UKESM1-0-LL, IPSL-CM6A-LR and MPI-ESM1.2-HR) and estimate their impact on the Antarctic contribution to sea level over the 21st century under the SSP2-4.5 scenario. To achieve this, we use a standalone ice-sheet model driven by the ocean through parameterised basal melting and by the atmosphere through emulated surface mass balance estimates. Internal climate variability affects the Antarctic contribution to changes in sea level until 2100 by 45 % to 93 % depending on the CMIP6 model. This may be a low estimate as the internal climate variability in the CMIP models is likely underestimated. For all the three climate models and for most Antarctic regions, the effect of atmospheric internal climate variability on the surface mass balance overwhelms the effect of oceanic internal climate variability on the dynamical ice-sheet mass loss by more than a factor of 3. The atmospheric internal climate variability is similar in the three CMIP6 models analysed in this study. Conversely, the amplitude of oceanic internal climate variability around Antarctica strongly depends on the climate model as underestimated convection, due to either biases in the sea-ice behaviour or in the ocean stratification, leads to weak mid-depth ocean variability. We then issue recommendations for future ice-sheet projections: use several members in the run and in its initialisation, favor 50-year averages to correct or weight simulations over the present-day period, and couple ice-sheet and climate models. [ABSTRACT FROM AUTHOR]

The mechanical influences involved in the interaction between the Antarctic sea ice and ocean surface current (OSC) on the subpolar Southern Ocean have been systematically investigated for the first time by conducting two simulations that include and exclude the OSC in the calculation of the ice-ocean stress (IOS), using an eddy-permitting coupled ocean-sea ice global model. By comparing the results of these two experiments, significant increases of 5%, 27%, and 24%, were found in the subpolar Southern Ocean when excluding the OSC in the IOS calculation for the ocean surface stress, upwelling, and downwelling, respectively. Excluding the OSC in the IOS calculation also visibly strengthens the total mechanical energy input to the OSC by about 16%, and increases the eddy kinetic energy and mean kinetic energy by about 38% and 12%, respectively. Moreover, the response of the meridional overturning circulation in the Southern Ocean yields respective increases of about 16% and 15% for the upper and lower branches; and the subpolar gyres are also found to considerably intensify, by about 12%, 11%, and 11% in the Weddell Gyre, the Ross Gyre, and the Australian-Antarctic Gyre, respectively. The strengthened ocean circulations and Ekman pumping result in a warmer sea surface temperature (SST), and hence an incremental surface heat loss. The increased sea ice drift and warm SST lead to an expansion of the sea ice area and a reduction of sea ice volume. These results emphasize the importance of OSCs in the air-sea-ice interactions on the global ocean circulations and the mass balance of Antarctic ice shelves, and this component may become more significant as the rapid change of Antarctic sea ice. [ABSTRACT FROM AUTHOR]

Ice sheet mass loss from Antarctica is greatest in the Amundsen Sea sector, where "warm" modified Circumpolar Deep Water moves onto the continental shelf and melts and thins the bases of ice shelves hundreds of meters below the sea surface. We use nearly 1000 paired salinity and oxygen isotope analyses of seawater samples collected on seven expeditions from 1994 to 2020 to produce a time series of glacial meltwater inventory for the southeastern Amundsen Sea continental shelf. Deep water column salinity– δ18 O relationships yield freshwater end-member δ18 O values from -31.3±1.0‰ to -28.4±1.0‰ , consistent with the isotopic composition of local glacial ice. We use a two-component meteoric water end-member approach that accounts for precipitation in the upper water column, and a pure glacial meteoric water end-member is employed for the deep water column. Meteoric water inventories are comprised of nearly pure glacial meltwater in deep shelf waters and of >74% glacial meltwater in the upper water column. Total meteoric water inventories range from 8.1±0.7 to 9.6±0.8 m and exhibit greater interannual variability than trend over the study period, based on the available data. The relatively long residence time in the southeastern Amundsen Sea allows changes in mean meteoric water inventories to diagnose large changes in local melt rates, and improved understanding of regional circulation could produce well-constrained glacial meltwater fluxes. The two-component meteoric end-member technique improves the accuracy of the sea ice melt and meteoric fractions estimated from seawater δ18 O measurements throughout the entire water column and increases the utility for the broader application of these estimates. [ABSTRACT FROM AUTHOR]

In Antarctica, the presence of sea ice in front of ice shelves promotes their stability and prevents the risk of catastrophic collapse as witnessed in recent events along the Antarctic Peninsula. Investigating past ice-proximal sea-ice conditions, especially across glacial-interglacial cycles, can provide crucial information pertaining to sea-ice variability and deepen our understanding of ocean-ice-atmosphere dynamics and feedbacks. In this study, we apply a multiproxy approach, analyzing the novel sea ice biomarker IPSO25 (a di-unsaturated highly branched isoprenoid (HBI)), open-water biomarkers (tri-unsaturated HBIs; z-/e-trienes), and the diatom assemblage and primary productivity indicators in a marine sediment core retrieved from Powell Basin, NW Weddell Sea. These biomarkers have been established as reliable proxies for reconstructing near-coastal sea ice conditions in the Southern Ocean, where the typical use of sea ice-related diatoms can be impacted by silica dissolution. Our data shed new light on the variability of sea ice since the penultimate deglaciation, ca. 145 ka before present, and reveal a highly dynamic glacial-interglacial sea-ice setting characterized by significant shifts from perennial ice cover to seasonal sea-ice cover and open marine environment. [ABSTRACT FROM AUTHOR]

The freezing point of water is negatively dependent on pressure; therefore in any ocean without external forcing it is warmest at the surface and grows colder with depth. Below floating ice on Earth (e.g., ice shelves or sea ice), this pressure dependence combines with gradients in the ice draft to drive an ice redistribution process termed the "ice pump": submerged ice melts, upwells, and then refreezes at shallower depths. Ice pumping is an exchange process between the ocean and overhead ice that results in unique ice compositions and textures and influences the distribution of sub‐ice habitats on Earth. Here, we scale recent observations from Earth's ice shelves to planetary conditions and find that ice pumping is expected for a wide range of possible sub‐ice shell pressures and salinity at other ocean worlds such as Europa and Enceladus. We show how ice pumping would affect hypothetical basal ice shell topography and ice thickness under varying ocean conditions and demonstrate how remote sensing of the ice shell draft can be used to estimate temperature gradients in the upper ocean ahead of in situ exploration. For example, the approximately 22 km gradient observed in Enceladus' ice shell draft between the south pole and the equator suggests a temperature differential of 0.18 K at the base of the ice shell. These concepts can extend the interpretation of observations from upcoming ocean world missions, and link ice shell topography to ice‐ocean material exchange processes that may prove important to overall ocean world habitability. Plain Language Summary: The freezing point of water depends on pressure. As pressure increases, the freezing point decreases, which can influence the melting or freezing of ice in an ocean. A helpful way to conceptualize this dependency is to recall that water expands as it freezes. As pressure increases, this expansion requires more work to displace the higher pressure surroundings, so the water must be even colder to freeze—a decrease in the freezing point. If ice is submerged, the deeper ice where the freezing point is colder can melt faster. This forms freshened meltwater that may rise to shallower depths where it is now colder than the shallower, lower pressure freezing point and can refreeze underwater. This process is referred to as an "ice pump", because it acts to equilibrate topography in submerged ice. In ice‐covered oceans on Earth, the ice pump is an important process that influences the composition and texture of the ice, and therefore the sub‐ice ecosystems. Here, we find that ice pumping is also likely at other ocean worlds in our solar system where it may similarly influence potential sub‐ice ecosystems and show how observations of planetary ice shell thicknesses can be used to bound ocean conditions. Key Points: When ice is submerged, a melting and freezing exchange process termed the "ice pump" can affect ice composition, texture, and thicknessWe find that ice pumping is likely beneath the ice shells of several ocean worlds in our solar systemThe ice pump concept enables inversion between ocean world ice shell thickness and ice‐ocean interface temperature ranges [ABSTRACT FROM AUTHOR]

Knowledge of the bathymetry of Antarctica's margins is crucial for models and interpretations of ice-ocean interactions and their influence on ongoing and future sea level change, but remains patchy where ice shelves and multi-year sea ice block measurements. Here, we present a bathymetric model for the central Dronning Maud Land margin, based on a constrained inversion of airborne gravity data. It shows the cavities beneath the region's two ice shelves to be much deeper than in existing bathymetric compilations, but to be shielded from Warm Deep Water ingress and basal melting by the presence of shallow bathymetric sills along the continental shelf. Over areas of multi-year sea ice, the model returns bathymetric estimates of similar accuracy to gravity interpolation-based methods over open water. Airborne gravity thus presents an opportunity to bathymetrically map hundreds of thousands of square kilometres of the most inaccessible margins of Antarctica at resolutions adequate for regional and global oceanographic and glaciological modelling and interpretation. [ABSTRACT FROM AUTHOR]

Sea ice is important for both regional and global climate, but comprehensive sea ice records are lacking pre-1978, when global-scale spaceborne observations began. Attempts to reconstruct sea ice conditions in different regions of Antarctica with the help of methane sulphonic acid (MSA) records from ice cores have had varying success, highlighting the often-regional relationship between ice core MSA and sea ice. This study uses MSA records from three firn cores and one ice core drilled on Fimbul Ice Shelf in Dronning Maud Land, East Antarctica, to investigate the relationship to satellite-derived sea ice extent (SIE) in the Southern Ocean. Chlorophyll-a concentrations, serving as a measure of phytoplankton biomass, are correlated to the MSA records to further test the MSA – SIE relationship. The relationship to both SIE and chlorophyll-a differs largely between the different firn and ice core MSA records. We find significant correlations for the MSA records from the two higher accumulation core sites to SIE and chlorophyll-a in the Weddell Sea, Western Pacific Ocean, and Ross Sea Sectors. Furthermore, the use of stacked MSA records introduced significant correlations between MSA from the lower accumulation core sites and SIE. The absence of coherent correlation patterns between the MSA records across the four investigated cores and SIE or chlorophyll-a in the Southern Ocean suggests that the Fimbul Ice Shelf MSA records are not consistent proxies for regional SIE. [ABSTRACT FROM AUTHOR]

Coupled ice sheet-ocean models are increasingly being developed and applied to important questions pertaining to processes at the Greenland and Antarctic Ice Sheet margins, which play a pivotal role in ice sheet stability and sea level rise projections. One of the challenges of such coupled modelling activities is the timescale discrepancy between ice and ocean dynamics. This discrepancy, combined with the high computational cost of ocean models due to their finer temporal resolution, limits the time frame that can be modeled. In this study, we introduce an "accelerated forcing" approach to address the timescale discrepancy and thus improve computational efficiency in a framework designed to couple evolving ice geometry to ice shelf cavity circulation. This approach is based on the assumption that the ocean adjusts faster to imposed changes than the ice sheet, with the ocean viewed as being in a slowly varying quasi-steady state over timescales of ice geometry change. By assuming that the ocean-induced ice draft change rate during one coupling interval can be reflected by a quasi-steady state change rate during a shortened coupling interval (equal to the regular coupling interval divided by a constant factor), we can reduce the ocean model simulation duration. We first demonstrate that the mean cavity residence time, derived from stand-alone ocean simulations, can guide the selection of suitable scenarios for this approach. We then evaluate the accelerated forcing approach by comparing basal melting response under the accelerated forcing with that under the regular forcing based on idealized coupled ice sheet ocean experiments. Our results suggest that: the accelerated approach can yield comparable melting responses to those under the regular forcing when the model is subjected to steady far-field ocean conditions or time-varying conditions with timescales much shorter than the cavity residence time. However, it is not suitable when the timescale of the accelerated ocean conditions is not significantly different from the cavity residence time. When used carefully, the accelerated approach can be a useful tool in coupled ice sheet-ocean modelling. [ABSTRACT FROM AUTHOR]

Warm water inflow from the Northeast Pacific has always been considered a crucial factor in early winter freeze-up in the Bering Sea. There is a strong correlation between changes in sea surface temperature (SST) on the eastern Bering Sea shelf and sea ice area in December. However, there is still limited research on the impact of Pacific inflow on SST on the eastern Bering Sea shelf, resulting in insufficient measurements of the impact of Pacific inflow on early freeze-up. In this article, the definition of marine heatwaves (MHW) is used to extract warm events (with a threshold of the 70th percentile) and cold events (with a threshold of the 30th percentile) from the eastern Bering Sea shelf in November. Self-organizing map (SOM) technology is utilized to classify extracted cold and warm events and the mixed-layer heat budget is ultimately used to explore the factors that generate and maintain these cold and warm events. Between 1993 and 2021, a total of 12 warm and 12 cold events are extracted and their cumulative intensity is found to be strongly correlated with the interannual variation in SST by 99.8%, indicating that these warm and cold events are capable of characterizing the interannual variation in SST. Among the 12 warm events, 9 of them can be attributed to abnormal warming of seawater before November and only 3 events are attributed to warm water inflow from the Northeast Pacific. During the development of warm events, there are only two events in which the warm inflow from the Northeast Pacific has a more profound regulatory effect on warm events in November. Moreover, both generation and regulatory factors of cold events are the net air–sea heat flux. Statistics indicate that the warm water inflow from the Northeast Pacific has a limited effect on SST on the eastern Bering Sea shelf during the early freeze-up period. Changes in local SST are more influenced by the residual heat before November and by local net air–sea heat flux. However, we highlight that long-term ocean heatwaves occurring in the Northeast Pacific can enlarge the residual heat of seawater in the eastern Bering Sea shelf before November, thereby impacting early freeze-up. The frequency of such events has significantly increased in the past decade, causing notable changes in the climate and ecosystem of the Bering Sea. Therefore, it is crucial to continue closely monitoring the occurrence and development of such events in the future. [ABSTRACT FROM AUTHOR]

The Totten Ice Shelf (TIS) and Moscow University Ice Shelf (MUIS), along the Sabrina Coast of Wilkes Land, are the floating seaward terminuses of the second-largest freshwater reservoir in the East Antarctic Ice Sheet. Being a marine ice sheet, it is vulnerable to the surrounding ocean conditions. Recent comprehensive oceanographic observations, including bathymetric measurements off the Sabrina Coast, have shed light on the widespread intrusion of warm modified Circumpolar Deep Water (mCDW) onto the continental shelf and the intense ice–ocean interaction beneath the TIS. However, the spatiotemporal coverage of the observation is very limited. Here, we use an ocean–sea ice–ice shelf model with updated bathymetry to better understand the regional ocean circulations and ocean–cryosphere interactions. The model successfully captured the widespread intrusions of mCDW, local sea ice production and the ocean heat and volume transports into the TIS cavity, facilitating an examination of the overturning ocean circulation within the ice shelf cavities and the resultant basal melting. We found notable differences in the temporal variability in ice shelf basal melting across the two adjacent ice shelves of the TIS and the western part of the MUIS. Ocean heat transport by mCDW controls the low-frequency interannual-to-decadal variability in ice–ocean interactions, but the sea ice production in the Dalton Polynya strongly modifies the signals, explaining the regional difference between the two ice shelves. The formation of a summertime eastward-flowing undercurrent beneath the westward-flowing Antarctic Slope Current is found to play an important role in the seasonal delivery of ocean heat to the continental shelf. [ABSTRACT FROM AUTHOR]

The intrusion of circumpolar deep water (CDW) onto the Antarctic continental shelf plays an important role in the heat budgets of the Antarctic shelf sea. In the Ross Sea, the Antarctic Slope Current is a strong vorticity barrier that prevents cross‐slope CDW exchange, yet observation evidence shows that CDW is able to get through this barrier in certain locations and reaches the edge of the Ross Ice Shelf (RIS). Previous studies often attribute the cross‐slope exchange to surface wind forcing, eddy and tide‐mediated fluxes. In this work, we highlight the role of buoyancy forcing from the continental shelf in the cross‐isobath exchange on the continental shelf break. The cross‐isobath transport along the Ross Sea continental shelf break is diagnosed with the depth‐averaged vorticity budget equation, using results from an ice‐ocean coupled numerical model. Our results show that the leading‐order balance of vorticity is between the advection of planetary vorticity and the joint effect of baroclinicity and relief (JEBAR). The JEBAR effect supplies negative vorticity and drives onshore transport over the eastern Ross Sea. The heterogeneous transport over eastern and western Ross Sea results in a zonal sea level gradient, with higher sea level over the eastern Ross Sea. The magnitude of JEBAR is determined by horizontal density gradient along the Ross Sea shelf break edge; numerical tracer experiments suggest that the along‐isobath density gradient is set up by the dense shelf water formed over the RIS and the inflow of glacial basal melt water from the Amundsen Sea. Plain Language Summary: In the Antarctic Ocean, poleward transport of warm circumpolar deep water (CDW) brings large amount of heat to the edge of the Antarctic coast, melting ice shelves, reducing global freshwater reserves and accelerating sea level rise. In the Ross Sea, a strong west‐flowing current named the Antarctic Slope Current (ASC) acts as a barrier that prevents the CDW from flowing onto the Ross Sea continental shelf. Even so, the warm water can sometimes penetrate this barrier, flows over the continental shelf and eventually reaches the edge of the Ross Ice Shelf. In this work, we propose that the cross‐shelf flow that penetrates the ASC barrier is driven by both bathymetry and stratification on the continental shelf break. We diagnosed the cross‐shelf transport using the method called vorticity budget analysis, and found that the strength of cross‐shelf transport is primarily determined by horizontal density gradient along the continental shelf break, which is controlled by heterogeneous density distribution from the Ross Sea continental shelf. Our results highlight the role of continental shelf buoyancy forcing in controlling the cross‐shelf exchange, in opposite to previous studies which mainly focus on local or open‐ocean forcings such as ocean surface winds, tides or eddies. Key Points: Cross‐isobath transport over the Ross Sea continental shelf break is diagnosed using vorticity budgets from an ice‐ocean coupled modelLeading order vorticity balance is found between advection of planetary vorticity and the joint effect of baroclinicity and relief (JEBAR)The strength of JEBAR is determined by buoyancy‐forced horizontal density gradient along the shelf break edge [ABSTRACT FROM AUTHOR]

The Antarctic Ice Sheet (AIS) holds the potential to raise global sea levels by a staggering 57 m. Ice shelves, extensions of these ice sheets into the ocean, play a crucial role in stabilizing the upstream ice sheet. The Brunt Ice Shelf (BIS), located in the Southern Weddell Sea region and proximal to the continental shelf break, stands as a vital indicator for the region's response to global climate warming. Hence, this study systematically employs a range of remote sensing and field data, including remote sensing data from 1963 to 2023 (ARGON images, Landsat1-9 images, Sentinel-1 images, ICESat-2 altimetry data, etc.) and in-situ ice flow velocity data since 1956, to conduct a comprehensive analysis of the BIS's calving cycle and evolution over nearly six decades. The results reveal a significant exacerbation of both dynamical and structural instabilities in the BIS compared to the calving cycle in the 1970s. Combining analyses of air temperature from meteorological station, water temperature from ocean models and in-situ measurements such as Conductivity-Temperature-Depth profiles, the study suggests that the increased instability of the BIS is likely linked to the intrusion of warmer currents over the continental shelf. This research provides valuable insights into the evolving behavior of the BIS in response to changing climate conditions, underscoring the critical role of remote sensing data in advancing our understanding of these processes on a global scale. [ABSTRACT FROM AUTHOR]

Abstract The ice streams flowing into the Amundsen Sea, West Antarctica, are losing mass due to changes in oceanic basal melting of their floating ice shelves. Rapid ice‐shelf melting is sustained by the delivery of warm Circumpolar Deep Water to the ice‐shelf cavities, which is first supplied to the continental shelf by an undercurrent that flows eastward along the shelf break. Temporal variability of this undercurrent controls ice‐shelf basal melt variability. Recent work shows that on decadal timescales the undercurrent variability opposes surface wind variability. Using a regional model, we show that undercurrent variability is induced by sea‐ice freshwater fluxes, particularly those north of the shelf break, which affect the cross‐shelf break density gradient. This sea‐ice variability is linked to tropical Pacific variability impacting atmospheric conditions over the Amundsen Sea. Ice‐shelf melting also feeds back onto the undercurrent by affecting the on‐shelf density, thereby influencing shelf‐break density gradient anomalies.