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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]

Ice shelf dynamics and morphology play an important role in the stability of floating bodies of ice by driving fracturing that can lead to calving, in turn impacting the ability of the ice shelf to buttress upstream grounded ice. Following a 2016 calving event at the Nansen Ice Shelf (NIS), East Antarctica, we collected airborne and ground-based radar data to map ice thickness across the shelf. We combine these data with published satellite-derived data to examine the spatial variations in ice shelf draft, the cause and effects of ice shelf strain rates, and the possibility that a suture zone may be channelizing ocean water and altering patterns of sub-ice-shelf melt and freeze-on. We also use our datasets to assess limitations that may arise from relying on hydrostatic-balance equations applied to ice surface elevation to determine ice draft morphology. We find that the Nansen Ice Shelf has a highly variable basal morphology driven primarily by the formation of basal fractures near the onset of the ice shelf suture zone. This morphology is reflected in the ice shelf strain rates but not in the calculated hydrostatic-balance thickness, which underestimates the scale of variability at the ice shelf base. Enhanced melt rates near the ice shelf terminus and in steep regions of the channelized suture zone, along with relatively thin ice in the suture zone, appear to represent vulnerable areas in the NIS. This morphology, combined with ice dynamics, induce strain that has led to the formation of transverse fractures within the suture zone, resulting in large-scale calving events. Similar transverse fractures at other Antarctic ice shelves may also be driven by highly variable morphology, and predicting their formation and evolution could aid projections of ice shelf stability. [ABSTRACT FROM AUTHOR]

Abstract. Grounding line discharge is a key component of the mass balance of the Antarctic Ice Sheet. Here we present an estimate of Antarctic Ice Sheet grounding line discharge from 1996 through to last month. We calculate ice flux at up to 100 m resolution through 16 algorithmically-generated flux gates, which are continuous around Antarctica. We draw on a range of ice velocity and thickness data to estimate grounding line discharge. For ice thickness, we use four bed topography datasets, two firn models and a temporally varying ice surface. For the ice velocity, we utilise a range of publicly-available ice velocity maps at resolutions ranging from 240 x 240 m to 1000 x 1000 m, as well as new, 100 x 100 m monthly velocity mosaics derived from intensity-tracking of Sentinel-1 image pairs, available since October 2014. The pixel-based ice fluxes and ice flux errors are integrated within all available Antarctic ice stream, ice shelf and glacier basins. Our dataset also includes the contributions to discharge from changes in ice thickness due to surface lowering, time-varying firn air content and surface mass change between the flux gates and grounding line. We find that Antarctic Ice Sheet grounding line discharge increased from 1,990 ± 23 Gt yr-1 to 2,205 ± 18 Gt yr-1 between 1996 and 2023, much of which was due to acceleration of ice streams in West Antarctica but with substantial contributions from ice streams in East Antarctica and glaciers on the Antarctic Peninsula. The uncertainties in our discharge dataset primarily result from uncertain bed elevation and flux gate location, which account for much of difference between our results and previous studies. It is our intention to update this discharge dataset each month, subject to continued Sentinel-1 acquisitions and funding availability. [ABSTRACT FROM AUTHOR]

Surface mass balance (SMB) of the Antarctic Ice Sheet must be better understood to document the current Antarctic contribution to sea-level rise. In situ point data using snow stakes and ice cores are often used to evaluate the state of the ice sheet's mass balance, as well as to assess SMB derived from regional climate models, which are then used to produce future climate projections. However, spatial representativeness of individual point data remains largely unknown, particularly in the coastal regions of Antarctica with highly variable terrain. Here, we compare ice core data collected at the summit of eight ice rises along the coast of Dronning Maud Land, as well as at the Dome Fuji site, and shallow ice-penetrating radar data over these regions. Shallow radar data have the advantage of being spatially extensive, with a temporal resolution that varies between a yearly and multi-year resolution, from which we can derive a SMB record over the entire radar survey. This comparison therefore allows us to evaluate the spatial variability of SMB and the spatial representativeness of ice-core-derived SMB. We found that ice core mean SMB is very local, and the difference with radar-derived SMB increases in a logarithmic fashion as the surface covered by the radar data increases, with a plateau ∼ 1–2 km away from the ice crest for most ice rises, where there are strong wind–topography interactions, and ∼ 10 km where the ice shelves begin. The relative uncertainty in measuring SMB also increases rapidly as we move away from the ice core sites. Five of our ice rise sites show a strong spatial representativeness in terms of temporal variability, while the other three sites show that it is limited to a surface area between 20–120 km 2. The Dome Fuji site, on the other hand, shows a small difference between pointwise and area mean SMB, as well as a strong spatial representativeness in terms of temporal variability. We found no simple parameterization that could represent the spatial variability observed at all the sites. However, these data clearly indicate that local spatial SMB variability must be considered when assessing mass balance, as well as comparing modeled SMB values to point field data, and therefore must be included in the estimate of the uncertainty of the observations. [ABSTRACT FROM AUTHOR]

Antarctic ice shelves are losing mass at increasing rates, yet the ice‐ocean interactions that cause significant ice loss are not well understood. A new approach of high‐resolution phase‐change simulations is used to model vertical ice melting into a stratified ocean. The ocean dynamics show complicated interplay between a turbulent buoyant meltwater plume and double‐diffusive layers, while the ice actively melts and changes topography. At room temperatures, the double‐diffusive layer thickness is closely linked to ice scalloping. At lower, more realistic ocean temperatures, the meltwater plume becomes prominent with a laminar‐to‐turbulent transition imprinting an indent on the melting ice. The double‐diffusive layer thickness is consistent with scaling prediction, while the real‐world application demonstrates reasonably good matching of the scaling prediction for some Antarctic regions. Our study is a key first step toward the future use of high‐resolution phase‐change fluid dynamics simulations to better understand Antarctic ice shelves in a changing climate. Plain Language Summary: Future climate scenarios and sea level rise are closely tied to the accelerating loss of Antarctic ice shelves, which lose significant mass by melting into the surrounding ocean. However, the extent of ice shelf mass loss in a changing climate is currently not well understood, with lack of knowledge on the fine‐scale ice‐ocean interactions presenting a key restriction on the accuracy of climate predictions. Here, we use a new suite of numerical computer simulations to model an ice face melting into the ocean. In particular, our simulations allow the ice face to melt back and change shape, which previous numerical simulations could not attempt. We see interesting ocean dynamics known as "double‐diffusive layers" that occur because temperature and salinity both affect the water density. In addition, we also see a buoyant meltwater plume evolve next to the ice face. Both the double‐diffusive layers and meltwater plume can influence the ice melting and shape. Our results are a first step in using these new phase‐change simulations to model ice‐ocean interactions, and will help to better understand the Antarctic response to a changing climate. Key Points: High‐resolution phase‐change simulations are used to examine a vertical ice face melting into a stratified ocean at low temperaturesA distinct laminar‐to‐turbulent transition occurs in the meltwater plume as it rises, accompanied by an indent in the ice at the transitionDouble‐diffusive layers adjacent to the turbulent plume are consistent with scaling predictions and are relevant to the ocean application [ABSTRACT FROM AUTHOR]

Gravity‐driven flow of large ice masses such as the Antarctic Ice Sheet (AIS) depends on both the geometry and the mass density of the ice sheet. The vertical density profile can be approximated as pure ice overlain by a firn layer of varying thickness, and for the AIS the firn thickness is not uncommonly 10%–20% of the total thickness, leading to not insignificant variation in horizontal density. Nevertheless, in most vertically integrated ice‐flow models today, the density is assumed constant, sometimes with an adjustment in thickness to compensate. In this study, we explore the treatment of horizontal density variations (HDVs) within vertically integrated ice‐sheet models. We assess the relative merits and shortcomings of previously proposed approaches and provide new formulations for including HDVs. We use perturbation analysis to derive analytical solutions that describe the impact of density variations on ice flow for both grounded ice and floating ice shelves, which reveal significant qualitative differences between each of the proposed density formulations. We recommend always including the horizontal gradient of the density in the body‐force term of the momentum equation, and in the mass‐conservationequation. Furthermore, by modeling the transient evolution of a large sector of the West Antarctic Ice Sheet (WAIS), we find that doing so leads to about a 10% correction in the estimated change in volume above flotation over 40 years. We conclude that including HDVs in flow modeling of the AIS is important for accurate predictions of mass loss. Plain Language Summary: Variation in the average ice‐density across large ice sheets such as the Antarctic Ice Sheet (AIS) will have an impact on the dynamics of the ice flow. The question we wish to answer in this study is how significant this impact is and how best to model the density variations within large‐scale numerical simulations. Variations in the average ice‐sheet density come from layers of compactified snow which have a lower density than the underlying ice. Within the AIS this compactified snow layer is approximately 10%–20% of the total thickness, which leads to not insignificant variation in the average density. Nevertheless, in most numerical models that simulate the flow of large ice sheets, these variations are either ignored completely or approximated by an adjustment in the total ice‐thickness. In all large‐scale numerical models, there is a trade‐off between computational complexity and an accurate depiction of the physical processes. We propose several formulations for including density variations and study the theoretical behavior of ice flows in each formulation. We find that numerical simulations of the Western AIS over 40 years suggest that explicitly including density variations could potentially lead to a 10% correction in estimated sea level rise. Key Points: We examine the impact of various approaches for including horizontal variations in ice density within large‐scale ice‐sheet simulationsWe recommend explicitly including the horizontal gradient of the ice density in the body‐force term of the momentum equationsTransient simulations of the Western Antarctic suggest this approach could potentially lead to a 10% correction in estimated sea level rise [ABSTRACT FROM AUTHOR]

The physical interactions between ice sheets and the atmosphere and ocean around them are major factors in determining the state of the climate system, yet many current Earth System models omit them entirely or treat them very simply. In this work we describe how models of the Greenland and Antarctic ice sheets have been incorporated into the global U.K. Earth System model (UKESM1) via substantial technical developments with a two‐way coupling that passes fluxes of energy and water, and the topography of the ice sheet surface and ice shelf base, between the component models. File‐based coupling outside the running model executables is used throughout to pass information between the components, which we show is both physically appropriate and convenient within the UKESM1 structure. Ice sheet surface mass balance is computed in the land surface model using multi‐layer snowpacks in subgrid‐scale elevation ranges and compares well to the results of regional climate models. Ice shelf front discharge forms icebergs, which drift and melt in the ocean. Ice shelf basal mass balance is simulated using the full three‐dimensional ocean model representation of the circulation in ice‐shelf cavities. We show a range of example results, including from simulations with changes in ice sheet height and thickness of hundreds of meters, and changes in ice sheet grounding line and land‐terminating margin of many tens of kilometres, demonstrating that the coupled model is computationally stable when subject to significant changes in ice sheet geometry. Plain Language Summary: Loss of mass from the ice sheets on Greenland and Antarctica makes an important contribution to global mean sea level (GMSL) rise, and one that will increase significantly in the coming decades and centuries. Our limited ability to predict exactly how the Earth's ice sheets will interact with the changing climate is the main reason we cannot say with confidence whether GMSL will rise by tens of centimeters or a meter or more in this century alone. One way to develop our understanding is to build tools capable of modeling the co‐evolution of ice sheets and climate, a difficult task made yet more challenging by the wide range of spatial‐ and time‐scales that need to be considered to model these systems simultaneously. UKESM1 is a state‐of‐the‐art Earth System model used to predict future climate change. Our work allows UKESM1 to be run with interactive models of the Greenland and Antarctic ice sheets. This is a new and complex model, and there are still problems to solve before such tools can be used to produce complete projections of GMSL rise. Our work nevertheless allows us to investigate new areas of climate physics in ways that have not been possible before. Key Points: A CMIP6 Earth System Model has been coupled to interactive models of both the Greenland and Antarctic ice sheets for the first timeSubstantial technical challenges have been overcome, our solutions and their limitations are describedOur system simulates climate and ice sheet physics reasonably well, and is computationally stable when subject to extreme ice sheet retreat [ABSTRACT FROM AUTHOR]

The outflow of supercooled Ice Shelf Water from the conjoined Ross and McMurdo ice shelf cavity augments fast ice thickness and forms a thick sub-ice platelet layer in McMurdo Sound. Here, we investigate whether the CryoSat-2 satellite radar altimeter can consistently detect the higher freeboard caused by the thicker fast ice combined with the buoyant forcing of a sub-ice platelet layer beneath. Freeboards obtained from CryoSat-2 were compared with 4 years of drill-hole-measured sea ice freeboard, snow depth, and sea ice and sub-ice platelet layer thicknesses in McMurdo Sound in November 2011, 2013, 2017 and 2018. The spatial distribution of higher CryoSat-2 freeboard concurred with the distributions of thicker ice-shelf-influenced fast ice and the sub-ice platelet layer. The mean CryoSat-2 freeboard was 0.07–0.09 m higher over the main path of supercooled Ice Shelf Water outflow, in the centre of the sound, relative to the west and east. In this central region, the mean CryoSat-2-derived ice thickness was 35 % larger than the mean drill-hole-measured fast ice thickness. We attribute this overestimate in satellite-altimeter-obtained ice thickness to the additional buoyant forcing of the sub-ice platelet layer which had a mean thickness of 3.90 m in the centre. We demonstrate the capability of CryoSat-2 to detect higher Ice Shelf Water-influenced fast ice freeboard in McMurdo Sound. Further development of this method could provide a tool to identify regions of ice-shelf-influenced fast ice elsewhere on the Antarctic coastline with adequate information on the snow layer. [ABSTRACT FROM AUTHOR]

Surface meltwater accumulating on Antarctic ice shelves can drive fractures through to the ocean and potentially cause their collapse, leading to increased ice discharge from the continent. Implications of increasing surface melt for future ice shelf stability are inadequately understood. The southern Amery Ice Shelf has an extensive surface hydrological system, and we present data from satellite imagery and ICESat‐2 showing a rapid surface disruption there in winter 2019, covering ∼60 km2. We interpret this as an ice‐covered lake draining through the ice shelf, forming an ice doline with a central depression reaching 80 m depth amidst over 36 m uplift. Flexural rebound modeling suggests 0.75 km3 of water was lost. We observed transient refilling of the doline the following summer with rapid incision of a narrow meltwater channel (20 m wide and 6 m deep). This study demonstrates how high‐resolution geodetic measurements can explore critical fine‐scale ice shelf processes. Plain Language Summary: Surface melting over Antarctica's floating ice shelves is predicted to increase significantly during coming decades, but the implications for their stability are unknown. The Antarctic Peninsula has already seen meltwater driven ice shelf collapses. We are still learning how meltwater forms, flows and alters the surface, and that rapid water‐driven changes are not limited to summer. We present high‐resolution satellite data (imagery and altimetry) showing an abrupt change on East Antarctica's Amery Ice Shelf in June 2019 (midwinter). Meltwater stored in a deep, ice‐covered lake drained through to the ocean below, leaving a deep, uneven 11 km2 depression of fractured ice (a "doline") in the ice shelf surface. The reduced load on the floating ice shelf resulted in flexure, with over 36 m of uplift centered on the former lake. Simple flexure modeling showed that this corresponds to about 0.75 km3 of water being lost to the ocean. ICESat‐2 observations in summer 2020 profiled a new narrow channel inside the doline as meltwater started refilling it from a new lake created by the flexure. ICESat‐2's capacity to observe surface processes at small spatial scales greatly improves our ability to model them, ultimately improving the accuracy of our projections. Key Points: Satellite images showed an 11 km2 depression on Amery Ice Shelf as an ice‐covered lake drained abruptly in winter 2019 forming an ice dolineICESat‐2 and WorldView data show elevation fell as much as 80 m in the depression, amidst 60 km2 of hydrostatic rebound and uplift over 36 mICESat‐2 photon data profiled a new meltwater channel, incised when a lake formed by the flexural uplift overflowed into the doline in 2020 [ABSTRACT FROM AUTHOR]

The formation of platelet ice is well known to occur under Antarctic sea ice, where subice platelet layers form from supercooled ice shelf water. In the Arctic, however, platelet ice formation has not been extensively observed, and its formation and morphology currently remain enigmatic. Here, we present the first comprehensive, long‐term in situ observations of a decimeter thick subice platelet layer under free‐drifting pack ice of the Central Arctic in winter. Observations carried out with a remotely operated underwater vehicle (ROV) during the midwinter leg of the MOSAiC drift expedition provide clear evidence of the growth of platelet ice layers from supercooled water present in the ocean mixed layer. This platelet formation takes place under all ice types present during the surveys. Oceanographic data from autonomous observing platforms lead us to the conclusion that platelet ice formation is a widespread but yet overlooked feature of Arctic winter sea ice growth. Plain Language Summary: Platelet ice is a particular type of ice that consists of decimeter sized thin ice plates that grow and collect on the underside of sea ice. It is most often related to Antarctic ice shelves and forms from supercooled water with a temperature below the local freezing point. Here we present the first comprehensive observation of platelet ice formation in freely drifting pack ice in the Arctic in winter during the international drift expedition MOSAiC. We investigate its occurrence under the ice with a remotely controlled underice diving robot. Measurements of water temperature from automatic measurement devices distributed around the central MOSAiC ice floe show that supercooled water and thus platelet ice occur widely in the winter Arctic. This way of ice formation in the Arctic has been overlooked during the last century, as direct observations under winter sea ice were not available and contrary to typical Antarctic observations; manifestation of platelet ice in Arctic ice core stratigraphy has been more challenging to identify. Key Points: Here we present extensive observations of platelet ice formation under Arctic winter sea iceThe subice platelet layer appears to form locally due to seed crystals in ocean surface supercooling [ABSTRACT FROM AUTHOR]

The response of near-Antarctic waters to freshening by increased glacial melt is investigated using a highresolution (0.18) global ocean–sea ice model with realistic Antarctic water-mass properties. Two meltwater perturbation experiments are conducted where the ocean model is forced with constant elevated glacial melt rates of 1.5 and 2.8 times the control rate. Within 10 years of the onset of enhanced meltwater forcing, the generation of Antarctic Bottom Water from Dense Shelf Water ceases, as shelf waters become increasingly buoyant. Increased ocean stratification triggers subsurface warming in Dense Shelf Water source regions, suggesting a localized positive feedback to melt. In a parallel response, meltwater forcing enhances the subsurface lateral density gradients of the Antarctic Slope Front that modulate the transport of warm Circumpolar Deep Water across the continental slope toward ice shelf grounding lines. Consequently, coastal freshening acts to isolate the Antarctic Ice Sheet from open ocean heat, suggesting a cooling response to melt that counteracts warming associated with stratification. Further, these strengthening density gradients accelerate westward geostrophic currents along the coast and shelf break, homogenizing shelf waters and amplifying remote feedbacks. The net effect on the continental shelf is transient warming, followed by cooling in both experiments; however, this signal is the aggregate of a complex pattern of regional warming and cooling responses. These results suggest coastal freshening by meltwater may alter the thermal forcing of the Antarctic ice sheet in ways that both accelerate and inhibit ice shelf melt at different locations along the Antarctic coastline. [ABSTRACT FROM AUTHOR]

The shape of ice shelf cavities are a major source of uncertainty in understanding ice‐ocean interactions. This limits assessments of the response of the Antarctic ice sheets to climate change. Here we use vibroseis seismic reflection surveys to map the bathymetry beneath the Ekström Ice Shelf, Dronning Maud Land. The new bathymetry reveals an inland‐sloping trough, reaching depths of 1,100 m below sea level, near the current grounding line, which we attribute to erosion by palaeo‐ice streams. The trough does not cross‐cut the outer parts of the continental shelf. Conductivity‐temperature‐depth profiles within the ice shelf cavity reveal the presence of cold water at shallower depths and tidal mixing at the ice shelf margins. It is unknown if warm water can access the trough. The new bathymetry is thought to be representative of many ice shelves in Dronning Maud Land, which together regulate the ice loss from a substantial area of East Antarctica. Plain Language Summary: Antarctica is surrounded by floating ice shelves, which play a crucial role in regulating the flow of ice from the continent into the oceans. The ice shelves are susceptible to melting from warm ocean waters beneath them. In order to better understand the melting, knowledge of the shape and depth of the ocean cavity beneath ice shelves is crucial. In this study, we present new measurements of the sea floor depth beneath Ekström Ice Shelf in East Antarctica. The measurements reveal a much deeper sea floor than previously known. We discuss the implications of this for access of warm ocean waters, which can melt the base of the ice shelf and discuss how the observed sea floor features were formed by historical ice flow regimes. Although Ekström Ice Shelf is relatively small, the geometry described here is thought to be representative of the topography beneath many ice shelves in this region, which together regulate the ice loss from a substantial area of East Antarctica. Key Points: Vibroseis seismic surveys used to map the ice shelf cavity beneath Ekström Ice Shelf in AntarcticaDeep trough with transverse sills and overdeepenings provide evidence of past ice streaming and retreatTwo ocean circulation regimes inferred in the shallow and deep parts of the cavity [ABSTRACT FROM AUTHOR]

The majority of Antarctic ice shelves are bounded by grounded ice rises. These ice rises exhibit local flow fields that partially oppose the flow of the surrounding ice shelves. Formation of ice rises is accompanied by a characteristic upward-arching internal stratigraphy ("Raymond arches"), whose geometry can be analysed to infer information about past ice-sheet changes in areas where other archives such as rock outcrops are missing. Here we present an improved modelling framework to study ice-rise evolution using a satellite-velocity calibrated, isothermal, and isotropic 3-D full-Stokes model including grounding-line dynamics at the required mesh resolution (< 500 m). This overcomes limitations of previous studies where ice-rise modelling has been restricted to 2-D and excluded the coupling between the ice shelf and ice rise. We apply the model to the Ekström Ice Shelf, Antarctica, containing two ice rises. Our simulations investigate the effect of surface mass balance and ocean perturbations onto ice-rise divide position and interpret possible resulting unique Raymond arch geometries. Our results show that changes in the surface mass balance result in immediate and sustained divide migration (>2.0 m yr -1) of up to 3.5 km. In contrast, instantaneous ice-shelf disintegration causes a short-lived and delayed (by 60–100 years) response of smaller magnitude (<0.75 m yr -1). The model tracks migration of a triple junction and synchronous ice-divide migration in both ice rises with similar magnitude but differing rates. The model is suitable for glacial/interglacial simulations on the catchment scale, providing the next step forward to unravel the ice-dynamic history stored in ice rises all around Antarctica. [ABSTRACT FROM AUTHOR]

Satellite-derived Antarctic sea ice extent has displayed a slight upward since 1979, but with strong temporal and regional variability—the drivers of which are poorly understood. Here, we conduct numerical experiments with a circum-Antarctic ocean–sea ice–ice shelf model driven by realistic atmospheric surface boundary conditions to examine the factors responsible for the temporal and spatial patterns in observed Antarctic sea ice variability. The model successfully reproduces observed seasonal and interannual variability in total sea ice extent and the temporal/spatial patterns of sea ice concentration and seasonality (days of advance and retreat and actual ice days) for 1979–2014. Sensitivity experiments are performed, in which the interannual variability in wind stress or thermodynamic surface forcing is ignored, to delineate their contributions to Antarctic sea ice fields. The results demonstrate that: (1) thermodynamic forcing plays a key role in driving interannual variability in sea ice extent and seasonality in most Antarctic sectors; (2) only in the Ross Sea the wind stress does become the main driver of sea ice extent variability; (3) thermodynamic forcing largely regulates interannual variability in the timing of sea ice advance, while wind stress largely controls the timing of the sea ice retreat; and (4) although both wind stress and thermodynamic forcing contribute to variability in total sea ice volume, the wind stress plays a dominant role in regulating sea ice volume variability in the near-coastal zone. [ABSTRACT FROM AUTHOR]

Relatively little is known about the physical mechanisms that drive the dynamics of the East Antarctic outlet glaciers. Here we conduct a remote-sensing investigation of the Polar Record Glacier (PRG), East Antarctica to analyze its ice flow acceleration, ice front variations and ice surface melting. Ice flow speeds at PRG increased by up to 15% from 2005 to 2015, with substantial interannual fluctuations. The ice velocities also showed seasonal variations, accelerating by up to 9% between September and January. Multiple mechanisms contribute to the observed seasonal variations: the initial acceleration may result from the lost back-stress provided by the sea ice in the austral spring and the later speedup relate to the surface meltwater that leads to weakened ice shelf and shear margins. The sensitivity of the PRG to oceanic forcing is confirmed by comparing the secular ice velocity increases with ocean temperatures. These measurements suggest that the dynamics of East Antarctic ice shelves are sensitive to melt at both the surface and base, at a range of timescales. [ABSTRACT FROM AUTHOR]

Ross seals Ommatophoca rossii breed in the Antarctic pack ice during November. There have been few studies of Ross seals during their breeding season because access in the pack ice is difficult then. The weight of Ross seal pups near birth has been reported rarely; estimates range from 16.8 to 27 kg. In November 1987, two pups were measured north of the Amery Ice Shelf near 65°S, 75°E, East Antarctica. One was considered to have been newborn because of its fleshy umbilicus, an after-birth on the ice floe and the absence of erupted teeth. It weighed 16.0 kg and had a standard length of 0.93 m. This is only the second report of a newborn Ross seal pup; both weights were between 16 and 17 kg. [ABSTRACT FROM AUTHOR]

Parameterized energy and mass balance models are often applied to estimate energy fluxes at the surface that are available for melting and sublimation of snow and ice surfaces. In this study we evaluate the suitability of quantifying transient energy and mass fluxes on frozen surface using the finite volume method in comparison with the traditional glaciological energy balance approach. To assess the model application, we apply the methods to two datasets: a glacier in the semiarid Andes, and an Antarctic ice shelf, estimating the effect of time varying surface irradiation, wind velocity, air temperature and humidity on the history of temperature, liquid water and heat fluxes during 30 months. Results of energy and mass balances are validated with previously published results of global balances and meteorological datasets. • Accurate estimation of surface temperature of glaciers by finite volume method, FVM. • Prediction of unsteady energy and mass balances for two different glacier types. • Accounting for the effect of porous composition on surface melting of ice shelves. • Transient diffusion model of liquid solid phase-change in snow-firm-ice structures. • Hourly computation of thermal heat and mass transfer in glaciers during 30 months. [ABSTRACT FROM AUTHOR]

Due to rapid global warming, the relationship between the mass loss of the Antarctic ice sheet and rising sea levels are attracting widespread attention. The Lambert–Amery glacial system is the largest drainage system in East Antarctica, and its mass balance has an important influence on the stability of the Antarctic ice sheet. In this paper, the recent ice flux in the Lambert Glacier of the Lambert–Amery system was systematically analyzed based on recently updated remote sensing data. According to Landsat-8 ice velocity data from 2018 to April 2019 and the updated Bedmachine v2 ice thickness dataset in 2021, the contribution of ice flux approximately 140 km downstream from Dome A in the Lambert Glacier area to downstream from the glacier is 8.5 ± 1.9   Gt · a − 1 , and the ice flux in the middle of the convergence region is 18.9 ± 2.9   Gt · a − 1 . The ice mass input into the Amery ice shelf through the grounding line of the whole glacier is 19.9 ± 1.3   Gt · a − 1 . The ice flux output from the mainstream area of the grounding line is 19.3 ± 1.0   Gt · a − 1 . Using the annual SMB data of the regional atmospheric climate model (RACMO v2.3) as the quality input, the mass balance of the upper, middle, and lower reaches of the Lambert Glacier was analyzed. The results show that recent positive accumulation appears in the middle region of the glacier (about 74–78°S, 67–85°E) and the net accumulation of the whole glacier is 2.4 ± 3.5   Gt · a − 1 . Although the mass balance of the Lambert Glacier continues to show a positive accumulation, and the positive value in the region is decreasing compared with values obtained in early 2000. [ABSTRACT FROM AUTHOR]

During the last glacial cycle, the Antarctic Ice Sheet (AIS) has passed from an interglacial state, warmer than present day (PD), slowly into a glacial state, known as the Last Glacial Maximum (LGM) and then deglaciated on a faster timescale into the Holocene and PD conditions. Although we have proxy data of the size and extent of the ice sheet for the LGM, neither the oceanic temperatures of the Southern Ocean, nor the precipitation fields are well constrained. Also the time evolution of the ice volume during the glacial cycle is not fully clear. It is well assumed that it follows a sawtooth pattern, but from a modelling perspective different combinations of parameters and boundary conditions can give rise to plausible Antarctic configurations. Here we aim to study the uncertainty in AIS evolution resulting from ice-sheet model parameters, as well as the imposed climatic fields used as forcing. For this purpose we use the three-dimensional thermomechanical hybrid ice-sheet-shelf model Yelmo, which treats ice dynamics via the shallow-ce and shallow-shelf approximations, and accounts for basal melt below ice shelves and a subgrid parameterisation for treatment of the grounding line. We will focus on the effect of different climatic fields, such as precipitation and oceanic temperatures, as well as the effect of different enhancement factors and basal drag choices for reproducing consistent Antarctic configurations in the LGM and the PD. Improving our understanding of the effect of different ice-dynamics configurations in various climatic scenarios will help to better understand the past evolution of the AIS and potentially constrain its future evolution as well. [ABSTRACT FROM AUTHOR]