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Mass loss of the Antarctic Ice Sheet has been driven primarily by the thinning of the floating ice shelves that fringe the ice sheet1, reducing their buttressing potential and causing land ice to accelerate into the ocean2. Observations of ice-shelf thickness change by satellite altimetry stretch back only to 1992 (refs. 1,3–5) and previous information about thinning remains unquantified. However, extending the record of ice-shelf thickness change is possible by proxy, by measuring the change in area of the surface expression of pinning points—local bathymetric highs on which ice shelves are anchored6. Here we measure pinning-point change over three epochs spanning the periods 1973–1989, 1989–2000 and 2000−2022, and thus by proxy infer changes to ice-shelf thickness back to 1973–1989. We show that only small localized pockets of ice shelves were thinning between 1973 and 1989, located primarily in the Amundsen Sea Embayment and the Wilkes Land coastline. Ice-shelf thinning spreads rapidly into the 1990s and 2000s and is best characterized by the proportion of pinning points reducing in extent. Only 15% of pinning points reduced from 1973 to 1989, before increasing to 25% from 1989 to 2000 and 37% from 2000 to 2022. A continuation of this trend would further reduce the buttressing potential of ice shelves, enhancing ice discharge and accelerating the contribution of Antarctica to sea-level rise.

The West Antarctic Ice Sheet overlies the West Antarctic Rift System about which, due to the comprehensive ice cover, we have only limited and sporadic knowledge of volcanic activity and its extent. Improving our understanding of subglacial volcanic activity across the province is important both for helping to constrain how volcanism and rifting may have influenced ice-sheet growth and decay over previous glacial cycles, and in light of concerns over whether enhanced geothermal heat fluxes and subglacial melting may contribute to instability of the West Antarctic Ice Sheet. Here, we use ice-sheet bed-elevation data to locate individual conical edifices protruding upwards into the ice across West Antarctica, and we propose that these edifices represent subglacial volcanoes. We used aeromagnetic, aerogravity, satellite imagery and databases of confirmed volcanoes to support this interpretation. The overall result presented here constitutes a first inventory of West Antarctica's subglacial volcanism. We identified 138 volcanoes, 91 of which have not previously been identified, and which are widely distributed throughout the deep basins of West Antarctica, but are especially concentrated and orientated along the >3000 km central axis of the West Antarctic Rift System.

Ice shelves play a vital role in regulating loss of grounded ice and in supplying freshwater to coastal seas. However, melt variability within ice shelves is poorly constrained and may be instrumental in driving ice shelf imbalance and collapse. High‐resolution altimetry measurements from 2010 to 2016 show that Dotson Ice Shelf (DIS), West Antarctica, thins in response to basal melting focused along a single 5 km‐wide and 60 km‐long channel extending from the ice shelf's grounding zone to its calving front. If focused thinning continues at present rates, the channel will melt through, and the ice shelf collapse, within 40–50 years, almost two centuries before collapse is projected from the average thinning rate. Our findings provide evidence of basal melt‐driven sub‐ice shelf channel formation and its potential for accelerating the weakening of ice shelves. Ice shelves act as safety bands around the Antarctic ice sheet. Many ice shelves are currently thinning, leading to acceleration of the grounded ice behind. Here we show that ice shelves' thinning is stronger along a channel structure formed by the ocean circulation under the ice shelf. The thinning is 3 times higher than the ice shelf's average, hence leading to a more rapid weakening of the ice shelf. This study provides evidence of basal melt‐driven sub‐ice shelf channel formation and its potential for accelerating the weakening of ice shelves. High‐resolution surface elevation change shows channelized thinning, unabated from the grounding line up to the calving frontThinning is related to channelized basal melting controlled by ocean circulation and cavity geometryProcess has been ongoing for over 25 years, thinning the shelf to 3 quarter of its original height, making it more vulnerable to collapse

Changes to the grounding line, where grounded ice starts to float, can be used as a remotely sensed measure of ice-sheet susceptibility to ocean-forced dynamic thinning. Constraining this susceptibility is vital for predicting Antarctica's contribution to rising sea levels. We use Landsat imagery to monitor grounding line movement over four decades along the Bellingshausen margin of West Antarctica, an area little monitored despite potential for future ice losses. We show that ~65% of the grounding line retreated from 1990 to 2015, with pervasive and accelerating retreat in regions of fast ice flow and/or thinning ice shelves. Venable Ice Shelf confounds expectations in that, despite extensive thinning, its grounding line has undergone negligible retreat. We present evidence that the ice shelf is currently pinned to a sub-ice topographic high which, if breached, could facilitate ice retreat into a significant inland basin, analogous to nearby Pine Island Glacier. Grounding line change mapped along Bellingshausen margin of West Antarctica with Landsat and InSAR from 1975 to 2015Results show majority of grounding line retreated along entire margin implicating ocean-forced dynamic thinningGrounding line at Venable Ice Shelf currently pinned but potential for retreat as at Pine Island Glacier

We use high‐resolution ground‐penetrating radar (GPR) to assess the continuity of the Blue Ice Area (BIA) horizontal climate record at Patriot Hills, Horseshoe Valley, West Antarctica. The sequence contains three pronounced changes in deuterium isotopic values at ~18 cal ka, ~12 cal ka, and ~8 cal ka. GPR surveys along the climate sequence reveal continuous, conformable dipping isochrones, separated by two unconformities in the isochrone layers, which correlate with the two older deuterium shifts. We interpret these unconformities as discontinuities in the sequence, rather than direct measures of climate change. Ice sheet models and Internal Layer Continuity Index plots suggest that the unconformities represent periods of erosion occurring, as the former ice surface was scoured by katabatic winds in front of mountains at the head of Horseshoe Valley. This study demonstrates the importance of high‐resolution GPR surveys for investigating both paleoflow dynamics and interpreting BIA climate records. Katabatic winds have scoured unconformities in the internal annual layers of the Blue Ice Area (BIA)Unconformities evidence paleo BIA and represent breaks in the paleo climate recordGround‐penetrating radar should be used to examine BIA and interpret climate records

Reviews of Geophysics is the top‐rated journal in Geochemistry and Geophysics (ISI Web of Knowledge category) reflecting the many excellent contributions we received. It is an important milestone achieved with the reviewers' investment of time and effort. Their expertise ensures that the papers published in this journal meet the standards that the research community expects. We sincerely appreciate the time the reviewers spent reading and commenting on manuscripts, and we are very grateful for their willingness and readiness to serve in this role. On behalf of the authors and readers of Reviews of Geophysics (RoG), the American Geophysical Union, and the broader scientific community, the editors wish to wholeheartedly thank those who reviewed manuscripts for RoG in 2021. The editorial board thanks the 2021 peer reviewers The editorial board thanks the 2021 peer reviewers

Meltwater generated beneath the Antarctic Ice Sheet exerts a strong influence on the speed of ice flow, in particular for major ice streams. The subglacial meltwater also influences ocean circulation beneath ice shelves, initiating meltwater plumes that entrain warmer ocean water and cause high rates of melting. However, despite its importance, the nature of the hydrological system beneath the grounded ice sheet remains poorly characterized. Here we present evidence, from satellite and airborne remote sensing, for large channels beneath the floating Filchner–Ronne Ice Shelf in West Antarctica, which we propose provide a means for investigating the hydrological system beneath the grounded ice sheet. We observe features on the surface of the ice shelf from satellite imagery and, using radar measurements, show that they correspond with channels beneath the ice shelf. We also show that the sub-ice-shelf channels are aligned with locations where the outflow of subglacial meltwater has been predicted. This agreement indicates that the sub-ice-shelf channels are formed by meltwater plumes, initiated by subglacial water exiting the upstream grounded ice sheet in a focused (channelized) manner. The existence of a channelized hydrological system has implications for the behaviour and dynamics of ice sheets and ice shelves near the grounding lines of ice streams in Antarctica.

We interpret seismic reflection and airborne potential field data acquired on Pine Island Glacier, West Antarctica and find variations in the subglacial geology which correlate with variations in ice dynamics. Immediately beneath the glacier is a mixture of soft, deforming sediments and harder, non-deforming sediments. Beneath this, a sedimentary basin lies under part of the main glacier, with another under one of its slower-moving tributaries. A tectonic boundary underlies the main trunk of the glacier separating these sedimentary basins to the north from crystalline rocks to the south, which also include a thick, rift-related magmatic intrusion. The boundary correlates with changes in the basal roughness, ice flow speed, and basal drag. Smoother bed, faster flow, and lower basal drag characterize the thicker sedimentary sequences, to the north, but there is no corresponding lateral change in the acoustic properties of the bed. Changes in the sub-bed (i.e., deeper than the ice-bed interface) lithology appear to account for the contrasting basal drag and ice velocity patterns over the glacier. Subglacial erosion could remove a thin layer of soft sediments to the south of the geological boundary, leading to increased basal drag and reduced ice flow in the future. We conclude that the subglacial geology plays a significant role in controlling the spatial pattern of present-day ice flow and that the consequences of subglacial erosion may be reflected in temporal changes to the ice dynamics in the past and perhaps also in the near future. Ice flow variations are controlled by subglacial geologyContinued subglacial erosion could result in a reduction in ice flowBetter knowledge of subglacial geology required for future ice sheet predictions

Ground‐penetrating radar (GPR) is widely used on polythermal glaciers to image bed topography and detect internal scatter due to water inclusions in temperate ice. The glaciological importance of this is twofold: bed topography is a primary component for modeling the long‐term evolution of glaciers and ice sheets, and the presence of temperate ice and associated englacial water significantly reduces overall ice viscosity. Englacial water has a direct influence on radar velocity, which can result in incorrect observations of bed topography due to errors in depth conversion. Assessment of radar velocities often requires multi‐offset surveys, yet these are logistically challenging and time consuming to acquire, hence techniques to extract velocity from common‐offset data are required. We calculate englacial radar velocity from common offset GPR data collected on Von Postbreen, a polythermal glacier in Svalbard. We first separate and enhance the diffracted wavefield by systematically assessing data coherence. We then use the focusing metric of negative entropy to deduce a migration velocity field and produce a velocity model which varies spatially across the glacier. We show that this velocity field successfully differentiates between areas of cold and temperate ice and can detect lateral variations in radar velocity close to the glacier bed. This velocity field results in consistently lower ice depths relative to those derived from a commonly assumed constant velocity, with an average difference of 4.9 ± 2.5% of local ice depth. This indicates that diffraction focusing and velocity estimation are crucial in retrieving correct bed topography in the presence of temperate ice. The internal structure and thickness of glaciers can often be mapped using a technique called ground‐penetrating radar (GPR). To do this, we emit pulses of radio waves into the ice from the surface, and record the returning energy reflected back to the surface. Reflections are a result of contrasts in the material properties within the ice or at the ice‐bed interface. Sometimes, glacier ice can have quantities of water stored within pores between the ice crystals; this complicates the mapping process as it scatters the radio signal, and distorts the image of the bed below by changing the speed at which radio waves travel through ice. In this paper, we apply a new technique to use this scatter to estimate the changes in radio wave velocity. We use this newly estimated radio wave velocity to improve our understanding of the shape of the bed, and to improve our understanding of water distribution within the glacier. We use diffractions in ground‐penetrating radar data to retrieve the radar velocity field of a polythermal glacierThe retrieved radar velocity field successfully differentiates between cold and temperate iceWe use the retrieved velocity field to improve bed topography relative to a constant velocity field We use diffractions in ground‐penetrating radar data to retrieve the radar velocity field of a polythermal glacier The retrieved radar velocity field successfully differentiates between cold and temperate ice We use the retrieved velocity field to improve bed topography relative to a constant velocity field

On behalf of the authors and readers of Reviews of Geophysics (RoG), the American Geophysical Union (AGU), and the broader scientific community, the editors wish to wholeheartedly thank those who reviewed manuscripts for RoG in 2020. The editorial board thanks the 2020 peer reviewers The editorial board thanks the 2020 peer reviewers

The englacial stratigraphic architecture of internal reflection horizons (IRHs) as imaged by ice‐penetrating radar (IPR) across ice sheets reflects the cumulative effects of surface mass balance, basal melt, and ice flow. IRHs, considered isochrones, have typically been traced in interior, slow‐flowing regions. Here, we identify three distinctive IRHs spanning the Institute and Möller catchments that cover 50% of West Antarctica's Weddell Sea Sector and are characterized by a complex system of ice stream tributaries. We place age constraints on IRHs through their intersections with previous geophysical surveys tied to Byrd Ice Core and by age‐depth modeling. We further show where the oldest ice likely exists within the region and that Holocene ice‐dynamic changes were limited to the catchment's lower reaches. The traced IRHs from this study have clear potential to nucleate a wider continental‐scale IRH database for validating ice sheet models. Ice‐penetrating radar is widely used to measure the thickness of ice sheets, critical to assessments of global sea level rise potential. This technique also captures reflections from chemical contrasts within the ice sheet, caused by the atmospheric deposition of conductive impurities, known as “internal reflection horizons” (IRHs) that can be traced over large distances. As these deposits are laid down in distinct events, most IRHs are isochronous age tracers and contain valuable information on past ice sheet processes. In this paper we trace and place age constraints on stratigraphic horizons across a large portion of the West Antarctic Ice Sheet, including regions where fast ice flow has disrupted the ice sheet stratigraphy. The resulting data set allows us to identify where the oldest ice is buried in the study region and provides evidence that flow of the ice sheet interior has been stable during the Holocene. Our results can be used to test the performance of ice sheet models, which seek to simulate the response of ice sheets to long‐term environmental change. We measure and date individual isochronal radar internal reflection horizons across the Weddell Sea sector of the West Antarctic Ice SheetHorizons dated to 1.9–3.2, 3.5–6.0, and 4.6–8.1 ka are widespread and linked to previous radar surveys of the Ross and Amundsen Sea sectorsThese form the basis for a wider database of ice sheet architecture for validating and calibrating ice sheet models of West Antarctica