Synchronous terminus change of East Antarctic outlet glaciers linked to climatic forcing

In recent years there has been a growing trend of acceleration, thinning and retreat of ocean-terminating outlet glaciers in both the Greenland and West Antarctic Ice Sheets, resulting in an increasing contribution to sea level rise. Similar changes in glacier elevation have been observed in major marine basins of the much larger East Antarctic Ice Sheet, but there are few measurements of glacier terminus positions. In this study, the frontal position of 175 marine terminating glaciers along a 5,400 km stretch of the East Antarctic coastline is analysed. Overall, between 1974 and 2010 there was little change in glacier frontal position (median: 0.7 m a-1). However, strong decadal trends have been observed, from 1974 to 1990, the majority of glaciers retreated (63%), whereas between 1990 and 2000, most glaciers advanced (72%), a pattern which dropped to fewer glaciers advancing (58%) in the most recent decade (2000 to 2010). The patterns in glacier frontal position change are consistent with a rapid and coherent response to atmospheric and oceanic/sea-ice forcing, which are ultimately driven by the dominant mode of atmospheric variability in the Southern hemisphere, the Southern Annular Mode. This indicates that the East Antarctic Ice Sheet may be more vulnerable to climate change than previously recognised. However, unlike in Greenland, there appears to be no clear link between recent changes in glacier elevation and frontal position, possibly due to the unconstrained (~90%) nature of the majority of glaciers in the study area

Slowdown of Shirase Glacier, East Antarctica, caused by strengthening alongshore winds

Around large parts of West Antarctica and in Wilkes Land, East Antarctica, increased wind-forced intrusions of modified Circumpolar Deep Water (mCDW) onto the continental shelf have been associated with mass loss over the last few decades. Despite considerable seasonal variability, observations in 2018 have also confirmed relatively high basal melt rates of up to 16 m a -1 underneath the Shirase ice tongue in Enderby Land, East Antarctica. These high basal melt rates are also caused by intrusions of mCDW onto the continental shelf, but the catchment of Shirase Glacier has been gaining mass, a trend often attributed to increased precipitation. Here, we document the dynamical ocean-driven slowdown, ice surface thickening and grounding line advance of Shirase Glacier, in response to strengthening easterly winds that reduce mCDW inflow and decrease basal melt rates. Our findings are significant because they demonstrate that warm ice shelf cavity regimes are not universally associated with glacier acceleration and mass loss in Antarctica, and they highlight the overlooked role of the impact of easterly winds in the recent mass gain of the Shirase Glacier catchment

Short- and long-term variability of the Antarctic and Greenland ice sheets

The variability of the Antarctic and Greenland ice sheets occurs on various timescales and is important for projections of sea level rise; however, there are substantial uncertainties concerning future ice-sheet mass changes. In this Review, we explore the degree to which short-term fluctuations and extreme glaciological events reflect the ice sheets’ long-term evolution and response to ongoing climate change. Short-term (decadal or shorter) variations in atmospheric or oceanic conditions can trigger amplifying feedbacks that increase the sensitivity of ice sheets to climate change. For example, variability in ocean-induced and atmosphere-induced melting can trigger ice thinning, retreat and/or collapse of ice shelves, grounding-line retreat, and ice flow acceleration. The Antarctic Ice Sheet is especially prone to increased melting and ice sheet collapse from warm ocean currents, which could be accentuated with increased climate variability. In Greenland both high and low melt anomalies have been observed since 2012, highlighting the influence of increased interannual climate variability on extreme glaciological events and ice sheet evolution. Failing to adequately account for such variability can result in biased projections of multi-decadal ice mass loss. Therefore, future research should aim to improve climate and ocean observations and models, and develop sophisticated ice sheet models that are directly constrained by observational records and can capture ice dynamical changes across various timescales

Landsat mosaics of Antarctic Ice Shelves from 2022

Mass loss of the Antarctic Ice Sheet has been primarily driven by thinning of the floating ice shelves that fringe the ice sheet, reducing their buttressing potential and causing land ice to accelerate into the ocean. However, observations of ice-shelf thickness change by satellite altimetry only stretch back to 1992 and prior information about thinning remains unquantified. Here, we present a new way of assessing ice-shelf thickness change that focusses on changes to pinning points, local bathymetric highs on which ice shelves are anchored and which are typically expressed as surface protuberances on the ice-shelves' surfaces. We utilise the full Landsat archive to map the evolution of pinning points around the Antarctic coastline over 50 years, and thus by proxy infer changes to ice-shelf thickness back to 1973. Ice shelves in the Amundsen Sea sector and in Wilkes Land were already thinning from 1973-1989, meaning the processes driving mass loss in these key sectors of Antarctica have been ongoing for at least 50 years. Ice-shelf thinning spreads rapidly into the 1990s and 2000s and is best characterised by the proportion of pinning points reducing in extent. Only 15% of pinning points reduced from 1973-1989, before increasing to 25% from 1990-2000 and 37% from 2000-2022. A continuation of this trend would further reduce the buttressing potential of ice shelves, enhancing ice discharge and accelerating Antarctica's contribution to sea-level rise. This dataset contains a collection of Landsat 8 and 9 images covering most of Antarctica’s ice shelves centred on 2022. These mosaics were utilized to track pinning point change over the past 5 decades. More details are available in the README and in the accompanying manuscript that has been submitted for peer review. The dataset is related to the upcoming publication Bingham, R. and B. Miles (in submission

Landsat mosaics of Antarctic Ice Shelves from 1973 and 1989

This dataset contains a collection near cloud-free, co-registered Landsat images covering most of Antarctica’s ice shelves centred on 1973 and 1989. These mosaics were utilized to track pinning point change over the past 5 decades. More details are available in the README and in the accompanying manuscript that has been submitted for peer review. The dataset is related to the upcoming publication Bingham, R. and B. Miles (in submission). Copyright: Courtesy of the U.S. Geological Survey (public domain without copyright restriction). https://www.usgs.gov/centers/eros/data-citation)

Antarctic ice shelf pinning point change classification 1973-2022

Mass loss of the Antarctic Ice Sheet has been primarily driven by thinning of the floating ice shelves that fringe the ice sheet, reducing their buttressing potential and causing land ice to accelerate into the ocean. However, observations of ice-shelf thickness change by satellite altimetry only stretch back to 1992 and prior information about thinning remains unquantified. Here, we present a new way of assessing ice-shelf thickness change that focusses on changes to pinning points, local bathymetric highs on which ice shelves are anchored and which are typically expressed as surface protuberances on the ice-shelves' surfaces. We utilise the full Landsat archive to map the evolution of pinning points around the Antarctic coastline over 50 years, and thus by proxy infer changes to ice-shelf thickness back to 1973. Ice shelves in the Amundsen Sea sector and in Wilkes Land were already thinning from 1973-1989, meaning the processes driving mass loss in these key sectors of Antarctica have been ongoing for at least 50 years. Ice-shelf thinning spreads rapidly into the 1990s and 2000s and is best characterised by the proportion of pinning points reducing in extent. Only 15% of pinning points reduced from 1973-1989, before increasing to 25% from 1990-2000 and 37% from 2000-2022. A continuation of this trend would further reduce the buttressing potential of ice shelves, enhancing ice discharge and accelerating Antarctica's contribution to sea-level rise. This dataset contains point shapefiles that map the direction of change in the surface area of pinning points across the Antarctic Ice Sheet from 1973-1989, 1989-2000, 2000-2022 and 1973-2022. More details are available in the README. The dataset is related to the upcoming publication Miles & Bingham (in submission)

The triggers of the disaggregation of Voyeykov Ice Shelf (2007), Wilkes Land, East Antarctica, and its subsequent evolution

The weakening and/or removal of floating ice shelves in Antarctica can induce inland ice flow acceleration. Numerical modelling suggests these processes will play an important role in Antarctica's future sea-level contribution, but our understanding of the mechanisms that lead to ice tongue/shelf collapse is incomplete and largely based on observations from the Antarctic Peninsula and West Antarctica. Here, we use remote sensing of structural glaciology and ice velocity from 2001 to 2020 and analyse potential ocean-climate forcings to identify mechanisms that triggered the rapid disintegration of ~2445 km2 of ice mélange and part of the Voyeykov Ice Shelf in Wilkes Land, East Antarctica between 27 March and 28 May 2007. Results show disaggregation was pre-conditioned by weakening of the ice tongue's structural integrity and was triggered by mélange removal driven by a regional atmospheric circulation anomaly and a less extensive latent-heat polynya. Disaggregation did not induce inland ice flow acceleration, but our observations highlight an important mechanism through which floating termini can be removed, whereby the break-out of mélange and multiyear landfast sea ice triggers disaggregation of a structurally-weak ice shelf. These observations highlight the need for numerical ice-sheet models to account for interactions between sea-ice, mélange and ice shelves

Response of the East Antarctic Sheet to Past and Future Climate Change

The East Antarctic Ice Sheet contains the vast majority of Earth’s glacier ice (about 52 metres sea-level equivalent), but is often viewed as less vulnerable to global warming than the West Antarctic or Greenland ice sheets. However, some regions of the East Antarctic Ice Sheet have lost mass over recent decades, prompting the need to re-evaluate its sensitivity to climate change. Here we review the response of the East Antarctic Ice Sheet to past warm periods, synthesize current observations of change and evaluate future projections. Some marine-based catchments that underwent notable mass loss during past warm periods are losing mass at present but most projections indicate increased accumulation across the East Antarctic Ice Sheet over the twenty-first century, keeping the ice sheet broadly in balance. Beyond 2100, high-emissions scenarios generate increased ice discharge and potentially several metres of sea-level rise within just a few centuries, but substantial mass loss could be averted if the Paris Agreement to limit warming below 2 degrees Celsius is satisfied