The Antarctic ice sheet (AIS) is the largest freshwater body on Earth and a major component of the sea level budget. Over the satellite era, the AIS has experienced ∼130 Gt/year of mass loss. Net ...losses are partially mitigated by snow accumulation that varies ∼100–130 Gt/yr, underscoring a need to understand the drivers of snowfall variability. Here, we evaluate impacts of decreased sea ice in the Amundsen Sea region of West Antarctica on the overlying atmosphere and surface mass balance of the adjacent AIS using composites, spatial correlations, and a causal effect network method. Importantly, our findings show sea ice declines in the Amundsen Sea lead to enhanced integrated water vapor that is subsequently transported to the AIS resulting in positive anomalies in West Antarctic ice sheet snowfall. Our results suggest future decreases in sea ice may likely enhance ice sheet snowfall, thus partially offsetting Antarctic sea level contributions.
Plain Language Summary
The Antarctic ice sheet (AIS) is the largest freshwater body on Earth and is a major component of the sea level budget. Since the start of the satellite record in 1980, the AIS has been losing mass at an increasing rate. These losses are attributed to increased flow of ice into the ocean and are partially balanced each year by the accumulation of snow across the ice sheet's surface. The degree to which it snows across Antarctica therefore controls how much the ice sheet contributes to sea level in any given year. Thus, it is crucial for us to understand the drivers of snowfall variability. Here, we evaluate the impacts of decreased sea ice in the Amundsen Sea region of West Antarctica on snowfall over the adjacent ice sheet. Importantly, our findings show that sea ice declines in this region lead to enhanced moisture in the atmosphere which is then transported over the West Antarctic ice sheet resulting in greater snowfall.
Key Points
Observations and reanalyzes reveal decreased sea ice leads to increased precipitation over the West Antarctic ice sheet
Causal discovery links low sea ice to enhanced water vapor and precipitation‐bearing clouds over the ice sheet
Past and future changes in sea ice hold implications for ice sheet surface mass balance
Ice flow models of the Antarctic ice sheet are commonly used to simulate its future evolution in response to different climate scenarios and assess the mass loss that would contribute to future sea ...level rise. However, there is currently no consensus on estimates of the future mass balance of the ice sheet, primarily because of differences in the representation of physical processes, forcings employed and initial states of ice sheet models. This study presents results from ice flow model simulations from 13 international groups focusing on the evolution of the Antarctic ice sheet during the period 2015–2100 as part of the Ice Sheet Model Intercomparison for CMIP6 (ISMIP6). They are forced with outputs from a subset of models from the Coupled Model Intercomparison Project Phase 5 (CMIP5), representative of the spread in climate model results. Simulations of the Antarctic ice sheet contribution to sea level rise in response to increased warming during this period varies between -7:8 and 30.0 cm of sea level equivalent (SLE) under Representative Concentration Pathway (RCP) 8.5 scenario forcing. These numbers are relative to a control experiment with constant climate conditions and should therefore be added to the mass loss contribution under climate conditions similar to present-day conditions over the same period. The simulated evolution of the West Antarctic ice sheet varies widely among models, with an overall mass loss, up to 18.0 cm SLE, in response to changes in oceanic conditions. East Antarctica ass change varies between -6.1 and 8.3 cm SLE in the simulations, with a significant increase in surface mass balance outweighing the increased ice discharge under most RCP 8.5 scenario forcings. The inclusion of ice shelf collapse, here assumed to be caused by large amounts of liquid water ponding at the surface of ice shelves, yields an additional simulated mass loss of 28mm compared to simulations without ice shelf collapse. The largest sources of uncertainty come from the climate forcing, the ocean-induced melt rates, the calibration of these melt rates based on oceanic conditions taken outside of ice shelf cavities and the ice sheet dynamic response to these oceanic changes. Results under RCP 2.6 scenario based on two CMIP5 climate models show an additional mass loss of 0 and 3 cm of SLE on average compared to simulations done under present-day conditions for the two CMIP5 forcings used and display limited mass gain in East Antarctica.
Surface melting and lakes are common to Antarctic ice shelves, and their existence and drainages have been invoked as a precursor for ice shelf collapse. Here, we present satellite observations over ...2014–2020 of repeated, rapid drainages of a supraglacial lake at the grounding zone of Amery Ice Shelf, East Antarctica. Post‐drainage imagery in 2018 reveals lake bottom features characteristic of rapid, vertical lake drainage. Observed lake volumes indicate drainages are not associated with a threshold meltwater volume. Instead, drainages typically coincide with periods of high daily tidal amplitude, suggesting hydrofracture is assisted by tidally forced ice flexure inherent to the ice shelf grounding zone. Combined with observations of widespread grounding zone lake drainages on Amery, these findings indicate ice shelf meltwater accumulation may be inhibited by grounding zone drainage events, thus representing a potential stabilizing mechanism despite enhanced melting common to these regions.
Plain Language Summary
The Antarctic ice sheet is the largest potential source of global sea level rise. Today, most mass losses from Antarctica result from enhanced ice flow into the ocean driven by ocean melting of the ice sheet's marine margins. Despite widespread and intense surface melting along the periphery of the ice sheet, little of this water is presently thought to run off into the ocean. However, surface melting is expected to play a greater role in future ice losses as the atmosphere continues to warm. One potential impact of increased surface melting is accumulation of water on the floating ice shelves that fringe much of the Antarctic ice sheet. As demonstrated in the 1990 and 2000s, large surface lake volumes can deepen fractures in the ice (i.e., hydrofracture), leading to catastrophic ice shelf collapse and accelerated ice flow into the ocean. Here, we report that drainages of lakes in zones of tidal ice shelf flexure on the largest ice shelf in East Antarctica may limit accumulation of meltwater and expect this process may exist elsewhere. While vertical lake drainages directly contribute runoff to the ocean, they may temporarily act to stabilize ice shelves by limiting surface meltwater accumulation.
Key Points
We report the repeated filling and rapid, vertical drainage of a supraglacial lake on Amery Ice Shelf
Lake drainages are associated with high amplitude tide cycles, likely facilitating hydrofracture
Frequent, widespread drainages of grounding line supraglacial lakes may act to protect ice shelves from enhanced meltwater production
Government policies currently commit us to surface warming of three to four degrees Celsius above pre-industrial levels by 2100, which will lead to enhanced ice-sheet melt. Ice-sheet discharge was ...not explicitly included in Coupled Model Intercomparison Project phase 5, so effects on climate from this melt are not currently captured in the simulations most commonly used to inform governmental policy. Here we show, using simulations of the Greenland and Antarctic ice sheets constrained by satellite-based measurements of recent changes in ice mass, that increasing meltwater from Greenland will lead to substantial slowing of the Atlantic overturning circulation, and that meltwater from Antarctica will trap warm water below the sea surface, creating a positive feedback that increases Antarctic ice loss. In our simulations, future ice-sheet melt enhances global temperature variability and contributes up to 25 centimetres to sea level by 2100. However, uncertainties in the way in which future changes in ice dynamics are modelled remain, underlining the need for continued observations and comprehensive multi-model assessments.
Melt and supraglacial lakes are precursors to ice shelf collapse and subsequent accelerated ice sheet mass loss. We used data from the Landsat 8 and Sentinel-2 satellites to develop a threshold-based ...method for detection of lakes found on the Antarctic ice shelves, calculate their depths and thus their volumes. To achieve this, we focus on four key areas: the Amery, Roi Baudouin, Nivlisen, and Riiser-Larsen ice shelves, which are all characterized by extensive surface meltwater features. To validate our products, we compare our results against those obtained by an independent method based on a supervised classification scheme (e.g., Random Forest algorithm). Additional verification is provided by manual inspection of results for nearly 1000 Landsat 8 and Sentinel-2 images. Our dual-sensor approach will enable constructing high-resolution time series of lake volumes. Therefore, to ensure interoperability between the two datasets, we evaluate depths from contemporaneous Landsat 8 and Sentinel-2 image pairs. Our assessments point to a high degree of correspondence, producing an average R2 value of 0.85, no bias, and an average RMSE of 0.2 m. We demonstrate our method’s ability to characterize lake evolution by presenting first evidence of drainage events outside of the Antarctic Peninsula on the Amery Ice shelf. The methods presented here pave the way to upscaling throughout the Landsat 8 and Sentinel-2 observational record across Antarctica to produce a first-ever continental dataset of supraglacial lake volumes. Such a dataset will improve our understanding of the influence of surface hydrology on ice shelf stability, and thus, future projections of Antarctica’s contribution to sea level rise.
The Greenland ice sheet (GrIS) is a growing contributor to global sea-level rise
, with recent ice mass loss dominated by surface meltwater runoff
. Satellite observations reveal positive trends in ...GrIS surface melt extent
, but melt variability, intensity and runoff remain uncertain before the satellite era. Here we present the first continuous, multi-century and observationally constrained record of GrIS surface melt intensity and runoff, revealing that the magnitude of recent GrIS melting is exceptional over at least the last 350 years. We develop this record through stratigraphic analysis of central west Greenland ice cores, and demonstrate that measurements of refrozen melt layers in percolation zone ice cores can be used to quantifiably, and reproducibly, reconstruct past melt rates. We show significant (P < 0.01) and spatially extensive correlations between these ice-core-derived melt records and modelled melt rates
and satellite-derived melt duration
across Greenland more broadly, enabling the reconstruction of past ice-sheet-scale surface melt intensity and runoff. We find that the initiation of increases in GrIS melting closely follow the onset of industrial-era Arctic warming in the mid-1800s, but that the magnitude of GrIS melting has only recently emerged beyond the range of natural variability. Owing to a nonlinear response of surface melting to increasing summer air temperatures, continued atmospheric warming will lead to rapid increases in GrIS runoff and sea-level contributions.
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