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Since distributed satellite observations of elevation change and velocity became available in the 1990s, Thwaites, Pine Island, Haynes, Pope, and Kohler Glaciers, located in Antarctica's Amundsen Sea Embayment, have thinned and accelerated in response to ocean-induced melting and grounding-line retreat. We develop a crevasse image segmentation algorithm to identify and map surface crevasses on the grounded portions of Thwaites, Pine Island, Haynes, Pope, and Kohler Glaciers between 2015 and 2022 using Sentinel-1A satellite synthetic aperture radar (SAR) imagery. We also develop a geometric 5 model for firn tensile strength dependent on porosity and the tensile strength of ice. On Pine Island and Thwaites Glaciers, which have both accelerated since 2015, crevassing has expanded tens of kilometers upstream of the 2015 extent. From the crevasse time series, we find that crevassing is strongly linked to principal surface stresses and consistent with von Mises fracture theory predictions. Our geometric model, analysis of SAR, and optical imagery, together with ice-penetrating radar data, suggest that these crevasses are near-surface features restricted to the firn. The porosity dependence of the near-surface tensile 10 strength of the ice sheet may explain discrepancies between the tensile strength inferred from remotely-sensed surface crevasse observations and tensile strength measured in laboratory experiments, which often focus on ice (rather than firn) fracture. The near-surface nature of these features suggests that the expansion of crevasses inland has a limited direct impact on glacier mechanics. [ABSTRACT FROM AUTHOR]

In order to improve projections of the future ice-sheet surface mass balance and the interpretation of the isotopic signals of past accumulation preserved in ice cores, it is critical to understand the mechanisms that transport water vapor to the Antarctic continent. Global Navigation Satellite System (GNSS) receivers distributed across Antarctica to monitor ice velocity and solid Earth motion can be used to understand accumulation, ablation, and snow redistribution at the ice-sheet surface. Here, we present a forward model for reflector height change between the GNSS antenna phase center and the snow surface and an inverse framework to determine accumulation rate and near-surface firn densification from the reflector height time series. We use this model to determine accumulation at the sites of three long-term on-ice GNSS receivers located in the Amundsen Sea Embayment (ASE) and at a network of GNSS receivers deployed in 2007-2008, 2008-2009, and 2009-2010 austral summers. From the GNSS-IR accumulation reconstructions, we find that extreme precipitation dominates total precipitation and that extreme event frequency varies seasonally. We use our GNSS-IR accumulation reconstructions together with reanalysis products to characterize the atmospheric conditions that promote extreme snowfall in the ASE. The blocking pressure systems that promote extreme accumulation on Thwaites Glacier are facilitated by tropical teleconnections, specifically convection that promotes Rossby waves trains from the Western Pacific, Indian, and Atlantic Oceans to the Amundsen and Bellingshausen Seas. [ABSTRACT FROM AUTHOR]

Atmospheric rivers (ARs) transport large amounts of moisture from the mid-to high-latitudes and they are a primary driver of the most extreme snowfall events on Antarctica. ARs also raise surface temperatures when they make landfall over Antarctica, leading to surface melting. In this study, we characterize the climatology and surface impacts of ARs on West Antarctica, focusing on the Amundsen Sea Embayment and Marie Byrd Land. First, we develop a climatology of ARs in this region, using an Antarctic-specific AR detection tool combined with MERRA-2 and ERA5 atmospheric reanalyses. We find that while ARs are infrequent, they cause intense precipitation in short periods of time and account for 11% of the annual surface accumulation. They are driven by the coupling of a blocking high over the Antarctic Peninsula with a low-pressure system known as the Amundsen Sea Low. Next, we use observations from automatic weather stations on Thwaites Eastern Ice Shelf to examine a case study of 3 ARs that made landfall in rapid succession from February 2 to 8, known as an AR family event. We use snow height observations to force the firn model SNOWPACK to reconstruct accumulation and surface melting during the event, and compare these results with accumulation higher up on the glacier derived from surface height changes using interferometric reflectometry. While accumulation dominates the surface impacts of the event on Thwaites Eastern Ice Shelf (>100 kg m-2), we find small amounts of surface melt as well (<5 kg m-2). West Antarctica currently experiences minimal surface melting, most of which is absorbed by the firn, but future atmospheric warming could lead to more widespread surface melting in West Antarctica. Combined with a future increase in AR intensity or frequency, this could limit the ability of the firn layer to absorb melt water, which could harm ice shelf stability, and ultimately accelerate mass loss of the West Antarctic Ice Sheet. The results presented here enable us to quantify the past impacts of ARs on West Antarctic surface mass balance and characterize their interannual variability and trends, enabling a better assessment of future AR-driven changes in the surface mass balance. [ABSTRACT FROM AUTHOR]