Assessing the Structural Stability of Thwaites Eastern Ice Shelf and Its Influence on the Future Evolution of Thwaites Glacier

The Thwaites Eastern Ice Shelf stands as the last remaining floating extent of the consequential Thwaites Glacier in West Antarctica. In the past, it has provided buttressing of the grounded glacier ice, but in the last decade the ice shelf has undergone significant weakening that has reduced its ability to buttress the glacier. Important signs of weakening include: 1) the ice flow measured by ground-based GPS shows continuous acceleration, nearly doubling in speed from 1.65 m/d in 2019 to 2.85 m/d by early 2023; 2) a recent breakout of sea ice has accelerated retreat at the western calving front of the Eastern Ice Shelf; 3) increased damage in a confined shear zone along the north-western pinning point has effectively separated the ice shelf from this pinning point.; 4) five rifts formed since 2016 and have propagated episodically into the center of the most coherent section of the shelf; and 5) several full thickness gashes have opened and continue to open parallel to and just downstream of the grounding zone to accommodate the recent ice-shelf speed up through localized strain. Due to these full-depth rifts, the ice shelf has nearly entirely detached from the upstream grounded ice, and is now functioning as a relatively thin, floating ice plate that provides minimal support to the grounded sections of Thwaites Glacier. This accumulation of damage in the ice shelf is happening during a period in which we observe suppressed basal melt rates and little measurable thinning, suggesting that melt is not the primary driver of ongoing changes. Here, we present the most up-to-date synthesis assessment of the structural integrity of this ice shelf, as well as its relation to ocean conditions underneath and the pinning point, and consider the stability of the ice shelf within the context of ice flow off the continent and projections for sea-level rise.