Recent Variability in Fracture Characteristics and Ice Flow of Thwaites Ice Shelf, West Antarctica

The rapidly changing Thwaites Ice Shelf is crucial for understanding ice-shelf dynamical processes and their implications for sea-level rise from Antarctica. Fractures, particularly their vertical structure, are key to ice-shelf structural integrity but remain poorly measured. To address this, we developed a fracture-characterization workflow using ICESat-2 ATL03 geolocated photon heights, producing the first time-series vertical measurements of fractures across Thwaites from 2018 to 2024. We introduced the fracture depth/freeboard ratio as a normalized metric to quantify vertical fracture extent, serving as an indicator of structural damage. This metric enabled us to track fracture evolution in both the eastern ice shelf and western glacier tongue. In the eastern section, fracturing intensified along the northwestern shear zone and near the grounding line, in a positive feedback loop between enhanced fracturing and accelerated flow. The western section maintained an active rift formation zone about 15 km downstream of the historical grounding line. Flow velocity changes in this section were primarily confined to the unconstrained downstream portion, exhibiting an overall deceleration trend, while the upstream area remained stable. This contrast highlights the role of lateral margin conditions in governing ice-shelf fracture and flow behavior. Changes in the eastern section showed some correspondence with warm winter air temperatures, reduced sea ice, and persistent warm ocean anomalies at shallower depths, suggesting that atmosphere-sea ice-ocean interactions influence ice-shelf structural integrity through basal processes. Future research should integrate satellite-derived fracture observations with numerical models of ice fracture and flow to better capture the dynamics of ice-shelf weakening and retreat.