Ocean-driven reactivation of basal melt and dynamic instability beneath Pine Island Glacier ice shelf since 2018

Lucille Gimenes , Romain Millan , Jean-Baptiste Barré, Amandine Clément, Jonas Kvist Andersen, Maud Bernat, Kaian Shahateet, Antoine Rabatel

Pine Island Glacier (PIG) is Antarctica's largest contributor to sea-level rise and a major source of mass loss from the West Antarctic Ice Sheet. Its ice shelf is vulnerable to incursions of warm Circumpolar Deep Water (CDW) and has experienced rapid grounding-line retreat, flow acceleration, and increased ice discharge since the 1990s. Here, we reconstruct a 20-year record of basal melt rates beneath the PIG ice shelf using high-resolution multi-sensor stereo-photogrammetric digital elevation models combined with precise laser altimetry measurements. Following a slowdown in basal melting between 2004 and 2010, we document a renewed intensification of melting within the Pine Island cavity since 2018, leading to cavity expansion and coinciding with a ~0.5{degree sign}C increase in ocean temperature below 400 m depth since 2019. Intense basal melting rates exceeding 50 m yr⁻¹ now affect all ice-ocean interfaces deeper than 400 m, representing 40% of the ice-shelf area, and exceed 200 m yr⁻¹ near the grounding line. The recent emergence of localized melt channels on the southern tributary coincides with flow acceleration, increased structural damage, and complete detachment from the main glacier trunk, leaving it largely unbuttressed. Together with the recent re-acceleration of grounding-line retreat and ice discharge, these observations indicate a renewed phase of dynamic instability and mass loss, with important implications for the future evolution of the West Antarctic Ice Sheet.