Past Antarctic Ice Sheet dynamics and retreat thresholds in the Wilkes Subglacial Basin

The Wilkes Subglacial Basin (WSB), the largest marine-based sector of the East Antarctic Ice Sheet (EAIS), contains 3-4 m sea level equivalent ice volume and is considered highly vulnerable to instability processes under future warming scenarios 1–3 . Loss of marine-based ice in WSB has been implied during Pliocene (5.3-2.6 Ma) interglacials when global temperatures were 2–3°C warmer and atmospheric pCO₂ exceeded ~400 ppm 4 . Ice retreat in the WSB has also been suggested within the last 400 kyr under more modest warming, although the magnitude of ice loss relative to the Pliocene remains uncertain 5–8 . Here, we present a continuous 6-million-year-long record of iceberg-rafted debris and geochemical provenance tracers sourced from the WSB, providing evidence for shifts in iceberg calving and subglacial erosion related to ice sheet dynamics. Climate and ice sheet modelling experiments reveal that, while the pacing of marine-based erosion and iceberg calving in WSB was consistently modulated in a near-linear manner by orbital forcing, expansive grounding-line retreat required crossing a critical atmospheric warming threshold when pCO₂ exceeded 400 ppm. Our results demonstrate non-linear behaviour in the WSB, whereby once a warming threshold is breached, accelerated basal ice flow, dynamic thinning and flotation of the ice margin at its present-day bathymetric high occurs - after which ice loss within the largest EAIS marine catchment becomes irreversible on multi-millennial timescales.