Uncovered bathymetry under Antarctica’s fourth largest ice shelf reveals potential for seasonal warm water inflow

Interactions of ice and ocean around Antarctica determine the stability of ice shelves and the onshore ice masses they buttress. These interactions and the exchange of water between the open ocean and ice shelf cavities depend heavily on seabed morphology and depth. However, vast areas of the Antarctic margin remain bathymetrically undersampled, and some, including the cavity beneath the ~44,000 km2 Riiser-Larsen Ice Shelf, Antarctica’s fourth largest, were never yet visited. Here, we use new aerogeophysical and existing oceanographical data to infer bathymetry under the cavity and assess the interactions of ice, ocean and bed. We find a bed shaped by its setting at an extended continental margin, and modified by glacial processes. A 520 m-deep bathymetric gateway at the continental shelf break permits seasonal intrusion of Warm Deep Water into a subglacial trough that allows the warm water to reach the 1000 m deep grounding zone at the ice shelf’s main inlet. The existence of analogous gateways at several ice shelves of Dronning Maud Land indicates that the buttressing effect on a large marine-based portion of the East Antarctic Ice Sheet, albeit whilst currently stable, may be approaching a serious tipping point with minimal changes to the oceanographic regime.