Last Interglacial subsurface warming on the Antarctic shelf triggered by reduced deep-ocean convection

The Antarctic ice-sheet could have contributed 3 to 5 m sea-level equivalent to the Last Interglacial sea-level highstand. Such an Antarctic ice-mass loss compared to pre-industrial requires a subsurface warming on the Antarctic shelf of similar to 3 degrees C according to ice-sheet modelling studies. Here we show that a substantial subsurface warming is simulated south of 60 degrees S in an equilibrium experiment of the Last Interglacial. It averages +1.2 degrees C at similar to 500 m depth from 70 degrees W to 160 degrees E, and it reaches +2.4 degrees C near the Lazarev Sea. Weaker deep-ocean convection due to reduced sea-ice formation is the primary driver of this warming. The associated changes in meridional density gradients and surface winds lead to a weakened Antarctic Circumpolar Current and strengthened Antarctic Slope Current, which further impact subsurface temperatures. A subsurface warming on the Antarctic shelf that could trigger ice-mass loss from the Antarctic ice-sheet can thus be obtained during warm periods from reduced sea-ice formation.