Fig. 4: Interplay between West Antarctic ice sheet (WAIS) dynamics and the Southern Ocean during Marine Isotope Stage (MIS) 11 based on proxy analyses at IODP Site U1540 (star).

a Cold water-cavity scenario – background conditions of MIS11c: strong isopycnal gradient at the Antarctic slope of the Ross Sea (gray line) prevents upwelling of Circumpolar Deep Water (CDW) onto the continental shelf (red arrow), leading to minimal basal melting beneath ice shelves and at the WAIS grounding line (dashed black line), favoring Dense Shelf Water (DSW) and Antarctic Bottom Water (AABW) formation (white lines) through supercooling underneath ice shelves and/or brine rejection in coastal polynyas. This leads to well-oxygenated conditions at IODP Site U1540. b Warm-water cavity scenario – deoxygenation events (E) EI and EII during MIS11c: isopycnal gradient at the Antarctic slope of the Ross Sea and/or Amundsen/Bellingshausen Seas (gray line) weakens, allowing more and/or warmer CDW to upwell onto the continental shelf. This causes strong basal melting and WAIS retreat (dashed black line), driving global sea-level rise (dark gray arrow). Two pathways for CDW supply to the Antarctic periphery are possible²³: to c the Ross Sea along Ross Gyre’s eastern limb and/or d the Amundsen- and Bellingshausen Sea via Ross Gyre expansion (see Discussion and text in figure). e Adjusted cold water-cavity scenario – deoxygenation event EIII during MIS11b: Global cooling leads to a northward advance of the WAIS grounding line (dashed black line), which decreases global sea-levels below present-day values (dark gray arrow) and is likely associated with ice shelf- and Antarctic sea ice expansion in the Ross Sea. Cooling of CDW could have changed the rate and/or mode of DSW- and AABW formation, and could have led to cold and low-O₂ AABW, as identified at IODP Site U1540. Possible glacio-isostatic adjustments are neglected here. Maps were created with Ocean Data View⁸⁴.