The role of ocean cooling in setting glacial southern source bottom water salinity

[1] At the Last Glacial Maximum (LGM), the salinity contrast between northern source deep water and southern source bottom water was reversed with respect to the contrast today. Additionally, Glacial Southern Source Bottom Water (GSSBW) was saltier than Antarctic Bottom Water (AABW), over and above the difference implied by the mean sea level change. This study examines to what extent cold temperatures, through their effect on ice formation and melting, could have caused these differences. Computational sensitivity experiments using a coupled ice shelf cavity–sea ice–ocean model are performed in a Weddell Sea domain, as a representative case study for bottom water formation originating from Antarctic continental shelves. Ocean temperatures at the domain open boundaries are systematically lowered to determine the sensitivity of Weddell Sea water mass properties to a range of cool ocean temperatures. The steady state salinities differ between experiments due to temperature-induced responses of ice shelf and sea ice melting and freezing, evaporation and open boundary fluxes. The results of the experiments indicate that reduced ocean temperature can explain up to 30% of the salinity difference between GSSBW and AABW, primarily due to decreased ice shelf melting. The smallest and most exposed ice shelves, which abut narrow continental shelves, have the greatest sensitivity to the ocean temperature changes, suggesting that at the LGM there could have been a shift in geographical site dominance in bottom water formation. More sea ice is formed and exported in the cold ocean experiments, but the effect of this on salinity is negated by an equal magnitude reduction in evaporation.