Southern Ocean upper water column structure over the last 140 kyr with emphasis on the glacial terminations

We use δ18O and δ13C isotopic records from both shallow- and deep-dwelling planktonic foraminiferal species to describe the transition of surface water column structure over the last two glacial terminations in the Atlantic sector of the Southern Ocean between 41°S–50°S. The δ18O differences between deep- and shallow-dwelling foraminifera are typically less pronounced before and during a termination than they are following a termination. Additionally, δ13C minima occur during terminations that may be linked to changes in thermohaline circulation mode. These observations collectively point toward water column structural changes that vary from relatively unstratified to relatively stratified during the course of a typical climate transition. The data can potentially be explained by southward retreats of surface water masses that previously advanced to the north during a typical glacial (i.e. frontal migration). Some of the δ18O phenomena can also be explained by subduction, entrainment, and advection of continental ice meltwater from higher latitudes. In either case, the glacial subantarctic between 41°S–50°S was less thermally stratified than it is today.