Productivity and Dissolved Oxygen Controls on the Southern Ocean Deep-Sea Benthos During the Antarctic Cold Reversal

The Antarctic Cold Reversal (ACR; 14.7 to 13 thousand years ago; ka) phase of the last deglaciation saw a pause in the rise of atmospheric CO2 and Antarctic temperature, that contrasted with warming in the North. A reexpansion of sea ice and a northward shift in the position of the westerly winds in the Southern Ocean are well-documented, but the response of deep-sea biota and the primary drivers of habitat viability remain unclear. Here, we present a new perspective on ecological changes in the deglacial Southern Ocean, including multifaunal benthic assemblage (foraminifera and cold-water corals) and coral geochemical data (Ba/Ca and delta B-11) from the Drake Passage. Our records show that, during the ACR, peak abundances of thick-walled benthic foraminifera Uvigerina bifurcata and corals are observed at shallow depths in the sub-Antarctic (similar to 300 m), while coral populations at greater depths and further south diminished. Our ecological and geochemical data indicate that habitat shifts were dictated by (a) a northward migration of food supply (primary production) into the sub-Antarctic Zone and (b) poorly oxygenated seawater at depth during this Antarctic cooling interval.

Automated summary

During the Antarctic Cold Reversal, peak abundances of thick-walled benthic foraminifera Uvigerina bifurcata and corals were observed at shallow depths in the sub-Antarctic, while coral populations at greater depths and further south diminished. The ecological and geochemical data suggest that habitat shifts were driven by a northward migration of food supply into the sub-Antarctic Zone and poorly oxygenated seawater at depth during this Antarctic cooling interval.