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 re-expansion 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 multi-faunal benthic assemblage (foraminifera and cold-water corals) and coral geochemical data (Ba/Ca and δ¹¹B) 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 (∼300 m), while coral populations at greater depths and further south diminished. Our ecological and geochemical data indicate that habitat shifts were dictated by (i) a northward migration of food supply (primary production) into the Subantarctic Zone and (ii) poorly oxygenated seawater at depth during this Antarctic cooling interval.