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

Joseph A Stewart,Andrea Burke,Peter T Spooner,Laura F Robinson,Tao Li,Tianyu Chen,Qian Liu,James W B Rae,Jenny Roberts,Sev Kender,Victoria Peck

doi:10.1029/2021pa004288

Abstract

AbstractThe 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 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 (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.

Highlights

The rise in atmospheric CO2 during the last deglaciation (18 to 11.5 ka) occurred primarily during Henrich Stadial 1 (HS1; 18 to 14.7 ka) and the Younger Dryas (YD; 13 to 11.5 ka) intervals that were associated with high-latitude cooling in the northern hemisphere and warming in the south
We use well-dated biotic and paleoceanographic records to answer the questions (1) What impact did a return to more glaciated conditions have on benthic ecology in the Southern Ocean during the Antarctic Cold Reversal (ACR)? (2) What were the primary drivers of deep-water habitat changes for marine calcifiers? We provide new benthic foraminifera and coldwater scleractinian coral abundance data and geochemical reconstructions from sites across the Drake Passage, spanning the Antarctic, Polar Front and Subantarctic Zones and occuping water depths from 300 to 1750 m (Figure 2)
Both percentage (Figure 3A) and raw benthic foraminiferal abundance count data (Figure 3B, C, D) from this core suggest that three taxa dominate the assemblage at different times during the deglaciation: Fursenkoina fusiformis prior to the ACR (~80%; 22 to 14.5 ka), Uvigerina bifurcata during the ACR (~80%; 14.5 to 13 ka), and Epistominella exigua after the ACR (~30%; 13 to 8 ka)

Summary

Introduction

The rise in atmospheric CO2 during the last deglaciation (18 to 11.5 ka) occurred primarily during Henrich Stadial 1 (HS1; 18 to 14.7 ka) and the Younger Dryas (YD; 13 to 11.5 ka) intervals that were associated with high-latitude cooling in the northern hemisphere and warming in the south. Despite the many records documenting changes in primary production (Anderson et al, 2002; Martínez-García et al, 2014) and shifts towards surface water biotic assemblages adapted to cooler conditions (Figure 1C & E; (Barker et al, 2009; Bianchi and Gersonde, 2004)), relatively little is known about associated impact on benthic marine organisms in the Southern Ocean during the ACR

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