Orbital- and millennial-scale Antarctic Circumpolar Current variability in Drake Passage over the past 140,000 years

Levin Dumm,Xu Zhang,Wenshen Xiao,Norbert Nowaczyk,Bernhard Diekmann,Jiabo Liu,Gerhard Kuhn,H Christian Hass,Helge W Arz,Frank Lamy,Ralf Tiedemann,Lester Lembke-Jene,Dirk Nürnberg,Xufeng Zheng,Shuzhuang Wu,Jürgen Titschack

doi:10.1038/s41467-021-24264-9

Abstract

The Antarctic Circumpolar Current (ACC) plays a crucial role in global ocean circulation by fostering deep-water upwelling and formation of new water masses. On geological time-scales, ACC variations are poorly constrained beyond the last glacial. Here, we reconstruct changes in ACC strength in the central Drake Passage in vicinity of the modern Polar Front over a complete glacial-interglacial cycle (i.e., the past 140,000 years), based on sediment grain-size and geochemical characteristics. We found significant glacial-interglacial changes of ACC flow speed, with weakened current strength during glacials and a stronger circulation in interglacials. Superimposed on these orbital-scale changes are high-amplitude millennial-scale fluctuations, with ACC strength maxima correlating with diatom-based Antarctic winter sea-ice minima, particularly during full glacial conditions. We infer that the ACC is closely linked to Southern Hemisphere millennial-scale climate oscillations, amplified through Antarctic sea ice extent changes. These strong ACC variations modulated Pacific-Atlantic water exchange via the “cold water route” and potentially affected the Atlantic Meridional Overturning Circulation and marine carbon storage.

Highlights

The Antarctic Circumpolar Current (ACC) plays a crucial role in global ocean circulation by fostering deep-water upwelling and formation of new water masses
The ACC strength is mainly driven by the southern westerly winds (SWW) and surface buoyancy forcing[14,15]
Modern observations[27] reveal that ACC flow speeds at ~3000 m water depth can reach up 40–60 cm s−1; such high flow speeds at the sea floor can potentially remove parts of the silt and even the sand fractions[24]

Summary

Introduction

The Antarctic Circumpolar Current (ACC) plays a crucial role in global ocean circulation by fostering deep-water upwelling and formation of new water masses. Time-slice reconstructions from the Scotia Sea downstream of the Drake Passage show only small flow speed changes for the Last Glacial Maximum (LGM) compared to the Holocene[5]. We reconstruct changes in Pacific-Atlantic ACC flow speed on millennial to glacial-interglacial time scales over the past 140 ka.

Results

Conclusion