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

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.

Variations in export production, lithogenic sediment transport and iron fertilization in the Pacific sector of the Drake Passage over the past 400 kyr

“…The study area at the Pacific entrance of the DP is strongly influenced by the ACC, as documented by highly variable current strengths on millennial and glacial-interglacial timescales (Lamy et al, 2015;Toyos et al, 2020;Wu et al, 2021). Our results indicate that this variability in current strength influenced changes in sedimentation patterns (Fig.…”

“…In the DP, the oceanographic fronts may act as barriers to mixing in the ocean, preventing cross-frontal movement and meridional exchange of water masses and their associated nutrients (Naveira Garabato et al, 2011;Paparazzo, 2016). On longer timescales, studies of sediment cores located upstream and downstream of the northern and central DP suggest a northward shift of the SO frontal system during glacial times, lower ACC flow speed and reduced transport through the DP (Lamy et al, 2015;Roberts et al, 2017;Toyos et al, 2020;Wu et al, 2021). Particularly at site PS97/093, a comparison between the SS record and the opal and TOC MAR records shows that decreases in current strengths correspond with increases in opal and TOC (Fig.…”

Variations in export production, lithogenic sediment transport and iron fertilization in the Pacific sector of the Drake Passage over the past 400 ka

“…The study area at the Pacific entrance of the DP is strongly influenced by the ACC, as documented by highly variable current strengths on millennial and glacial-interglacial timescales (Lamy et al, 2015;Toyos et al, 2020;Wu et al, 2021). Our results indicate that this variability in current strength influenced changes in sedimentation patterns (Fig.…”

“…In the DP, the fronts act as barriers to mixing in the ocean, preventing cross-frontal movement and meridional exchange of water masses and their associated nutrients (Naveira Garabato et al, 2011;Paparazzo, 2016). On longer timescales, studies of sediment cores located upstream and downstream of the northern and central DP suggest a northward shift of the SO frontal system during glacial times, lower ACC flow speed and reduced transport through the DP (Lamy et al, 2015;Roberts et al, 440 2017;Toyos et al, 2020;Wu et al, 2021). Particularly at site PS97/093, a comparison between the SS record, and the opal and TOC MAR records shows that decreases in current strengths correspond with increases in opal and TOC (Fig 3).…”

One‐To‐One Coupling Between Southern Ocean Productivity and Antarctica Climate

“…During cold stadials, the thermal bipolar seesaw associated with weakened AMOC may reduce oceanic heat transport into the North Atlantic, inducing a southward shift of the Intertropical Convergence Zone and the SHW (Anderson et al., 2009; Wang et al., 2004). The coupled atmosphere‐ocean process could enhance wind stress forcing at the latitude of the Drake Passage, resulting in a stronger ACC and then transportation of more water masses through the Drake Passage and the Scotia Sea (Lamy et al., 2015; Wu et al., 2021) to induce upwelling to the surface (Toggweiler et al., 2006). In addition, surface buoyancy forcing could be altered complementing the increased wind stress due to heat flux changes, Antarctic warming, southward‐intensified SHW, and/or the melting of sea ice (Anderson et al., 2009; Skinner et al., 2020; Toggweiler et al., 2006; Watson & Naveira Garabato, 2006).…”