Orbital- and millennial-scale variability of the Antarctic Circumpolar Current 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 over the past 140,000 years, based on grain-size and geochemical characteristics. We found significant glacial-interglacial changes of ACC flow speed, with reduced ACC intensity during glacials and a more vigorous 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 hypothesize that the ACC is closely linked to Southern Hemisphere millennial-scale climate oscillations, amplified through Antarctic sea ice extent changes. These strong ACC variations regulated Pacific-Atlantic water exchange via the “cold water route” and affected the Atlantic Meridional Overturning Circulation and marine carbon storage.

Bottom‐Current Variability and the Relationship With Topography and Sedimentary Processes in the Drake Passage

“… Bathymetric maps and mean sortable silt ($$\overline{SS}$$) of surface sediments (from Wu et al., 2019b) for the northern region of the West Drake Passage zone (a) and the center region of the Shackleton fracture zone (b) (IBCSO_v2 and multibeam bathymetry from the cruise PS97), showing the irregular and rough topography that characterizes these areas. (c–e) PARASOUND profiles showing current dominated sedimentation and erosion.…”

“… (a) Bathymetric map at the southern region of the Shackleton fracture zone (IBCSO_v2 and multibeam bathymetry from the cruise PS97) showing the location of current‐related sedimentary features and mean sortable silt ($$\overline{SS}$$) of surface sediments (from Wu et al., 2019b). (b)‐(e) Seismic reflection profiles showing the presence of moats and contourite drifts.…”

“…In our study, we used the grain size analyses of surface sediment samples (0–1 cm below the seafloor) carried out by Wu et al. (2019a, 2019b); in particular, the mean sortable silt, which is the mean size between 10 and 63 μm and is a proxy for paleoceanographic reconstructions (McCave et al., 1995). All data are available within the Pangaea data base (https://doi.org/10.1594/PANGAEA.907140).…”

“…The data collected during the PS97 cruise can be accessed in PANGAEA (https://www.pangaea.de/): PARASOUND profiles (Kuhn, 2016, https://doi.org/10.1594/PANGAEA.864950), multibeam bathymetry (Dorschel & Jensen, 2016, https://doi.org/10.1594/PANGAEA.864807), and CTD measurements (Lamy & Rohardt, 2016, https://doi.org/10.1594/PANGAEA.862944). Grain size data can be also accessed in PANGAEA (Wu et al., 2019a, https://doi.pangaea.de/10.1594/PANGAEA.907140). Also from PANGAEA can be download the International Bathymetric Chart of the Southern Ocean Version 2 (IBCSO v2) (Dorschel et al., 2022, https://doi.org/10.1038/s41597-022-01366-7).…”