Reconstruction of the Antarctic Circumpolar Current strength over the past million years

The Antarctic Circumpolar Current (ACC) is a crucial component of global ocean circulation, exerting a major influence on Earth's climate and the dynamics of the Antarctic Ice Sheet. However, its spatiotemporal variability throughout the Pleistocene is poorly constrained. To address this, we reconstruct ACC flow speed using a meridional transect of sediment cores from the Indian Sector of the Southern Ocean. Our records reveals zonally asymmetric changes in ACC strength on orbital timescales: the ACC intensified in the South Indian Ocean yet weakened in the South Pacific during glacial and low-obliquity intervals, with the opposite pattern occurring during interglacial and high-obliquity periods. We propose this anti-phased behavior represents an integrated response to bathymetric constraints, latitudinal shifts in the Southern Hemisphere westerlies, and changes in sea-ice extent and buoyancy forcing. Notably, this zonally asymmetric pattern persisted even during Pleistocene intervals warmer than today, providing a potential analog for future ACC changes under anthropogenic warming.