Extremely poleward shift of Antarctic Circumpolar Current by eccentricity during the Last Interglacial

The Antarctic Circumpolar Current (ACC) exerts substantial control on the physical, chemical, and biological properties of the Southern Ocean, playing a key role in modulating the global carbon cycle and climate. However, the orbital-scale forcing and future changes in the strength and position of the ACC remain elusive. Here, we reconstruct the history of ACC extending back to the Last Interglacial (LIG; 128-113 ka) using sediment cores from the Scotia Sea. Based on high-resolution measurements of sortable silt mean grain size, we find that bottom current speed is synchronized with eccentricity, superimposed by precession. During the LIG when both eccentricity and precession reached their maxima, current speed peaked in the region south of the Southern ACC front, suggesting that the Polar Front shifted ~5° southward. We propose that the low-frequency ACC frontal migration is primarily controlled by eccentricity-driven shifts in the Southern Hemisphere Westerlies, while precession-driven shifts contribute to high-frequency migration. Our findings imply under future orbital-scale scenarios, the ACC position is likely to shift north.