In the Indian sector of the Southern Ocean, the main Antarctic Circumpolar Current (ACC) transport is associatedwith the subantarctic jet and deviates around several subantarctic islands and volcanic plateaus. This formsregional eddies that are hotspots for productivity, nutrient and CO2 cycling. Though ACC jet migrations related topast climate variations have been reported in previous studies, little is known about their effect on verticalmixing where fronts interact with bathymetry. Here, we investigate past frontal shifts and their impacts on watercolumn structure in the Del Ca˜no Rise, Crozet Archipelago, and Conrad Rise regions over the last 160,000 yearsby reconstructing surface and subsurface temperatures from siliceous microfossils assemblages in four sedimentcores. Our results suggest that the ACC core was displaced equatorward during the last glacial period (70–18kyrs), away from bathymetric features of the Indian sector of the Southern Ocean. This equatorward shiftprobably reduced front/bathymetry interactions and, with it, mixing of the upper layer of the ocean in the lee ofsubantarctic islands and plateaus. We propose that this process participated in the regional isolation of AntarcticSurface Water from deeper water masses. During Marine Isotope Stage (MIS) 5e (132–118 kyrs), an interglacialepisode with a warmer-than-modern climate, the reverse situation is reconstructed, whereby the tightening ofthe ACC fronts against volcanic plateaus probably resulted in enhanced vertical mixing.< Réduire