Co-ordinated shifts in deep-water formation and Gulf Stream migration during abrupt climate changes.

Theory and models suggest the Gulf Stream may shift northwards under projected Atlantic Meridional Overturning Circulation weakening. Yet Gulf Stream behaviour during past abrupt cold events remains poorly constrained. Here we present high-resolution paleoceanographic records from the Northwest Atlantic during the last deglaciation. During the Younger Dryas cold period, we document a northward Gulf Stream shift evidenced from coherent surface and subsurface warming. Our sortable silt data suggest a strengthening of upper North Atlantic Deep Water that opposes weakening lower North Atlantic Deep Water, consistent with a seesaw feedback between the Nordic overflows and subpolar gyre. Our results constrain a co-ordinated sequence at the Younger Dryas onset: initial lower North Atlantic Deep Water weakening and subpolar sea‑ice expansion, lagged (58 ± 38 yr) by an increase in upper North Atlantic Deep Water and an eventual atmospheric reorganization (84 ± 51 yr after onset). These findings provide empirical support for model projections of future Gulf Stream shifts.