The Younger Dryas, the last large millennial-scale climate oscillation (12.9–11.6 ka), has been widely attributed to a massive meltwater discharge event that disrupted ocean circulation and plunged the circum–North Atlantic back into a near-glacial state. Low-resolution deep-water reconstructions indicate lower North Atlantic Deep Water (NADW) production during the Younger Dryas, though the Δ14C record requires some deep-water production. Herein, we reconstruct deep-water mass variations using a southern Gardar Drift sediment core with an expanded Younger Dryas section. We show that southern-sourced water invaded the deep North Atlantic to start the Younger Dryas, but was replaced by NADW within 500 yr. Southern-sourced waters briefly reappeared at the end of the Younger Dryas. These deep-water reorganizations to start and end the Younger Dryas suggest that increased meltwater fluxes were limited temporally and focused on regions where deep-water convection occurred during the deglaciation.