Multi-phase retreat of the Laurentide Ice Sheet and associated freshwater release from Hudson Bay during the last deglaciation.

During the final retreat of the Laurentide Ice Sheet, large volumes of meltwater from the Hudson Bay region entered the North Atlantic leading to one of the strongest freshwater perturbations of the Holocene. The resulting 8.2 ka cold event is a key benchmark for understanding ice-sheet–ocean interactions, yet the timing, structure, and mechanisms of this freshwater release from Hudson Bay remain debated. New sediment records from Hudson Strait document a sequence of ice–ocean reorganisations and associated freshwater regimes between ~ 9.0 and 8.0 ka. They include (1) background deglacial meltwater and limited iceberg export prior to ~ 8.8 ka; (2) a short-lived episode of marine intrusion, ice-shelf formation, and subsequent ice-shelf breakup accompanied by transient iceberg discharge; and (3) a prolonged, multi-phase freshwater release between ~ 8.2 and 8.0 ka linked to the final collapse of the Hudson Bay ice saddle and drainage of glacial Lake Agassiz–Ojibway. Notably, the duration of this final freshwater phase is coeval, within uncertainty, with the 8.2 ka climate anomaly recorded in Greenland ice cores, consistent with a causal connection. This refined stratigraphic framework demonstrates that freshwater forcing from Hudson Bay was temporally structured and temporally sustained, highlighting the importance of ice-margin geometry and meltwater routing in modulating early Holocene climate perturbations.