ABRUPT DEGLACIAL CHANGES IN THE NORTH PACIFIC OCEAN AND IMPLICATIONS FOR HUMAN COASTAL MIGRATIONS INTO NORTH AMERICA

Paleoceanographic reconstructions from the North Pacific reveal a dynamic environment during the last deglacial transition, including rapid changes in sea surface temperature (SST) and sea-ice extent, pulses of iceberg and meltwater discharge from the Cordilleran Ice Sheet, and ocean hypoxic events. Understanding how these abrupt changes impacted marine ecosystems and shaped human migrations provides insight into past histories and possible future scenarios arising from climate-ecosystem interactions. Here we synthesize new and previously published paleoceanographic reconstructions of SST, sea-ice, paleo-salinity, ice-rafted debris (IRD), and marine hypoxia, together with model simulations of changes in ocean current strength from the last glacial maximum (LGM) to early Holocene, to assess the most viable time periods for a coastal migration from Beringia into North America. Our synthesis indicates that the period between 19-17 ka was the coldest of the last 20 ka, with a 1-2°C cooling relative to LGM conditions, extensive seasonal sea-ice, episodic reductions in sea surface salinities, and peak deposition of IRD during the ‘Siku 1’ glacial surge event, indicating cold and ice-choked conditions that would have made a coastal passage highly challenging. Model simulations indicate that the velocity of the Alaska Coastal Current (ACC) would have been strengthened during glacial conditions (relative to modern), and in response to freshwater input, making a southward transit against this cyclonic current particularly difficult for seafarers during the LGM and early deglacial period. Starting around 16.5-16.0 ka, SST began to increase in the Northeast Pacific, sea-ice retracted, and deposition of IRD began to wane, reflecting the most likely first window for human migration into North America along a coastal route. Abrupt ocean warming occurred at the onset of the Bølling-Allerød (14.7-12.9 ka), accompanied by a transition to severe hypoxia at intermediate depths, reflecting an expansion of the oxygen minimum zone (OMZ). It remains unknown whether the expanded OMZ may have negatively impacted upper ocean ecosystems, such as the kelp forest ecosystems that have been hypothesized to have supported early coastal seafarers, possibly limiting coastal habitation during this time.