| Summary: | The shallow (~53 m deep) Bering Strait separates the Asian and North American continents and is the only Northern Hemisphere connection between the Pacific and Atlantic Oceans. The transport of low salinity, nutrient-rich waters across the Bering Strait impacts both upper ocean stratification and biogeochemical cycling within the Arctic and North Atlantic. While it is established that postglacial sea-level rise flooded the Bering Strait around 11,500 years ago (11.5 ka), the history of Bering Strait submergence prior to the Last Glacial Maximum is poorly known. Here we present a continuous reconstruction of Bering Strait flooding history since 50 ka using foraminifera-bound nitrogen isotopes from Arctic Ocean sediments as a proxy for Pacific nutrient input to the Arctic. We test this nutrient input history with a gravitationally self-consistent simulation of relative sea-level at the Bering Strait. The data and model indicate that the Bering Strait was flooded during Marine Isotope Stage 3 (MIS 3) until 36 ka, with the Bering Land Bridge forming thereafter. This flooding history is consistent with recent global ice volume reconstructions in which MIS 3 ice volume was < 50% that of the Last Glacial Maximum, in contrast to the long-dominant view of only modest ice retreat during MIS 3. Implications of the findings for the mechanisms underlying the glacial cycles, the necessary background conditions for millennial-scale climate variability, and the arrival of human populations in the Americas will be discussed.
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