Episodic isolation of the Arctic Mediterranean from the North Atlantic during late Pleistocene glacials

Abstract It has been proposed that the Arctic Ocean and Nordic Seas (“the Arctic Mediterranean”) were not only episodically covered by an ice shelf during late Pleistocene glaciations, but disconnected from the North Atlantic and filled with freshwater. Originally based on the widespread occurrence of marine sediments with intervals barren of 230 Th xs (a function of salinity) and low in cosmogenic 10 Be (interpreted as ice cover), this interpretation is highly debated. Alternative explanations state that sediment pulses could instead have diluted both isotopes. Here, we trace the connection between the Arctic Mediterranean and the North Atlantic using reactive 10 Be/ 9 Be, a water mass tracer resilient to sedimentation variations. We find uniformly low 10 Be/ 9 Be that coincide with the 230 Th xs -minima and more than one order of magnitude below the coeval North Atlantic, consistent with an isolated Arctic Mediterranean. Our findings suggest a highly dynamic coupling between the Arctic Mediterranean and the North Atlantic, opening questions about its impact on global climate.