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

Abstract

Abstract It has been proposed that the Arctic Ocean and Nordic Seas (together referred to as the “Arctic Mediterranean” - AM) were not only covered by a thick ice shelf during past Pleistocene glaciations 1 but also filled with freshwater 2 implying a disconnection from the North Atlantic. Such interpretation was based on widespread intervals in marine sediments that are barren of 230 Th xs (a function of salinity 3 ) and low in meteoric cosmogenic 10 Be (interpreted as ice cover). However, this interpretation is highly debated 4–6 and alternative explanations have been proposed 7,8 stating that sudden sediment pulses below multi-year sea ice could dilute both isotopes, generating apparent minima without necessarily requiring isolation and freshening of the AM. To test this hypothesis and to trace the connection between the North Atlantic and the AM through Glacial/Interglacial periods, we use the authigenic 10 Be/ 9 Be ratio, a water mass tracer 9,10 resilient to sedimentation variations 11–14 . We find uniformly low 10 Be/ 9 Be in the fully glacial AM that is more than one order of magnitude lower than in the coeval North Atlantic, consistent with strongly reduced exchange across the Greenland-Scotland Ridge. Our findings suggest a highly dynamic coupling between the AM and the North Atlantic, alternating between glacial isolation and rapid reconnection during deglaciation, opening questions about the relevance of this link for shaping the global conveyor belt.