| Summary: | The Nordic Seas are the primary location where the warm waters of the North Atlantic Current densify to form North Atlantic Deep Water, which plays a key part in the modern Atlantic Meridional Overturning Circulation. The formation of dense water in the Nordic Seas and Arctic Ocean and resulting ocean circulation changes were likely driven by and contributed to the regional and global climate of the last glacial maximum (LGM). Here, we map the source and degree of mixing of deep-water in the Nordic Seas, and through the Arctic Gateway (Yermak Plateau) over the last 35 thousand years using neodymium isotopes (εNd) measured on authigenic phases in deep-sea sediments with a high spatial and temporal resolution. We find that a large-scale reorganisation of deep-water formation in the Nordic Seas took place between the LGM (23-18 thousand years ago) and the rapid climate shift that accompanied the subsequent deglaciation (18-10 thousand years ago). We show that homogeneous εNd signatures across a wide range of sites support LGM deep- water formation in the Nordic Seas. In contrast, during the deglaciation disparate and spatially variable εNd values are observed leading to the conclusion that deep-water formation may have been reduced during this time. Deep-water formation processes in the Nordic Seas regulate the global climate via the redistribution of heat by the surface ocean and the capacity of the deep ocean to store carbon 1 . At present the Atlantic Meridional Overturning Circulation (AMOC) links polar and sub-polar climate with the formation of North Atlantic Deep Water (NADW), a major component of the global oceanic thermohaline circulation. The densest northern-sourced waters in the modern AMOC are formed in the Nordic Seas, primarily by deep convection and gradual transformation of North Atlantic surface waters2 . NERC studentship (NE/L002507/1), with support from Murray Edwards College and the Geological Society’s Elspeth Matthews Fund.
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