Distant origin of circulation changes in the Indian Ocean during the last deglaciation

Well-dated benthic foraminifera isotopic records reveal that circulation changes repeatedly took place in the tropical Indian Ocean around 2000 m depth over the last deglaciation. We show that the observed changes can be explained by large-scale reorganization of intermediate water masses in the Atlantic and Indian Oceans. More specifically, during Heinrich event 1 and the Younger Dryas, while the formation of North Atlantic Deep Water was greatly reduced, brine formation in the North Atlantic and Nordic Seas led to the production of intermediate waters that extended far enough in the South Atlantic to be deflected by the circumpolar currents into the Indian Ocean basin, creating a circulation branch at intermediate depths that was more active than today. In contrast, during the Last Glacial Maximum, the Bolling-Allerod, and after the Younger Dryas, there was no rapid transport of intermediate waters from the North Atlantic to the South Atlantic or Indian Ocean around 2000 m depth.