Deglacial circulation changes in the Nordic Seas, a switchboard of changes in AMOC and 'Nordic Heat Pump'

Differences in salt content of North Atlantic surface waters drive variations in Nordic Seas' overturning circulation. These form a switchboard for changes in the oceanic heat transport to North European high latitudes, the 'Nordic Heat Pump', and for Atlantic Meridional Overturning Circulation (AMOC). We deduced changes in the Nordic Seas' overturning circulation during the peak last glacial and early deglacial from two high-resolution marine sediment cores with centennial-scale age resolution based on the technique of radiocarbon plateau tuning (22-15 cal. ka). Sediment data suggest that the salinity of surface water, advected from the North Atlantic, started to drop about 18 400 years ago. This drop accompanied a 3C rise in temperature and a drop in ventilation and radiocarbon ventilation age of Denmark Strait Overflow waters feeding the AMOC. Also, it paralleled a massive rise in the radiocarbon reservoir age of surface waters up to 2000 yr and an abrupt breakdown of Nordic Seas' deep-water convection off Norway. Accordingly, Atlantic waters were replaced by less saline polar waters, marking a breakdown of the Nordic Heat Pump and start of 'Heinrich Stadial 1' as reflected by a coeval cooling documented on top of the Greenland ice sheet, lasting until ~15.1 cal. ka.