Peak glacial-to-Heinrich-1 changes in Denmark Strait Overflow and seawater stratification in the Nordic Seas, a switchboard of changes in Atlantic Meridional Overturning Circulation and the ’Nordic Heat Pump’

Today, the sub-surface Denmark Strait Overflow (DSO) and the Iceland Scotland Overflow form the starting points of Atlantic Meridional Overturning Circulation and compensate for the poleward flowing Norwegian and Irminger branches of the North Atlantic surface current that drive the 'Nordic Heat Pump'.During peak glacial and early deglacial times, ice sheets on Iceland and Greenland, and ice-induced isostatic and eustatic sea-level changes reduced the Denmark Strait aperture and DSO.Nonetheless, extremely high benthic stable carbon and oxygen isotope values together with very high ventilation ages of bottom waters reflect a north-south density gradient of intermediate-waters and persistent flow of partially Arctic-sourced waters through both the Denmark Strait and the Faeroe Channel, similar to today.The first arrival of Heinrich -1 meltwaters northwest of Iceland, arriving from the southwest around 18.4 cal ka, accompanied a tipping point in DSO circulation, documented by reduced ventilation and ventilation ages, a 3°C warming, and increased radiogenic Nd isotope signatures in sediments at luff-side Site PS2644.These records suggest a sudden subsurface incursion of Atlantic intermediate waters across basaltic sediments from S.E. of Iceland.Deep-water convection off Norway then was replaced by weak brine water formation, coeval with a breakdown of the 'Nordic Heat Pump' evidenced by a temperature drop on Greenland.After 16.2 cal.ka, a major meltwater outbreak from the Barents ice shelf led to modified Heinrich-1-style circulation until ˜15.1 cal ka.Vice-versa, the DSO intensified during interstadial and Holocene times, then causing sediment hiatuses at site PS2644.