Today, the sub-surface Denmark Strait Over ow (DSO) and the Iceland Scotland Over ow form the starting points of Atlantic Meridional Overturning Circulation and compensate for the poleward owing 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 re ect a north-south density gradient of intermediate-waters and persistent ow of partially Arctic-sourced waters through both the Denmark Strait and the Faeroe Channel, similar to today. The rst 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 lu -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 o 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 modi ed Heinrich-1-style circulation until ~15.1 cal ka. Vice-versa, the DSO intensi ed during interstadial and Holocene times, then causing sediment hiatuses at site PS2644.