The Atlantic meridional overturning circulation (AMOC), consisting of a warm, northward flow in the upper layer of the Atlantic, the formation of North Atlantic Deep Water (NADW) at high latitudes, and southward return flow at depth, moves immense amounts of heat northwards (Hall & Bryden, 1982; Trenberth et al., 2019). Ocean circulation is thus an active player in the global climate system. A causal link has been proposed between changes in the AMOC and the climate swings of the last glacial cycle (Broe

The last glacial millennial Heinrich and Dansgaard–Oeschger events have been the subject of many studies in recent decades. However, significant uncertainties remain, notably regarding associated oceanic mechanisms. Here we investigate the evolution of hydrographical conditions in the 3–41 ka cal BP interval of core MD99‐2285 located in the southern Norwegian Sea. Our results reveal an unusual scheme with: (i) warm Greenland interstadials marked by a relatively cold and homogeneous upper water column seasonally ice‐covered and active deep water formation, (ii) cold Greenland and Heinrich stadials marked by a warm, low‐salinity and nearly sea ice‐free surface layer with iceberg calving, separated by a strong halocline from a colder and saltier subsurface layer, as well as strongly reduced deep convection, and (iii) close to modern Holocene oceanic conditions, but showing significant differences from interstadial conditions. Hence, our work strongly suggests different deep‐water convection modes in the Nordic Seas, with, notably, interstadial deep water formation mainly forced by brine release. According to our results, the transition from the glacial mode of deep water formation to the modern open ocean convection mode might have occurred at the end of deglaciation/beginning of the Holocene, when both modes probably occurred.