In general, carbonate sedimentation in the Norwegian Sea is closely related to heat export from the North Atlantic. However, a strong front between the North Atlantic and the Norwegian Sea was present throughout most of the last 3.1 m.y. Thus, the circulation type was different from that of the late Pleistocene interglacials, without extending into the Norwegian Sea.
The onset of major Northern Hemisphere glaciation was time-transgressive between the studied sites. In the North Atlantic, a first drop in carbonate coeval with an increase in IRD was observed at 2.8 Ma, although the interval since ~2.5 Ma was dominated by carbonate sedimentation. In contrast, at Site 985 glacial conditions (most likely with discontinuous sea-ice cover) occurred as early as 3.05 Ma and lasted until ~1.1 Ma.
At Site 982, long-term cooling culminated at 2.5 Ma, leading to a more glacial-dominated period until 1.65 Ma. In this interval, heat export from the North Atlantic to the Norwegian Sea was possibly restricted by cold surface temperatures of the North Atlantic. Increased northward penetrations of relatively warm Atlantic water to the Norwegian Sea were restricted to short phases at ~1.9 and 1.4 Ma.
In addition, the faunal response to sea-surface heat import from the North Atlantic was weak; thus, only limited production of carbonate was possible. A stepwise adaptation of N. pachyderma sin. to the polar environment from 1.1 to 0.65 Ma increased carbonate production. The optimum adaptation of N. pachyderma sin. after 0.65 Ma leads to enhanced carbonate production, reflecting the intensity of heat import from the North Atlantic, especially during interglacials.