Millennial-scale fluctuations in North Atlantic heat flux during the last 150,000 years

Surface water and deep ocean palaeoclimate records obtained from North Atlantic core SU90-03 (40°N, 32°W) exhibit pronounced fluctuations at sub-orbital time scales. Surface temperature variability in the mid-latitude Atlantic over the last 150 kyr is dominated by forcing at precession (21 kyr) and semi-precession harmonics (11 kyr). Abrupt changes in sea surface temperatures show that the northward transport of heat by the North Atlantic Current was curtailed during ice rafting events. Sea surface temperatures were about 12°C colder than modern values during the most intense cooling episodes associated with major ice rafting events (Heinrich events 1, 4, 6 and 11) and 10°C below modern values during the later part of isotope stage 3 (40–30 ka). During these cold intervals, the North Atlantic Current was displaced to south of 40°N as the cold meltwaters penetrated southwards into what is now the subtropical ocean. These changes in surface ocean heat exchange were most probably allied to a latitudinal migration and increase in zonality of atmospheric circulation patterns. Concurrent shifts in IRD concentration, sea surface temperatures and benthic δ13C values provide evidence of coupling between sea surface processes and the deep-water circulation, and suggest that decreases in surface temperature and salinity during ice rafting events culminated in a significant reorganisation of North Atlantic Deep Water production.