LATE-PLEISTOCENE INTERGLACIAL CONDITIONS IN THE POLAR NORTH ATLANTIC REGION

Sediment records suggest that during the last 500,000 years interglacial boundary conditions in the Northern North Atlantic (Nordic seas) with strongly reduced occurrence of iceberg-rafted debris (IRD) and high carbonate bioproductivity existed only in marine isotopes stages (MIS) 11, 5e, and 1. A detailed comparison of these three Late Pleistocene interglacial intervals shows that the specific climate conditions have varied significantly. It is indicated that IRD occurs on the central Iceland Plateau continuously during MIS 11 in contrast to the results from the later interglaciations MIS 5e and MIS 1. These observations also differ from the situation in the western Norwegian Sea, where all three interglaciations show IRD-free intervals. Foraminiferal assemblage data suggest that sea-surface temperatures (SST) in the Nordic seas were in general significantly lower in MIS 11 than in MIS 1. These findings point to a different pattern of surface water circulation and a geographical shift in the position of the major water mass boundaries in the Nordic seas during MIS 11 when compared with MIS 5e and 1. Thus, during MIS 11 the Polar Front, i.e., the boundary between the cold water masses of the East Greenland Current and the more temperate surface waters of the Arctic and Atlantic domains, was positioned further east, implying a much steeper SST gradient between the polar and subpolar region and an overall reduced thermohaline activity in the polar latitudes. Further differences among the interglacial intervals are evident from the carbonate preservation record, where a strong increase of carbonate corrosion occurs in MIS 11. Although the reason for this reduced carbonate preservation remains speculative, it indicates differences in the interglacial marine carbonate system between MIS 11 and MIS 5e and 1.