Age models and foraminifera assemblages from sediment profiles of the North Atlantic

Based on foraminiferal transfer-functions, the distribution patterns of early Holocene sea- surface temperatures (SST) were studied, using the information from 154 deep-sea sediment cores (92 Atlantic, 62 Indian Ocean and Western Pacific). For our reconstruction, we employed a uniform high-resolution, AMS 14C-calibrated d18O-chronology, converted to a calendar timescale, and the new SIMMAX-Transfer-Technique in the Atlantic Oceans (Pflaumann et al. in press). The short-term SST fluctuations during the last 30,000 years are not directly related to the relatively slow changes in insolation during this period, reaching maximum seasonal deviations from modern values at approximaterly 11,000 years B.P. Although seasonal changes in solar radiation must have triggered global warming to the modern, interglacial mode, there is little evidence for linear warming and heat transport by ocean currents. The SIMMAX-temperature estimates indicate an early and rapid warming in the Equatorial Atlantic, as well as in the eastern North Atlantic, where modern SSTs were reached for a short time between 20,000 to 16,000 kalendar-years B.P. On a core transect crossing the Island-Faroer Ridge, the history of high-latitude warming along the eastern margins of the big North Atlantic gyres was reconstructed. Prior to the Younger Dryas cold interval (12,000 kalendar years), SSTs of the Norwegian Greenland Sea were still at glacial levels. After the Younger Dryas, there was a rapid inflow of warm Atlantic surface waters into the Norwegian-Greenland basins. In the northern Indian Ocean, the SST-patterns were totally different from the Atlantic during the last 20,000 years. Temperature variations did not exeed 2-3°C in the open ocean. During the Last Glacial Maximum (18,000 years B.P.), temperatures were higher than today whereas they were lowest during the early Holocene. This was caused by changes in the monsoon-induced oceanic upwelling intensity. At this time trade winds off Northwest Africa were also stronger, related to the stronger seasonal constrasts in insolation. Perhaps, the atmospheric circulation was generally enhanced at 10,000 years B.P. High-resolution SST-records from the southern Ocean (Pichon et al. 1992) indicate a slight asymmetry between the two Hemispheres. At 10,000 years B.P, SSTs were 1-2°C higher than today in the southern Indian Ocean. At the same time, somewhat colder SSTs imply still cool, boreal conditions in the middle and high latitudes of the northern hemisphere. Although SSTs of both seasons are only little different from the modern patterns, differences in the direction and strength of the major ocean currents are indicated by internally consistent positive and negative temperature anomaly fields. They were found in both, in the lower and in the high latitudes. The distribution of the anomalies in the North Atlantic further suggests, that the remnants of the ice shields still had a strong impact on the SST distribution. The particulary stronger insolation in the high northern latitudes during summers had nearly no influence. Finally, many details in the SST fluctuations and in the distribution of temperature anomalies imply a more dynamic surface circulation than today which may be the most characteristic difference between the early Holocene and modern surface ocean