Rapid climatic variability of the North Atlantic Ocean and global climate: a focus of the IMAGES program

In the mid-latitudes of the North Atlantic Ocean, six large iceberg surges, called Heinrich events, have been recognised between 60 and 10 kyr BP. They are characterised by meltwater events associated with iceberg discharges from both the Laurentide and the Fennoscandian-Greenland ice sheets. The hydrological conditions associated with these surges show changes in sea surface temperature (2-6 degrees C drop) and in sea surface salinity (1-3 parts per thousand decrease). Carbon isotopic analyses tend to show that the thermohaline circulation is affected by such discharges with a significant decrease in the ventilation of deep waters. During the same period, ice cores record large climatic fluctuations, called Dansgaard-Oeschger events, which have been recognised in the North Atlantic Ocean and in the Norwegian Sea, and more recently, in various sedimentary environments world wide. Interglacial periods, with reduced continental ice sheets, allow us to investigate rapid climatic variability in the absence of large Northern Hemisphere ice masses. There are no major instabilities during the Eemian period but the transition from a full interglacial period into glacial time is abrupt, in less than 400 years. (C) 1999 Elsevier Science Ltd. All rights reserved.