Climatic variability and thermohaline circulation in the North Atlantic ocean and the Norway sea during upper Quaternary

The variations in the insolation latitudinal distribution are responsible for long term cyclic climatic variations. Recently, more rapid and abrupt climatic changes, with frequencies close to the millennium, have also been observed, and seem to be related to internal oscillations of the climate system, at least during the last glacial period. In order to build reliable predictive models, it is necessary to understand what are the mechanisms involved in the climatic changes, and how they interact. The aim of this work is to study the climate evolution during the last climatic cycle in the North Atlantic area, since it is the location of the thermohaline convection, which transfers important amounts of heat to the European regions. We have focused on the period between 70,000 and 150,000 years (marine isotopic stage 5), because it has been marked by major changes in the insolation distribution. The establishment of a common stratigraphic framework was a crucial step, and was based on the analysis of benthic foraminifera δ¹⁸O. This work has shown that sea-ice formations produced a strong local imprint on the Nordic Seas records. The ocean δ¹⁸O changes resulting from the global ice volume changes have then been reconstructed for the last 150,000 years. The comparison of these results to the sea level reconstructions obtained from the coral terraces allowed us to establish a sea level curve for the last climatic cycle, and to improve noticeably the absolute time scale of our marine records. Finally, the study of the surface and deep hydrology in the North Atlantic region suggests that the thermal gradient between high and low latitudes, by modifying the water vapor transfers to the Nordic areas, has a major impact on our climate. (author)