ENHANCED RAINFALL IN THE MEDITERRANEAN REGION DURING THE LAST SAPROPEL EVENT

Sea-surface temperature (SST) estimates for the last 10,000 years have been derived from foraminiferal fauna variations in ten cores from th e Mediterranean Sea. For the eastern cores, modern analogs of fossil a ssemblages are found in the eastern Mediterranean Sea. In the Alboran and Tyrrhenian Seas, the bet analogs originate from modern fauna locat ed either in the western Mediterranean Sea or in the North Atlantic Oc ean. During the last sapropel event, centred at about 8,000 years B.P. , SSTs were similar to present in the eastern basin, whereas they were colder than today by about 1.5 degrees C in the Alboran Sea and 2.5 d egrees C in the Tyrrhenian Sea. Oxygen isotope measurements agree with ecological studies to show that Globigerina bulloides and Globigerino ides ruber alba grow their shell respectively in April-May and October -November. Assuming that these species deposited their shell in isotop ic equilibrium with ambient water, we reconstructed Mediterranean surf ace water delta(18)O and salinity during the last sapropel event (S-1) . In contrast with the modern pattern in which evaporation dominates a nd salinity increases from west to east, the surface salinity during S -1 became almost homogeneous over the whole basin. This pattern sugges ts that the freshwater budget (precipitation plus runoff minus evapora tion, P + R - E) was nearly equilibrated and that the Mediterranean Se a had ceased to be a concentration basin. In the western Mediterranean Sea, the observed cooling can account for the formation of intermedia te and deep waters with densities only slightly higher than that of th e Atlantic subsurface water at the Gibraltar sill level. The Mediterra nean outflow was then drastically reduced and the residence time of th e Mediterranean deep water increased. In the eastern basin, no signifi cant temperature change occurred during the Holocene. During the sapro pel event S-1, surface salinities were not significantly different fro m those of the western basin and deep water colder and denser than tho se of the western basin could not form. At the level of the Siculo-Tun isian Strait, the cold western intermediate water penetrated the deep eastern Mediterranean Sea. As a consequence, a permanent pycnocline wa s established between surficial and intermediate waters, preventing wi nter overturning and the supply of dissolved oxygen in the deeper part of the basin. This hydrological structure was responsible for the est ablishment of anoxia and the preservation of organic matter at the bot tom in the eastern Mediterranean Sea.