Mediterranean pluvial periods and sapropel formation over the last 200 000years

Three Mediterranean deep sea cores have been studied to reconstruct the hyd rological conditions at the time of deposition of interglacial and glacial sapropels during the time interval 200-60 kyr BP. The isotopic and sea surf ace temperature records of planktonic foraminifera were used to estimate th e oxygen isotopic composition of surface water (delta(w)) in the Tyrrhenian Sea and Levantine basin. Our results show a strong delta(w)/salinity decre ase in both basins associated with each sapropel. These delta(w) decreases reflect a drastic change in the local freshwater budget and were comparable to that observed during the last sapropel (S-1) centred at ca. 8 kyr BP. A strong precipitation increase transformed the whole Mediterranean Sea into a non-concentration basin. The low surface salinity was responsible for th e water column stratification, while nutrients brought in by the runoff enh anced productivity. It resulted in a significant reduction in the rate of d eep water oxygenation and sapropel formation in the eastern basin. In addit ion, the Mediterranean Sea delta(18)O record is very similar to that of the Bay of Bengal. As the latter is very sensitive to the summer monsoon rain, this similarity suggests that both glacial and interglacial sapropels resu lt from enhanced monsoon-like precipitation due to an increase in summer in solation driven by precession variations. (C) 2000 Elsevier Science B.V. Al l rights reserved.