13. STABLE ISOTOPE CHRONOLOGY AND PALEOCEANOGRAPHIC HISTORY OF SITES 963 AND 964, EASTERN MEDITERRANEAN SEA1Michael W. Howell,2,6 Robert C. Thunell,3 Enrico Di Stefano,4 Rodolfo Sprovieri,4 Eric J. Tappa,3 and Tatsuhiko Sakamoto5 |
ABSTRACTOxygen and carbon isotope measurements were performed on the planktonic foraminifer Globigerina bulloides from Ocean Drilling Program Site 963 in the Strait of Sicily and Site 964 in the Ionian Sea. Isotope records from both sites reflect regional climate changes in the Mediterranean superimposed on a global climatic signal. The early to late Pleistocene delta18O record of Site 963 indicates that major climatic coolings occurred at approximately 0.98 and 0.45 Ma. The Site 964 delta18O record extends into the early Pliocene and indicates that significant decreases in temperature and/or global ice volume occurred at 2.6, 0.98, and 0.46 Ma. Oxygen isotope records from both sites exhibit large amplitude fluctuations during the late Pleistocene associated with the reduction of surface-water salinities because of regional changes in evaporation and precipitation. The magnitude of these regional climate events appears to have been strongly influenced by the extent of global cooling and increases in ice volume. Carbon isotope records from both sites suggest (1) increased input of terrestrial organic matter, (2) higher nutrient concentrations within the photic zone, and (3) intensified surface-water stratification during the formation of sapropels. Data from both sites indicate no difference in the frequency of the surface-water salinity reductions, despite the fact that the deeper site (Site 964) exhibits a higher frequency of sapropels. This suggests that the reduction of surface-water salinities in the Strait of Sicily may have played a different role in the formation of sapropels at that site. |
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