41. PLIOCENE-PLEISTOCENE OCCURRENCE OF SAPROPELS IN THE WESTERN MEDITERRANEAN SEA AND THEIR RELATION TO EASTERN MEDITERRANEAN SAPROPELS 1

Sedimentological and organic geochemical analyses of sediments along five Leg 161 drill sites document the occurrence of sapropels throughout the Western Mediterranean Sea. Two hundred and seventeen well-dated sapropel events are found at these sites ranging in age from 0.01 to about 3 Ma. Total organic carbon (TOC) content has a wide variation, ranging from 6%. The highest sapropel TOC values are found in the Tyrrhenian Sea. Sapropel TOC values decrease to the west and are lowest in the Alboran Sea. In contrast, background TOC in nonsapropel sediments increases from east to west, with values ranging from 0.1%‐0.3% in the Tyrrhenian Sea to 0.3%‐0.5% in the Alboran Sea. In view of this TOC variability, sapropels in this study are defined as sediment horizons with higher-than-background TOC concentrations. Sapropels that comply with this definition can often be recognized by distinctive color changes. That is, rather than using a narrowly defined, m inimum TOC value as a cutoff line for defining sapropels, the concept of using color changes and above-background TOC levels allows to detect sapropel events in much better detail. This is especially true for the western Mediterranean, where sapropels are sometimes less distinctive in the sedimentary record than in the eastern Mediterranean. Applying this concept and using detailed oxygen isotope stratigraphies (Pierre et al., Chap. 38, this volume; von Grafenstein et al., Chap. 37, this volume) an d high-resolution biostratigraphy (de Kaenel et al., Chap. 13, this volume) show that most sapropels in the eastern and western Mediterranean are well correlated. Exceptions to this observation point to the importance of local phenomena such as hydrological and productivity fronts that are associated with the Atlantic inflow and wind-driven meso-scale gyres in the western Mediterranean. From the Leg 161 paleoceanographic studies it must be concluded that sapropels are Mediterranean-wide phenomena. This warrants revision of our views about the origin of sapropels and their paleoceanographic and paleoclimatic implications.

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