Development of Late Miocene Delta 13C stratigraphy and assessment of changes in global ice volume and deep-water circulation (6-12 Ma, Site 1237; Leg 202)

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The goal is to expand the astronomically calibrated benthic isotope stratigraphy into the Miocene and to examine changes in global ice-volume and deep-water circulation (6-12 Ma). Oxygen isotope stratigraphy is the primary tool for dating marine sedimentary sequences of the last 5 Ma. Recently, Tiedemann, Sturm, et al. (in press) demonstrated that the extension of the established benthic Delta18O stratigraphy (0-5.3 Ma) into the Miocene is hampered by the fact that the structure of globally distributed oxygen isotope records is different over long time intervals and thus provides no global signal - lacking the major precondition for expanding the oxygen isotope stratigraphy. Instead, we identified the benthic Delta l3C-signal as an alternative and a powerful tool to develop an astronomically calibrated stratigraphy for the late Miocene, as the structure and cyclic changes in 6I3C revealed a global response to climate change. We selected the sediment record from Leg 202 site 1237 as particularly suitable because it is the only marine site that meets nearly all critera of providing a complete Neogene reference section by integrating the excellent framework of both magnetostratigraphy and biostratigraphy into an orbitally tuned isotope stratigraphy. Superimposed on orbital controlled variations in Delta13C are trends on tectonic time scales that will provide new insights into changes in deep-water circulation including basin-related fractionations in nutrient distributions.