Re-organization of ocean circulation during the Miocene transition from Greenhouse to Icehouse: The role of the Indian Ocean

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We will test the overarching hypothesis that the boundary conditions for the modern global ocean-atmosphere circulation were established during the middle-late Miocene in a stepwise manner, involving threshold changes in inter-ocean heat and carbon transfer. To achieve this goal, we will create continuous, high resolution, orbitally tuned deep water paleoceanographic (benthic stable isotope supplemented by benthic Mg/Ca) time series for the middle to late Miocene interval in the newly drilled Site U1443 in the central Indian Ocean. Previous low-resolution studies indicated that the bottom water saturation state in Indian Ocean deep and intermediate waters experienced a maximum during the Miocene Climate Optimum and decreased stepwise during the late Miocene in line with declining atmospheric pCO2 levels, global cooling and cryosphere expansion. The complete record of Site U1443 is ideally suited to assess changes in inter-ocean heat and carbon gradients and, thus, to evaluate the global extent of large-scale deep ocean carbon isotope changes and their phase relationship to benthic oxygen isotope fluctuations. In particular, we intend to test the hypotheses that the deep Indian Ocean played a crucial role in the storage and transfer of heat and carbon during the middle-late Miocene climate transition and, thus, mediated the transition between different equilibrium states of the ocean/climate system.