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

我们将测试一个总体假设，即现代全球海洋-大气环流的边界条件是在中新世中晚期逐步建立的，涉及海洋间热量和碳转移的阈值变化。为了实现这一目标，我们将在印度洋中部新钻探的U1443地点创建连续的、高分辨率的、轨道调谐的中新世中晚期深水古海洋学（底栖生物稳定同位素补充底栖生物Mg/Ca）时间序列。以往的低分辨率研究表明，印度洋深层和中间水域的底水饱和状态在中新世气候最适期达到最大值，在晚中新世期间随着大气pCO2水平下降、全球变冷和冰冻圈扩张而逐步降低。U1443站点的完整记录非常适合评估海洋间热量和碳梯度的变化，从而评估大尺度深海碳同位素变化的全球范围及其与底栖动物氧同位素波动的相位关系。在中新世中晚期气候转变过程中，印度洋深处在热量和碳的储存和转移中发挥了至关重要的作用，从而介导了海洋/气候系统不同平衡状态之间的转变。

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.