Ocean circulation and carbon cycling during Eocene 'greenhouse' warmth

海洋环流通过向极地输送热量和盐分来强烈地影响气候。更新世深海沉积物记录表明，海洋环流可以通过主导海洋颠覆的半球的开关(千年尺度丹斯加德-奥施格气候周期的“两极拉锯”)和通过其在二氧化碳储存和释放方面的作用(例如，跨越冰川-间冰期周期)来推动全球气候。然而，尚不清楚海洋环流对截然不同的大气二氧化碳水平有多敏感。人为的二氧化碳排放预计将使大气中这种温室气体的浓度上升到本世纪末将比始新世以来的任何时候都高的水平。然而，几乎没有来自始新世的适当数据来测试这种以高二氧化碳水平、最小大陆冰量和不同碳循环模式为特征的温室气候制度下海洋环流的性质和稳定性。这项工作旨在通过始新世早期和中期的关键区间重建全球海洋环流的结构和相对强度。我将使用综合大洋钻探计划从纽芬兰边缘恢复的深海沉积物序列，以及世界各地的一系列地点。海底有孔虫方解石的稳定氧和碳同位素分析将提供世界各地沉积物序列之间的强有力的对比，并作为重建海洋环流模式的替代。对浮游有孔虫成岩涂层和鱼牙氟磷灰石的钕同位素分析将为重现海洋环流的变化提供独立的工具。

Ocean circulation strongly influences climate by poleward transport of heat and salt. The Pleistocene deep-sea sediment record shows that ocean circulation can drive global climate via switches in the hemisphere dominating ocean overturning (the 'bipolar seesaw' of millennial-scale Dansgaard-Oeschger climate cycles) and via its role in storage and release of carbon dioxide (e.g. across glacial-interglacial cycles). However, what is not known is how sensitive ocean circulation is to radically different levels of atmospheric carbon dioxide. Man-made CO2 emissions are projected to elevate atmospheric concentrations of this greenhouse gas to levels that, by the end of this century, will be higher than at any time since the Eocene epoch. Yet there are virtually no appropriate data from the Eocene with which to test the nature and stability of ocean circulation during such 'greenhouse' climate regimes characterized by high CO2 levels, minimal continental ice volume and contrasting modes of carbon cycling.This work aims to reconstruct the global configuration and relative strength of ocean circulation through key intervals of the early and middle Eocene. I will use deep sea sediment sequences recovered by the Integrated Ocean Drilling Program from the Newfoundland margin, in addition to a series of locations worldwide. Stable oxygen and carbon isotope analyses of benthic foraminiferal calcite will provide robust correlations between sediment sequences worldwide and a proxy for reconstructing ocean circulation patterns. Neodymium isotope analyses of planktic foraminiferal diagenetic coatings and of the fluorapatite of fish teeth will provide independent tools for reconstructing changes in ocean circulation.