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Reconstructing South Atlantic Ocean Circulation changes across the Eocene-Palaeocene

重建始新世-古新世南大西洋环流变化

基本信息

批准号：
NE/X002039/1
负责人：
Philip Sexton
金额：
$ 6.95万
依托单位：
The Open University
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2022
资助国家：
英国
起止时间：
2022 至无数据
项目状态：
未结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FX002039%2F1
关键词：
Reconstructing South Atlantic Ocean Circulation

项目摘要

The Atlantic meridional overturning circulation (AMOC) is a system of surface and deep ocean currents, which constitutes a major component of modern global ocean circulation. The AMOC distributes heat, salt, and bio-essential nutrients around the global oceans and has a fundamental influence on global and regional climates. Yet, we do not know how stable the current AMOC is and how it may change owing to ongoing climate change. To help us improve our understanding of how the AMOC might change in a warmer climate, we can investigate intervals in the geological past to determine how ocean circulation may have operated during warmer-than-modern climates. The Eocene and Palaeocene (34 to 65 million years ago) epochs were intervals of time when the climate was considerably warmer than modern, and similar to projections for the level of warmth for our medium- to long-term future. Because the Eocene-Paleocene are useful approximations for our future climate, we propose to reconstruct the ocean circulation during these epochs to provide invaluable insights into how the modern AMOC might change its operation with ongoing global warming. To reconstruct past ocean circulation, we use geochemical techniques such as measurements of the carbon isotopes (d13C) of fossil shells of benthic foraminifera (microscopic sea-floor dwelling organisms). The carbon isotopes of fossil benthic foraminifera record the dissolved carbon of the ambient seawater at the time they grew their shells. In the ocean, microscopic plankton in the uppermost ocean take up nutrients and carbon, preferentially removing the light carbon isotope (12C). As these plankton die and settle through the ocean, remineralization of their organic remains in deeper waters releases nutrients and 12C-enriched carbon, imparting a relatively low d13C signature at depth. Along the main deep ocean flow-path, progressive organic carbon remineralisation gives rise to a progressive decrease in d13C, which is termed water mass 'ageing'. Carbon isotopes can thereby tell us how recently the deep waters were last at the ocean surface i.e. a rough approximation of the water-mass' relative 'age'. Oxygen isotopes (d18O) of the same fossil benthic foraminifera will be used to provide a record of deep ocean temperature and salinity during the Eocene-Palaeocene. A third technique utilises neodymium isotopes (eNd) measured on fossil fish teeth to identify and trace the flow directions of deep water masses. Ocean basins acquire distinctive eNd signatures from the weathering of isotopically distinct material from the surrounding continents, with the water masses bathing these ocean basins reflecting these unique eNd signatures. eNd data also allow the determination of any mixing between water masses. These three methods will be applied to samples obtained during the International Ocean Discovery Program (IODP) Expedition 390/393 in the South Atlantic. This will allow the following objectives to be accomplished:1. Assess the spatial structure of ocean circulation across the South Atlantic during the Eocene-Palaeocene. New records from Expedition 390/393 will be compared to similar datasets generated from the south-east Atlantic (Expedition 208).2. Reconstruct the evolution of the AMOC structure through the Eocene-Palaeocene, with the objective to investigate the timing of when northern sourced waters first extended into the South Atlantic, similar to today's AMOC. This will be achieved by combining new records generated in this project with previously generated Eocene-Paleocene eNd and d13C records from the North Atlantic and Tropical Atlantic.3. Determine the role of Atlantic ocean circulation, particularly the South Atlantic, in regulating global climate change during the climatic transition from the extreme greenhouse warmth of the Paleocene and early Eocene to the cooler icehouse of the latest Eocene.

大西洋纬向翻转环流（AMOC）是一个表层和深层洋流系统，是现代全球海洋环流的主要组成部分。AMOC在全球海洋中分配热量，盐和生物必需的营养物质，并对全球和区域气候产生根本影响。然而，我们不知道目前的AMOC有多稳定，以及由于持续的气候变化，它可能会如何变化。为了帮助我们更好地了解AMOC在温暖的气候中如何变化，我们可以调查过去地质时期的间隔，以确定海洋环流在比现代更温暖的气候中如何运作。始新世和古新世（3400万至6500万年前）是气候比现代温暖得多的时间间隔，与我们中长期未来的温暖程度预测相似。由于始新世-古新世是我们未来气候的有用近似，我们建议重建这些时期的海洋环流，以提供宝贵的见解，现代AMOC如何随着全球变暖而改变其运作。为了重建过去的海洋环流，我们使用地球化学技术，如测量底栖有孔虫（微观海底生物）化石外壳的碳同位素（d13 C）。底栖有孔虫化石的碳同位素记录了它们生长外壳时周围海水中溶解的碳。在海洋中，海洋最上层的微生物浮游生物吸收营养物质和碳，优先去除轻碳同位素（12 C）。当这些浮游生物死亡并在海洋中定居时，它们的有机残留物在更深的沃茨中的矿化释放出营养物质和富含12 C的碳，在深度上赋予相对较低的d13 C信号。沿着主要的深海流动路径，有机碳的逐渐矿化导致d13 C的逐渐减少，这被称为水团“老化”。因此，碳同位素可以告诉我们深海沃茨最后出现在海洋表面的时间，也就是说，这是水团“相对”年龄“的粗略近似值。同一化石底栖有孔虫的氧同位素（d18 O）将用于提供始新世-古新世期间深海温度和盐度的记录。第三种技术利用在鱼牙齿化石上测量的钕同位素（eNd）来识别和追踪深水团的流向。海洋盆地获得独特的eNd签名从周围大陆的同位素不同的材料的风化，与水团沐浴这些海洋盆地反映这些独特的eNd签名。eNd数据还允许确定水团之间的任何混合。这三种方法将应用于国际海洋发现计划（IODP）在南大西洋进行的第390/393次考察期间获得的样本。这将实现以下目标：1。评估始新世-古新世期间南大西洋海洋环流的空间结构。来自远征390/393的新记录将与东南大西洋（远征208）产生的类似数据集进行比较。重建始新世-古新世AMOC结构的演变，目的是调查北方来源的沃茨首次延伸到南大西洋的时间，类似于今天的AMOC。这将通过将本项目中产生的新记录与以前产生的北大西洋和热带南极始新世-古新世eNd和d13 C记录相结合来实现。确定大西洋环流，特别是南大西洋，在从古新世和始新世早期的极端温室温暖到最后始新世的较冷冰库的气候过渡期间调节全球气候变化的作用。