Intermediate water circulation changes in the western equatorial Atlantic over the past 20,000 years

南极中层水环流对全球海洋气候系统有重要贡献。在现代海洋中，AAIW提供了平衡北大西洋深水（NADW）向南输出所需的大部分向北流动，因此代表了大西洋纬向翻转环流（AMOC）的关键角色。尽管它的关键作用，详细了解AAIW在过去的20,000年，以及它如何参与AMOC仍然是一个重大的挑战，在气候研究由于缺乏高时间分辨率的气候档案。在过去的20，000年中，与AMOC减少相关的AAIW向北渗透的突然变化被假设为突然的冷事件。在这些冷事件期间，关于AAIW向北的流动是增强还是减弱的争论仍然存在。因此，很明显，需要更好地了解AAIW的可变性及其如何参与AMOC。高时间分辨率的气候档案从西赤道大西洋（以下简称为WEA）可以揭示一些AAIW在促进AMOC变化的潜在作用。从过去20,000年的气候事件链中产生了两个关键问题：（1）过去AAIW翻转环流的扰动在多大程度上影响了AMOC，从而有利于AAIW在突然寒冷时期的增强或减弱？(2)南半球气候变率在驱动AAIW翻转环流的过去扰动中起什么作用？为了解决这些问题，我们建议重建AAIW/NADW的变化，通过应用补充代理6个选定的沉积物芯在WEA，涵盖了整个范围的南部和北方水团之间的接口的横断面。WEA形成了全球海洋传送带的关键位置，因此对于了解全球海洋气候变化至关重要。首先，我们将分析底栖有孔虫的稳定同位素组成，以重建过去的变化在中间水团的几何形状。其次，我们将测量钕同位素比率从中深度WEA样带。这种方法也可以被用来作为一个强大的工具，以限制过去的变化，水团混合，驱动的重组的AMOC。第三，我们将测量由海底溶解氧量控制的氧化还原敏感金属的浓度。该方法可用于评估有关AAIW源的潜在形成过程的信息。本文提出的对WEA中AMOC可能变化的适当评估成为一个主要问题，因为预测未来几十年AMOC将减弱。因此，全面了解WEA的不同可能行为是预测未来气候的关键因素。

The circulation of Antarctic Intermediate Water (AAIW) is thought to make an important contribution to the global ocean-climate system. In the modern ocean, AAIW supplies a large fraction of the northward flow required to balance the southward export of North Atlantic Deep Water (NADW), and thus represents a key player in the Atlantic meridional overturning circulation (AMOC). Despite of its critical role, a detailed understanding of AAIW over the past 20,000 years and how it participates in the AMOC remains a significant challenge in climate research due to the lack of high temporal resolution climate archives. Abrupt changes in northward penetration of AAIW associated with reductions of the AMOC have been hypothesized for abrupt cold events over the last 20,000 years. Controversy persists as to whether the northward flow of AAIW is waxing or waning during these cold events. Thus, it is clear that a better understanding of the AAIW variability and how it participates in the AMOC is required. High temporal resolution climate archives from the western equatorial Atlantic (referred to hereafter as WEA) can shed some light on the potential role the AAIW plays in contributing to AMOC changes. Two key questions arise from the chain of climate events of the past 20,000 years: (1) To what extent was the AMOC affected by past perturbation in the AAIW overturning circulation, thereby favoring a waxing or waning of AAIW during abrupt cold periods? (2) Which role Southern Hemisphere climate variability plays in driving past perturbation in the AAIW overturning circulation? To address these questions, we propose to reconstruct changes in AAIW/NADW by applying complementary proxies on a transect of 6 selected sediment cores in the WEA that covers the full range of the interface between southern- and northern water masses. The WEA forms a key location in the global ocean conveyor belt, and it thus critical in understanding global ocean-climate changes. First, we will analyze the stable isotopic composition of benthic foraminifera to reconstruct past changes in the intermediate water mass geometry. Second, we will measure the neodymium isotope ratios from the mid-depth WEA transect. This method can also be used as a powerful tool to constrain past changes in water-mass mixing, driven by reorganizations of the AMOC. Third, we will measure the concentrations of redox-sensitive metal which are controlled by the amount of dissolved oxygen at the sea floor. This method can be used to assess information about the underlying formation processes at the AAIW source. The appropriate evaluation of the possible changes in AMOC in the WEA as proposed herein became a major issue, since a weakening in AMOC is predicted for the coming decades. Accordingly, a comprehensive understanding of the different possible behaviors of the WEA is a key element in predicting future climate.