Collaborative Research: Examining linkages between the Agulhas Leakage and ocean overturning in the last glacial cycle and through the mid-Pleistocene transition

研究地球过去的气候和海洋对于了解气候系统中可能的行为范围非常重要。该项目旨在重建从印度洋到大西洋的“Agulhas泄漏”的历史，并了解这种泄漏的变化如何与过去的气候和海洋环流有关。阿古拉斯海流是一个大型的边界海流（类似于墨西哥湾流），沿着东南非洲边缘向南流动。当它到达非洲南端时，大部分洋流转向东方，但有些环会旋转进入大西洋。这种泄漏将比大西洋水更咸的水带入大西洋，这些盐被包括墨西哥湾流在内的表面水流带到远北大西洋，在那里它有助于形成北大西洋深水。因此，阿古拉斯洋流系统是海洋大规模翻转环流的关键部分。过去气候因素的变化可能导致了该系统的变化，本项目的目标是通过结合国际海洋发现计划（IODP）361号考察队收集的沉积物岩心中的表层和深海环流证据来调查这种变化。地点U1479是制作表层和深海代用记录的理想地点，因此有可能使用一套广泛的地球化学工具同时检查Agulhas泄漏和NADW生产之间的变化和联系。该项目涉及与探险队科学家的广泛国际合作，并将包括培训和指导一个多元化的研究团队，包括本科生，研究生，该项目旨在详细说明在末次冰期循环中Agulhas泄漏和北大西洋深层水（NADW）变化的相对时间（0-150 kyr）和中更新世过渡（MPT，0.7-1.3 Ma），这是在基本轨道强迫没有变化的情况下发生的气候系统重组的重要时期。将使用详细的陆源粘土物源分析来研究Agulhas渗漏的变异性，而NADW的变异将使用鱼牙齿和有孔虫涂层中的Nd同位素来研究。提议的深层和表层综合信号的主要站点是国际海洋学勘探项目站点U1479，该站点目前处于北大西洋重水中，位于阿古拉斯环流入南大西洋的地方，包括阿古拉斯泄漏。此外，粘土物源代理从站点U1474，这是位于附近的开始完全构成的阿古拉斯电流，将限制任何端元的变化，阿古拉斯端元的陆源成分。由于这两套代用指标的数据将从相同的样品收集，而且也从正在处理用于海底同位素地层学的相同样品收集，因此将共同记录Agulhas端元组成变化的相对时间、Agulhas泄漏量和NADW的变化。IODP第361次考察收集了来自更广泛的Agulhas海流系统的沉积记录，为详细研究Agulhas泄漏和大西洋经向翻转环流（AMOC）之间的联系提供了无与伦比的机会该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的知识产权进行评估来支持。优点和更广泛的影响审查标准。

Studies of Earth's past climate and oceans are important for developing an understanding of the range of possible behaviors in the climate system. This project seeks to reconstruct the history of the "Agulhas Leakage" from the Indian Ocean into the Atlantic Ocean, and to understand how changes in this leakage are related to past climate and the ocean's circulation. The Agulhas Current is a large boundary current (similar to the Gulf Stream) that flows southward along the southeast African margin. When it gets to the southern tip of Africa, most of the current turns back to the east, but some rings spin off into the Atlantic. This leakage brings water that is saltier than Atlantic water into the Atlantic, and this salt is carried by surface currents, including the Gulf Stream, to the far North Atlantic where it contributes to the formation of North Atlantic Deep Water. Thus, the Agulhas Current system is a key part of the ocean's large-scale overturning circulation. Changes in climate factors in the past may have led to changes in this system, and the goal of this project is to investigate such changes by combining evidence for the surface and deep ocean circulation from sediment cores collected on International Ocean Discovery Program (IODP) Expedition 361. The location of Site U1479 is ideal for making proxy records for both the surface and deep ocean, so it will be possible to simultaneously examine the changes and linkages between Agulhas Leakage and NADW production using a broad suite of geochemical tools. The project involves extensive international collaboration with the scientists from the expedition and will include training and mentorship of a diverse research team that includes undergraduates, graduate students, a postdoctoral fellow and an early career faculty member.The project seeks to detail the relative timing of variability in Agulhas Leakage and North Atlantic Deep Water (NADW) through the last glacial cycle (0-150 kyr) and over the mid-Pleistocene transition (MPT, 0.7-1.3 Ma), an important time of reorganization of the climate system that took place in the absence of changes in the underlying orbital forcing. The variability of Agulhas Leakage will be studied using detailed terrigenous clay provenance analyses, while the NADW variations will be studied with Nd-isotopes in fish teeth and foraminifera coatings. The primary site proposed for the combined deep and surface signal is IODP Site U1479, which is currently bathed in NADW and located where the Agulhas rings are shed into the South Atlantic, comprising the Agulhas Leakage. Additionally, clay provenance proxies from Site U1474, which is located near the beginning of the fully-constituted Agulhas Current, will constrain any end-member changes to the terrigenous composition of the Agulhas endmember. Because the data for both sets of proxies will be collected from the same samples, and also from the same samples that are being processed for benthic isotope stratigraphy, the relative timing of changes in the composition of the Agulhas endmember, the amount of Agulhas leakage, and the changes in NADW will be co-registered. IODP Expedition 361 collected sedimentary records from the broader Agulhas Current System that provide an unparalleled opportunity to examine in detail linkages between the Agulhas Leakage and Atlantic Meridional Overturning Circulation (AMOC) as well as linkages between the Agulhas Current System and southern African climates.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.