A Critical Test of the Nd Paleocirculation Proxy

钕（Nd）同位素作为“准保守”水团示踪剂越来越多地用于古海洋学研究。然而，这种代理的局限性还没有被完全理解。提出的工作旨在通过批判性地评估Nd同位素作为水质量混合示踪剂的行为来解决这种不确定性。该项目由哥伦比亚大学Lamont-Doherty地球观测站的研究人员领导，将分析在GEOTRACES巡航期间沿着西南大西洋（0至50度S）的经向样带收集的现有海水和地表沉积物样本。该样品套件将用于测试1)Nd同位素比值是否偏离沿环流输送路径混合的预期值；2)Nd同位素在远离大陆边缘时是否表现准保守；3)海底特征（如大陆架、火山海山）是否向系统中添加了显著的外部Nd，以及4)南半球风带是否通过风成沉积影响Nd同位素值。首次对自生表层沉积物与上覆海水中Nd同位素的关系进行了标定。通过测试一种研究过去海洋动力学的新兴工具，这项研究将使人们能够更准确地了解海洋气候系统的变化。该项目将支持一名早期研究人员和一名研究生。本科生将通过美国国家科学基金会支持的LDEO暑期实习项目参与。

Neodymium (Nd) isotopes are increasingly used in paleoceanographic studies as "quasi-conservative" water mass tracers. However, the limitations of this proxy are not yet fully understood. The proposed work aims to address this uncertainty by critically evaluating the behavior of Nd isotopes as tracers of water mass mixing. The project, led by researchers at Columbia University's Lamont-Doherty Earth Observatory, will analyze in-hand seawater and surface sediment samples collected along a meridional transect in the southwest Atlantic (0 to 50 degrees S) during a GEOTRACES cruise. The sample suite will be used to test 1) whether Nd isotope ratios deviate from expected values for mixing along circulation transport paths, 2) whether Nd isotopes behave quasi-conservatively away from continental margins, 3) whether seafloor features (e.g., continental shelf, volcanic seamounts) add significant external Nd to the system, and 4) whether the Southern Hemisphere wind zones impact Nd isotope values through aeolian deposition. The relationship between Nd isotopes in authigenic surface sediments and those in the overlying seawater will be calibrated for the first time. By testing an emerging tool in the study of past ocean dynamics, this research will enable a more accurate understanding of changes in the ocean-climate system. The project will support an early-career researcher and a graduate student. Undergraduate students will be involved through an NSF-supported summer internship program at LDEO.