A Critical Test of the Nd Paleocirculation Proxy

钕同位素作为“准保守”水团示踪剂在古海洋学研究中得到越来越多的应用。然而，这一代理的局限性尚未得到充分理解。拟议的工作旨在解决这种不确定性，严格评估行为的Nd同位素示踪剂的水团混合。该项目由哥伦比亚大学拉蒙特-多尔蒂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）的一个纵断面收集的海水和表面沉积物样本。样品组将用于检验：1）Nd同位素比值是否偏离混合沿着环流输送路径的预期值，2）Nd同位素在远离大陆边缘的地方是否表现出准保守性，3）海底特征（例如，大陆架，火山海山）增加了显着的外部Nd的系统，以及4）是否南半球风区影响Nd同位素值通过风成沉积。首次标定了自生表层沉积物中Nd同位素与上覆海水中Nd同位素的关系。 通过测试过去海洋动力学研究中的一种新兴工具，这项研究将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职业研究人员和一名研究生。本科生将通过NSF支持的暑期实习计划在LDEO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.