Collaborative Research: U.S. GEOTRACES North Atlantic Section: Analysis of 230Th, 232Th and 231Pa

在这个项目中，四个合作实验室-伍兹霍尔海洋研究所、罗得岛大学、明尼苏达大学和拉蒙特-多尔蒂-将在美国GEOTRACES北大西洋部分测量230 Th和231 Pa的溶解和颗粒浓度，这两种同位素被指定为GEOTRACES计划成功的“关键”或关键。此外，他们还将测量232 Th浓度，并提供粒子成分的支持分析。拟议的工作实现了美国GEOTRACES北大西洋实施计划中定义的科学目标。这些新的231 Pa，230 Th和232 Th数据预计将导致在流域范围内改进边界和内部大西洋之间的物质交换模型。该项目将使研究小组和海洋放射地球化学界能够检验关于环流、粒子组成和粒子通量区域变化的相对重要性的假设，这些区域变化影响到与粒子有关的元素，包括碳、微量金属和污染物在大陆架/斜坡区域和大西洋内陆盆地之间的重新分布。此外，获得新的水柱231 Pa和230 Th数据将允许测试一个关键假设：230 Th大部分在北大西洋内被移除，而现场产生的231 Pa中有近一半随北大西洋深水输出。沉积物中231 Pa/230 Th比值已成为评估大西洋经向翻转环流（AMOC）过去变化的主要指标。完成拟议的工作将表征粒子组成的231 Pa/230 Th分馏的重要性，从而限制使用231 Pa/230 Th作为AMOC的运动学代理的潜在偏差。这些结果，反过来，将导致一个更可靠的评估AMOC变异在过去的气候变化中的作用。更广泛的影响本提案中概述的假设和目标是国际GEOTRACES计划的核心，其重点是全球海洋分布的微量元素和同位素在海水中。231 Pa和230 Th是GEOTRACES科学计划中指定的关键参数，因为它们在所有截面上的测量被认为是这个国际海洋科学计划成功的关键。拟议的研究将为研究生（LDEO）和博士后（UMinn）研究经验提供新的机会，加强美国几个机构（LDEO，URI，UMinn，WHOI）之间的海洋科学互动，促进与国际GEOTRACES同事的合作，并为现有的科学教育计划做出贡献。

In this project four collaborating labs -- Woods Hole Oceanographic Institution, University of Rhode Island, University of Minnesota and Lamont-Doherty -- will undertake measurements on the US GEOTRACES North Atlantic section of the dissolved and particulate concentrations of 230Th and 231Pa, two isotopes designated as "key" or critical to the success of the GEOTRACES program. In addition, they will measure 232Th concentrations and provide supporting analyses of particle composition. The proposed work fulfills scientific objectives defined in the U.S. GEOTRACES North Atlantic Implementation Plan.These new 231Pa, 230Th and 232Th data are expected to lead to improved models of material exchange between the boundaries and interior Atlantic on a basin-wide scale. This project will permit the research team and the marine radiogeochemical community to test hypotheses regarding the relative importance of regional variations in circulation, particle composition, and particle flux that influence the redistribution of particle-associated elements, including carbon, trace metals and contaminants, between the continental shelf/slope regions and interior basins in the Atlantic. Furthermore, obtaining new water column 231Pa and 230Th data will allow testing of a key hypothesis: that 230Th is largely removed within the North Atlantic, whereas nearly half of the 231Pa produced in-situ is exported with North Atlantic Deep Water. Sedimentary 231Pa/230Th ratios have become the principal proxy used to evaluate past changes in Atlantic Meridional Overturning Circulation (AMOC). Completing the proposed work will characterize the importance of particle composition for 231Pa/230Th fractionation, and thereby constrain the potential bias in using 231Pa/230Th as a kinematic proxy for AMOC. These results, in turn, will lead to a more reliable assessment of the role of AMOC variability in past climate change.Broader Impacts The hypotheses and objectives outlined in this proposal are central to the International GEOTRACES program, whose focus is on the global-ocean distribution of trace elements and isotopes in seawater. 231Pa and 230Th are designated key parameters in the GEOTRACES Science Plan as their measurement on all sections is deemed to be critical to the success of this international ocean science program. The proposed research will provide new opportunities for graduate student (LDEO) and post doc (UMinn) research experience, enhance ocean science interactions between several US institutions (LDEO, URI, UMinn, WHOI), foster collaboration with international GEOTRACES colleagues, and contribute to existing science education programs designed for teachers and the public.