Collaborative Research: US GEOTRACES PMT: Sources and Rates of Trace Element and Isotope Cycling Derived from the Radium Quartet

国际GEOTRACES计划的目标是了解微量化学元素及其同位素在海洋中的分布。镭元素的天然放射性同位素可用于测量海洋中重要过程的速率。反过来，在收集其他微量元素和同位素数据的同时进行这些速率测量能够更完整地解释这些数据。研究人员建议在2018年从阿拉斯加到塔希提岛的美国GEOTRACES探险中测量镭的四种同位素- Ra-223，Ra-224，Ra-226和Ra-228。镭同位素数据将特别有助于调查与海洋边界（河流、大陆架和洋底）和大洋中脊热液喷口及其中性浮力羽流的远距离扩散有关的微量元素输入和清除过程。研究人员还将研究控制寿命最长的同位素Ra-226的内部循环的过程，与钡元素相比，钡元素与镭具有非常相似的化学性质。拟议的工作将处理一些关键问题，涉及海洋边界的微量元素输入及其对海洋生产力和海洋地球化学的潜在影响。由于铁是海洋浮游植物的重要营养物质，研究人员将量化从阿拉斯加湾边缘到亚北极东北太平洋近海高营养低叶绿素区域的横向微量元素运输速率。在海洋地下，他们将设法了解与高温热液喷口有关的微量元素通量，以及微量元素和同位素通过沿着热液羽流清除而被清除的速率。最后，这项工作将通过调查海洋上层的Ra-226和钡分馏过程，提高对海洋碳酸盐沉积物测年技术的认识。该项目将涉及两个美国机构和一个法国合作伙伴之间的合作，后者将分析一些样本。两名研究生将参与该项目。摩尔将通过南卡罗来纳州少数民族参与联盟监督一名本科生，并将鼓励这名学生根据他们对这个项目的参与制定一篇高年级论文。

The goal of the international GEOTRACES program is to understand the distributions of trace chemical elements and their isotopes in the oceans. Naturally occurring radioactive isotopes of the element radium can be used to measure the rates of important processes in the ocean. In turn, making these rate measurements at the same time as other trace element and isotope data are collected enables a more complete interpretation of these data. The investigators propose to measure the four isotopes of radium -- Ra-223, Ra-224, Ra-226, and Ra-228 -- on a U.S. GEOTRACES expedition from Alaska to Tahiti in 2018. The radium isotope data will be particularly useful in investigating trace element input and removal processes associated with ocean boundaries (rivers, continental shelves, and the ocean bottom) and with mid-ocean ridge hydrothermal vents and the long-range dispersal of their neutrally buoyant plumes. The investigators will also investigate the processes controlling the internal cycling of the longest-lived isotope, Ra-226, compared to the element barium, which has a very similar chemistry to radium. The proposed work would address a number of key questions regarding trace element inputs from ocean boundaries and their potential impact on ocean productivity and biogeochemistry. As iron is an important nutrient for marine phytoplankton, the investigators will quantify the rates of lateral trace element transport from the Gulf of Alaska margin out to and including the offshore High Nutrient Low Chlorophyll region of the subarctic Northeast Pacific Ocean. In the ocean subsurface, they will seek to understand the trace element fluxes associated with high temperature hydrothermal venting, and the rate at which trace elements and isotopes are removed via scavenging along the hydrothermal plume. Lastly, the work will lead to an improved understanding of a marine carbonate sediment dating technique via an investigation of Ra-226 and barium fractionation processes in the upper ocean. The project will involve collaboration between two U.S. institutions and a partner in France who will analyze some of the samples. Two graduate students will participate in the project. Moore will supervise an undergraduate student through the South Carolina Alliance for Minority Participation, and will encourage this student to develop a senior thesis based on their participation in this project.