Collaborative Research: U.S. GEOTRACES Arctic Section: Thorium-230, Thorium-232, and Protactinium-231 tracers of trace element supply and removal.

为支持2015年美国地质调查局北极探险，该项目将重点研究北冰洋中天然放射性同位素的去向和分布。这些信息有助于理解为什么其他化学物质，无论是天然的还是人造的，都会出现在海洋中的地方。与参与国际地质勘测计划的其他国家倡议一样，美国北极探险队的目标是确定控制海洋中关键微量元素和同位素(TEI)分布的过程和通量，并确定这些分布对不断变化的环境条件的敏感性。与海洋痕量元素专家组成的多机构团队一起在海上工作，该项目的调查人员将确定预计位于盆地边缘和海底附近的TEI清除率异常高的区域。通过将他们对自然存在的钍和钚的测量与其他参与调查人员收集的TEI数据相结合，他们预计能够将这些比率转化为可应用于其他TEI的信息。像大多数其他参与的调查人员一样，这个小组将包括研究生作为研究小组的一部分，并将参加阿拉斯加社区的各种公共教育推广活动。这项研究将对230和231Pa2的溶解和颗粒浓度进行测量，这两种同位素被指定为GEOTRACES计划成功的关键或关键。此外，该小组将测量溶解和颗粒的232Th浓度，并分析有限数量的气溶胶样本、气溶胶渗滤液、海冰、融化的池水和表层沉积物中的这些放射性核素。工作计划将分为五项任务，分别是：(1)确定与加拿大盆地南缘附近富颗粒水域有关的231Pa和230th的边界清除速率；(2)确定与北冰洋普遍存在的类星状层有关的231pa和230th的底部清除速率；(3)评估在北冰洋周围富有机沉积物的早期成岩作用期间形成的包裹着MnO2的颗粒对加拿大盆地清除的贡献；(4)利用来自230th的信息确定边缘沉积物的成岩232Th的供应速率；通过232Th和230Th的联合研究，确定了海冰对成岩232Th的供应速率，包括它们所输送的气溶胶和冰排沉积物。这项拟议的工作实现了美国地理追踪北极实施计划中定义的核心科学目标。

In support of the 2015 U.S.GEOTRACES Arctic expedition, this project will focus on the fate and distributions of naturally-occurring radioisotopes in the Arctic Ocean. Such information is useful for understanding why other chemical substances, both natural and man-made, occur where they do in the ocean. Like other national initiatives involved in the International GEOTRACES Program, the goals of this U.S. Arctic expedition are to identify processes and quantify fluxes that control the distributions of key trace elements and isotopes (TEI) in the ocean, and to establish the sensitivity of these distributions to changing environmental conditions. Working at sea alongside a multi-institutional team of ocean trace element experts, investigators on this project will define regions of unusually high rates of TEI removal, anticipated to be located near basin margins and near the sea floor. By combining their measurements of naturally-occurring thorium and protactinium with TEI data collected by other participating investigators, they expect to be able to translate these rates into information that can be applied to other TEIs. Like most other participating investigators, this group will include graduate students as part of the research team and will participate in a variety of public educational outreach activities for Alaskan communities.This study will undertake measurements of the dissolved and particulate concentrations of 230Th and 231Pa, two isotopes designated as key or critical to the success of the GEOTRACES program. Additionally the team will measure dissolved and particulate 232Th concentrations and analyze a limited number of aerosol samples, aerosol leachates, sea ice, melt pond water and surface sediments for these radionuclides. The work plan will be broken down into five tasks geared to: (1) determine the rates of boundary scavenging of 231Pa and 230Th associated with the particle-rich waters near the southern margin of the Canada Basin; (2) determine the rates of bottom scavenging of 231Pa and 230Th associated with nepheloid layers that are prevalent in the Arctic Ocean; (3) assess the contribution to scavenging in the Canada basin by MnO2-coated particles, formed during early diagenesis in organic-rich sediments surrounding the Arctic Ocean; (4) determine the rate of supply of lithogenic 232Th from margin sediments using information derived from 230Th; and (5) determine the rate of supply of lithogenic 232Th from sea ice, including the aerosols and ice-rafted sediments that they transport, by the combined study of 232Th and 230Th. The proposed work fulfills core scientific objectives defined in the U.S. GEOTRACES Arctic Implementation Plan.