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

合作研究：美国 GEOTRACES 北极部分：Thorium-230、Thorium-232 和 Protactinium-231 微量元素供应和清除示踪剂。

• 批准号: 1434886
• 负责人: Richard Edwards
• 金额: $ 45.49万
• 依托单位: University of Minnesota-Twin Cities
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-01-01 至 2018-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1434886&HistoricalAwards=false
• 关键词: Collaborative; Research; U.S.; GEOTRACES; Arctic

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.

为了支持2015年美国GEOTRACES北极考察，该项目将重点关注北冰洋天然放射性同位素的命运和分布。 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。与其他参与国际GEOTRACES计划的国家计划一样，这次美国北极考察的目标是确定控制海洋中关键微量元素和同位素（TEI）分布的过程和量化通量，并确定这些分布对环境条件变化的敏感性。 该项目的研究人员与一个由海洋微量元素专家组成的多机构团队一起在海上工作，将确定TEI去除率异常高的区域，预计这些区域将位于盆地边缘和海底附近。 通过将他们对天然存在的钍和钚的测量与其他参与研究者收集的TEI数据相结合，他们希望能够将这些速率转化为可应用于其他TEI的信息。像大多数其他参与的研究人员，这个小组将包括研究生作为研究团队的一部分，并将参加各种公共教育推广活动，为阿拉斯加communities.This study will carry the dissolved and particulate concentrations of 230 Th and 231 Pa，two isotopes designed as key or critical to the success of the GEOTRACES program.此外，该小组将测量溶解和颗粒232 Th浓度，并分析数量有限的气溶胶样品，气溶胶沥滤物，海冰，融化的池塘水和表面沉积物中的这些放射性核素。 该工作计划将分为五项任务：（1）确定与加拿大海盆南缘附近富含颗粒物的沃茨有关的231 Pa和230 Th的边界清除率;（2）确定与北冰洋普遍存在的霞状层有关的231 Pa和230 Th的底部清除率;（3）评估北冰洋周围富含有机质的沉积物中在早期成岩作用期间形成的MnO_2包覆颗粒对加拿大海盆的清除作用的贡献：（4）利用~（230）Th的信息确定边缘沉积物中成岩~（232）Th的供应速率;（5）通过~（232）Th和~（230）Th的联合研究，确定了海冰（包括其输送的气溶胶和冰筏沉积物）对成岩~（232）Th的供给速率。 拟议的工作实现了美国GEOTRACES北极实施计划中定义的核心科学目标。