Collaborative Research: U.S. GEOTRACES Pacific Meridional Transect: Thorium-232, Thorium-231 and Protactinium-231 as tracers of trace element supply and removal

合作研究：美国 GEOTRACES 太平洋经线横断面：Thorium-232、Thorium-231 和 Protactinium-231 作为微量元素供应和去除的示踪剂

• 批准号: 1737224
• 负责人: Robert Anderson
• 金额: $ 69.96万
• 依托单位: Columbia University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2017
• 资助国家: 美国
• 起止时间: 2017-11-01 至 2023-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1737224&HistoricalAwards=false
• 关键词: Collaborative; Research; U.S.; GEOTRACES; Pacific

The goal of the international GEOTRACES program is to understand the distributions of trace chemical elements and their isotopes in the oceans. Many trace elements are essential for life and their extremely low concentrations in seawater are thought to limit biological productivity (fertility) throughout much of the ocean. This limitation, in turn, partially constrains the level of fisheries that can be supported by marine ecosystems as well as the ocean's capacity to absorb carbon dioxide from the atmosphere. Whereas the importance of these trace-element micronutrients is well established, many basic features of their ocean distribution remain unknown. Measurements of other elements and isotopes can be used to understand the processes that influence the distributions of the micronutrient elements. Two naturally-occurring radioactive isotopes that are particularly important in this regard are thorium-230 and protactinium-231, which have been designated as key parameters to be measured as part of GEOTRACES. This project will focus on the measurement of these two isotopes in order to provide critical information about the processes that supply iron to the Pacific Ocean, as well as the rates of those processes. The project will support an early career investigator, a postdoctoral researcher, and students at the undergraduate and graduate levels.Samples of seawater and of suspended particulate material will be collected along a north-south transect between Alaska and Tahiti to examine the processes that supply and remove trace elements. These samples will be analyzed for naturally-occurring radionuclides thorium-232, thorium-230 and protactinium-231. Aerosol samples and sediments collected along the transect will be analyzed as well. In collaboration with other investigators involved in the expedition, this project will:1) Interpret the distributions of thorium-232 and thorium-230 to quantify the supply of iron and other trace elements delivered by dust as well as the trace elements supplied by chemical reactions in volcanic sediments along the Alaskan margin, 2) Determine the sinking flux of major particulate phases and of particulate trace elements throughout the water column to quantify their rate of removal from the ocean, and 3) Compare the rate of trace element removal among contrasting environmental regimes to be encountered along the Alaska to Tahiti transect to identify the key physical, chemical and biological factors, such as dust supply and biological productivity, that regulate the rate of trace element removal from the ocean.

国际 GEOTRACES 计划的目标是了解海洋中微量化学元素及其同位素的分布。许多微量元素对生命至关重要，它们在海水中的极低浓度被认为限制了整个海洋的生物生产力（肥力）。这种限制反过来又部分限制了海洋生态系统所能支持的渔业水平以及海洋从大气中吸收二氧化碳的能力。尽管这些微量元素的重要性已众所周知，但其海洋分布的许多基本特征仍然未知。其他元素和同位素的测量可用于了解影响微量营养元素分布的过程。在这方面特别重要的两种天然放射性同位素是钍 230 和镤 231，它们已被指定为 GEOTRACES 的一部分进行测量的关键参数。该项目将重点关注这两种同位素的测量，以便提供有关向太平洋供应铁的过程以及这些过程的速率的关键信息。该项目将为一名早期职业研究员、一名博士后研究员以及本科生和研究生提供支持。海水和悬浮颗粒物质的样本将沿着阿拉斯加和塔希提岛之间的南北横断面采集，以检查供应和使用的过程。去除微量元素。将分析这些样品中天然存在的放射性核素钍 232、钍 230 和镤 231。沿横断面收集的气溶胶样本和沉积物也将进行分析。与参与此次探险的其他研究人员合作，该项目将：1) 解释钍 232 和钍 230 的分布，以量化灰尘提供的铁和其他微量元素的供应以及化学反应提供的微量元素在阿拉斯加边缘的火山沉积物中，2) 确定整个水柱中主要颗粒相和颗粒微量元素的下沉通量，以量化它们从海洋中去除的速率，以及 3) 比较沿阿拉斯加至塔希提岛横断面遇到的对比环境状况中微量元素去除率，以确定控制海洋微量元素去除率的关键物理、化学和生物因素，例如灰尘供应和生物生产力。