Collaborative Research: US GEOTRACES GP17-OCE: Dissolved concentrations, isotopes, and colloids of the bioactive trace metals

国际地学研究计划的目标是了解海洋中痕量化学元素及其同位素的分布。根据定义，许多微量金属的含量很低，是生命所必需的，因此被认为是浮游植物生长的营养物质。其他元素可以用于追踪其他海洋过程，有些元素(如铅)很重要，因为它们是污染物。该项目将涉及三个主要目标：1)测量海水中微量营养素铁、锰、锌、铜、镉、镍和污染物铅的溶解浓度和大小分配，从大溪地流向南极洲，然后再回到南美洲；2)分析海水、悬浮颗粒、气溶胶和淡水中铁、锌、镉、镍和铜的同位素比率--同一化学元素不同形式的相对丰度--因为同位素提供了对来源、汇和金属转化的诊断性见解，而不仅仅是浓度测量所能提供的；3)使用海洋模型来限制海洋过程的速率和海洋环流对痕量金属和同位素分布的影响。该项目跨越三个美国实验室，四名研究生和几名本科生将参与其中。它还将为其他几个合作小组提供超滤样本和数据作为服务。美国地理跟踪GP17-OCE探险计划于2021年底或2022年进行，旨在确定横跨对营养和碳循环具有全球重要性的地区的横断面上微量元素和同位素的分布，横跨南太平洋环流、南极环极洋流的铁限制水域、具有热液输入的太平洋深海以及智利边缘附近水域。南太平洋环流和南太平洋部分是全球海洋内热量、碳和营养物质转移的气候关键区域，浮游植物的生长通常受到表层海洋中铁(Fe)浓度较低的限制。研究人员将使用各种分析方法，以及其他项目合作者所做的分析，以解决该区域与溶解微量营养素生物地球化学有关的四个主要目标：1)来自粉尘、沉积物和南极大陆输入的溶解金属向南太平洋环流和ACC水域表层水域的相对通量是多少？2)太平洋深水向南大洋输送的痕量金属，特别是铁的通量是什么？这些通量是热液成因的还是海底成因的？溶解的金属是由太平洋-南极海脊提供给深海南大洋的吗？3)从环流到ACC水域，微量营养元素的吸收化学计量比是如何在初级生产力、群落组成和营养限制的梯度上变化的？这些如何受到金属形态的影响？4)地表水中预先形成的生物特征，再加上沿途的再生和回收，如何影响TEI的区域和全球分布？该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The goal of the international GEOTRACES program is to understand the distributions of trace chemical elements and their isotopes in the oceans. Many trace metals, which are by definition present in very low amounts, are essential for life and thus considered nutrients for phytoplankton growth. Other elements can be useful for tracing other ocean processes, and some (such as lead) are important because they are pollutants. This project will address three main objectives: 1) to measure the dissolved concentrations and size partitioning of micronutrients iron, manganese, zinc, copper, cadmium, nickel, and pollutant lead in seawater from Tahiti towards Antarctica and then back northeast to South America; 2) to analyze the isotope ratios - the relative abundance of different forms of the same chemical element - of iron, zinc, cadmium, nickel, and copper in seawater, suspended particles, aerosols, and porewaters from this section, as isotopes provide diagnostic insights into sources, sinks, and metal transformations beyond what is provided by concentration measurements alone; and 3) to use ocean models to constrain the rates of ocean processes and effects of ocean circulation on trace metal and isotope distributions. This project spans three US labs, and four graduate students and several undergraduate students will participate. It will also provide ultrafiltered samples and data to several other collaborating groups as a service.The U.S. GEOTRACES GP17-OCE expedition, planned for late 2021 or 2022, aims to determine the distribution of trace elements and isotopes along a transect spanning regions of global importance to nutrient and carbon cycling, crossing the South Pacific Gyre, the iron-limited waters of the Antarctic Circumpolar Current, Pacific Deep Waters with hydrothermal inputs, and waters near the Chilean margin. The South Pacific Gyre and Pacific sector of the Southern Ocean are climate-critical regions for the transfer of heat, carbon, and nutrients within the global ocean, and they are a region where phytoplankton growth is typically limited by low concentrations of iron (Fe) in the surface ocean. The investigators will use a variety of analytical approaches, along with analyses made by other project collaborators, to address four major objectives related to dissolved micronutrient biogeochemistry in this region: 1) What are the relative fluxes of dissolved metals from dust, sediments, and Antarctic continental inputs to surface waters of the South Pacific gyre and ACC waters? 2) What fluxes of trace metals, especially Fe, are delivered by Pacific Deep Water to the Southern Ocean for upwelling to the surface waters? Are these fluxes hydrothermal or benthic in origin? Are dissolved metals supplied by the Pacific-Antarctic Ridge to the abyssal Southern Ocean? 3) How do micronutrient metal uptake stoichiometries change across gradients of primary production, community composition, and nutrient limitation from the gyre to ACC waters? How are these affected by metal speciation? 4) How do pre-formed biological signatures in surface waters, combined with regeneration and scavenging along the transport path, influence the regional and global distribution of TEIs?This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.