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

国际GEOTRACES项目的目标是了解海洋中微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，但它们对生命至关重要，因此被认为是浮游植物生长的营养物。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。该项目将解决三个主要目标：1)测量从塔希提岛到南极洲，然后返回东北到南美洲的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；2)分析海水、悬浮颗粒、气溶胶和孔隙水中的铁、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；3)利用海洋模式来限制海洋过程的速率和海洋环流对微量金属和同位素分布的影响。该项目横跨三个美国实验室，将有四名研究生和几名本科生参与。它还将向其他几个合作小组提供超滤样品和数据作为服务。美国GEOTRACES GP17-OCE考察计划于2021年底或2022年进行，目的是确定微量元素和同位素在横断面上的分布，横断面横跨对全球营养和碳循环具有重要意义的区域，穿越南太平洋环流、南极环极流的铁限制水域、有热液输入的太平洋深水以及智利边缘附近的水域。南太平洋环流和南大洋的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，也是浮游植物生长通常受到海洋表面低浓度铁（Fe）限制的区域。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，以解决与该地区溶解的微量营养素生物地球化学有关的四个主要目标：1)来自尘埃、沉积物和南极大陆输入的溶解金属到南太平洋环流和太平洋环流水域的地表水的相对通量是多少？2)太平洋深水向南大洋上涌至地表水的微量金属，特别是铁的通量是多少？这些流体的来源是热液还是底栖生物？溶解的金属是由太平洋-南极脊向深海南大洋提供的吗？3)微量元素金属吸收化学计量学如何在初级生产、群落组成和从环流到ACC水域的养分限制梯度中变化？这些是如何受到金属形态的影响的？4)地表水中预先形成的生物特征，以及沿运输路径的再生和清除，如何影响TEIs的区域和全球分布？该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值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.