US GEOTRACES GP17-OCE: Hydrogen sulfide as a strong ligand affecting the speciation and solubility of key trace metals

海洋中痕量金属的浓度非常低，但尽管它们很稀缺，但许多金属，如铁和锌，对被称为浮游植物的微型植物的生长至关重要。其他物质，如汞和砷，是有毒的。除了极低的浓度外，痕量金属的基本性质或有毒性质还取决于元素的化学形式--作为自由溶解离子本身，或者作为带电离子与其他无机或有机离子相互作用。海水中与痕量金属强烈相互作用的无机离子之一是二硫化物，这是恶臭气体硫化氢的离子形式。它与金属的反应性很强，会形成金属硫化物颗粒，然后沉入水中并被去除。这项研究项目将研究硫化氢如何与镉、铜、汞、镍和锌等痕量金属相互作用，形成溶解的络合物，使这些金属对其他离子和浮游植物的反应较小，或去除金属的不溶颗粒。研究人员将在从塔希提岛到南极洲周围冰缘再到智利的海洋探险中进行这些研究，这是美国地理跟踪计划的一部分，许多其他研究人员将测量从表面到海底的痕量金属。所有这些，甚至更多，都将成为研究生博士研究的主题。除了学习如何在一次重大的海洋探险中工作以及与其他研究人员合作外，她还将在一个博客上交流她的经验和发现，所有追随者都可以使用它。她还将帮助创建一个关于她的科学的演示文稿，这将成为学校、图书馆/博物馆、节日和公共演示的虚拟现实体验的一部分。美国GEOTRACES GP17-OCE邮轮从大溪地到南极冰缘再到智利，将对浮游植物生物量和物种、常量营养素和痕量金属的大梯度水域进行采样。随着含氧水柱中硫化氢浓度和物相的预期变化，横断面提供了一个量化硫化氢与镉、铜、锌等生物活性金属以及有毒元素汞的联系循环的理想机会。以量化上层含氧海洋中痕量金属和硫化物的耦合循环为总体目标，我们这项研究的具体研究目标将是：(1)量化与关键微量金属循环有关的溶解和颗粒状硫化物的源和汇，以便准确地连接它们的循环；(2)建立游离硫化物与镉、铜和锌等痕量金属反应和沉淀的条件，并量化这一去除条件；以及(3)评估热液烟柱中是否存在纳米级/胶体黄铁矿及其相对于胶体氢氧化铁对铁的迁移的贡献。为实现这些目标，设计了一套完全集成的船上测量、实验室研究以及数据合成和形态模拟。该方法包括与溶解和微粒痕量金属及其形态的调查以及与使用各种示踪剂研究混合过程的人员的密切合作。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。

Trace metals are present at very low parts per trillion concentrations in the ocean but in spite of their scarcity many, like iron and zinc, are essential to the growth of the microscopic plants called phytoplankton. Others, like mercury and arsenic, are toxic. In addition to very low concentrations, the essential or toxic nature of a trace metal also depends on the chemical form of the element – as a free dissolved ion all by itself or as charged ion interacting with other inorganic or organic ions. One of the inorganic ions in seawater that strongly interacts with trace metals is bisulfide, the ionic form of the foul-smelling gas hydrogen sulfide. Its reactivity with metals can be so strong that it forms metal-sulfide particles that sink out and are removed from the water. This research project will study how hydrogen sulfide interacts with trace metals like cadmium, copper, mercury, nickel, and zinc to form dissolved complexes that make these metals less reactive to other ions and phytoplankton, or insoluble particles that remove the metals. The researchers will conduct these studies on an oceanographic expedition from Tahiti to the ice edge around Antarctica to Chile as part of the U.S. GEOTRACES program with many other researchers measuring trace metals from the surface to the ocean bottom. All of this and more will be the subject of a graduate student’s doctoral research. In addition to learning how to work on a major oceanographic expedition and with other researchers, she will communicate her experiences and findings on a blog available to all who follow it. She will also help to create a presentation about her science that will be part of the “Sailing with GEOTRACES” virtual reality experience for schools, libraries/museums, festivals, and public presentations.The US GEOTRACES GP17-OCE cruise from Tahiti to the Antarctic ice edge to Chile will sample waters with large gradients in phytoplankton biomass and species, macronutrients, and trace metals. With anticipated changes in the concentrations and phases of hydrogen sulfide in the oxic water column, the transect offers an ideal opportunity to quantify the linked cycles of hydrogen sulfide and bioactive metals like cadmium, copper, and zinc, and the toxic element mercury. With an overall goal of quantifying the coupled cycles of trace metals and sulfide in the upper, oxic ocean, our specific research objectives for this research will be: (1) Quantify the sources and sinks of dissolved and particulate sulfide as it pertains to the cycling of key trace metals in order to accurately link their cycles; (2) Establish the conditions under which free sulfide reacts with and precipitates trace metals such as cadmium, copper, and zinc, and quantify this removal term; and (3) Evaluate whether nanoparticulate/colloidal pyrite exists in hydrothermal plumes and its contribution to iron transport relative to colloidal iron oxyhydroxides. A fully integrated set of shipboard measurements, laboratory studies, and data synthesis and speciation modeling are designed to meet these objectives. The approach includes close collaborations with investigations of dissolved and particulate trace metals and their speciation, as well as with those studying mixing processes using a variety of tracers.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.