US GEOTRACES PMT: hydrogen sulfide as a strong ligand affecting trace metal cycling

铁和锌等微量金属对于在阳光明媚的表层海洋中主导光合作用的微型植物(浮游植物)的生长是必不可少的。其他微量金属，如铜或汞，对这些生物都有很强的毒性。即使浓度低至一万亿克海水中的一克，微量元素也可以改变社区对二氧化碳的消耗和海洋生态系统产生的氧气。由此产生的有益和/或有毒反应取决于每种痕量金属的化学形态。这些金属溶解在海水中，既可以作为单独的自由离子存在，也可以与其他溶解的化合物结合在一起，通常称为配体。络合是痕量金属化学结合到配体上的过程。这个项目将研究六种具有生物重要性的痕量金属与一种称为硫化氢的配体的络合作用。在从阿拉斯加到塔希提岛的太平洋探险期间所做工作的数据将为硫化氢在控制各种海洋水域中基本和有毒金属生物有效性方面的重要性提供新的科学见解，从而对海洋碳和生态系统模型产生科学影响。一名研究生将在该项目中发挥主导作用。通过与其他世界级科学家合作，作为一个大型合作项目的参与者，教育机会将大大增加。其他研究生学习和外展将包括通过博客与公众交流经验和研究成果，以及作为助教与本科生互动。在富氧的海洋中，硫化氢是在阳光明媚的表层水域中生物产生的，并从洋脊上的热液喷口排放出来。然后，它可以使溶解的痕量金属络合，或者与它们反应形成不溶的金属硫化物。在这两种情况下，必需微量元素的丰度和循环都会受到影响，这些反应的重要性目前尚不清楚。这些硫化物痕量金属研究将作为2018年美国地质调查局太平洋子午线(PMT)的一部分进行，这是一条邮轮路径，允许对生产性沿海水域、低营养地表水以及靠近海底的富含金属和硫化物的热液水域进行采样。收集后不久，将在海上测量硫化氢的溶解离子。颗粒中和颗粒上含有的金属硫化物也将被过滤和分析。这个项目将解决几个具体的科学问题。硫化物的络合作用随着所遇到的各种生物和化学制度的不同而变化到什么程度？是否通过在上层水柱中用硫化氢沉淀除去必需金属？金属与硫化氢在热水中的反应是否稳定了这些溶解的络合物，并允许远距离运输？相关研究将通过与GEOTRACES其他科学家的密切合作开展，研究痕量金属及其与硫化物以外的配体的络合作用，为全面了解海洋中的微量元素循环提供总体背景和新的能力。

Trace metals like iron and zinc are essential for the growth of the microscopic plants (phytoplankton) that dominate photosynthesis in the sunlit surface ocean. Other trace metals like copper or mercury are highly toxic to these same organisms. Even at concentrations of as low as one gram in a trillion grams of seawater, trace elements can alter the community consumption of carbon dioxide and the production of oxygen by ocean ecosystems. The resulting beneficial and/or toxic response depends on the chemical form of each trace metal. Dissolved in seawater, these metals can exist either as individual, free ions or attached to other dissolved chemical compounds, generically called ligands. Complexation is the process by which trace metals become chemically attached to ligands. This project will study the complexation of six biologically important trace metals with a ligand known as hydrogen sulfide. Data from work done during an expedition in the Pacific Ocean from Alaska to Tahiti will provide new scientific insight on hydrogen sulfide's importance in controlling essential and toxic metal bioavailability in various marine waters and thus have scientific impact on ocean carbon and ecosystem models. A graduate student will play a leading role in the project. Educational opportunities will be greatly enhanced by working alongside other world-class scientists as a participant in a large collaborative program. Additional graduate learning and outreach will include communicating experiences and research findings with the public with a blog and by interactions with undergraduate students as a teaching assistant. In the oxygenated ocean, hydrogen sulfide is biologically produced in sunlit surface waters and emitted from hydrothermal vents on ocean ridges. It can then complex dissolved trace metals or react with them to form insoluble metal sulfides. In both cases, the abundance and cycling of essential trace elements would be affected and the importance of these reactions are currently not known. These sulfide - trace metal studies will be conducted as part of the 2018 US GEOTRACES Pacific Meridional Transect (PMT), a cruise track that allows sampling of productive coastal waters, low nutrient surface waters, and plumes of metal- and sulfide-rich hydrothermal waters near the bottom. The dissolved ions of hydrogen sulfide will be measured at sea soon after collection. Metal sulfides contained in and on particles will also be filtered and analyzed. This project will address several specific scientific questions. To what degrees does sulfide complexation vary as a function of the various biological and chemical regimes encountered? Are essential metals removed by precipitating with hydrogen sulfide in the upper water column? Does the reaction of metals with hydrogen sulfide in hydrothermal waters stabilize these dissolved complexes and allow long range transport? Related study will develop from close collaborations with other GEOTRACES scientists studying trace metals and their complexation with ligands other that sulfide, providing overall context and novel capacity to fully understand trace element cycles in the ocean.