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

像铁和锌这样的微量金属对于在阳光照射的海洋表面主导光合作用的微观植物（浮游植物）的生长是必不可少的。其他微量金属，如铜或汞，对这些生物也有剧毒。即使在一万亿克海水中只有1克的浓度，微量元素也能改变海洋生态系统对二氧化碳的消耗和对氧气的产生。由此产生的有益和/或毒性反应取决于每种微量金属的化学形态。这些金属溶解在海水中，既可以作为独立的自由离子存在，也可以附着在其他溶解的化合物上，这些化合物通常被称为配体。络合是微量金属与配体发生化学反应的过程。该项目将研究六种重要的生物微量金属与硫化氢配体的络合作用。在从阿拉斯加到塔希提岛的太平洋探险期间所做的工作数据将为硫化氢在控制各种海洋水域中必需和有毒金属生物可利用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。一名研究生将在这个项目中起主导作用。作为一个大型合作项目的参与者，与其他世界级科学家一起工作，将大大增加受教育的机会。额外的研究生学习和拓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。在含氧的海洋中，硫化氢是在阳光照射下的表层水中产生的，并从海洋脊上的热液喷口排放出来。然后，它可以使溶解的微量金属复合或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GEOTRACES太平洋子午样带（PMT）的一部分进行，这是一条巡航轨道，可以对富有生产力的沿海水域、低营养地表水以及靠近底部的富含金属和硫化物的热液水域进行采样。硫化氢的溶解离子将在收集后不久在海上进行测量。颗粒内和颗粒上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。硫化物络合作用在多大程度上随所遇到的各种生物和化学机制而变化？在上层水柱中用硫化氢沉淀去除必需金属吗？金属与硫化氢在热液中的反应是否稳定了这些溶解的配合物并允许远距离运输？相关研究将与其他GEOTRACES科学家密切合作，研究微量金属及其与硫化物以外的配体的络合，为全面了解海洋中的微量元素循环提供总体背景和新能力。

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.