西印度洋热液流体与海水混合过程中Fe行为：δ56Fe示踪

铁（Fe）限制了全球40%的海域中固氮生物和浮游植物的生长，其源/汇机制及生物地球化学循环过程一直是海洋科学研究的前沿。近年来，GEOTRACES发现洋中脊热液口喷发的溶解态Fe能扩散至数千公里以外，是大洋中Fe的重要来源，因此量化热液源Fe通量成为一个研究热点。然而，目前针对超慢速扩张洋脊的研究程度较低，导致该类洋脊热液源Fe的贡献被极大低估。本项目将使用ROV搭载痕量洁净采样装置采集西印度洋热液流体、羽流水样，对样品中Fe的存在形态及Fe同位素组成进行测试，并结合热液流体及羽流的理化参数，确定流体与海水混合过程中的Fe的存在形态及δ56Fe值变化，揭示影响其变化的重要地球化学过程，并建立基于Fe同位素的端元模型估算该区域热液源Fe通量。本项目将为精确量化超慢速扩张洋脊热液源Fe的贡献提供重要的研究数据，并为完善大洋Fe的源/汇机制及地球化学循环过程做出贡献。

Iron (Fe) limits the growth of diazotroph and phytoplankton in 40% of global ocean, therefore the sources, sinks and biogeochemical cycling processes of Fe has been the frontier of ocean science studies. In recent years, the international scientific project GEOTRACES found out that the dissolved Fe (dFe) discharged from hydrothermal activity can transport to thousands of kilometers away, which becomes a potentially importance source of dFe in Open Ocean. Iron is a key parameter in the global climate model, therefore there is an urgent need to quantify the contribution of hydrothermal Fe in Open Ocean. Currently, the research on quantifying hydrothermal Fe discharged from ultra-slow spreading ridges is in general lacking, resulting in an overly underestimation of its contribution to global Fe budget. This project will use the trace metal-clean water sampling devices coupled with the ROV to collect fluid and water samples near the hydrothermal vents in western Indian Ocean. The speciation and isotope composition of Fe will be measured in those samples, along with environment physiochemical parameters, in order to determine the changes on Fe speciation and δ56Fe values during the mixing process between hydrothermal fluids and seawater. The important geochemical processes affecting the changes of Fe speciation and isotope composition will be revealed and the endmember model will be established to quantify the hydrothermal input in the study region. This project will provide important data to quantify hydrothermal Fe in ultra-slow spreading ridges, and contribute to the mechanism study of source, sink and geochemical cycling process of Fe in Open Ocean.