Metal-sulfide speciation and cluster formation at deep-sea hydrothermal vents

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Abstract (0424789) - LutherThis project for the Ridge 2000 Postdoctoral Fellowship is an investigation of zinc (Zn),iron (Fe), and sulfide speciation at hydrothermal vents and the mechanisms of metal-sulfide cluster formation at these extreme environments. The approach is based on previous observations at hydrothermal vents of the East Pacific Rise that biological community structure is a function of sulfide and Fe speciation. Sulfide speciation is expected to influence the distribution of organisms at other hydrothermal vent locations such as the Lau Basin. High concentrations of Zn have been measured in vent fluid at the East Lau Spreading Center of the Lau Basin. Because Zn binds to sulfide faster than Fe, Zn is expected to play a key role in sulfide speciation at vents in the Lau Basin. In waters surrounding hydrothermal vents, metals such as Fe and Zn can form clusters with sulfide. These soluble clusters are multinuclear complexes that are stable at concentrations of micromolar or lower. They are likely to serve as building blocks for particles and minerals. Because FeS cluster have been measured at East Pacific Rise vents, ZnS clusters are expected to form at Lau Basin vent habitats. ZnS clusters are particularly stable in aquatic environments; however, much remains unknown concerning the mechanisms of ZnS cluster formation, cluster structure and stability at vent locations.The hypothesis to be tested is chemosynthetic organisms do not thrive near diffuse flowvent waters where metal-sulfide clusters dominate sulfide speciation. In order to betterunderstand metal-sulfide speciation and biological communities at vent habitats, this project will focus on the following objectives: (1) comparison of sulfide and metal speciation in vent diffuse flow regions at the two vent locations; (2) correlation between Zn-sulfide speciation and vent community structure at the Lau Basin site, and (3) assessment of physicochemical conditions that determine ZnS cluster structure, stability and reactivity at vent locations. These objectives will be achieved through a combination of field and laboratory studies. Field studies will focus on vents in the area between 9 degrees 49' and 9 degrees 51'N at the East Pacific Rise and vents at the Valu Fa Ridge in the Lau Basin. Sulfide and metal speciation will be measured by previously established in-situ voltammetric methods. To complement field observations, a series of laboratory studies will attempt to elucidate the mechanism of ZnS cluster formation and cluster structure at these vent habitats. Additional studies are proposed to investigate the reactivity of ZnS clusters with other competing metals and with natural organic matter. This research will have broader impacts by fostering interdisciplinary research andCollaborations. The fellowship will provide a unique opportunity to a postdoctoral fellow who is new to ridge crest science but has research experience in metal-sulfide geochemistry. This research will also contribute to fundamental knowledge of metal and sulfide chemistry in other aquatic systems. Outcomes of this research are expected to have implications for trace metal sulfide biogeochemistry in a variety of aquatic environments ranging from marine sediments to municipal wastewater.