Input, particle reactivity, and (bio)geochemical cycling of the transition metals from subgroups IV, V, and VI (Ti-Zr-Hf, V-Nb-Ta, Cr-Mo-W) in the Atlantic

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The focus of this proposal is the marine geochemistry of the trace element groups Ti-Zr-Hf, V-Nb-Ta, and Cr-Mo-W, elements of which the behavior and processes in seawater are partly not well understood. However, they are of importance in the marine system either biologically (as micronutrients or microtoxins), or contribute to the formation of valuable ore deposits on the seafloor, such as ferromanganese nodules and crusts. Several of them also serve (especially via their isotopic signatures) as proxies for elemental sources into the ocean, water mass movements, or paleo redox conditions. Correspondingly, the impact of dust or riverine sources and subsequent (bio)geochemical cycling of the particle-reactive elements of the first two groups, and of different redox conditions in the oxygen minimum zone on the group of redox-sensitive elements (Cr, Mo, in contrast to W), will be investigated. Apart from the listed 9 elements, we will include Al (as a tracer for dust input), Fe (as a potential trace metal scavenger in the form of Fe oxyhydroxides), Y as a well characterized particle -reactive element, and U (to compare with the geochemically similar Mo) to interpret sources and cycling. The samples for the project were taken by trace-metal clean sampling of the water column at 17 CTD stations across the Atlantic during cruise M81/1. Apart from the determination of total concentrations, physical (dissolved – colloidal – particulate) and chemical speciation analyses (free ions, organic complexes, redox speciation) will be part of the work schedule.