Distribution and Geochemical Cycling of Cerium and Cobalt inthe Upper Water Column

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This is a study of the oxidation and reduction chemistry of the trace elements Co and Ce in the upper marine water column to evaluate the role redox processes play in their geochemistries. Existing data suggest that both elements have similar upper water column distributions and undergo similar redox transformations analogous to Mn in seawater. Particularly, all three elements frequently exhibit surface concentration maxima. For Mn this has been partially attributed to a dynamic photochemical/microbial redox cycle, although the relative importance of redox and non-redox processes are not known. Measurements of redox and adsorption kinetics made at ambient levels in the field will be incorporated into an upper ocean scavenging model for these elements and compared with actual distributions to evaluate the importance of the redox reactions. Non-redox processes for Ce will be constrained by following its non-redox reactive neighbor lanthanides simultaneously. Ce and Co will be studied comparatively to determine how the role of Co as a biologically essential element (cf. Ce) influences its upper water column geochemistry and distribution.