Collaborative Research: Influences of Atmospheric Deposition, Organic Complexation and Photochemical Processes on the Redox Cycle of Iron in Surface Waters

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ABSTRACTOCE-9911339OCE-0000351Phytoplankton productivity in high nutrient, low chlorophyll areas is limited by the bioavailability of iron. Iron uptake by marine microorganisms appears to be strongly influenced by the redox and solution speciation of dissolved Fe, yet very little is known about the physical-chemical processes such as photochemical reduction, colloid formation, and organic complexation that affect Fe chemistry and bioavailability in the oceans. For this reason, the principal investigators propose to undertake a set of process-oriented studies to investigate (1) the diel photochemical and thermochemical redox cycling of Fe in the upper 100 meters of the Gulf of Mexico (GOM); (2) the redox speciation of dissolved Fe supplied by wet (rainfall) and dry (aerosol) deposition, and the physical-chemical transformations that occur within the first few hours following deposition; and (3) the complexation and potential reduction of Fe(III) by colloidal and low molecular weight dissolved organic ligands in the open oligotrophic GOM, and including ligands from natural diatom blooms, harmful algae (dinoflagellate) blooms, and from riverine input of terrestrial aquatic organic ligands. It is expected that results from this study will further our understanding of the abiotic, inorganic processes regulating the distribution and speciation of Fe, as well as provide data required to model oceanic Fe cycling.