The Effects of Animal-Sediment Interaction on Geochemical Processes Near the Sediment-Water Interface

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9314132 ALLER The activities of marine bottom-dwelling animals dramatically alter material transport and reaction distributions in surface sediments over much of the modern seafloor. It is the purpose of this research to continue to quantitatively examine and conceptualize the effect of these activities on the rates of diagenetic reactions, sediment-water solute exchange, and storage of organic or mineral phases in sedimentary deposits. A variety of field and laboratory observations demonstrate that particle reworking and irrigation activities of benthic fauna promote the remineralization of organic matter. Of the many simultaneous factors involved, two may be particularly important: (1) repetitive oscillation of redox conditions in the bioturbated zone, and (2) low metabolite build- up. Both factors likely decrease eventual storage of organic matter, or specific groups of organic compounds, in marine sediments. Experimental diffusion cells which mimic redox and diffusive transport conditions in the bioturbated zone will be used to further investigate these processes and test conceptual models of remineralization in surface sediments. Macrobenthic bioturbation also enhances the importance of secndary oxidants sucha s MN O2 and controls relative rates of coupled redox reactions in surface sediments. These cycles couple strongly with other elements, such as a variety of trace metals. Detailed experimental measures of Mn oxidation and reduction rates will be used simultaneously with measures of particle reworking, net fluxes, and solute profiles to develop a model of Mn cycling and associated redox balances in bioturbated deposits. The potential semipermeability of biogenic structures to components of the dissolved organic carbon pool (DOC) has major implications for models of sedimentary DOC distributions, microbial activity, and net sediment-water fluxes. Diffusion cell measurements will be performed to examine possible DOC fractionation across tube and b urrow walls. The long term goals of this research are a quantitative description (model) of the types of transport and reaction balances during early diagenesis and the exploration of the corresponding geochemical and ecological implications.