Collaborative Research (USC/Caltech): Evaluation of Opal Dissolution Kinetics and Factors That May Regulate Opal Accumulation in Margin Sediments

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ABSTRACTOCE - 0351169 / OCE - 0351498The marine biogeochemical cycles of carbon and silicon are directly linked through the activities of diatoms, so the behavior of the carbon cycle cannot be predicted without a firm understanding of what factors regulate the oceanic Si budget. It is clear that Si removal from the ocean occurs primarily through opal (bSi = biogenic silica) burial, and several algorithms that relate bSi burial to bSi rain rate have been proposed, based on observations in deep sea environments. Unfortunately, these algorithms have limited utility because we do not have a mechanistic understanding of the factors linking bSi dissolution to the bSi rain reaching the seabed, and because they fail to work in margin environments. Margin environments have recently been recognized as the sink for 30-45% of the bSi buried in the entire ocean. The relative rates of sediment accumulation and the kinetics of bSi interaction with aluminosilicates appear to be critical factors that regulate bSi dissolution, although other factors may play a role.In this study, researchers at the University of Southern California and the California Institute of Technology will use a relatively new technique, stirred flow reactors, to measure the kinetics of bSi dissolution and Al release from margin sediments, in an effort to evaluate how these factors may govern bSi burial. Measurements will be made on freshly collected samples (planktonic material, particles falling into traps, and the sediments) representing the entire particle export pathway in two California borderland basins. Results will be compared with kinetics deduced from modeling pore water profiles of silicic acid and dissolved Al. The goal is to develop an algorithm based on readily measured characteristics of sediments that will provide a reliable measure of bSi burial susceptibility. This information will be of value for interpreting the significance of the bSi sedimentary record and for developing biogeochemical models that incorporate the effect of the Si cycle on carbon dynamics. The project will also provide for the support and training of graduate and undergraduate students.