The Importance of Iron Complexation to Organic Matter Preservation in Suboxic Sediments

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ABSTRACTOCE-9911364Unusually high organic carbon concentrations are found in sediments accumulating under suboxic water columns where the oxygen-deficient zone impinges on the continental shelf. Although several factors are believed to be responsible for these high concentrations and are a matter of ongoing debate, a mechanism to explain why a substantial fraction of sedimentary organic matter (OM) resists bacterial degradation only under suboxic water columns is still lacking. The PIs propose to study interactions between iron and OM in sediments from the Mexican coast to test their premise that the unusually high OM concentrations in sediments result from inner-sphere Fe-OM complexation and "refractorization" of the more labile OM. This scientific team believes that the complexation takes place because of the absence of significant amounts of kinetically faster competing species such as O2, NO3-, IO3-, Mn oxides and HS- in the sedimentary horizon where complexation takes place. Results from this study will prove or disprove whether this iron-complexation process indeed is a viable mechanism to explain the unusually high OM concentrations in sediments on the Mexican coast, as well as provide information on the kinetics of competing reactions (ie. O2, NO3-, IO3-, Mn oxides and HS-) leading to the speciation of Fe in oxic, suboxic and sulfidic sediments.