Cycling of Labile Intermediates at the Oxic/Anoxic Interface

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More than 90% of the organic carbon buried in marine sediments each year is found in sediments which are anoxic within a few centimeters of the sediment-water interface. In addition, the amount of organic carbon which is remineralized under anoxic conditions has been estimated to be between about 10% and almost 100% of the amount remineralized in oxic environments and anaerobic decomposition plays an important role in determining the quantity and chemical composition of the material which is ultimately buried. However, the effect of anoxic conditions on the decomposition rate of specific organic compounds is poorly understood. One environment in which we can study the relative importance of changes in turnover rate constant and changes in production rate to concentrations of organic compounds is the oxic/anoxic transition zone. The oxic/anoxic interface is a region of stratified microbiological populations, and of rapidly changing properties. This study will be one of the first to focus on the processes affecting the distribution and turnover of fermentation intermediates (hydrogen, acetate, propionate, low molecular weight amines) and of DOC near the oxic/anoxic interface, and will thus provide valuable information on sites of water column carbon regeneration in such systems. The results also will provide insights on how turnover rates of labile compounds vary within redox gradients, and whether variations in the turnover rates or in production rates are responsible for concentration maxima. When compared with microbiological data, the results will also provide qualitative information about the roles played by the different microbial populations in carbon turnover.