THE FLUORESCENCE OF DISSOLVED ORGANIC-MATTER IN POREWATERS OF MARINE-SEDIMENTS

The fluorescence of porewaters from marine sediment cores from six dif ferent areas was measured. In most cases, fluorescence was affected pr imarily by the diagenesis of organic carbon first through sulfate redu ction and subsequently by methane generation. Typically, fluorescence, dissolved organic carbon (DOC), absorbance, alkalinity, and ammonium ion concentrations correlate quite well, increasing in the upper secti ons of anoxic sediments and co-varying in deeper sections of these cor es. The good correlation of DOC with fluorescence in the three cores i n which DOC was measured indicates that fluorescence can be used to ma ke a first order estimate of DOC concentration in anoxic porewaters. D ata are consistent with a model in which labile organic matter in the sediments is broken down by sulfur reducing bacteria to low molecular weight monomers. These monomers are either remineralized to CO2 or pol ymerize to form dissolved, fluorescent, high molecular weight molecule s. The few exceptions to this model involve hydrothermally generated h ydrocarbons that are formed in situ in the Guaymas Basin or are horizo ntally advected along the decollement in the Nankai Trench.