Dissolved organic carbon concentrations in marine pore waters determined by high-temperature oxidation

We have developed sampling methods and an analytical system to determine the concentration of dissolved organic C (DOC) in marine pore waters. Our analytical approach is a modification of recently developed high-temperature, Pt-catalyzed oxidation methods; it uses Chromatographic trapping of the DOC-derived CO,, followed by reduction to CH, and flame ionization detection. Sampling experiments with nearshore sediments indicate that pore-water separation by whole-core squeezing causes artificially elevated DOC concentrations, while pore-water recovery by sectioning and centrifugation does not appear to introduce DOC artifacts. Results from a set of northwestern Atlantic continental slope cores suggest that net DOC production accounts for>50 % of the organic C that is recycled at the sediment-water interface. Dissolved organic C (DOC) is an abundant, but poorly understood component of the pore waters of marine sediments. Previous pore-water studies of both deep-sea and nearshore locations consistently found high concentra-tions of DOC in the top few centimeters of the sediments (e.g. Suess et al. 1980; Sholkovitz and Mann 1984; Heggie et al. 1986,1987). The measured interfacial DOC gradients deter-mined in these studies ranged from a mini-mum of 50 % of the gradient of metabolically derived dissolved inorganic C (DIC) in a near-shore location to>5 times the DIC gradient in sediments of the northwest Atlantic conti-nental rise. If these measurements are correct and if the effective diffusivity of pore-water DOC is even 10 % of that of DIC (e.g. Mackin 1986; Cornel et al. 1986; Burdige et al. 1992), then DOC must be a quantitatively significan