Dissolved organic carbon (DOC) in marine interstitial waters has been extensively studied in surficial sediments. These studies, conducted on short cores at the centimeter scale, have led to important conclusions regarding the role of DOC in carbon remineralization, nutrient recycling, and dissolved metal complexation in marine sediments (reviewed in Burdige, 2002). The pool of DOC comprises a heterogeneous assemblage of organic molecules that vary greatly in their composition and molecular weight. The concentration of DOC in sediments is higher than DOC concentrations in the overlying water column, indicating that DOC is produced in the sediments from the degradation of particulate organic carbon (POC). Diagenesis sequentially produces more and more refractory organic material, and size fractionation studies indicate that the refractory products of diagenesis are of relatively low molecular weight (Amon and Benner, 1994; Benner et al., 1992). Although the measurement of DOC as a bulk property can indicate metabolic activity, it does not distinguish between the individual components, or even classes of organic matter.