Dissolved Organic Carbon in Interstitial Waters from Sediments of Middle Valley, Leg 139

Abstract

High-temperature combustion oxidation measurements of nonvolatile dissolved organic carbon (DOC) have been determined for pore waters from sediments of Middle Valley, Ocean Drilling Program Leg 139, as well as for overlying and near-bottom seawater. The DOC values in the interstitial waters are generally greater than those in the overlying water column, ranging from 0.1 to 86 mg/L of carbon. Some of the profiles of DOC in the pore waters are similar to total organic carbon, total carbon, and total inorganic carbon profiles. At Site 855 the concentrations of DOC in interstitial waters generally decrease with depth. DOC maxima at shallow depths of Site 858 are probably enriched due to higher temperature alteration of organic matter. At Sites 856 and 857, besides the decreasing trend above, the DOC increases at greater depths, also due to the hydrothermal activity. The values of DOC correlate with MnO and MgO profiles in Hole 856B. The changes below 30 mbsf in the DOC depth profiles of Site 858 parallel those of the volatile hydrocarbon gases.