Pore waters and sediments were analysed in two gravity cores from the Cinarcik Basin and the southern shelf of the Marmara Sea. The sediments are organic-rich (1.1 and 1.3 wt% C(org)) and have been deposited at rates of 1.9 and 0.45 m/ka, respectively. The oxic+suboxic zone is 0.50-0.80 m thick and the sulphate-methane interface (SMI; defined here as the depth at which pore-water sulphates diminish below 1 mM) is 3.4 and 2.4 metres below sea floor (mbsf) in the southern shelf and Cinarcik Basin cores, respectively. Changes in the phosphate and ammonium gradients suggest that the sulphate reduction occurs by simple microbial organic matter degradation. Steep sulphate gradients at both sites may suggest that a part of the sulphate reduction may occur by anaerobic methane oxidation.