Organic carbon distribution in the surface sediments of the Sea of Marmara and its control by the inflows from adjacent water masses

Abstract

The organic carbon contents and textural composition of a total of 166 surficial sediment samples (from 10 to 1226 m water depths) together with data on primary productivity rates and dissolved oxygen concentrations have been studied to investigate the main controls on the distribution of organic carbon buried within the modern sediments across the Sea of Marmara. The distribution of average annual primary production rates in the Sea of Marmara exhibits great lateral variations; the highest values are calculated for the southern shelf (161 gCm −2 year −1), the areas with high terrigenous input supplied by the southerly major rivers, and on the northeastern shelf (104 gCm −2 year −1) where organic- and nutrient-rich surface inflow from the Black Sea is prominent. The low primary productivities estimated for the southwestern shelfof the Sea of Marmara (64 gCm −2 year −1) suggest influences from the relatively organic- and nutrient-poor subsurface inflow from the Aegean or Mediterranean. Organic carbon contents in sediments from the northeastern (0.37–2.16%), northern (0.57–1.64%), southern (0.44–1.90%) and southwestern shelf regions (0.37–1.51%) all appear to be within the same range and show no direct relationship with surface productivity and oxygen deficiency in the Sea of Marmara. Production and accumulation of organic matter in the Sea of Marmara are believed to have been mostly affected by the inflow of relatively organic-rich Black Sea waters, by the southerly major rivers, and by inflow of organic-poor Aegean or Mediterranean waters. Lateral offshore transport in surface waters must have resulted in the decrease of organic carbon fluxes to the sediments.