Distribution of organic carbon in sediments of the north western continental shelf of India

127-129Organic carbon in the sediments varies from 0.24 to 2.42 % (av. 0.95 %) which is far below the world average for the nearshore sediments. Fine grained terrigenous sediments of the shelf off Saurashtra coast and those in the inner shelf between Bombay and Port Dabhol are characterised by relatively high organic carbon content (> 1%); fine grained sediments of the inner shelf between Gulf of Cambay and the shelf between Indus canyon and Gulf of Kutch and the coarse grained carbonate relict sediments on the outer shelf are characterised by low organic carbon content (< 1%). Differences found in the organic carbon contents of the fine grained sediments of different regions can be traced mainly to the differences in the productivity of the overlying waters. Although in the outer shelf regions also, areas of high and low productivity are encountered, the low organic carbon content in these sediments appears to be due to a combination of several factors-coarse grained nature of the sediments, relatively low rate of sedimentation and lack of enough fine grained terrigenous material for the protection and preservation of organic matter in the sediments. The generally low organic carbon content recorded in this area when compared to world average for the shelf sediments, can be attributed to the oxidation because of high dissolved oxygen content of bottom water or grazing by zooplankton and other higher organisms