Selected organic matter source indicators in the Orinoco, Nile and Changjiang deltas

Abstract

Carbon isotopic composition, carbon to nitrogen ratios, carbon preference ( n-C 23 to n-C 32), and microscopic examination of selected samples were compared and contrasted as organic matter source indicators. The Orinoco, Nile, and Changjiang deltas were sampled and analyzed. The δ 13C of organic matter increased with distance offshore at all three locations. Organic carbon content decreased seaward on the Orinoco and Changjiang deltas but increased on the Nile delta. C/N ratios decreased regularly with distance offshore on the Orinoco delta, ranged from 10 to 25, and correlated positively with δ 13C OM. Estimations of the relative input of marine versus terrestrial organic matter to the sediments was dependent on the parameter analyzed. These discrepancies were primarily due to the definition of end-member compositions and the fraction of the total organic matter that is measured by a given parameter. Multiple-source indicators must be measured and integrated and end-members must be properly defined in order to obtain realistic input estimates.