Changes in organic matter from surface waters to continental slope sediments off the Sao Francisco River, eastern Brazil

Suspended matter, settling particles and sediments from the continental margin off the Sao Francisco, the largest river of eastern Brazil, were analyzed for amino acids, hexosamines and carbohydrates. Their concentrations and spectral distributions are comparable to those observed in other marine regions and exhibit variations which are related to the degree of dilution with lithogenic material. Preferential degradation and transformation of organic constituents within the water column during settling affect the nature and quantity of organic matter. The variations in the amino acid spectra indicate that high bottom water oxygen contents and low sedimentation rates are the factors responsible for severe degradation of organic matter at the sediment-water interface. (C) 1999 Elsevier Science B.V. All rights reserved.