Characteristics of the sedimentary organic matter on the inner and middle continental shelf between Guanabara Bay and Sمo Francisco do Sul, southeastern Brazilian margin

A total of 111 Petersen grab sediment samples, collected during two cruises in 1991 and 1993, on the inner and middle continental shelf between Guanabara Bay and São Francisco do Sul, on the southeastern Brazilian margin, were analyzed for the purpose of understanding the nature and distribution of the organic matter in the surface sediments. The analysis of the distribution of the different parameters related to the organic matter revealed the existence of an important distinction between the sediments to the south and to the north of the São Sebastião Island. Six sedimentary zones characterized by different mean values of the organic matter parameters can be identified. The analysis of the δ13C and C/N ratios distribution suggest an increasing contribution of land derived organic matter toward the north. The distribution of the organic matter in the area can be explained qualitatively by a model of water mass dynamics, which acts over the southeastern shelf of Brazil.