Modern sedimentary processes and the distribution of organic carbon and nitrogen in São Sebastião Channel (SP) and adjacent inner shelt

Abstract

The sedimentary distribution in São Sebastião Channel and adjacent inner shelf, evaluated through the granulometry and the sedimentary organic matter contents, indicates the presence of low values of organic carbon and nitrogen, associated to a small input of organic matter and the hydrodynamic behavior of the area. Higher contents in the São Sebastião Channel occurs due to anthropogenic inputs, associated to the domestic sewage and harbor activities in its central area. The hydrodynamic and the channel bottom topography, creates low energy areas, allowing the deposition of muds and a higher retention of organic matter. The west-southwestern section of inner shelf presents low contents of organic matter, which are associated with the bottom wave action, that reworks the sediments avoiding the preservation of organic contents. A lower organic input, due to incipient coastal drainage and the presence of oligotrophic water masses occurs in this region too. In the east-southeastem part ofinner shelfarea is observed the presence ofpelitic sediments and higher organic matter contents, due to the São Sebastião Island that acts as a physical barrier to the wave action and as a source ofmaterial. The Central Atlantic South Water (CASW) ingression may cause localized increase of organic nitrogen in the area.