Seasonal sedimentary processes and the coarse fraction analysis in Sueste Bay, Fernando de Noronha, Pernambuco

Abstract

The Fernando de Noronha archipelago is top of an extinct volcanic mountain, has 21 volcanic islands and is located 540 km from Recife-PE, in the south equatorial Atlantic (4°S/32°W). Due to the building of a dam and a road, the main freshwater input to the mangrove and bay of Sueste has been drastically reduced in the last years, affecting the hydrology and morphodynamics of the beach. The objective of the research is to evaluate the analysis of the sandy fraction as a tool to refine the sedimentary data of surface sediments from Sueste bay system (beach, mangrove, lagoon, dune and bay), located in the southern coast of the main island. A collection of 146 surface sediments were sampled in seven seasonal field works in 2010/2011. The research methods included coarse fraction, grain-size, calcium carbonate, elemental and isotopic organic matter analysis. The samples are predominantly sandy, moderately well sorted and bioclastic, with high carbonate contents (>90% in 83.5% of the samples). The coarse fraction analysis indicated a spatial and temporal homogeneity of the grains, presenting predominantly the MB rate of 0.80-0.85 and indicating strong marine influence in the modern sedimentary processes, being mainly composed by fragments of mollusks, shells and corals. The general obtained data values show a strong marine influence in the sedimentary organic matter (C/N<12 e δ13C>-19‰PDB) and in the erosive character of the beach profiles.