Carbon and nitrogen stable isotopes compositions of organic matte in marine sediments cores from the abrolhos region: indicators of sources and preservation
Organic matter is an important source of information on the transport and consolidation processes of sediments. In this study, were utilized the isotopes of carbon and nitrogen (δ13C and δ15N), total organic carbon (TOC), total nitrogen, carbon/nitrogen (C/N) ratio and 13C-NMR to understand the origin and behavior of organic material in the Abrolhos region. Were analyzed nine sediment cores taken from a mangrove, a channel between the mainland and the coral reefs. The average value of the carbon/nitrogen ratio in the mangrove was 18, which characterizes purely terrigenous areas. For the reefs, the average value of the C/N ratio was 8,which is characteristic of marine and coastal regions. For the sediment cores taken from the channel, the average value of the C/N ratio was 10, a typical value of areas under the influence of mangroves. The mean values of δ13C were -26.9‰ for the mangrove, -20.7‰ for the channel region and -18.2‰ for the reefs. This variation is associated with the main source of organic matter, which in the mangrove is derived from vascular plants (mainly C3 metabolism), and for the reefs is derived from phytoplankton. The 13C-NMR results corroborate the results of isotopic and elemental analyses. The analyses of these cores indicates that the anthropogenic influence on the coast did not significantly alter the composition of the material that has been deposited in about the last 80 years in the region of study.
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