Oceanographic parameters in continental margin of the State of Ceará (northeastern Brazil) deduced from C and O isotopes in foraminifers

Abstract

Specimens of Recent foraminifera of Amphistegina radiata, Peneroplis planatus and Globigerinoides ruber, from fifty samples of surface sediments of the continental margin of the State of Ceará, Brazil, have been analyzed for carbon and oxygen isotopes to investigate oceanographic parameters and determine the values of δ18O of the oceanic water. From a comparison between values of δ18O obtained for ocean water using the linear equations by (Craig and Gordon 1965) and the one by Wolff et al. (1998), it became evident that the former yielded a more reliable value (0.2◦/◦◦ SMOW) than the latter. Lower values of δ18O for the ocean water in this continental margin resulted from continental water influence. Values of 18O (−0.3◦/◦◦ to −1.5◦/◦◦ PDB for benthic foraminifera and −0.6◦/◦◦ to −2.4◦/◦◦ PDB for planktic foraminifera), attest to a variation of temperatures of oceanic water masses, in average, between 20 to 22◦C in deep water and 24 to 27◦C, in surface water. Values of δ13C from +3.2◦/◦◦ to −0.2◦/◦◦ PDB (benthic foraminifera) reflect a variation in the apparent oxygen utilization (AOU) in the continental margin and indicate that the environments of bacteriological decomposition of organic matter are not continuous along the investigated area.