Environmental changes recorded in last 5,000 years in Guanabara Bay (RJ - Brazil) based on foraminifera and Stable Isotopes

Abstract

This study aimed to identify Holocene paleoenvironmental changes in Guanabara Bay through the foraminifera assemblages associated with isotopes A. tepidaδ13C and A. tepidaδ18O . Seven absolute datings (C14) at the core BG28 (5.8 m) indicate the age of ± 5200 years B.P. Along the stratigraphic column were identified 18 genera and 30 species of foraminifera. The most constant species were Ammonia tepida and Buliminella elegantissima demonstrating environmental characteristics confined in the region. However, the occurrence of oceanic species in some intervals associated with the values of A. tepidaδ18O indicated the existence of five events of environmental changes in the bay. Two most influential events of the ocean water (5130 ± 40 years / 4763 ± 40 and 4522 ± 40 years / 3586 ± 40 years BP) are characterized by the occurrence of Buccella frigida, Bulimina patagonica, Fursenkoina pontoni, Nonionella opima, Oolina vilardeboana and Uvigerina striatula and more negative values of A. tepidaδ18O . Two other reduction events in the marine water supply (4728 ± 40 years / 4608 ± 40 years BP and 3001 ± 40 years / 2136 ± 40 years BP) that have been related to the occurrence of indicator species of environmental stress as Ammonia tepida, Buliminella elegantissima and Cribroelphidium excavatum, associated with the most positive values of A. tepidaδ18O . And the last event occurred from 1335 ± 40 B.P. until the recent demonstrated the stabilization of the bay.