Ecologia e paleoecologia de foraminíferos do holoceno na Baia de Guanabara, RJ

Abstract

This study aimed to contribute with ecological and paleoecological informations generated in the Guanabara Bay based on the distribution of benthic foraminifera assemblages. In this study were collected 30 samples of surface sediments along three transect distributed in the bay and one core of 6 m length extracted near to Ilha do Governador. In the surface samples were identified 30 genera and 52 species which the most constant species were Ammonia tepida e Bolivina translucens exhibit the major constancy. Marine species were identified in several stations indicating good efficiency of tidal landward transport. In the surface stations analyzed, 10 located around Ilha do Governador doesn`t contain foraminifera tests, perhaps as a result of sediment acidification caused by oil spill occurred at year 2000. The confinement index associated to cluster analysis and DCA indicated the presence of three influenced environmental sectors by COT and grain size. The first section between Copacabana Itaipú and Santos Dumont airport Ilha de Boa Viagem was the marine environment, the second section between Santos Dumont airport Ilha de Boa Viagem and Ilha do Governador Ilha de Paquetá São Gonçalo coast can be classified like a inferior estuarine environment or bay with great marine influence and a third section between Ilha do Governador Ilha de Paquetá São Gonçalo coast and the inner of the bay as the most confined environment. In the core were done 7 dating indicating an age approximately 5180±40 years BP. The dating also reveal that in the last years the sedimentation rate increase and could be related with the European colonization period. Were found 18 genera and 30 species of foraminifera which the most constant specie was Ammonia tepida followed by Buliminella elegantissima. The distribution pattern of this species occurred with higher abundance of B. elegantissima in most inferior portions from the core and major abundance of A. tepida in most superior portions. The confinement index combined with cluster analysis and isotopes curves showed that was a few oscillations in the input of marine water in that region. Isotope analysis of C13/C14 and O16/O18 doens`t followed usual inverse pattern in other studies, possibly influenced by the proximity with the coast. The cluster analysis indicated that in the last 5180 years BP the bay didn`t suffer large environmental variations, that means the west region of the bay even presenting modification through the years it was not sufficient to modify the characteristics of the confinement. Analysis in the distribution pattern of foraminiferal assemblages demonstrated to be efficient tools to the environmental and paleoenvironmental characterization of Guanabara Bay.