Palynological analysis of a sediment core obtained in Guanabara Bay, Rio de Janeiro, Brazil

Abstract

The sediment of a core collected about 2 km north of Paquetá Island, Guanabara Bay, was submitted to pollen analysis, in order to recognize the dynamics of the regional vegetation, and the anthropic influence. Radiocarbon dating of a sample next to the bottom of the core indicates an age of 4.210 ± 40 14 C yrs B.P (calibrated age). It was possible to establish four palynological zones. Starting at the bottom of the core, a decrease in palynomorph concentration, the presence of degraded pollen grains and spores, and the predominance of ombrophilous forest pollen grains were observed in the basal portion of Zone I. These data may indicate the presence of an exuberant Atlantic Forest, dominated by a marine regressive event. The concentration of well-preserved palynomorphs increased in Zone II, with the predominance of the ombrophilous forest vegetation also, and an expressive increase of hygrophytes, indicating more humid environmental conditions. Palynomorph concentration decreased again toward the top of Zone III, and the fi eld vegetation was predominant. In the upper Zone IV occurred a strong decrease in pollen and spore concentration, with predominance of fi eld vegetation also, and the appearance of exotic pollen grains, showing the anthropic influence at this time.

Spatial distribution of pollen grains and spores in surface sediments of Guanabara Bay, Rio de Janeiro, Brazil

“…According to Jackson (1990), pollen grains dispersed by animals tend to be deposited next to the plant source and are not adapted to dispersion by the wind. Barreto et al (2007) and Barth et al (2004) The largest percentages of exotic genera were observed mainly within the sector of the Bay entrance and in the Fundão Island. These regions were highly impacted by human activities.…”

O Histórico Das Intervenções Humanas Na Baía De Guanabara (Brasil) E O Registro Do Antropoceno Em Quatro Unidades Sedimentares

“…Essa camada apresenta variações de granulometria que indicam uma diminuição dos sedimentos depositados no fundo da baía e aumento relevante dos teores de matéria orgânica sedimentar, a partir de cerca de 1500, em plena "Pequena Idade do Gelo". Estes efeitos, foram considerados como marcos do início do Antropoceno na baía, juntamente com as alterações quali e quantitativas verificadas à época nos grupos polínicos estudados no testemunho T8 por Barreto et al (2007). 15-40.…”

Análise Palinológica e a Vegetação

“…Figura 7 Palinodiagrama de percentagem dos tipos de vegetação e grupos ecológicos reconhecidos em sedimentos de um testemunho da Baía de Guanabara (simplificado de Barreto et al, 2007).…”