Late Holocene mangrove dynamics of Marajo Island in Amazonia, northern Brazil

Two sediment cores from the eastern coastal region of Marajo Island, Para State, northern Brazil have been studied by pollen analysis to reconstruct late Holocene mangrove dynamics and environmental changes. Seven AMS radiocarbon dates provide time control. Mangrove vegetation became established at the Barra Velha site at about 2750 B.P. (2880 cal B.P.) and at the Praia do Pesqueiro, site at about 650 B.P. (670 cal B.P.). Rhizophora was the dominant mangrove tree throughout the recorded period, while Avicennia and Laguncularia were rare. Existing remnants of the former coastal Amazon rain forest were replaced by mangrove in the Barra Velha area between about 2750 and 740 B.P. (2880-760 cal B.P.) and at Praia do Pesqueiro area between about 650 and 530 B.P. (670-540 cal B.P.), suggesting a rise in relative sea level or, alternatively, an increase in discharge from the river Amazon. Areas of coastal shrub and herb vegetation, the so-called restinga vegetation, also became slightly reduced during the late Holocene. The largest area of mangrove at the two sites suggests that the highest sea level was probably reached during the last 200-250 years. The only evidence of human activity at the two sites is an indication of cattle pastureland at the Barra Velha area during the last decades.