Relative sea-level and climatic changes in the Amazon littoral during the last 500 years.

An integrated approach focused on sedimentology, geochemistry, palynology, C and N isotopes and radiocarbon dating of a sediment core from an herbaceous plain not flooded by tides of the Amapá littoral, near the Amazon River mouth, allowed identification of two phases with marine and terrestrial influences. Mangroves occurred over tidal mud flats with marine influence between > 5610–5470 and 470–310 cal yr BP. The absence of mangrove vegetation since 470–310 cal yr was followed by the transition of brackish water organic matter to terrestrial C 3 plants. Also, the geochemical data indicate a decrease in sea water influence during this last time interval. Likely, the displacement of mangrove forest to lower surfaces was caused by a relative sea-level fall that may be associated with drier conditions with less rainfall during the second part of the last millennium. As suggested by this work, slight relative sea-level fluctuations caused by regional or global climatic change may affect significantly the current mangrove area. [ABSTRACT FROM AUTHOR]