Tannin as a New Indicator of Paleomangrove Occurrence within an Amazonian Coastal Region

Three sediment cores, sampled from a (1) mangrove zone, (2) mangrove-varzea zone, and (3) varzea zone at the Marajo Island-Amazonian coastal region were studied to compare the pollen and the sedimentological signals with tannin concentrations in sediments accumulated during the last millennium. The integration of these data allowed the interpretation of mangrove paleoecology based on pollen content along stratigraphic sequences. Most stratigraphy of the cores indicated a direct relationship between Rhizophora mangle (red mangrove) pollen content and tannin content. Some stratigraphic intervals showed a high percentage of R. mangle pollen, which may be interpreted as the mangrove forest mainly being occupied by R. mangle. A decrease of tannin content suggests a decrease of R. mangle density or a late mangrove colonization. The spectrophotometric method using tannin concentrations, proposed in this paper and supported by pollen data, may be considered an additional tool for the paleoenvironmental reconstruction of mangrove areas and an innovative tool that will allow reduction of costs in the studies of paleomangrove environment identification. (AU)