Tannin as an indicator of paleomangrove in sediment cores from Amapa, Northern Brazil

Abstract

Two sediment cores sampled from a varzea (N 02 degrees 34'38 ', W 50 degrees 53'17 ') and mangrove area (N 02 degrees 35'59 ', W 50 degrees 52'08 ') in Amapa littoral, northern Brazil, were studied through pollen and spectrophotometric analysis in order to compare biological and chemical signals of mangrove vegetation recorded by sediments during the late Holocene. According to the pollen study, probably the core base (145-65 cm) of varzea vegetation accumulated sediments devoid of vegetation. Later, this site was dominated by herbaceous vegetation and it concluded with a varzea forest. Based on spectrophotometric analysis, this core did not present significant tannin concentrations. This is likely due to the mangrove absence during the vegetation development at this site. The core sampled from a mangrove area also presented a relationship between palaeovegetation and the sediment biogeochemistry. However, the mangrove core presented significant tannin content along the mangrove phases. Thus, this spectrophotometric method supported by the pollen data may be considered as a complementary tool to identify palaeomangrove deposits.