Holocene palaeoenvironmental reconstruction in northeastern Brazil inferred from pollen, charcoal and carbon isotope records

Soils in the Barreirinhas region, Maranhao State, were sampled for delta(13)C analysis and buried charcoal fragments in the soils were radiocarbon dated. Three soil profiles collected in forested areas around the Lagoa do Caco and one in a woody savanna (mixture of non-arboreal and arboreal species) located approximately 10 km southeast of the Lagoa were studied. A high-resolution pollen record was obtained from lake sediments, showing that forest vegetation was predominant in the area in the early Holocene. From approximately 10 000 C-14 yr BP the pollen spectrum gradually changed, suggesting the dominance of open savanna communities, these were transformed to a more forested landscape ( woody savanna) from approximately 7500 yr BP. The lake sediments also record evidence of fire ( indicated by buried charcoal particles at several soil depths) during the Holocene. The delta(13)C analysis of soil organic matter (SOM) indicates that from between approximately 10 000 yr BP and 9000 yr BP to similar to 4000 yr BP, a woody savanna prevailed at two sites around the lake, probably reflecting a drier climate. From similar to 4000 - 3000 yr BP to the present, the results indicate a moderate and progressive increase in arboreal vegetation around the lake as a result of the return to more humid climate conditions probably similar to the present-day. The carbon isotope results from the site located 10 km from the lake indicate the presence of an open vegetation from the early Holocene. In general, there is agreement between the palaeovegetation patterns inferred from the pollen and carbon isotope data. However, a much less uniform landscape, with a mosaic of different ecosystems at any given time, is inferred from the carbon isotope record