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Holocene palaeoenvironmental reconstruction in norteastern Brazi inferred from polen,, charcoal and carboon isotope records

Laboratorio de 14,Centro de Energia Nuclear na Agricultura (CENA), Box 96, 1340-00, PiracicabalSP, Brazil; pessenda{at}cena.usp.br

M. P. Ledru

Institut de Recherche pour le Developpement IRD, Geosciences InstitutelUniversity of Sao Paulo, 05508-900, Sao PauloISP, Brazil; University of Montpellier 2, Institut des Sciences de lEvolution, CC 61, 34095 Montpellier cedex, France

S. E.MN. Gouveia,

Laboratorio de 14,Centro de Energia Nuclear na Agricultura (CENA), Box 96, 1340-00, PiracicabalSP, Brazil

R. Aravena

University of Waterloo, Waterloo Ontario N2L3GI, Canad

A. S. Ribeiro

Uiesae Federal de Sergipe, A racajulSE, Bazil

J. A. Bendashsollil

Laboratorio de 14,Centro de Energia Nuclear na Agricultura (CENA), Box 96, 1340-00, PiracicabalSP, Brazil

R. Boulet

IRD, Ins titu to de Geocien is Un iversidade de Sao Paulo, 05508-900., Sao PauloISP, Brazil

Soils in the Barreirinhas region, Maranhao State, were sampled for 613 C analysis and buried charcoal fragments in the soils were radiocarbon dated. Three soil profiles collected in forested areas around the Lagoa do Caqö 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 14C 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 613 C analysis of soil organic matter (SOM) indicates that from between approximately IO0000 yr BP and 9000 yr BP to -4000 yr BP, a woody savanna prevailed at two sites around the lake, probably reflecting a drier climate. From -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 agreernent 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.

Key Words: Pollen • lacustrine sediment • soil • carbon isotopes • charcoal • palaeovegetation • Holocene • northeastern Brazil

The Holocene, Vol. 15, No. 6, 812-820 (2005)
DOI: 10.1191/0959683605hl855ra


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