Holocene vegetation and climate changes in Brazil using carbon isotopes of soil organic matter and lacustrine sediment pollen analysis
by
Luiz Carlos Ruiz Pessenda
C-14 Laboratory - CENA/USP- Avenida Centenário no. 303, 13 416 -000 Piracicaba, SP, Brazil
Coauthors: Gouveia S.E.M. (C-14 Laboratory - Centre for Nuclear Energy in Agriculture-CENA, University of São Paulo-USP, Brazil), Ledru M.P. (IRD; University of Montpelier 2, France), Aravena R. (University of Waterloo, Canada), Boulet R. (IRD, France), Ribeiro A. S. (Federal University of Sergipe, Aracaju, Brazil), Bendassolli, J.A. (Stable Isotope Laboratory – CENA, USP, Brazil), Freitas H. A. (Stable Isotope Laboratory – CENA, USP, Brazil) and Vidotto, E . (Stable Isotope Laboratory – CENA, USP, Brazil).

Palaeoenvironmental reconstructions in the tropics have been carried out using a multidisciplinary approach and the results have provided new insights into regional palaeoclimatic settings. The use of carbon isotopes of soil organic matter and lacustrine sediment pollen analysis has proved to be effective in various areas of Brazil. During the early Holocene (10,000 yr BP) carbon isotopes point to a dominance of C4 plants (grasses) in southern and southeastern Brazil and an expansion of savanna over the forest (from ~9000 yr BP up to ~4000-3000 yr BP) in the northwestern/northern (Amazon region) and northeastern regions. These results were interpreted as the presence of a dry climate in the early - mid Holocene period. Between 10,000 and 7000 yr BP, the pollen record shows an open landscape everywhere in the tropics south of the equator except for southern and northeastern part of Minas Gerais State, southeastern Brazil, where two pollen records attest to an expansion of the moist and cold forest and carbon isotopes of SOM characterize the presence of a mixture of C3 and C4 plants. At Salitre, center western Minas Gerais, the cool rain forest progressively disappears in favor of a seasonal forest and an open landscape between 10,000 and 6000 yr BP and the same pattern at the same time period, a progressive change of rainforest to an arid landscape is also recorded at São Francisco Valley, Bahia State, northeastern Brazil. Two lacustrine records from the lowlands indicate a dry event at c. 5000 yr BP characterized by a sharp decrease in arboreal content replaced by pioneer species such as Piper at Carajás, Amazon region, and dry herbs of the Asteraceae and Apiaceae families at Salitre. Afterwards, progressive establishment of the modern vegetation is recorded until it became fully developed after 3000 yr BP.

Date received: October 28, 2004

Copyright © 2004 by the author(s). The author(s) of this document and the organizers of the conference have granted their consent to include this abstract in Atlas Conferences Inc. Document # caod-12.