HR: 17:30h
AN: B44C-07    [Abstracts]
TI: Holocene Charcoal Deposition From Brazilian Forest Fires
AU: * Turcq, B
EM: bturcq@geoq.uff.br
AF: IRD, Programa de GeoquĦmica, UFF, Morro do Valonguinho s/n, Niteroi, RJ 24020-007 Brazil
AU: Cordeiro, R C
EM: rccordeiro@geoq.uff.br
AF: Departamento de GeoquĦmica, Universidade Federal Fluminense, Morro do Valonguinho s/n, Niteroi, RJ 24020-007 Brazil
AU: Albuquerque, A S
EM: analuspa@uol.com.br
AF: Departamento de GeoquĦmica, Universidade Federal Fluminense, Morro do Valonguinho s/n, Niteroi, RJ 24020-007 Brazil
AU: Simoes, F L
EM: flamego@ird.gov.br
AF: Instituto de Radioprotecao e Dosimetria, Avenida Salvador Allende s/n Jacarepagua, Rio de Janeiro, RJ 22780-160 Brazil
AU: SIFEDDINE, A
EM: abdel.sifeddine@bondy.ird.fr
AF: IRD Centre d'Ile de France, 32 avenue Henri varagnat, Bondy cedex, 93143 France
AB: Determination of charcoal accumulation rate in lacustrine sediments allows to reconstruct the fire history of the region surrounding the lake. Our studies have been achieved in three Amazonian sites and one site in Atlantic rainforest. Charcoal fragments are identified and counted under a microscope. Typical size of these charcoals is around ten micrometers and they probably have been subject to eolian transport. The highest charcoal accumulation rates were obtained in sediments from Middle Holocene in Caraj s region, eastern Amazonia. These rates are on the same order than the present day charcoal accumulation rate in Alta Floresta, a region of Amazonia which is being submited to intense slash and burn. The lowest values were found in Lagoa da Pata in Sao Gabriel da Cachoeira, a very humid area in western Amazon. We observed from the D. Helv‚cio record, in the Atlantic rainforest, fire occurrences from 8,400 to 6,400 cal years BP. For Caraj s lake, surrounded by tropical rain forest, we had identified fires during the period between 8,000 and 5,300 cal years BP. Finally, the lake Caracarana, which is surrounded by grass savanna, showed a record of main fire occurrence phase at 9,750 cal yrs BP and a second phase marked by charcoal peaks at 7,680, 6,990 and 6,460 cal yrs BP. The synchronism of the fire occurrence periods in different Brazilian regions is related to the Middle Holocene dry climate phase provoked by the low summer insolation. Differences in the accumulation rates can be attributed to differences in biomass availability and fire return time. The carbon released in the atmosphere by this fires must have contributed to the observed increase of CO2, poorer in 13C, during the middle Holocene.
DE: 9360 South America
DE: 9604 Cenozoic
DE: 3344 Paleoclimatology
DE: 1815 Erosion and sedimentation
DE: 1615 Biogeochemical processes (4805)
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting