CHARCOAL DEPOSITION RELATED TO PAEOENVIRONMENTAL CHANGES AND LAND USE CHANGES EVENTS

Fires records were obtained through the charcoal particles flux analyses in lacustrine sediments (Lagoa da Pata, São Gabriel da Cachoeira (AM); Carajás N4, (PA); Dom Helvecio Lake (MG) and Caracarana (RO); resevoir sediment (Alta Floresta, MT), and an annual cicle of atmospheric deposition (Porto Velho, RO). The charcoal analyses could have also a great importance in evaluating the impact of dry climates in different tropical ecosystems. Determination of fire frequencies and dimensions in key areas of South America, during the Holocene, is a first step to understand the global carbon transference between terrestrial and atmospheric systems. The deposition of charcoals in the sediments results from local or regional burns, caused by dry climates, associated or not to anthropogenic action. The highest charcoal fluxes values were obtained in the period of intense land use change in Alta Floresta and in sediments that represent the medium Holocene in Serra Sul Carajás region. The lowest values were found in Lagoa da Pata in São Gabriel da Cachoeira, a humid region in Amazon and in Porto Velho region from atmospheric deposition in a humid season. We observed from the D. Helvécio record, which is located in a region covered with semi-decidual forests, fire occurrences from 8,400 to 6,400 cal years BP. For Carajás record, surrounded by tropical rain forest, we had identified fires during the period between 8,000 and 5,300 cal years BP. Finally, the Caracaranã record, which is surrounded by grass savanna, showed a 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. In the Lagoa da Pata record an increase in charcoal fluxes were observed at Last Glacial maximum. The synchronism among the fires occurrences showed a good relation with the middle Holocene dry climate phase in Brazil. Discrepancy in the flux values could be attributed to differences in biomass availability provided by these ecoystems and paleofire intensity.