Late Pleistocene and Holocene vegetation changes in northeastern Brazil determined from carbon isotopes and charcoal records in soils

Abstract

Northeastern Brazil represents a strategic area in terms of Quaternary records of environmental changes in South America due to its distinct semi-arid climate in near equatorial latitudes. In this study, carbon isotope and charcoal distribution records in soils are used to characterize vegetation dynamics, forest fires and their relation to climate change since the Late Pleistocene in the States of Ceará, Piauí and Paraíba, Northeastern Brazil. At the Ceará site, the carbon isotope record showed an enrichment trend from −24‰ to −19‰ during the early-mid Holocene, indicating an opening of vegetation and expansion of savanna vegetation (C 4 plants) during this period. A trend toward more depleted δ 13C values (~− 32‰) in the late Holocene indicates an expansion of forest vegetation (C 3 plants). A similar trend is observed at the Piauí and Paraíba sites where values of ~− 24‰ are associated with open forest vegetation during the late Pleistocene. In the early-mid Holocene, δ 13C values of up to −18.0‰ suggest the expansion of C 4 plants. Based on the carbon isotope data, it is postulated that from ~ 18,000 cal yr B.P. to ~ 11,800 cal yr B.P.–~ 10,000 cal yr B.P. arboreal vegetation was dominant in northeastern Brazil and is associated with humid climates. The savanna expanded from ~ 10,000 cal yr B.P. to ~ 4500–3200 cal yr B.P. due to a less humid/drier climatic phase, also supported by the significant presence of fires (charcoal fragments in the soil). From approximately 3200–2000 cal yr B.P. to the present, carbon isotope records suggest forest expansion and a more humid phase. These results form part of a regional pattern since they are in agreement with paleovegetation records obtained in regions of Maranhão, northeastern Brazil and in the Amazon and Rondonia States, northern Brazil.