Neogene climate evolution in Amazonia and the Brazilian Northeast

Climate change follows from the interaction between global atmospheric and oceanic processes with regional processes. In this chapter we review which factors determined climate evolution in Amazonia and the Brazilian Northeast and present a recompilation of Neogene palynological and paleobotanical records. These records suggest generally warm and humid conditions throughout this region during the Neogene. The uplift of the Andes, in the western half of South America, created a pattern of intense orographic precipitation in Western Amazonia that derived from humid air masses of Atlantic origin. During this time interval uplift of the Borborema Plateau, in the northern Brazilian Highlands, also formed an orographic barrier that allowed the development of a lush forest on the Atlantic side (Mata Atlantica), while rain shadow on the western flank gave place to the semi-arid Caatinga vegetation. The arid conditions in the Brazilian Northeast were further exacerbated by the evolution of the oceanic current system in the Atlantic, a system that was also responsible for the creation of the Namib Desert. The palynological and paleobotanical data illustrate the long history of Amazonia’s tropical forest, but also the influence of the Andes formation on this region. The limited paleobotanical remains from the Brazilian Northeast tentatively point at longstanding humid conditions that, in the latter part of the Neogene transformed into the predominantly arid conditions that characterize the area at present.