6000 years of monsoon-driven east–west antiphasing of northeastern Brazil vegetation

Northeastern Brazil (NEB) is characterized by irregular rainfall distribution and various vegetation types, such as the xerophilous Caatinga in the east, Cerrado and Amazon rainforests in the west. Sediment cores and speleothems show that the region was subjected to strong climatic changes during the Holocene. To reconstruct related vegetation responses and biomass burning, we present a synthetic review based on nine pollen published records covering the last 6000 years. Our regional environmental reconstructions reveal four intervals of changes, influenced by the position and intensity of an east-west moisture band across NEB, in phase with South America Summer Monsoon variability. Between 6.0 and 5.2 ka BP and 5.2–4.2 ka BP, changes in the distribution of the dry forest Caatinga, Cerrado and Amazon Forest were driven by oscillating precipitation in a general pattern dry western/moist eastern NEB. Similar changes amongst sites were correlated to their location either within or outside the moisture band. Between 4.2 and 2.6 ka BP, Caatinga expanded in the eastern NEB, while Cerrado and Amazon forests became established in western NEB. This vegetation shift matches the moist western/dry eastern NEB climate around 4.2 ka BP, consistent with TraCE-21k simulations and speleothem records. From 2.6 ka BP onwards, biomass burning observed under dry or wet conditions was related to a marked increase in anthropogenic activities. For the last 6000 years NEB's vegetation boundaries have been in phase with the summer insolation, the oscillations of the South America Summer Monsoon, and the positions of the convergence zones which delimited a band of moisture throughout specific location of NEB. Human activities were not found to be directly affected by the humidity gradient; instead, humans have relied on each biome's resources. Investigating the extent of climatic and human influences on NEB vegetation in the past is crucial to discussing the effectiveness of current conservation policies in the region. • Changes in NEB vegetation were driven by a precipitation gradient over the Holocene. • Position of the moisture band led to differences between coastal and inland areas. • Western Cerrado and eastern montane forests were sensitive to extreme dryness. • Changes in fire activity were often linked to human presence after 4.0 ka BP. • Human activities in the Cerrado and Caatinga do not follow regional moisture trends.