Paleoclimatic and paleoenvironmental changes in Amazonian lowlands over the last three millennia

Abstract

The paleoclimatic and paleoenvironmental history of the Amazon basin over the last millennia and the behavior of the South American Monsoon System (SAMS) throughout the lowlands have not yet been thoroughly examined due to a lack of records from more central portions of the basin. Here we discuss these past changes based on new high-resolution δ18O and δ13C records from speleothems collected in the southwestern Amazon Basin, at the core region of the convective activity of the SAMS. We demonstrate that the δ18O from these new records is representative of SAMS variations and that this convective system provides distinct precipitation patterns over the basin. The SAMS was in a neutral phase with homogeneous precipitation between 1000 BCE and 300 CE, whereas drier conditions prevailed over the western side of the basin between 700 and 1200 CE and an east-west climatic dipole was established over the Amazon Basin after 1450 CE when wetter conditions prevailed over our study site. The speleothem δ13C record indicates an overall tendency toward a more humid tropical forest during the studied period, except for a drier period which correlates with the Medieval Climate Anomaly (MCA). The dynamics of pre-Columbian cultures from southwestern Amazonia seem to have been related to paleoclimatic and environmental changes reported for the region.