Last millennium decoupling of the South American Summer Monsoon and local hydroclimate of central Brazil

Abstract

The South American Monsoon System is the dominant convective system over tropical South America during austral summer that is critical to a region heavily dependent on agricultural and hydroelectric production. An understanding of the controls on moisture conditions throughout Brazil is critical to assessing recurrent droughts and global climate change responses. An increasing number of monsoon reconstructions from δ¹⁸O records provide insight into last millennium variation of regional monsoon intensity. However, the relationship between past variations in monsoon intensity and local moisture conditions has yet to be investigated. In this study, we develop speleothem ⁸⁷Sr/⁸⁶Sr values as a paleo-moisture proxy from a cave site located in central Brazil. Increasing speleothem ⁸⁷Sr/⁸⁶Sr values and decreasing δ²³⁴U values over the last millennium indicate progressively wetter conditions. A similar trend in monsoon intensity is not evident in δ¹⁸O records from the region, suggesting that monsoon intensity is decoupled from the local moisture conditions through the late Holocene. The potential decoupling between the monsoon and local moisture conditions suggests that processes independent from those governing monsoon intensity may play a critical role in dictating moisture variability in the region.