Speleothem-based reconstruction of Holocene changes in monsoonal patterns and environmental conditions in Central Brazil

Abstract

The east-west precipitation dipole that occurs in South America has been vastly investigated in previous studies using paleoclimate records from east and west of the continent, but the climate dynamics of central-eastern Brazil remains less understood. While δ18O values have been widely used to study past rainfall variability over South America, their ability to resolve local hydrological changes in central Brazil during the Holocene has been proven to be difficult. Recent studies in the region have used δ13C values and 87Sr/86Sr ratios from speleothems to assess local paleo-hydrology and environmental conditions. Here, we revisit this topic for the last 11,000 years based on a novel multi-proxy record (δ18O, δ13C, and 87Sr/86Sr) from a stalagmite collected in central Brazil at the northern side of the present day South Atlantic Convergence Zone (SACZ). The overall climate shifted from drier to wetter conditions throughout the Holocene, reflecting the increasing southern insolation and the monsoon-driven wetting trend based on the local and regional δ13C and pollen records. Changes in atmospheric circulation patterns during the Holocene might have been responsible for the increase in δ18O values through time. A north-eastern climate influence during the weaker monsoon phase from early-to-mid Holocene contrasts the late Holocene and present-day influence of SACZ over the area. Hence, a negative correlation between δ18O and δ13C indicates a decoupling of monsoon activity from local climate conditions. The Sr isotope signals in our site may be influenced by mixed lithology or increased dust input from nearby sandstone during drier periods, revealing the complexity of this proxy. The São Mateus record highlights the complex, non-stationary interplay between monsoon strength, SACZ dynamics, and atmospheric processes in shaping central Brazil's hydroclimate.