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

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 δ 18 O 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 δ 13 C values and 87 Sr/ 86 Sr 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 (δ 18 O, δ 13 C, and 87 Sr/ 86 Sr) 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 δ 13 C and pollen records. Changes in atmospheric circulation patterns during the Holocene might have been responsible for the increase in δ 18 O 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 δ 18 O and δ 13 C 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. • Holocene high-resolution multi-proxy speleothem record for central-eastern Brazil. • δ 18 O values track long-term shift in moisture source and large-scale climate patterns. • Combination of δ 13 C, δ 18 O, 87 Sr/ 86 Sr enables disentangling local from regional signals. • Mid-Holocene pronounced dry-to-wet transition led by strengthened SASM–SACZ system.