Assessing response of local moisture conditions in central Brazil tovariability in regional monsoon intensity using speleothem 87Sr/86Sr values

Delineating the controls on hydroclimate throughout Brazil is essential to assessing potential impact of global climate change on water resources and biogeography. An increasing number of monsoon reconstructions from delta O-18 records provide insight into variations in regional monsoon intensity over the last millennium. The strength, however, of delta O-18 as a proxy of regional climate limits its ability to reflect local conditions, highlighting the need for comparable reconstructions of local moisture conditions. Here, speleothem Sr-87/Sr-86 values are developed as a paleo-moisture proxy in central Brazil to complement existing delta O-8-based reconstructions of regional monsoon intensity. Speleothem Sr-87/Sr-86 values are resolved using laser ablation and conventional solution mass spectrometry at high resolution relative to existing (non-delta O-18-based) paleo-moisture reconstructions to allow comparisons of centennial variability in paleo-monsoon intensity and paleo-moisture conditions. Variations in speleothem Sr-87/Sr-86 values from Tamboril Cave are interpreted to reflect varying extents of water interaction with the carbonate host rock, with more interaction resulting in greater evolution of water isotope values from those initially acquired from the soil to those of the carbonate bedrock. Increasing speleothem Sr-87/Sr-86 values over the last millennium suggest progressively less interaction with the carbonate host rock likely resulting from higher infiltration rates, expected under wetter conditions. Increasingly wetter conditions over the last millennium are consistent with an overall trend of increasing monsoon intensity (decreasing delta O-18 values) preserved in many existing delta O-18 records from the region. Such a trend, however, is absent in delta O-18 records from our site (central Brazil) and Cristal Cave (southeast Brazil), suggesting the existence of divergent (relevant to delta O-18(precip)) shifts in the climate patterns within and outside the core monsoon region. (C) 2017 Elsevier B. V. All rights reserved.