NOAA/WDS Paleoclimatology - Tamboril Cave, Brazil 2000 Year Strontium and Oxygen Isotope Data

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 d18O records provide insight into variations in regional monsoon intensity over the last millennium. The strength, however, of d18O 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 87Sr/86Sr values are developed as a paleo-moisture proxy in central Brazil to complement existing d18O-based reconstructions of regional monsoon intensity. Speleothem 87Sr/86Sr values are resolved using laser ablation and conventional solution mass spectrometry at high resolution relative to existing (non-d18O-based) paleo-moisture reconstructions to allow comparisons of centennial variability in paleo-monsoon intensity and paleo-moisture conditions. Variations in speleothem 87Sr/86Sr 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 87Sr/86Sr 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 d18O values) preserved in many existing d18O records from the region. Such a trend, however, is absent in d18O records from our site (central Brazil) and Cristal Cave (southeast Brazil), suggesting the existence of divergent (relevant to d18Oprecip) shifts in the climate patterns within and outside the core monsoon region.