Stable Oxygen and Hydrogen Isotopes in Drip and Rain Waters at the Belum Cave,Andhra Pradesh,India

We report here the first δ¹⁸O and δD measurements of cave drip water collected during 2007-2009 and 2011 CE from the Belum Cave, peninsular India. Stalagmites found here have a great potential for providing monsoon reconstruction for hundreds of thousands of years. Rain samples were also collected from the top of the Belum Cave from May 2010 to Jan 2011 CE; their δ¹⁸O values indeed exhibit a significant negative correlation with the amount of rain recorded at a nearby (<10 km) meteorological station. Changes in δ¹⁸O and δD values of drip water samples confirm that the cave drip water do respond to the amount-dependent isotopic changes in local precipitation. The d-excess values of the rain water samples shift from ~10‰ during the initial phase to ~30‰ during the final phase of the southwest monsoon, indicating varying humidity at the surface boundary layer of the Northern Indian Ocean, and also a significant mixing of evapo-transpired vapour with the incoming marine vapour in the latter phase.