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

We report here the first delta O-18 and delta D 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 delta O-18 values indeed exhibit a significant negative correlation with the amount of rain recorded at a nearby (<10 km) meteorological station. Changes in delta O-18 and delta D 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 similar to 10 parts per thousand during the initial phase to similar to 30 parts per thousand 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.