Monsoon reconstruction from radiocarbon dated tropical Indian speleothems

Abstract

The potential of tropical speleothems as a climate proxy has been investigated. Amplitudes of ¹⁸0 and 8¹³C variations are found to be large and are likely to be primarily controlled by past rainfall. Contribution from past temperature variations seems to be relatively small. The amount effect in rainfall has been observed and quantified by analysing rainwater samples collected during a monsoon season. A tentative chronology to these speleothems is asssigned by the ¹⁴C radiometric dating method. Assuming that the variations in the ¹⁸0 of cave carbonates are solely due to the past variations in rainfall, a history of the latter has been reconstructed. A high-resolution rainfall reconstruction up to the last ~3400 years is now available from Gupteswar cave, Orissa, subject to validation of dates by the U-Th method. It is observed that in a tropical speleothem 5¹³C is dominantly controlled by rainfall. The study has shown that tropical Indian speleothems faithfully record the annual (~monsoon) rainfall in the cave site.