Amount dependency of monsoon rainfall δ18O on multiple time scales: observations from south western India

Abstract

Paleoclimatic interpretation of stable isotope based proxies from India is complex due to lack of local amount effect (negative relation between rainfall and its heavy isotopic content observed over tropics) in most places. Recent studies revealed that regional or upstream rainfall/ convective activity plays a major role on daily rainfall δ18O variability. Here we extensively analyze the isotopic variability of Indian Summer Monsoon (ISM) rainfall of south western peninsular India. ISM rainfall δ18O of south western coast of India show significant correlation with the upstream convective activity and the associated rainfall over eastern Arabian Sea on daily, monthly and yearly time scales. A comparative dry–wet–dry (wet–dry–wet) rainfall pattern is observed over north eastern India, peninsular India and the equatorial Indian Ocean during the occurrence of low (high) values of rainfall δ18O at south western coast of India on all time scales. Thus the ISM rainfall δ18O of south western India captures not only the local or upstream convective activities, but reflects the rainfall pattern of a large domain including the Indian subcontinent and Indian Ocean. 18O variations of climatic proxies from south western coast of India can be thus better interpreted in terms of these results.