A positive 'amount effect' in the Sahayadri (Western Ghats) rainfall

We present stable oxygen isotopic ratios (δ18O) of rainfall collected over three years (July to October 2000-02) at Mangalore. We observe an apparent positive correlation between the monthly, amount-weighted mean oxygen isotopic ratio of the rainwater and monthly total rainfall, contrary to the generally expected negative trend in many island and continental stations. We offer an explanation for this observation and propose that the 'amount effect' in the annual rainfall still remains with a negative slope, and thus can be useful in palaeomonsoon reconstruction using oxygen isotopic variations of annually laminated speleothems.