Geochemical Implications of Summer Monsoonal Rainwater Composition over India

Abstract

Rainwater was sampled from ten coastal and inland stations over India during the entire monsoon period of 1975. Major sea salt constituents were analytically determined. Sea salt deposition values based on the sodium content are presented for each station. It is estimated that during a monsoon period some 4 000 000 tons of sea salt is likely to be transported into the country. With the exception of calcium, the overall seasonal proportions of sea salt constituents in coastal rainwater indicate either minor or no differences as compared with the composition of seawater. A high excess of calcium has been found in all rainwater samples. Average excess at the coast is found to be 400–1000% over that expected on the basis of the sodium content. The calcium is uniformly distributed over the country with average concentration of 1.1 mg 1⁻¹ for the present network of sampling stations. It is proposed that the excess calcium is predominantly of desert origin and is mostly from Arabia and/or Iran. Excesses of potassium and sulfate and depletion of chloride have been observed in inland rainwater. The two excesses are believed to be of local continental origin.