A Pre-Feasibility Study of Isotopes for Investigation of Monsoon Dynamics

Abstract

Atmospheric moisture is an important component in the water cycle and its movement is controlled by sources and sinks of moisture and atmospheric dynamics. Major flux of moisture on the Indian subcontinent comes through southwest monsoon which transports large amount of moisture that arrives through Arabian Sea and Bay of Bengal branches. The process of tracking the journey of water molecules using stable isotopes of oxygen and hydrogen can lead to quantitative understanding of the involved physical processes because of the isotopic fractionation being proportional to the extent the process has advanced. In the present paper, stable isotope (d18O) of air moisture is used to identify spatial correlation in moisture variability between two stations in Indo-gangetic plains-Roorkee and Kanpur. The isotopic composition of water vapours has shown a good correlation in time domain in inferring monsoon signal which opens up a possibility to use isotopes in air moisture for monsoon studies. The isotopic composition of vapours associated with monsoon is always depleted in comparison to non-monsoon vapours; therefore, isotopes may be used to track movement of monsoon vapours. The extent of depletion in isotopic composition of moisture and period over this depletion are directly linked with monsoon strength. The isotopic composition of water in vapour shows similar effects as that observed in precipitation, i.e., with the increased strength of moisture content (similar to amount effect) isotopic composition of vapour depletes and the depletion increases with the distance away from the coast (continental effect).