Hydrogen and oxygen isotopic compositions of water vapor over the Bay of Bengal during monsoon

Abstract

δDv and δ18Ov of ~70 water vapor samples collected at 6 and 25 m above sea level over the Bay of Bengal (BoB) during July-August 2012 are reported. This helps characterize the isotopic signature of monsoon vapor. No significant vertical variation is observed in δDv, δ18Ov, or deuterium excess (defined as δD-8δ18O); δDv and δ18Ov are significantly correlated (r = 0.92) at each height; the deuterium excess values do not, because the variation of δDv and δ18Ov relative to their uncertainties is much larger than that of the latter. The temporal variations of δDv and δ18Ov correlate well with air temperature rather than sea surface temperature. The control of normalized humidity on deuterium excess is less prominent. While the distribution of water vapor isotopologues over the BoB is primarily determined by the ocean surface conditions, they are significantly altered by laterally advected vapor from rain en route during the monsoon. Key Points Demonstration of deviation from Model values on rainy spells over ocean Relations between the ocean surface condition and isotopic composition of vapor Influence of rain along the parcel trajectory on isotopic composition of vapor ©2013. American Geophysical Union. All Rights Reserved.