Stable isotopic composition of water vapor in the tropics

Water vapor samples collected during tropical field experiments at Puerto Escondido, Mexico, near Kwajalein (KWAJEX), and near Key West, Florida (CAMEX 4), were analyzed for their stable isotope contents, (H2O)-H-1-O-18:(H2O)-H-1-O-16 and (H1HO)-H-2-O-16:(H2O)-H-1-O-16. Highest delta(18)O values approached isotopic equilibrium with seawater during quiescent weather or in regions of isolated or disorganized convection. Lowest delta(18)O values occurred in or downwind from regions of organized mesoscale weather disturbances and ranged as low as 15% below isotopic equilibrium with seawater. The mean delta(18)O value of vapor over the sea surface therefore decreases as storm activity and organization increases.