HR: 0800h
AN: C51B-1047    [Abstracts]
TI: Field measurements of isotope fractionation during evaporation
AU: * Smith, R B
EM: ronald.smith@yale.edu
AF: Yale University, P.O. Box 208109, New Haven, CT 06420 United States
AU: Williams, J K
EM: john.k.williams@yale.edu
AF: Yale University, P.O. Box 208109, New Haven, CT 06420 United States
AU: Lee, X
EM: xuhui.lee@yale.edu
AF: Yale University, P.O. Box 208109, New Haven, CT 06420 United States
AB: The isotopic fractionation associated with evaporation from bodies of water is an important process for the interpretation of isotope data from the atmosphere and in the development of ice core climate records. Existing theories include the resistance model of Craig and Gordon [1965] summarized by Gat [1996], and the exchange model of Merlivat and Jouzel [1979, MJ79]. The MJ79 model was recently extended by He and Smith [1999, HS99] to include a limited exchange between the liquid at depth and the air-liquid interface. These theories are relatively complex as they must include not only equilibrium fractionation but also the kinetic effects of diffusion and the influence of the "back-flux" of water vapor to the surface. Laboratory experiments by Craig et al. (1963), Merlivat and Coantic [1975], Merlivat [1978] and Cappa et al. (2003) have added new insight and generated proposals for parameterizations. Field testing of these theories and parametrizations has received little attention however. The primary difficulty to be overcome is that water vapor collected near the liquid interface is not representative of the evaporative flux, as it contains a significant proportion of vapor from the free atmosphere above. We overcome this problem using a two-level sampling technique developed by Keeling [1960] for carbon isotopes and applied to water vapor by Yakir and Wang [1996], Gat [2000], and He and Smith [2003] among others. Vapor collections were carried out over the Hudson River in the summer 2003 at altitudes of 12 and 190 centimeters. Samples from the two levels showed systematic differences in specific humidity and isotope ratio, allowing the isotope ratio in the net flux to be determined. In general, flux isotope ratios were significantly lighter than the collected vapor. Furthermore, the flux ratios are significantly lighter than that in equilibrium with river water samples. This small data set provides an opportunity to evaluate existing theories of isotope fractionation and to guide future ocean surveys of isotope flux ratios.
DE: 3307 Boundary layer processes
DE: 1655 Water cycles (1836)
DE: 1704 Atmospheric sciences
DE: 1833 Hydroclimatology
DE: 1854 Precipitation (3354)
SC: Cryosphere [C]
MN: 2004 AGU Fall Meeting