Non-Equilibrium Fractionation Factors for D/H and 18O/16O During Oceanic Evaporation in the North-West Atlantic Region

• Main Authors: Zannoni, Daniele, Steen-Larsen, Hans Christian, Peters, Andrew J., Wahl, Sonja, Sodemann, Harald, Sveinbjörnsdóttir, Árný E.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: 2022
• Subjects: Steen; North West Atlantic; Northwest Atlantic
• Online Access: https://zenodo.org/record/7326925; https://doi.org/10.5281/zenodo.7326925

Accepted version of the paper "Non-Equilibrium Fractionation Factors for D/H and 18O/16O During Oceanic Evaporation in the North-West Atlantic Region". An edited version of this paper was published by AGU. Copyright (2022) American Geophysical Union. Zannoni, D., Steen‐Larsen, H. C., Peters, A. J., Wahl, S., Sodemann, H., & Sveinbjörnsdóttir, A. E. Non‐Equilibrium Fractionation Factors for D/H and 18O/16O During Oceanic Evaporation in the North‐West Atlantic Region. Journal of Geophysical Research: Atmospheres, e2022JD037076. https://doi.org/10.1029/2022JD037076 In accordance with the the Dual Publication Policy of AGU. Abstract Ocean isotopic evaporation models, such as the Craig-Gordon model, rely on the description of non-equilibrium fractionation factors that are, in general, poorly constrained. To date, only a few gradient-diffusion type measurements have been performed in ocean settings to test the validity of the commonly used parametrization of non-equilibrium isotopic fractionation during ocean evaporation. In this work we present six months of water vapor isotopic observations collected from a meteorological tower located in the northwest Atlantic Ocean (Bermuda) with the objective of estimating non-equilibrium fractionation factors (k, ‰) for ocean evaporation and their wind speed dependency. The Keeling plot method and Craig-Gordon model combination was sensitive enough to resolve non-equilibrium fractionation factors during evaporation resulting into mean values of k18= 5.2±0.6 ‰ and k2= 4.3±3.4 ‰. Furthermore, we evaluate the relationship between k and 10-m wind speed over the ocean. Such a relationship is expected from current evaporation theory and from laboratory experiments made in the 1970s, but observational evidence is lacking. We show that (i) in the observed wind speed range [0 – 10 m s-1] the sensitivity of k to wind speed is small, in the order of -0.2 ‰ m-1s for k18, and (ii) there is no empirical evidence for the presence of a discontinuity between smooth and rough wind speed ...