LAUSR

The turbulent humidity flux at the Earth’s surface continuously exchanges water between the land and marine reservoirs to the atmosphere. On the global scale, sublimation and evaporation move up to half a million cubic kilometers of water per year (Bengtsson, 2010; Trenberth et al., 2007). This water vapor flux has important implications for the frozen reservoir of water in the form of ice sheets. The humidity flux influences the surface mass balance (SMB) of the ice sheet, both directly in the form of sublimation and deposition, and indirectly, as part of the local energy balance (Fausto et al., 2016; Lenaerts et al., 2019). Currently, the net water vapor flux between the snow surface and the atmosphere in the interior dry snow region of the Abstract Surface processes in high latitudes play an important role in global climate and thus understanding the physics of these systems is critical for improving climate projections. The characterization of the stable water isotopologue flux between the surface and the atmosphere offers the potential to constrain parameterizations of these physical surface exchange processes in numerical models. In addition, observations of isotopologue surface fluxes allow the evaluation of surface fluxes as a process influencing the formation of the climate signal retrieved from ice core isotopologue records. Here, we present a record of stable water isotopologue surface fluxes measured in-situ in the accumulation zone of the Greenland Ice Sheet at the East Greenland Ice Core Project site. We measured isotopologue fluxes above the snow surface directly by combining high-frequency eddy covariance measurements with low-frequency isotopologue measurements from a cavity ring-down spectrometer (CRDS). We developed a method to correct for the high-frequency loss of the CRDS by combining humidity measurements from both the CRDS and eddy covariance instruments. Using this approach our measurements provide the first direct observations of water isotopologue fluxes in polar areas. We observed a clear diurnal cycle in the fluxes of the different water isotopologues. The isotopic composition of the sublimation and deposition flux showed to be dependent on the snow and vapor isotopic composition, respectively. To a first order, the isotopic composition of the sublimation flux could be derived assuming equilibrium fractionation during sublimation.