Atmosphere to Surface Profiles of Water-Vapor Isotopes and Meteorological Conditions Over the Northeast Greenland Ice Sheet

Abstract

On polar ice sheets, water vapor interacts with surface snow, and through the exchange of water molecules, imprints an isotopic climate signal into the ice sheet. This exchange is not well understood due to sparse observations in the atmosphere. There are currently no published vertical profiles of water isotopes above ice sheets that span the planetary boundary layer and portions of the free troposphere. Here, we present a novel data set of water-vapor isotopes (${\delta }^{18}$O, $\delta$D, $dxs$) and meteorological variables taken by fixed-wing uncrewed aircraft on the northeast Greenland Ice Sheet (GIS). During June–July (2022), we collected 104 profiles of water-vapor isotopes and meteorological variables up to 1,500 m above ground level. Concurrently, surface snow samples were collected at 12-hr intervals, allowing connection to surface-snow processes. We pair observations with modeling output from a regional climate model as well as an atmospheric transport and water-isotope distillation model. Climate model output of mean temperature and specific humidity agrees well with observations, with a mean difference of +0.095°C and −0.043 g/kg (−2.91%), respectively. We find evidence that along an air parcel pathway, the distillation model is not removing enough water prior to onsite arrival. Below the mean temperature inversion ($\sim$200 m), water-isotope observations indicate a kinetic fractionating process, likely the result of mixing sublimated vapor from the ice sheet surface along with an unknown fraction of katabatic wind vapor. Modeled $dxs$ does not agree well with observations, a result that requires substantial future analysis of kinetic fractionation processes along the entire moisture pathway.