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 dataset of water-vapor isotopes
( δ18O , δD,
dxs) and meteorological variables taken by fixed-wing uncrewed
aircraft on the northeast Greenland Ice Sheet (GIS). During June-July
(2022), we collected 105 profiles of water-vapor isotopes and
meteorological variables up to 1500 m above ground level. Concurrently,
surface snow samples were collected at 12-hour 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
(~200m), 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.