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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 (O, D, ) 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 (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 does not agree well with observations, a result that requires substantial future analysis of kinetic fractionation processes along the entire moisture pathway. 

Paleoclimate records are rich sources of information about the past history of the Earth system. Information theory provides a new means for studying these records. We demonstrate that weighted permutation entropy of water-isotope data from the West Antarctica Ice Sheet (WAIS) Divide ice core reveals meaningful climate signals in this record. We find that this measure correlates with accumulation (meters of ice equivalent per year) and may record the influence of geothermal heating effects in the deepest parts of the core. Dansgaard-Oeschger and Antarctic Isotope Maxima events, however, do not appear to leave strong signatures in the information record, suggesting that these abrupt warming events may actually be predictable features of the climate’s dynamics. While the potential power of information theory in paleoclimatology is significant, the associated methods require well-dated and high-resolution data. The WAIS Divide core is the first paleoclimate record that can support this kind of analysis. As more high-resolution records become available, information theory could become a powerful forensic tool in paleoclimate science.