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The isotopic composition of water in ice cores is used as a proxy for past climate. Traditional interpretation of this recorded climate signal is that during formation precipitation captures a snapshot of the column integrated atmosphere. In recent work, observations have documented that the snow isotopic composition changes during the post-depositional interaction with the near-surface atmosphere. To more accurately interpret the climate signal in ice cores an better understand the surface mass balance budget, it is necessary to understand the source of the water vapor in the planetary boundary layer (PBL), as well as the vertical mixing and transportation in the polar atmosphere. However, the dynamics in the polar PBL are poorly constrained in most climate models due to a lack of observations. Here we present insights from the first Arctic in-situ water-vapor isotope record both within and above the PBL up to 1500 meters above the Greenland Ice Sheet (GrIS) from the EastGRIP ice core camp 2022 summer field campaign. A total of 105 flights were performed with a fixed-wing uncrewed aircraft recording high resolution atmospheric profiles. Moreover, air is sampled in glass flasks and brought to the surface for determination of δ18O and δD of water vapor. Based on observed temperature, humidity and isotopic profiles we identify the typical atmospheric structure above the GrIS. We evaluate the vertical atmospheric representation of the polar regional climate model MAR and the isotope-enabled global climate models. Finally, from observations, we provide evidence for the role of sublimated water vapor in determining the isotopic composition of water above the surface.

Presentation by Kevin Rozmiarek, Graduate Student Geological Sciences, CU Boulder