Surface processes and drivers of the snow water stable isotopic composition at Dome C, East Antarctica – a multi-datasets and modelling analysis

The ability to infer past temperatures from ice core records has in the past relied on the assumption that after precipitation, the stable water isotopic composition of the snow surface layer is not modified before being buried deeper into the snowpack and transformed into ice. However, in extremely dry environments, such as the East Antarctic plateau, the precipitation is so sparse that the surface is exposed to the atmosphere for significant time before burial. Several processes have been recently identified as impacting the snow isotopic composition after snowfall, including moisture exchanges between the snow and the lower atmosphere, wind effects and diffusion inside the snowpack. Here we present the result of a study that combines existing and new datasets of the precipitation, snow surface and subsurface isotopic compositions (δ18O and d-excess), meteorological parameters, ERA5 reanalysis products, outputs from the isotope-enabled climate model ECHAM6-wiso and a simple modelling approach to investigate the transfer function of water stable isotopes from precipitation to the snow surface and subsurface at Dome C, East Antarctica. We find that (i) moisture fluxes at the surface of the ice sheet lead to a net sublimation of snow throughout the year, from 3.1 to 3.7 mm water equivalent over the 2018-2021 period, (ii) the precipitation isotopic signal only cannot account for the intra-annual to seasonal variability observed in the snow isotopic composition and (iii) the cumulative impact of post-depositional processes at the surface over five years lead to an enrichment in δ18O of the snow surface by 3.3‰ and a lowering of the snow d-excess by 3.5‰ compared to the precipitation isotopic signal. This study reinforces previous findings about the complexity and multiple origin of the snow isotopic composition at Dome C and provides a first step toward a quantitative attribution of the different processes building up of the isotopic signal in the snow surface that is crucial for the interpretation of isotopic records from ice cores.