Antarctic water stable isotopes in the global atmospheric model LMDZ6: from climatology to boundary layer processes

Water-stable isotopic compositions of snow or ice (here δ¹⁸O and δD) represent the main way to reconstruct past temperature in Antarctica, and one way to interpret these isotopic signals is through the use of isotope-enabled atmospheric general circulation models. In this study, we combine isotopic observations from surface snow samples, daily precipitation and water vapour to evaluate the LMDZ6iso model in Antarctica from climatic to seasonal and sub-daily time scale. Time-averaged δ¹⁸O in precipitation from LMDZ6iso for the period 1980-2022 is in excellent agreement with δ¹⁸O of surface snow samples across the continent, but there is a strong disagreement for d-excess at cold temperature sites. For sub-annual time scale analyses, we focus on two sites in East Antarctica: the coastal station Dumont d'Urville and the continental station Concordia. The model accurately reproduces the seasonal isotopic cycle of daily precipitation at both stations, with better performances at Concordia. Moving from statistical evaluation to process analyses, we use water vapour isotopes to study water exchanges in the boundary layer. LMDZ6iso performs well in representing the observed diurnal isotope cycle at both sites. However, the model simulates a larger vapour δ¹⁸O depletion than observed during the night at Concordia. We analyse the contribution of each physical process affecting isotope concentrations in LMDZ6iso to show what controls the vapour isotope signal. At Concordia, surface sublimation during the day is the main driver of the diurnal cycle of vapour isotopes, whereas at Dumont d'Urville, daily isotope variations are driven by surface sublimation and turbulence during the day and by air advection from the katabatic flow during the night.