From atmospheric water isotopes measurement to firn core interpretation in Adelie Land: A case study for isotope-enabled atmospheric models in Antarctica

Abstract. In a context of global warming and sea level rise acceleration, it is key to estimate the evolution of the atmospheric hydrological cycle and temperature in the polar regions, which directly influence the surface mass balance of the Arctic and Antarctic ice sheets. Direct observations are available from satellite data for the last 40 years and a few weather data since the 50’s in Antarctica. One of the best ways to access longer records is to use climate proxies in firn or ice cores. The water isotopic composition in these cores is widely used to reconstruct past temperature variations.

In order to progress in our understanding of the influence of the atmospheric hydrological cycle on the water isotopic composition, we first present a 2-year long time series of vapor and precipitation isotopic composition measurement at Dumont d’Urville station, in Adélie Land. We characterize diurnal variations of meteorological parameters (temperature, humidity and δ¹⁸O) for the different seasons and to determine the evolution of key relationships (δ¹⁸O versus temperature or humidity) along the year: we found mean annual slopes of 0.5 and 0.4 ‰ °C⁻¹ for the relationship of δ¹⁸O vs. temperature in the water vapor and in the precipitation respectively. Then, this data set is used to evaluate the Atmospheric General Circulation Model ECHAM6-wiso (model version with embedded water stable isotopes) in a region where local conditions are controlled by strong katabatic winds which directly impact the isotopic signal. We show that a combination of continental (79 %) and oceanic (21 %) grid cells leads model outputs (temperature, humidity and δ¹⁸O) to nicely fit the observations, even winter extreme synoptic events are represented in the model. Therefore we demonstrate the added value of long-term water vapor isotopic composition records. Then, as a clear link is found between water vapor and precipitation isotopic composition, we evaluate how isotopic enabled models can help interpreting short firn cores.