To better constrain the origin of surface accumulation and recent climate change in Terre Adélie via the contribution of water isotopes (ADELISE)

Quantification of fluxes of snow and water vapor at the Antarctic surface as well as links with climatic variations is a major challenge for projections of climate and water cycle organization in this region. Still, large uncertainties prevent such quantification. On the one hand, precipitation amount is difficult to estimate because of the influence of wind, a process particularly important on the coastal areas because of the strong katabatic winds. On the other hand, it is particularly difficult to quantify the direct snow exchanges with atmosphere (sublimation / condensation) because of badly constrained processes within the boundary layer (blowing snow, supersaturation, turbulence influence,…). Finally, climatic variations over the last decades to centuries are often bad documented because of a lack of instrumentation in this region.

Water isotopic measurements on shallow ice or snow cores in Antarctica is currently one of the best tools to reconstruct the climatic variability (temperature, accumulation) in the absence of weather station instrumentation. Indeed, because of isotopic distillation from low to high latitudes, it is possible to link temperature to the snow isotopic composition at the seasonal and interannual scale. However, the snow isotopic composition is also sensitive to other effects during snow formation and deposition (e.g. kinetic fractionation, re-evaporation of falling or blowing snow) and after deposition (diffusion, sublimation and hoar deposition). These effects increase the complexity for direct interpretation of snow isotopic composition in term of temperature but also permit to retrieve other information on the snow deposition conditions and water fluxes at the ice sheet surface.

Within the ADELISE project, we propose to perform continuous isotopic measurements on the water vapor, precipitation, blowing snow and surface snow at Dumont d’Urville over 2 consecutive years. The isotopic measurements will complement the measurements performed on the LIDAR, RADAR and pluviometers already in place at this station in order to characterize water cycle processes in the atmospheric column and at the snow surface. The isotopic measurements will be combined with long-term chemistry measurements on aerosol filters within the CESOA program (and following program from 2020) and will permit to better interpret the isotopic and chemistry records obtained on shallow cores drilled recently in Adélie Land within the ASUMA project. Finally, a parallel system of continuous measurements of water vapor isotopic composition will be installed over the same period at Dome C within the NIVO2 project. Combination of the two records with back-trajectories will permit to better understand the isotopic transfer function between the coast and East Antarctica hence improving our interpretation of water isotopes in the Dome C deep ice core.

This project also includes a significant part of modeling through the atmospheric regional model MAR already largely applied for Adélie Land. MAR is also currently being equipped with water isotopes. This project will thus permit the validation of the MARiso model as well as its use for interpretation of shallow ice cores recently drilled in Adélie Land.