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Zoom: https://uib.zoom.us/j/68473038190?pwd=T3JzY0Z5UXQ4ZUdmcE56c0VrcFhhQT09

Niels Dutrievoz – “Water vapour isotopes in Antarctica as tracers of boundary layer processes and large-scale dynamics”

The study of water isotopes connects two complementary fields: reconstructing past climates from ice cores and analysing the present-day Antarctic water cycle. Understanding the climatic and atmospheric drivers of isotopic signals in vapour and snow—archived in firn and ice—is key to interpreting past variability and anticipating future changes in surface mass balance. Such understanding requires models that integrate both large-scale moisture transport and air–snow exchanges. The aim of this PhD thesis is to improve our understanding of the Antarctic water cycle using isotopes as tracers of boundary-layer processes and large-scale dynamics, through a combined approach of observations and modelling with LMDZiso. First, we assess model performance over Antarctica and identify optimal configurations to minimise isotopic biases. We then investigate isotopic variability in vapour: at Concordia, East Antarctica Plateau (3233m), diurnal cycles are mainly controlled by surface fluxes, while at Dumont d’Urville, a coastal site, they result from both surface fluxes and katabatic advection. The analysis of two atmospheric river events (December 2018 and March 2022) reaching Concordia shows that isotopic variability cannot be explained by synoptic transport alone and requires a detailed representation of local boundary-layer processes. Then we investigate snow–vapour isotopic fluxes. We improve the agreement between the observed and simulated amplitudes of the diurnal cycle of vapour isotopes by introducing fractionation during sublimation and by applying the same formulation for isotopic condensation. Adding an active snow layer of about one centimetre further improves the representation of vapour isotopic anomalies during the March 2022 atmospheric river characterised by intense snowfall. All of these results provide a better understanding of the processes controlling atmospheric isotopic variability in Antarctica and improve the representation of the isotopic signal archived in snow, thereby opening promising perspectives on the interpretation of ice cores.