Articles | Volume 16, issue 13
Atmos. Chem. Phys., 16, 8521–8538, 2016
Atmos. Chem. Phys., 16, 8521–8538, 2016

Research article 13 Jul 2016

Research article | 13 Jul 2016

Continuous measurements of isotopic composition of water vapour on the East Antarctic Plateau

Mathieu Casado1,2, Amaelle Landais1, Valérie Masson-Delmotte1, Christophe Genthon4,5, Erik Kerstel2,3, Samir Kassi2, Laurent Arnaud4,5, Ghislain Picard4,5, Frederic Prie1, Olivier Cattani1, Hans-Christian Steen-Larsen6, Etienne Vignon4,5, and Peter Cermak7 Mathieu Casado et al.
  • 1Laboratoire des Sciences du Climat et de l'Environnement – IPSL, UMR 8212, CEA-CNRS-UVSQ, Gif-sur-Yvette, France
  • 2CNRS, LIPHY, 38000 Grenoble, France
  • 3Université Grenoble Alpes, LIPHY, 38000 Grenoble, France
  • 4Université Grenoble Alpes, LGGE, 38041 Grenoble, France
  • 5CNRS, LGGE, 38041 Grenoble, France
  • 6Centre for Ice and Climate, University of Copenhagen, Copenhagen, Denmark
  • 7Department of Experimental Physics, Faculty of Mathematics, Physics and Informatics, Comenius University, Mlynska dolina F2, 842 48 Bratislava, Slovakia

Abstract. Water stable isotopes in central Antarctic ice cores are critical to quantify past temperature changes. Accurate temperature reconstructions require one to understand the processes controlling surface snow isotopic composition. Isotopic fractionation processes occurring in the atmosphere and controlling snowfall isotopic composition are well understood theoretically and implemented in atmospheric models. However, post-deposition processes are poorly documented and understood. To quantitatively interpret the isotopic composition of water archived in ice cores, it is thus essential to study the continuum between surface water vapour, precipitation, surface snow and buried snow.

Here, we target the isotopic composition of water vapour at Concordia Station, where the oldest EPICA Dome C ice cores have been retrieved. While snowfall and surface snow sampling is routinely performed, accurate measurements of surface water vapour are challenging in such cold and dry conditions. New developments in infrared spectroscopy enable now the measurement of isotopic composition in water vapour traces. Two infrared spectrometers have been deployed at Concordia, allowing continuous, in situ measurements for 1 month in December 2014–January 2015. Comparison of the results from infrared spectroscopy with laboratory measurements of discrete samples trapped using cryogenic sampling validates the relevance of the method to measure isotopic composition in dry conditions. We observe very large diurnal cycles in isotopic composition well correlated with temperature diurnal cycles. Identification of different behaviours of isotopic composition in the water vapour associated with turbulent or stratified regime indicates a strong impact of meteorological processes in local vapour/snow interaction. Even if the vapour isotopic composition seems to be, at least part of the time, at equilibrium with the local snow, the slope of δD against δ18O prevents us from identifying a unique origin leading to this isotopic composition.

Short summary
Climatic conditions in Concordia are very cold (−55 °C in average) and very dry, imposing difficult conditions to measure the water vapour isotopic composition. New developments in infrared spectroscopy enable now the measurement of isotopic composition in water vapour traces (down to 20 ppmv). Here we present the results results of a first campaign of measurement of isotopic composition of water vapour in Concordia, the site where the 800 000 years long ice core was drilled.
Final-revised paper