Water stable isotopic composition on the East Antarctic Plateau : measurements at low temperature of the vapour composition, utilisation as an atmospheric tracer and implication for paleoclimate studies
Ice cores enable reconstruction of past climates, from among others water stable isotopic composition (δ18O, δ17O et δD). On the East Antarctic Plateau, very cold temperature and low accumulation provide the longest ice core records (up to 800 000 years) but embrangle the interpretation of isotopic...
Main Author: | |
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Other Authors: | , , , , , , , , |
Format: | Doctoral or Postdoctoral Thesis |
Language: | English |
Published: |
HAL CCSD
2016
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Subjects: | |
Online Access: | https://theses.hal.science/tel-01409702 https://theses.hal.science/tel-01409702v2/document https://theses.hal.science/tel-01409702v2/file/76478_CASADO_2016_archivage.pdf |
Summary: | Ice cores enable reconstruction of past climates, from among others water stable isotopic composition (δ18O, δ17O et δD). On the East Antarctic Plateau, very cold temperature and low accumulation provide the longest ice core records (up to 800 000 years) but embrangle the interpretation of isotopic composition. First, reconstructions of temperature variations from ice core water isotopic composition are based on models used to describe the evolution of the isotopic composition of the vapour and of the condensed phase over the entire water cycle. These models have been developed during the last decades and depend upon precise determinations of isotopic fractionation coefficients associated to each phase transition and upon hypotheses to describe cloud microphysics.During the formation of snowflakes at low temperature, two types of isotopic fractionations need to be taken into account: equilibrium fractionation, associated to the vapour to ice phase transition and kinetic fractionation associated to the difference of diffusivity of the different isotopes. At low temperature, determinations of equilibrium fractionation coefficients present important discrepancies and have never been realised for temperature below -40°C. However, mean annual temperature at Dome C is around -54°C reaching -85°C in winter. For the diffusivities of the different isotopes, they have never been measured at temperature below 10°C. All these gaps result in important uncertainties on the link between isotopic composition and temperature, especially for cold and dry conditions such as encountered on the East Antarctic Plateau.Furthermore, because of the very low amount of precipitation, physical processes affecting the isotopic composition of the snow after the deposition of snowflakes can results in an important contribution to the isotopic budget. In order to estimate the impact of the post-deposition processes on the water vapour isotopic composition, it is necessary to characterise the isotopic fractionation at the snow/atmosphere ... |
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