EVOLUTION OF SNOW AND AIR CIRCULATING IN SNOW BEYOND THE SURFACE OF ANTARCTIC ICE SHEET
Supervisors: A. Landais (CNRS-LSCE, FR), P. Martinerie (CNRS-IGE)
Academic secondments: CNRS-IGE (FR), Univ. of Bern (CH), Univ. of Copenhagen (DK); Non-academic secondments: Air Liquide (USA)
Abstract: In ice core, air bubbles are only trapped in the ice 60 to 120 m under the ice sheet surface at the bottom of the firn. The composition of air and structure of snow is strongly modified during the firn densification process and bubble closure entrapment with important consequences to understand ice core records. In this phD project, we propose to explore two important effects:
- Thermal effect on the elemental and isotopic composition of the air; This effect will be studied using a firn air diffusion model constrained by new data (isotopic and elemental composition of inert gases and of oxygen) obtained through a firn air pumping campaign installed for a whole year on the top 20 m of the firn.
- Modification of the snow structure down to the pore close-off due to the combined effects of snow metamorphism at the surface and snow densification; We propose to improve our understanding on how snow microstructure evolves with depth using the detailed snowpack model Crocus. Using the snowpack model, we will first investigate the impact of insolation changes on surface snow microstructure.
To support the modeling effort and as for the previous effect, observational constraints will be obtained from firn air campaigns with a focus here on the deeper part of the firn with analysis of air content and O2/N2 ratio, both in the closed and open porosity of the bubble close-off zone.
Key words: firn, densification, bubble, metamorphism, snowpack, snow.
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