Seasonal variations of isotope ratios and CO2 concentrations in firn air

Weiler, Karin; Schwander, Jakob; Leuenberger, Markus; Blunier, Thomas; Mulvaney, Robert; Anderson, Philip S.; Salmon, Rhian; Sturges, William T. (2009). Seasonal variations of isotope ratios and CO2 concentrations in firn air. Low temperature science, 68(Suppl.), pp. 247-272. The Institute of Low Temperature Science, Hokkaido University

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A first year- round firn air sampling carried out at the British Antarctic station Halley in 2003 shows isotope and CO2 changes owing to diffusive mixing driven by seasonal variations of surface temperature, and gas composition of the atmosphere.
Seasonal firn temperatures are well reproduced from the atmospheric temperature history. Based on these profiles thermal diffusion is forced with thermal diffusion factors αT with respect to air. Application of the available literature data for αT(15N14 / N2) leads to a proper prediction of the seasonal thermal amplitude during the entire year. By forcing thermal fractionation with αT as derived from two different model approaches and taking into account literature data reasonable results can be achieved for CO2 but not for thermal fractionation of 18O16O and16O2 in air. The latter is attributed to an inappropriate reproduction of the intermolecular interaction forces by either model.
Neither thermal diffusion nor annual variations in the atmospheric CO2 concentration seem to have a substancial effect on the CO2 concentration finally conserved in air bubbles at the close-off level.

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