Atmos. Chem. Phys. Discuss., 12, 18499-18530, 2012
© Author(s) 2012. This work is distributed
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This discussion paper has been under review for the journal Atmospheric Chemistry and Physics (ACP). Please refer to the corresponding final paper in ACP.
Extreme 13C depletion of CCl2F2 in firn air samples from NEEM, Greenland
A. Zuiderweg1, R. Holzinger1, P. Martinerie2, R. Schneider3, J. Kaiser4, E. Witrant5, D. Etheridge6,8, M. Rubino6,8, V. Petrenko7, T. Blunier8, and T. Röckmann1
1Institute for Marine and Atmospheric Research (IMAU), Universiteit Utrecht, Utrecht, The Netherlands
2UJF – Grenoble 1/CNRS, Laboratoire de Glaciologie et Géophysique de l'Environnement (LGGE), UMR5183, Grenoble, 38041, France
3Climate and Environmental Physics, Physics Institute and Oeschger Centre for Climate Change Research, University of Bern, Bern, Switzerland
4School of Environmental Sciences, University of East Anglia, Norwich, UK
5UJF – Grenoble 1/CNRS, Grenoble Image Parole Signal Automatique (GIPSA-lab), UMR5216, B.P. 46, 38402 St Martin d'Hères, France
6Centre for Australian Weather and Climate Research, CSIRO Marine and Atmospheric Research, Aspendale, Australia
7Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY, USA
8Centre for Ice and Climate, Niels Bohr Institute, University of Copenhagen, København Ø, Denmark

Abstract. A series of 12 high volume air samples collected from the S2 firn core during the North Greenland Eemian Ice Drilling (NEEM) 2009 campaign have been measured for mixing ratio and stable carbon isotope composition of the chlorofluorocarbon CFC-12 (CCl2F2). While the mixing ratio measurements compare favorably to other firn air studies, the isotope results show extreme 13C depletion at the deepest measurable depth (65 m), to values lower than δ13C = −80‰ vs. VPDB (the international stable carbon isotope scale), compared to present day surface tropospheric measurements near −40‰. Firn air modeling was used to interpret these measurements. Reconstructed atmospheric time series indicate even larger depletions (to −120‰) near 1950 AD, with subsequent rapid enrichment of the atmospheric reservoir of the compound to the present day value. Mass-balance calculations show that this change must have been caused by a large change in the isotopic composition of anthropogenic CFC-12 emissions, probably due to technological changes in the CFC production process over the last 80 yr. Propagating the mass-balance calculations into the future demonstrates that as emissions decrease to zero, isotopic fractionation by the stratospheric sinks will lead to continued 13C enrichment in atmospheric CFC-12.

Citation: Zuiderweg, A., Holzinger, R., Martinerie, P., Schneider, R., Kaiser, J., Witrant, E., Etheridge, D., Rubino, M., Petrenko, V., Blunier, T., and Röckmann, T.: Extreme 13C depletion of CCl2F2 in firn air samples from NEEM, Greenland, Atmos. Chem. Phys. Discuss., 12, 18499-18530, doi:10.5194/acpd-12-18499-2012, 2012.
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