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, 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 is likely to have been
caused by a large change in the isotopic composition of anthropogenic CFC-12
emissions, probably due to technological advances in the CFC production
process over the last 80 yr, though direct evidence is lacking.
Citation: Zuiderweg, A., Holzinger, R., Martinerie, P., Schneider, R., Kaiser, J., Witrant, E., Etheridge, D., Petrenko, V., Blunier, T., and Röckmann, T.: Extreme 13C depletion of CCl2F2 in firn air samples from NEEM, Greenland, Atmos. Chem. Phys., 13, 599-609, doi:10.5194/acp-13-599-2013, 2013.