Atmos. Chem. Phys. Discuss., 9, 2501-2531, 2009
© Author(s) 2009. 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.
36Cl bomb peak: comparison of modeled and measured data
U. Heikkilä1,*, J. Beer1, J. Feichter2, V. Alfimov3, H.-A. Synal3, U. Schotterer4, A. Eichler4, M. Schwikowski5, and L. Thompson6
1EAWAG, Dübendorf, Switzerland
2MPI-MET Hamburg, Germany
3ETH/PSI, Zurich, Switzerland
4Division of Climate and Environmental Physics, Physics Institute, Univ. of Bern, Switzerland
5PSI, Villigen, Switzerland
6School of Earth Sciences, The Ohio State University, USA
*now at: Bjerknes Centre for Climate Research (BCCR), Allegaten 55, 5007 Bergen, Norway

Abstract. The extensive nuclear bomb testing of the fifties and sixties and the final tests in the seventies caused a strong 36Cl peak that has been observed in ice cores world-wide. The measured 36Cl deposition fluxes in eight ice cores (Dye3, Fiescherhorn, Grenzgletscher, Guliya, Huascarán, North GRIP, Inylchek (Tien Shan) and Berkner Island) were compared with an ECHAM5-HAM general circulation model simulation (1952–1972). We find a good agreement between the measured and the modeled 36Cl fluxes assuming that the bomb test produced global 36Cl input was ~80 kg. The model simulation indicates that the fallout of the bomb test produced 36Cl is largest in the subtropics and mid-latitudes due to the strong stratosphere-troposphere exchange. In Greenland the 36Cl bomb signal is quite large due to the relatively high precipitation rate. In Antarctica the 36Cl bomb peak is small but is visible even in the driest areas. The model suggests that the large bomb tests in the Northern Hemisphere are visible around the globe but the later (end of sixties and early seventies) smaller tests in the Southern Hemisphere are much less visible in the Northern Hemisphere. The question of how rapidly and to what extent the bomb produced 36Cl is mixed between the hemispheres depends on the season of the bomb test. The model results give an estimate of the amplitude of the bomb peak around the globe.

Citation: Heikkilä, U., Beer, J., Feichter, J., Alfimov, V., Synal, H.-A., Schotterer, U., Eichler, A., Schwikowski, M., and Thompson, L.: 36Cl bomb peak: comparison of modeled and measured data, Atmos. Chem. Phys. Discuss., 9, 2501-2531, doi:10.5194/acpd-9-2501-2009, 2009.
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