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Volume 12, issue 22 | Copyright
Atmos. Chem. Phys., 12, 11229-11244, 2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 27 Nov 2012

Research article | 27 Nov 2012

Iodine emissions from the sea ice of the Weddell Sea

H. M. Atkinson1,2, R.-J. Huang3, R. Chance4,*, H. K. Roscoe1, C. Hughes2,**, B. Davison5, A. Schönhardt6, A. S. Mahajan7, A. Saiz-Lopez7, T. Hoffmann3, and P. S. Liss2 H. M. Atkinson et al.
  • 1British Antarctic Survey, Cambridge, UK
  • 2School of Environmental Science, University of East Anglia, Norwich, UK
  • 3Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg University of Mainz, Mainz, Germany
  • 4Department of Chemistry, University of York, York, UK
  • 5Department of Environmental Sciences, Lancaster University, Lancaster, UK
  • 6IUP, University of Bremen, Bremen, Germany
  • 7Laboratory for Atmospheric and Climate Science, CSIC, Toledo, Spain
  • *now at: School of Environmental Science, University of East Anglia, Norwich, UK
  • **now at: Department of Chemistry, University of York, York, UK

Abstract. Iodine compounds were measured above, below and within the sea ice of the Weddell Sea during a cruise in 2009, to make progress in elucidating the mechanism of local enhancement and volatilisation of iodine. I2 mixing ratios of up to 12.4 pptv were measured 10 m above the sea ice, and up to 31 pptv was observed above surface snow on the nearby Brunt Ice Shelf – large amounts. Atmospheric IO of up to 7 pptv was measured from the ship, and the average sum of HOI and ICl was 1.9 pptv. These measurements confirm the Weddell Sea as an iodine hotspot. Average atmospheric concentrations of CH3I, C2H5I, CH2ICl, 2-C3H7I, CH2IBr and 1-C3H7I were each 0.2 pptv or less. On the Brunt Ice Shelf, enhanced concentrations of CH3I and C2H5I (up to 0.5 and 1 pptv respectively) were observed in firn air, with a diurnal profile that suggests the snow may be a source. In the sea ice brine, iodocarbons concentrations were over 10 times those of the sea water below. The sum of iodide + iodate was depleted in sea ice samples, suggesting some missing iodine chemistry. Flux calculations suggest I2 dominates the iodine atom flux to the atmosphere, but models cannot reconcile the observations and suggest either a missing iodine source or other deficiencies in our understanding of iodine chemistry. The observation of new particle formation, consistent with the model predictions, strongly suggests an iodine source. This combined study of iodine compounds is the first of its kind in this unique region of sea ice rich in biology and rich in iodine chemistry.

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