ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-11229-2012 Iodine emissions from the sea ice of the Weddell Sea Atkinson H. M. 1 2 Huang R.-J. 3 Chance R. 4 8 Roscoe H. K. 1 Hughes C. 2 9 Davison B. 5 Schönhardt A. 6 Mahajan A. S. 7 Saiz-Lopez A. 7 Hoffmann T. 3 Liss P. S. 2 British Antarctic Survey, Cambridge, UK School of Environmental Science, University of East Anglia, Norwich, UK Institute of Inorganic and Analytical Chemistry, Johannes Gutenberg University of Mainz, Mainz, Germany Department of Chemistry, University of York, York, UK Department of Environmental Sciences, Lancaster University, Lancaster, UK IUP, University of Bremen, Bremen, Germany Laboratory 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 27 11 2012 12 22 11229 11244 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/12/11229/2012/acp-12-11229-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/11229/2012/acp-12-11229-2012.pdf

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. I<sub>2</sub> 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 CH<sub>3</sub>I, C<sub>2</sub>H<sub>5</sub>I, CH<sub>2</sub>ICl, 2-C<sub>3</sub>H<sub>7</sub>I, CH<sub>2</sub>IBr and 1-C<sub>3</sub>H<sub>7</sub>I were each 0.2 pptv or less. On the Brunt Ice Shelf, enhanced concentrations of CH<sub>3</sub>I and C<sub>2</sub>H<sub>5</sub>I (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 I<sub>2</sub> 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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