ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-12-11609-2012 Latitudinal distribution of reactive iodine in the Eastern Pacific and its link to open ocean sources Mahajan A. S. 1 5 Gómez Martín J. C. 1 4 Hay T. D. 1 Royer S.-J. 2 Yvon-Lewis S. 3 Liu Y. 3 Hu L. 3 Prados-Roman C. 1 Ordóñez C. 1 6 Plane J. M. C. 4 Saiz-Lopez A. 1 Laboratory for Atmospheric and Climate Science (CIAC), CSIC, Toledo, Spain Institut de Ciències del Mar (CSIC), Barcelona, Spain Oceanography Department, Texas A&M University, College Station, Texas, USA School of Chemistry, University of Leeds, Leeds, UK now at: Indian Institute of Tropical Meteorology (IITM), Pune, India now at: British Met Office, Exeter, UK 05 12 2012 12 23 11609 11617 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/12/11609/2012/acp-12-11609-2012.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/12/11609/2012/acp-12-11609-2012.pdf

Ship-based Multi-Axis Differential Optical Absorption Spectroscopy measurements of iodine monoxide (IO) and atmospheric and seawater Gas Chromatography-Mass Spectrometer observations of methyl iodide (CH<sub>3</sub>I) were made in the Eastern Pacific marine boundary layer during April 2010 as a part of the HaloCarbon Air Sea Transect-Pacific (HaloCAST-P) scientific cruise. The presence of IO in the open ocean environment was confirmed, with a maximum differential slant column density of 5 × 10<sup>13</sup> molecules cm<sup>−2</sup> along the 1° elevation angle (corresponding to approximately 1 pptv) measured in the oligotrophic region of the Southeastern Pacific. Such low IO mixing ratios and their observed geographical distribution are inconsistent with satellite estimates and with previous understanding of oceanic sources of iodine. A strong correlation was observed between reactive iodine (defined as IO + I) and CH<sub>3</sub>I, suggesting common sources. In situ measurements of meteorological parameters and physical ocean variables, along with satellite-based observations of Chlorophyll <i>a</i> (Chl <i>a</i>) and Chromophoric Dissolved Organic Matter (CDOM) were used to gain insight into the possible sources of iodine in this remote environment. Surprisingly, reactive iodine showed a negative correlation (> 99% confidence) to Chl <i>a</i> and CDOM across the cruise transect. However, a significant positive correlation (> 99% confidence) with sea surface temperature (SST) and salinity instead suggests a widespread abiotic source related to the availability of aqueous iodine and to temperature.

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