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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Volume 12, issue 23 | Copyright
Atmos. Chem. Phys., 12, 11609-11617, 2012
https://doi.org/10.5194/acp-12-11609-2012
© Author(s) 2012. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 05 Dec 2012

Research article | 05 Dec 2012

Latitudinal distribution of reactive iodine in the Eastern Pacific and its link to open ocean sources

A. S. Mahajan1,*, J. C. Gómez Martín1,4, T. D. Hay1, S.-J. Royer2, S. Yvon-Lewis3, Y. Liu3, L. Hu3, C. Prados-Roman1, C. Ordóñez1,**, J. M. C. Plane4, and A. Saiz-Lopez1 A. S. Mahajan et al.
  • 1Laboratory for Atmospheric and Climate Science (CIAC), CSIC, Toledo, Spain
  • 2Institut de Ciències del Mar (CSIC), Barcelona, Spain
  • 3Oceanography Department, Texas A&M University, College Station, Texas, USA
  • 4School of Chemistry, University of Leeds, Leeds, UK
  • *now at: Indian Institute of Tropical Meteorology (IITM), Pune, India
  • **now at: British Met Office, Exeter, UK

Abstract. 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 (CH3I) 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 × 1013 molecules cm−2 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 CH3I, suggesting common sources. In situ measurements of meteorological parameters and physical ocean variables, along with satellite-based observations of Chlorophyll a (Chl a) 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 a 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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