Determinations of methyl iodide in the Antarctic atmosphere and the south polar sea

Methyl iodide (CH₃I) concentrations were determined in the atmosphere and in surface sea water near the Antarctic Peninsula with a GC/ECD system during October–December 1987. The mean air concentration of methyl iodide was 2.4 pptv with a corresponding seawater concentration of 2.6 ng l⁻¹. In addition chloroiodomethane (CH₂ClI) was detected in some of the seawater samples as a second volatile organoiodine species. No relationship between methyl iodide and biogenic brominated methanes was found. From this it follows that methyl iodide has a different pathway of biogenic production in marine organisms than the brominated methanes. Based on a two-phase model a global sea-to-air flux for methyl iodide of 8 × 10¹¹ g yr⁻¹ was calculated. This is important for the balance of the global biogeochemical iodine cycle assuming that methyl iodide is by far the dominant volatile organoiodine species in the environment.