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Biogeosciences An interactive open-access journal of the European Geosciences Union
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Volume 10, issue 6 | Copyright
Biogeosciences, 10, 4211-4225, 2013
© Author(s) 2013. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 25 Jun 2013

Research article | 25 Jun 2013

Numerical modelling of methyl iodide in the eastern tropical Atlantic

I. Stemmler1, M. Rothe1,*, I. Hense1, and H. Hepach2 I. Stemmler et al.
  • 1Institute for Hydrobiology and Fisheries Science, CEN, University of Hamburg, Hamburg, Germany
  • 2GEOMAR Helmholtz Centre for Ocean Research Kiel, Kiel, Germany
  • *now at: Leibniz Institute of Freshwater Ecology and Inland Fisheries, Berlin, Germany

Abstract. Methyl iodide (CH3I) is a volatile organic halogen compound that contributes significantly to the transport of iodine from the ocean to the atmosphere, where it plays an important role in tropospheric chemistry. CH3I is naturally produced and occurs in the global ocean. The processes involved in the formation of CH3I, however, are not fully understood. In fact, there is an ongoing debate whether production by phytoplankton or photochemical degradation of organic matter is the main source term. Here, both the biological and photochemical production mechanisms are considered in a biogeochemical module that is coupled to a one-dimensional water column model for the eastern tropical Atlantic. The model is able to reproduce observed subsurface maxima of CH3I concentrations. But, the dominating source process cannot be clearly identified as subsurface maxima can occur due to both direct biological and photochemical production. However, good agreement between the observed and simulated difference between surface and subsurface methyl iodide concentrations is achieved only when direct biological production is taken into account. Production rates for the biological CH3I source that were derived from published laboratory studies are shown to be inappropriate for explaining CH3I concentrations in the eastern tropical Atlantic.

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