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A Global Model for Iodine Speciation in the Upper Ocean
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  • Martin Robert Wadley,
  • David P. Stevens,
  • Tim Jickells,
  • Claire Hughes,
  • Rosie Chance,
  • Helmke Hepach,
  • Lucy J. Carpenter,
  • Helmke Hepach,
  • Liselotte Tinel
Martin Robert Wadley
University of East Anglia, University of East Anglia
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David P. Stevens
University of East Anglia, University of East Anglia
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Tim Jickells
University of East Anglia, UK, University of East Anglia, UK
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Claire Hughes
University of York, University of York
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Rosie Chance
University of York, University of York
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Helmke Hepach
University of York
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Lucy J. Carpenter
University of York, UK, University of York, UK
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Helmke Hepach
GEOMAR Helmholtz Centre for Ocean Research Kiel

Corresponding Author:[email protected]

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Liselotte Tinel
Department of Chemistry, University of York, U.K.
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Abstract

An ocean iodine cycling model is presented, which predicts upper ocean iodine speciation. The model comprises a three-layer advective and diffusive ocean circulation model of the upper ocean, and an iodine cycling model embedded within this circulation. The two primary reservoirs of iodine are represented, iodide and iodate. Iodate is reduced to iodide in the mixed layer in association with primary production, linked by an iodine to carbon (I:C) ratio. A satisfactory model fit with observations cannot be obtained with a globally constant I:C ratio, and the best fit is obtained when the I:C ratio is dependent on sea surface temperature, increasing at low temperatures. Comparisons with observed iodide distributions show that the best model fit is obtained when oxidation of iodide back to iodate is associated with mixed layer nitrification. Sensitivity tests, where model parameters and processes are perturbed, reveal that primary productivity, mixed layer depth, oxidation, advection, surface fresh water flux and the I:C ratio all have a role in determining surface iodide concentrations, and the timescale of iodide in the mixed layer is sufficiently long for non-local processes to be important. Comparisons of the modelled iodide surface field with parameterisations by other authors shows good agreement in regions where observations exist, but significant differences in regions without observations. This raises the question of whether the existing parameterisations are capturing the full range of processes involved in determining surface iodide, and shows the urgent need for observations in regions where there are currently none.