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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-443
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-443
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 25 Nov 2019

Submitted as: research article | 25 Nov 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Common features of iodate to iodide reduction amongst a diverse range of marine phytoplankton

Helmke Hepach1,a,*, Claire Hughes1,*, Karen Hogg2, Susannah Collings1, and Rosie Chance3 Helmke Hepach et al.
  • 1Department of Environment and Geography, University of York, York, UK
  • 2Department of Biology, University of York, York, UK
  • 3Wolfson Atmospheric Chemistry Laboratory (WACL), University of York, York, UK
  • anow at: GEOMAR Helmholtz Centre for Ocean Research Kiel, RD2, Biological oceanography, Kiel, Germany
  • *These authors contributed equally to this work.

Abstract. The reaction between ozone and iodide at the sea surface is now known to be an important part of atmospheric ozone cycling, causing ozone deposition and the release of ozone-depleting reactive iodine to the atmosphere. The importance of this reaction is reflected by its inclusion in chemical transport models (CTMs). Such models depend on accurate sea surface iodide fields but measurements are spatially and temporally limited. The ability to predict current and future sea surface iodide fields requires the development of process-based models which in turn require a thorough understanding of the key processes controlling inorganic iodine cycling. The aim of this study was to inform the development of ocean iodine cycling models by exploring if there are common features of iodate to iodide reduction amongst diverse marine phytoplankton. In order to achieve this, rates and patterns of changes in inorganic iodine speciation were determined in 10 phytoplankton cultures grown at ambient iodate concentrations. Where possible these data were analysed alongside results from previous studies. Iodate loss and some iodide production was observed in all cultures studied, confirming that this is a widespread feature amongst marine phytoplankton. We found no significant difference in log-phase, cell-normalised iodide production rates between key phytoplankton groups (diatoms, prymesiophytes including coccolithophores and phaeocystales) suggesting that a Phytoplankton Functional Type (PFT) approach would not be appropriate for building an ocean iodine cycling model. Iodate loss was greater than iodide formation in the majority of the cultures studied, indicating the presence of an as yet unidentified missing iodine fraction. Iodide yield at the end of the experiment was significantly greater in cultures that had reached a later senescence stage. This suggests that models should incorporate a lag between peak phytoplankton biomass and maximum iodide production, and that cell mortality terms in biogeochemical models could be used to parameterize iodide production.

Helmke Hepach et al.
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Short summary
Tropospheric iodine takes part in numerous atmospheric chemical cycles including tropospheric ozone destruction and aerosol formation. Due to its significance for atmospheric processes, it is crucial to constrain its sources and sinks. Recently, it has been suggested that up to 75 % of marine tropospheric iodine originates from iodide in the sea surface. This paper aims at investigating and understanding features of biogenic iodate to iodide reduction in microalgal monocultures.
Tropospheric iodine takes part in numerous atmospheric chemical cycles including tropospheric...
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