The marine iodine cycle has remained enigmatic despite decades of research. As a redox active element that is accumulated by many marine organisms, it exists in multiple oxidation states and phases in the oceans. Abiotic, photochemical and biological processes occurring at the ocean surface, at depth, and at the sediment-water interface all drive transformations between iodine species. A recent resurgence in interest in marine iodine speciation has been driven by its importance in a diverse range of fields, from atmospheric chemistry to paleoceanography.

Iodine from the oceans plays an important role in atmospheric chemistry, impacting air quality and climate. The sea-air iodine flux is dependent on iodine speciation at the ocean surface, especially reactions of iodide-iodine. Organic iodine species are also important contributors to the sea-air flux. Meanwhile, iodate-iodine trapped in carbonate sediments is being exploited as an indicator of oxygenation in the paleo-ocean. Iodine species, including anthropogenic radioisotopes, are also being used as tracers of water masses and sedimentary inputs.

The processes governing iodine speciation are not well understood, and rates are poorly constrained. This hinders accurate quantification of sea-air fluxes, and creates uncertainty where iodine species are used as tracers. The impacts of a changing ocean on the iodine cycle, and particularly on sea-air fluxes, also need to be better understood.

Marine iodine research is currently very active internationally and across multiple disciplines. A key aim of this Research Topic is to create bridges between these often disparate communities. It will build upon the renewed interest in marine iodine cycling and the advances this has brought. For example, sophisticated biogeochemical models of iodine cycling are now available, new isotopic techniques have been applied to ambient rate measurements, and potential new microbiological drivers have been identified. It is hoped that this Research Topic will showcase the most exciting new findings from across all research communities interested in marine iodine, and that by bringing together this work in one place, it will spark new collaborations and ideas. We would also like to include a call for a global intercalibration of iodine speciation methods for dissolved and particulate phases to ensure data quality, and generate guidance on ‘best practice’.

The Research Topic will span a wide range of fields, including but not necessarily limited to marine biogeochemistry, air-sea interactions, paleo-oceanography, algal and microbial biochemistry, environmental chemistry, and analytical chemistry. It will address controls on iodine speciation and rates of transformations in the oceans past and present, and predictions of how these may change in the future. Modeling, experimental and field studies will all be considered. Potential subjects could for example include oceanic lifetimes of iodine species, microbiological transformations including the role of nitrifying bacteria, iodine in marine aerosols, use of iodine as a tracer, ocean modeling, and new analytical techniques.

We welcome relevant manuscripts of all types, including original research, methods, mini-reviews, data reports, and perspectives.

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Frontiers in Marine Science

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