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- Title
Description and drivers of the sea surface iodide distribution.
- Authors
Chance, Rosie; Tinel, Liselotte; Wadley, Martin; Hughes, Claire; Sherwen, Tomás; Hepach, Helmke; Barton, Eleanor; Jickells, Tim; Stevens, David; Mahajan, Anoop; Sarkar, Amit; Carpenter, Lucy
- Abstract
The reaction of ozone with iodide at the sea surface is an important sink for troposphericozone, and the dominant source of reactive iodine to the troposphere. Rates of both processesare dependent on iodide concentration, which varies by 1-2 orders of magnitude across theocean surface. Observations of sea surface iodide are relatively scarce, and the drivers of thisvariation remain poorly understood. We present an expanded, global dataset of 1342 sea surface (<20m) iodideobservations, which is a 45% increase on an earlier compilation (Chance et al. 2014).Observations span 70˚ S to 68˚ N, and include measurements made in the IndianOcean, a previously undersampled region. The expanded dataset confirms a stronglatitudinal gradient, with highest iodide concentrations occurring at lower latitudes.The extended observational data set has been used to evaluate commonly used seasurface iodide parameterisations, and to develop a new parameterisation using amachine learning approach. We also present measurements of iodide in the sea surfacemicrolayer, and discuss whether (or not) this crucial reaction zone may be enhanced iniodide. The marine iodide distribution is thought to be controlled by biologically mediatedproduction and loss processes, additional abiotic reactions, vertical mixing and advection. Wesummarise evidence for the microbiologically mediated interconversion of iodine species,including new results suggesting that iodide oxidation, the dominant iodide loss process, maybe associated with bacterial nitrification, specifically the conversion of ammonium tonitrite. A biogeochemical model of iodine cycling has been embedded in the OCCAMoceanographic framework, and calibrated using the observational dataset. In the model,iodide production is driven by primary production. Model-observation residuals weresubstantially reduced by linking iodide oxidation to biological nitrification, and increasing theratio of iodide produced to carbon fixed (by primary production) with latitude. Using sectiondata from the Indian Ocean, we explore how biological productivity, oxidation, mixing andadvection drive the sea surface iodide distribution.References Chance, R., A. R. Baker, L. Carpenter, and T. D. Jickells. 2014. ’The distribution ofiodide at the sea surface’, Environmental Science-Processes & Impacts, 16: 1841-59.
- Subjects
IODIDES; PHYSIOLOGICAL oxidation; BIOLOGICAL productivity; SEAS; OZONE layer; OZONE
- Publication
Geophysical Research Abstracts, 2019, Vol 21, p1
- ISSN
1029-7006
- Publication type
Article