Methyl iodide production in the open ocean

[摘要] Production pathways of theprominent volatile organic halogen compound methyl iodide (CH₃I) are notfully understood. Based on observations, production of CH₃I viaphotochemical degradation of organic material or via phytoplanktonproduction has been proposed. Additional insights could not be gained fromcorrelations between observed biological and environmental variables or frombiogeochemical modeling to identify unambiguously the source of methyl iodide. In this study, we aim toaddress this question of source mechanisms with a three-dimensional globalocean general circulation model including biogeochemistry(MPIOM–HAMOCC (MPIOM – Max Planck Institute Ocean Model HAMOCC – HAMburg Ocean Carbon Cycle model)) by carrying out a series ofsensitivity experiments. The simulated fields are compared with a newlyavailable global data set. Simulated distribution patterns and emissions ofCH₃I differ largely for the two different production pathways. Theevaluation of our model results with observations shows that, on the globalscale, observed surface concentrations of CH₃I can be best explainedby the photochemical production pathway. Our results further emphasize thatcorrelations between CH₃I and abiotic or biotic factors do not necessarilyprovide meaningful insights concerning the source of origin. Overall, we finda net global annual CH₃I air–sea flux that ranges between 70 and260 Gg yr⁻¹. On the global scale, the ocean acts as a net source ofmethyl iodide for the atmosphere, though in some regions in boreal winter,fluxes are of the opposite direction (from the atmosphere to the ocean).

[学科分类] 地球化学与岩石