Biogeochemical iodine cycle: Inventories are in Tg iodine per year. Labeled flux arrows are in Gg iodine per year. Unlabeled inventories (sinks) and fluxes are of unknown quantities. Iodine cycles through the lithosphere, atmosphere, hydrosphere, and biosphere. [1][2][3][4] Freshwater iodine is calculated by subtracting oceanic iodine[4] from total iodine in the hydrosphere.[1] In oceans sediments and crust, iodine is replenished by sedimentation[1] and is cycled into seawater through release as brine during subduction.[4] Marine biota uptake iodine from seawater[1] where it may be volatilized by transformation to methyl iodide.[3] Sea spray aerosolization, volcanic activity, and fossil fuel burning cycles iodine from the hydrosphere and lithosphere into the atmosphere as well,[1] while wet[2] and dry deposition remove iodine from the atmosphere.[1] In soil, small quantities of iodine are cycled through weathering of parent rock.[1] Terrestrial biota uptake and remove iodine from soil, and bacteria volatilize iodine by methylizing it.[1]