[4] Marine biota, including seaweed and fish, accumulate iodine from the seawater and return it during decomposition.
[3] Iodine rarely occurs naturally in mineral form, so it comprises a very small portion of rocks by mass.
[1] Soils contain a much higher concentration of iodine compared to their parent rock, though most of it is bound to organic and inorganic matter, potentially due to microbial activity.
[1] A much larger anthropogenic impact is through the burning of fossil fuels, which releases iodine into the atmosphere.
[1] Iodine-129, a radioisotope of iodine, is a waste product of nuclear power generation and weapons testing.
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
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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
]
