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![[Figure 1]](hi0109fig1mag.jpg)
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Figure 1
Simplified biogeochemical cycle of iodine. In sea water, iodine (total concentration 0.5 µM) is mainly present as iodate, yet up to 50% of this can be converted to iodide in the euphotic zone, presumably as a side reaction of nitrate reductase of planktonic algae and bacteria (e.g. Farrenkopf et al., 1997  ; Wong et al., 2002). Iodide can be taken up, possibly by the action of vanadium-containing haloperoxidase (Wever et al., 1991), by a variety of algae (Küpper et al., 1998), which constitute the major biogeochemical pump of iodine from the ocean to the atmosphere, in the form of iodinated halocarbons (Carpenter et al., 2000). Besides emission by algae, a non-biological pathway to methyl iodide formation has been suggested, based in the reaction of organic matter in sea water with I2 or HOI formed by oxidation of I− in the upper water column (for review, see Luther et al., 1995). Iodocarbons are rapidly photolyzed and oxidized, resulting in the formation of iodine oxide (Alicke et al., 1999). IO has recently been recognized as a contributor of condensation nuclei for cloud formation in the coastal atmosphere (O'Dowd et al., 2002), resulting in its deposition by precipitation. On land, iodine is accumulated by both terrestrial plants and animals, being an essential trace element for the biosynthesis of the thyroid hormone, thyroxine, by the action of lactoperoxidase. Part of the iodine entering the agricultural and human food chain nowadays originates from sea foods, including seaweeds, and from iodine supplements added to table salt from fossil iodide/iodate deposits. |
![[Figure 1]](hi0109fig1.jpg)
 | JOURNAL OF SYNCHROTRON RADIATION |
ISSN: 1600-5775
