Seaweed have long been known to release iodine into the atmosphere, which then act as nuclei around which clouds form. But why seaweed were storing iodine was a mystery. Now an international team of researchers has shown that large brown kelp store iodine in the form of iodide and release the ion in response to stress.

The iodide mops up reactive oxygen species and so protects the kelp from damage when its exposed to strong sunlight or in danger of drying out during low tides. That means the iodide is acting as the first known inorganic – and the most simple – antioxidant in any living system, according to the team.

Kelp

‘When kelp experience stress, for example when they are exposed to intense light, desiccation or atmospheric ozone during low tides, they very quickly begin to release large quantities of iodide from stores inside the tissues,’ explains lead author, Frithjof Küpper from the Scottish Association for Marine Science. ‘These ions detoxify ozone and other oxidants that could otherwise damage kelp, and, in the process, produce molecular iodine. Our new data provide a biological explanation why we can measure large amounts of iodine oxide and volatile halocarbons in the atmosphere above kelp beds and forests.’

There are extensive kelp beds around rocky coastal areas in the UK, including the Hebrides, Robin Hood’s Bay and Anglesey, says Gordon McFiggans, an atmospheric scientist from the University of Manchester’s School of Earth, Atmospheric and Environmental Sciences (SEAES). ‘The increase in cloud condensation nuclei by kelps could lead to more extensive, longer lasting cloud cover in the coastal region – a much moodier, typically British coastal skyline,’ he says.

Iodide probably doesn’t have the same role in humans however – our bodies couldn’t cope with the high concentrations of iodine required. However Sebastiano Venturi has suggested that the iodine that accumulates in the thyroid may have originally had a role as an antioxidant.

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