Fertilising the oceans with iron to absorb carbon dioxide could increase concentrations of a chemical that can kill marine mammals, a study has found. Iron stimulates growth of marine algae that absorb CO2 from the air, and has been touted as a "climate fix".
Now researchers have shown that the algae increase production of a nerve poison that can kill mammals and birds.
Writing in Proceedings of the National Academy of Sciences, they say this raises "serious concern" over the idea.
The toxin - domoic acid - first came to notice in the late 1980s as the cause of amnesiac shellfish poisoning.
If the end goal is to use it to fight climate warming, then we have to understand the consequences for marine life Dr William Cochlan San Francisco State University
It is produced by algae of the genus Pseudonitzschia, with concentrations rising rapidly when the algae "bloom".
Now, its presence in seawater often requires the suspension of shellfishing operations, and is regularly implicated in deaths of animals such as sealions.
Domoic acid poisoning may also lie behind a 1961 incident in which flocks of seabirds appeared to attack the Californian town of Capitola - an event believed to have shaped Alfred Hitchcock's interpretation of Daphne du Maurier's The Birds in his 1963 thriller.
Carbon focus
Over the last decade, about 10 research projects have investigated iron fertilisation, with mixed results.
But only two of them measured domoic acid production, and only then as an afterthought, explained William Cochlan from San Francisco State University, a scientist on the new project.
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