The Hot Zone

Toxic Waters

Posted by Alison Hawkes on March 16, 2010
Category : The Oceans

By Alison Hawkes

Remember the old idea that we could escape climate change by dumping a bunch of iron into the ocean? Iron “seeding” or “fertilization” rests on the notion that iron could be added to the nutrient-deprived deep sea to cause massive phytoplankton blooms, which would capture carbon and, as they died, sink it to the ocean floor.

Sounds good, except many people have gotten cold feet over human-induced iron seeding – after all, it seems like too much tampering with ocean ecosystems. And one recent study lowered estimates of how much carbon could realistically be stored using this method.

Adding new caution to the heap is a study published yesterday in the Proceedings of the National Academy of Sciences, which found that iron seeding could promote the growth of a toxic type of phytoplankton called Pseudonitzschia. The name sounds like a serious psychological disorder. And it can mess you up. Pseudonitzschia produces neurotoxic domoic acid, like what’s seen during red tides, and can bioaccumulate in shellfish, anchovies, and sardines causing lethal results in mammals, including humans. Not the kind of stuff you want floating around the ocean.

Red algal bloom off the coast of New Zealand, courtesy of Miriam Godfrey

Red algal bloom off the coast of New Zealand, courtesy of Miriam Godfrey

It was previously thought that the toxic form of Psuedonitzschia is limited to coastal waters, but this study found “unequivocally” that the mid-ocean variety did, indeed, produce the toxin. The study’s authors, led by Charles Trick of the University of Western Ontario wrote:

“Although the total toxin concentrations generated in some of these preliminary experiments may not be enough to generate acute toxicity at higher trophic levels, it is unclear whether higher concentrations may result under conditions of large-scale and persistent iron enrichments designed to obtain carbon credits.”

In other words, dumping iron into the sea on the scale of a carbon credit program could potentially make ocean waters highly toxic. It appears that the toxin itself allows Pseudonitzschia to outcompete other species of phytoplankton, ensuring its perpetuation. Pretty nasty stuff.

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