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Ocean seeding fails the acid test
12 June 2008
From New Scientist Print Edition.
Michael Reilly

It all seemed too easy by half: to beat global warming just sprinkle some iron in the ocean, then watch as algae bloom en masse, sucking up carbon dioxide by the tonne. Now the idea is looking increasingly unlikely to go ahead in a big way. In the wake of a UN moratorium on the practice, the latest research suggests that seeding will trigger the build-up of an acid that can be lethal to marine organisms and humans.

The idea of ocean seeding has been controversial ever since it was first explored over a decade ago. Not enough is known about where the carbon goes once algae gobble it up, for instance, or whether the plants even bloom enough to appreciably lower atmospheric CO2 levels (New Scientist, 15 September 2007, p 42).

Last month, the UN Convention on Biological Diversity agreed that the potential dangers outweigh the benefits: its 191 member nations agreed to a ban pending further research. The decision will be a blow for companies that were hoping to profit by selling the carbon credits they would earn by triggering algal blooms. Some of these firms are already facing obstacles: last month, for example, San Francisco-based Climos was reportedly seeking further funds for large-scale tests. And in February, Planktos, of Foster City, Calfornia, shut down due to a lack of cash. It blamed a "highly effective disinformation campaign waged by anti-offset crusaders".

Yet the moratorium may have been a prescient move. As the UN conference was coming to a close in Bonn, Germany, Mary Silver of the University of California, Santa Cruz, was presenting her latest findings at a meeting of the American Geophysical Union in Fort Lauderdale, Florida. Her results suggest that iron encourages the growth of large populations of some ocean algae species that produce domoic acid- a potent neurotoxin.

In coastal waters, domoic acid is infamous. Shallow water blooms of algae in the genus Pseudo-nitzschia create large quantities of the poison, which can sicken and kill marine mammals, birds and even people who eat contaminated shellfish (New Scientist, 16 June 2007, p 18).

This type of alga has rarely been found in the deep ocean - where the iron would be sprinkled - but that's not because it is absent, according to Silver. Instead, she says, deep ocean species of Pseudo-nitzschia are too scarce to be detected in the usual way. "Most seawater samples are tens or hundreds of millilitres, and that's not enough to see them."

Silver collected hundreds of litres of water before she found a few Pseudo-nitzschia cells. Even then they contained less acid than their coastal counterparts. However, when Silver seeded the samples with iron, the Pseudo-nitzschia population exploded, and so did domoic acid levels. "They're really the first responders in the iron experiments," says Silver. "And domoic acid is a big reason why." The acid is a "chelator", she explains, binding to iron to make more of it available to the algae. Easy access to this nutrient would allow algae to out-compete other species.

Silver cautions that her results don't necessarily mean that iron fertilisation would create widespread poisoning of the seas. "But it's a major warning sign." We should carefully consider the consequences of tinkering with life in the deep ocean, she says.

Other researchers agree. "These systems are very complex," says Alan Robock of Rutgers University in New Jersey. "Much more evaluation is needed to understand the effects of any geoengineering plan before we start doing it."

From issue 2660 of New Scientist magazine, 12 June 2008, page 7

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