This notion has been around for a while, but a geo-engineering company, called Planktos, Inc., is ready to dump iron-filings into the Pacific Ocean, off the Galapogos Islands, in a full-scale test to see if this can remove CO2 from the atmosphere. However, this has met with opposition from some conservationists who claim that dumping iron without a permit is illegal under the International London Dumping Convention and also under US law.
It is known that "seeding" ocean areas, where plankton does not grow in quantity, with iron-filings creates plankton blooms, which absorb thousands of tonnes of CO2 in their formation. However, those opposed to the scheme think that the full effects of the presence of iron on the Pacific ecosystems have not been fully researched, and there are good reasons to believe it will be harmful to them. According to Planktos' web-site, the company will, this month, begin depositing 100 tons of iron-filings in an area of 100 square kilometers from its ship, the Weatherbird II. Their view is that: "Planktos will begin plankton restoration by replenishing forest-sized areas of ocean with natural iron-rich dust, just as Mother Nature does. This will regenerate vast plankton blooms that will not only pull large quantities of CO2 from the air, but will also nourish collapsing fisheries, buffer ocean acidity [...from dissolved CO2 presumably?], and produce saleable carbon credits for emerging environmental markets."
The latter credits will be sold to individuals who want to offset their personal carbon credits. This sounds like a good way to fund the whole enterprise and make a good profit, so it is a convincing business plan.
The Weatherbird II is a US-flagged vessel which would be subject to the US Ocean-Dumping act, but there are apparently documents submitted by the US government to the London Dumping Convention that suggest it is "a non-US flagged vessel" that is intended to be used and which is not subject the the act. The Galapagos National Park authorities are concerned that the influence of large amounts of iron could damage marine food-chains. The US government have called for the company's activities to be "evaluated carefully." Jim Thomas of the Canadian environmental oragisation, ETC,which has been monitoring Planktos said: "It is rank hypocrisy that Planktos, which claims to be a "green" company is now planning to outsource their dumping to a foreign ship in order to evade US environmental oversight. The overwhelming scientific conclusion ...is that iron seeding is risky and may only temporarily sequester CO2 ...leaving [it] below the surface just long enough for private geo-engineers to cash their cheques."
However, Russ George, chief executive of Planktos, said: "How could this be illegal? The letter of the law says that if concentrations do not reach 0.01 of the acute toxicity of a substance you are not required to seek a permit to dump." [...presumably they have calculated that the "regional" concentration of iron in that part of the Pacific will be less than this. Mixing rates and so forth?] He goes on, "The US EPA allows people to put vastly more than that into the ocean. We are putting rock-dust in the ocean." [...are they? I thought it was actually metallic iron powder, which is not the same thing at all?]. "Billions of tons of dust from the Gobi desert blow into the ocean every year. How could anybody say we are polluting the sea?" He emphasises Planktos' green mission and that he has steered the Greenpeace Rainbow Warrior himself and that to portray them as "money grubbing capitalists" is a perversion of the truth.
Of course, the money to fund the project has to come from somewhere and if they are a company they need to make a profit to stay in business. It is debatable how much difference this approach will really make to atmospheric CO2 levels, how safe it is to the marine environment - especially if it is adopted on the huge scale necessary to offset the world's carbon emissions, and how well sequestered the CO2 might prove to be in the longer run. It is presumed that the dead phytoplankton (and dead sea-life that fed on them), will sink harmlessly to the ocean floor in carbon-rich "showers of marine snow".
The phytoplanktons of the oceans (and related species) are thought to absorb around half of the CO2 that is taken-up altogether from the atmosphere through photosynthesis. Hence, in principle the method could be significant. It remains a matter of conjecture how safe it is to artificially promote the growth of algal blooms on a large scale. After all, that's why we banned phosphates from soap-powders, isn't it, and replaced them with zeolites? There is surely the risk that other algae might be also encouraged that are are toxic to plants and animals, depending on what other nutrients are present in the ocean.
I am concerned in general about the various schemes of "geo-engineering" that I read about, which each focus on a single aspect of systems that are so complex we don't really understand the interplay of all their components, and so might bring about undesired consequences, indirectly related to the matter it is wished to address.
(1) "Mass Dump of iron filings 'to remove CO2', by Charles Clover. http://www.telegraph.co.uk/core/Content/display/Printable