ye olde iron fertilizing effect

So apparently people now think they can make money by throwing iron into the ocean... YES, throwing iron into the ocean.

Here's the, actually very good, story on NYTimes.com: [The Energy Challenge: Recruiting Plankton to Fight Global Warming]

The basic idea is that plankton reproduce like mad when the conditions are right, and in large swaths of the ocean the conditions are right. Except there isn't enough iron. So, when you dump some iron on those areas, plankton bloom, creating regions of increased biological activity. The upside to this, according to some, is that the plankton use carbon from the ocean to make their little calcium carbonate exoskeletons, which when the critters die, can sink to the bottom of the ocean. This means that carbon is removed from the atmosphere-ocean system... it is sequestered, like an OJ juror. So now at least two companies, so cleverly named Planktos and Climos, think they can get governments (or companies working under cap and trade systems) to pay them to go throw some iron into the ocean.

I do not reject this idea outright. There are clearly some good ideas here, but we have to be careful. Here are a couple of my primary concerns.

First, I'm worried that these plankton species will produce a lot of methane waste, possibly negating any decrease in atmospheric CO2 that they might be responsible for. There is similar concern with nitrous oxide, apparently.

Second, the amount of carbon actually deposited might be less than has been thought recently. This is actually in this week's Science [LINK].

Third, as these operations scale up, will they account for their own carbon emissions. Boats are notoriously bad for emissions, and there's going to have to be a lot of boating involved. Also, where is this iron coming from, and how much energy (i.e., carbon) is going into collecting and transporting it?

Finally, there are possible feedbacks that could negate any good this will do. Including the old DMS-cloud condensation nuclei, in which more biology produces more aerosol (in the form of dimethylsulfide, DMS) which acts as nucleation sites for cloud droplets, making more cloud. The effect could be to shade the surface, reduce SST, and thus reduce biological productivity, leaving a rusty sea surface instead of a nice, healthy green one. I don't know if this is feasible, but things like this always seem to come up.

Also consider the amount of carbon dioxide that needs to be removed from the atmosphere. I've just come from a talk that reminded me of this. Carbon dioxide, when frozen, has about the same density as water. That means that a ton of CO2 is about one cubic meter (size of a coffee table). You're now talking about removing billions of tons of carbon dioxide annually, which is an enormous mass, many cubic kilometers of frozen CO2. The ocean is a big place, but we've got to be careful about how and where such deposits are made, or they'd just be mixed back up to the atmosphere. There's just so many potential pitfalls that it is hard to imagine a successful implementation. But as I said at the beginning, I'm willing to keep an open mind on the subject, and would be happy to see a successful strategy.