Not ready for prime time

Seawater from the Southern Ocean (left) and seawater collected from a patch in the Southern Ocean after scientists enriched it with iron to create a phytoplankton bloom (right).

It's been fascinating to follow the rise and fall of ocean fertilization over the last few years. 

2007 - The business view
Recruiting Plankton to Fight Global Warming
 Can plankton help save the planet?

2008 - The environmental backlash
Planktos Dead in the Water
A highly effective disinformation campaign waged by anti-offset crusaders has provoked widespread opposition to plankton restoration in the environmental world, and has caused the company to encounter serious difficulty in raising the capital needed to fund its planned series of ocean research trials.

2008 - A view from the ivory tower
2008 Ocean Iron Fertilization--Moving Forward in a Sea of Uncertainty
It is premature to sell carbon offsets from ocean iron fertilization unless research provides the scientific foundation to evaluate risks and benefits. 
The bottom of the Science paper links to some more recent articles that cited it.

Here's one last article, from the more popular press, that seems to cover the debate in a fairly even handed way
Seeding the Sea: Will releasing iron into the oceans to combat climate change help — or harm — the planet?