Tried to post this on the Island of Doubt, but it wouldn't let me. So here it is, in response to:
The iron fertility controversy
The problem is, previous studies have shown that only about 5% of the carbon generated by the enhanced productivity actually exits the surface ocean and sinks into the deep ocean (as organic carbon, detritus or fish/zooplankton poop). All the rest of the carbon gets recycled -- fish and zooplankton get fatter -- and when they get et and pooped, the carbon just gets "remineralized" by bacteria back into inorganic dissolved carbon, which then slightly shifts the oceanic carbonate and bicarbonate ions a bit such that the ocean waters with more carbon release it back into the atmosphere. The ocean conserves its carbon and is very efficient at it. So iron fertilization might be good for fishing, if you catch the fatter fish. The problem with that is fish have learned where to go to get more food, and they don't stay in one place. They migrate (which is why bluefin tuna are such fast, efficient swimmers). That's why the Grand Banks system produced so much cod -- they followed a seasonal cycle of reproduction and growth. Bottom line: iron fertilization is not a viable geoengineering solution for increasing atmospheric carbon dioxide.
Some linkage on this:
Iron Enriching Southern Ocean Pulls Carbon Dioxide From Atmosphere (gotta do it continuously -- during the summer, of course -- in the wildest oceans in the world)
And here's a more recent article about why it won't work:
Ocean Fertilization 'Fix' For Global Warming Discredited By New Research