The Oceans are a possible answer to the accumulating carbon dioxide consequent upon excess burning of fossil fuels. If the algal growth could be increased then carbon dioxide take would increase. The main Ocean where this might take place is the Southern Ocean. Adding iron to the oceanic waters, both naturally as iron rich dust blown off the Crozet Islands or added artificially as is happening with the Indo-German vessel which adding 20 tonnes of iron to the water.
However as study reported in Nature suggests that the effect or benefit of such iron is less than anticipated.
Crozet rich dust may add some 270 tonnes of iron and a two to three fold increase in biological activity over an area equivalent to the area occupied by Ireland. But the deeper water are not affected to any extent. The export of carbon to the deeper levels is less than anticipated.
Maybe the type of iron used could be important.
Nature Ocean fertilization: dead in the water. vol 457, 520-1
- Martin Eastwood