Since we are talking about iron. Just read about this geo-engineering, an intentional 2012 iron-dust 'fertilization' was closely monitored and indicated an enormous plankton bloom, carbon dioxide absorption/scrubbing, salmon/fish population increase... /http://www.popsci.com/article/science/rogue-geoengineering-project-may-have-increased-salmon-numbers
The entrepreneur counters that strong oceanic underwater currents stir iron sediments and occasional 'natural' volcanic eruptions sow airborne iron dust and the trigger the same plankton explosions.
There are other oceanic experiments but is this environmental stewardship or 'pollution'?
Russ George's blog on how to bring back the fish.