So, you've seen The Legend and Prophecy of Johnny Ironseed, but if you'd like to learn more about the iron hypothesis, here are some links to some of the more interesting/informative articles:

http://www.palomar.edu/oceanography/iron.htm [1]

http://news.nationalgeographic.com/news/2004/06/0609_040609_carbonsink.html [2]

http://www.csa.com/discoveryguides/oceangard/overview.php [3]