Wikipedia:
Iron fertilization is the intentional introduction of iron to the upper ocean to stimulate a phytoplankton bloom. This is intended to enhance biological productivity, which can benefit the marine food chain and is under investigation with regards to being a successful means of facilitating increased carbon dioxide removal from the atmosphere.
This sounds really cool but also has the potential to go horribly, horribly wrong when the phytoplankton swear revenge and build a giant robot with all the iron.
(Via Julio Capote)