Fertilizing the oceans with iron has been proposed as a way of fighting climate change. The idea is that iron will promote blooms of phytoplankton that will remove carbon dioxide from the atmosphere through photosynthesis. When the phytoplankton dies and sinks, the carbon will effectively be sequestered in the deep ocean.
http://www.nytimes.com/2010/03/16/science/16obiron.html?src=twt&twt=nytimesscience