This idea has been around for a while, but I didn't realise there were field experiments going on. Basically, iron particles are dumped into the ocean which encourages a massive algal bloom. A proportion of the algae will sink to the bottom of the ocean, trapping the carbon. John Martin, an oceanographer, famously quipped: "Give me half a tanker of iron, and I’ll give you the next ice age.”<p>There's a better article here: <a href="http://planetsave.com/2012/07/22/geoengineering-news-controversial-ocean-iron-fertilization-experiment-succeeds-as-carbon-sink/" rel="nofollow">http://planetsave.com/2012/07/22/geoengineering-news-controv...</a>