“Give me half a tanker of iron, and I’ll give you an ice age,” said  biogeochemist John Martin, former director of the Moss Landing Marine Laboratory, several years ago. While admitting to hyperbole, Martin had a point: his discovery that iron dust could trigger phytoplankton blooms in certain parts of the ocean has led some to argue humans should help reverse climate change by fertilizing the microscopic marine plants that remove carbon dioxide from the atmosphere.
David Billett was part of a research team from the U.K.'s National Oceanography Centre studying how natural iron fertilization affects deep sea biology. "All options in mitigating the increase in atmospheric CO2 need to be kept open," Billett wrote Fast Company in an email. "[This work] needs to be supported because it will take time to build up results to assess the best [geoengineering] methods and how they might be applied."
The chemical process is quite simple. The growth of phytoplankton is limited by trace elements such as iron. By fertilizing vast swaths of the open ocean with iron, city-sized blooms of tiny marine plants could sequester carbon dioxide and send it sinking to the ocean floor as dead biomass. How much CO2? Early climate models suggest fertilizing Antarctica's entire Southern Ocean  could suck up 1 to 2 billion tons of carbon emissions each year, equal to about 10 to 25 percent of the world’s annual total , says the Woods Hole Oceanographic Institute.
Although these efforts, known as geoengineering, are extremely controversial, scientists are not ruling them them out entirely. We are already "engineering" a warmer planet by pumping greenhouse gasses, particulates and chemicals into the atmosphere. It may be that humans can take countermeasures to reverse the process on a comparable scale, although the risks and uncertainties are enormous. Iron fertilization of the oceans is one of those options.
Billett's team sailed to the Crozet Islands in Indian Ocean, a natural deep-sea laboratory where natural iron from volcanic islands creates large phytoplankton blooms, while adjacent the area remains bloom-free. They studied life three miles below the surface, where "one big mud patch stretches for thousands of kilometers-- rather like the Great Plains--hardly changing in depth for great distances."
Yet all sorts of life survives on those plains, eating the organic matter raining down from above. Fertilizing the surface with iron, it was presumed, changes the food supply at the sea floor and the species who feed on plankton. "Life in the deep ocean is dependent on this food so changes in its supply have the potential to cause large ecosystem changes," writes Billett. "Our work shows, for the first time, this is so."
Samples from trawls, sediment cores, and video cameras of the seafloor at the iron-rich sites show an abundance of deep-sea animals such as sea cucumbers and brittle stars with biodiversity characteristic of the productive North East Atlantic, 10,000 miles away, rather than iron-poor sites next door. The conclusion? "Some geo-engineering schemes … would significantly affect deep-sea ecosystems."
What the consequences on the entire ecosystem of sea cucumbers and starfish run rampant would be is harder to pin down, but altering the food chain in any way is bound to have serious effects. To this point, though, it's not much of an immediate concern: CO2 sequestration in the field has proven disappointingly meager compared to laboratory experiments. Much of the carbon sequestered in the blooms is immediately "grazed" by zooplankton (microscopic marine animals) and re-released. But that hasn't stopped some companies from pursuing iron fertilization as a commercial venture: Planktos  and Climos  are both investing in the approach.
Science, however, will not give us a definitive answer anytime soon about whether iron fertilization is a good idea. Moss Landing Marine Lab director Kenneth Coale told a WHOI publication  that past experiments have tried to answer the question: "'How does the world work?,' not 'How do we make the world work for us?'"
"They’re totally separate," said Coale. "We have not done the experiment to address the issues that we’re talking about today.”
[Image: Flickr user angies ]