4 Oceanus Magazine Vol. 46, no. 1, 2008 www.whoi.edu/oceanus1000 1200 1400 1600 1800 2007 Year280Atmospheric CO2 (ppm)380360340320300“give me half a tanker of iron, and i’ll give you an ice age” may rank as the catchiest line ever uttered by a biogeochemist. The man responsible was the late John Martin, former director of the Moss Landing Marine Laboratory, who discovered that sprinkling iron dust in the right ocean waters could trigger plankton blooms the size of a small city. in turn, the billions of cells produced might absorb enough heat-trap-ping carbon dioxide to cool the earth’s warming atmosphere.never mind that Martin was only half serious when he made the remark (in his “best Dr. strangelove accent,” he later recalled) at an infor-mal seminar at Woods Hole Oceanographic institution (WHOi) in 1988. With global warming already a looming problem, others were inclined to take him seriously.at the time, ice-core re-cords suggested that during past glacial periods, naturally occurring iron fertilization had repeatedly drawn as much as 60 billion tons of carbon out of the atmosphere. Laboratory experiments suggested that every ton of iron added to the ocean could remove 30,000 to 110,000 tons of carbon from the air. early climate models hinted that intentional iron fer-tilization across the entire southern Ocean could erase 1 bil-lion to 2 billion tons of carbon emissions each year—10 to 25 percent of the world’s annual total.since 1993, 12 small-scale ocean experiments have shown that iron additions do indeed draw carbon into the ocean—though perhaps less efficiently or permanently than first thought. scientists at the time agreed that disturbing the bot-tom rung of the marine food chain carried risks.Twenty years on, Martin’s line is still viewed alternately as a boast or a quip—an opportunity too good to pass up or a misguided remedy doomed to backfire. Yet over the same pe-riod, unrelenting increases in carbon emissions and mount-ing evidence of climate change have taken the debate beyond academic circles and into the free market.Today, policymakers, investors, economists, environ-mentalists, and lawyers are taking notice of the idea. a few companies are planning new, larger experiments. The ab-sence of clear regulations for either conducting experiments at sea or trading the results in “carbon offset” markets complicates the picture. But economists conclude that the growing urgency to solve our emissions problem will reward anyone who can make iron fertilization work.in past experiments “we were trying to answer the question, ‘how does the world work?’—not ‘how do we make the world work for us?’ ” Ken-neth coale, the present-day director of Moss Landing Marine Lab, said recently. “They’re totally separate. We have not done the experiment to address the issues that we’re talking about today.” “We’re in a learning process that involves a balance of science, commercial, and a whole variety of social activities and interests,” said anthony Michaels, director of the Wrig-ley institute for environmental studies at the university of southern california. “We’ve got to set up a measured process for moving forward.”The two scientists were speaking at a fall 2007 conference that brought together some 80 participants representing the Fertilizing the Ocean with IronIs this a viable way to help reduce carbon dioxide levels in the atmosphere?Ocean Iron FertilizationAn argument for: Faced with the huge consequences of climate change, iron’s outsized ability to put carbon into the oceans isn’t just an opportunity, it’s a responsibility.An argument against: It’s a meager, temporary, unverifiable proposition involving private individuals dumping materials into the common waters of the world’s oceans.A middle ground: Careful experiments conducted by scientists are our best hope for learning how much carbon can be sequestered without harming the ocean ecosystem.WOODs HOLe OceanOgrapHic insTiTuTiOn 51000 1200 1400 1600 1800 2007 Year280Atmospheric CO2 (ppm)380360340320300scientific, commercial, regulatory, and economic sides of the debate. The conference was convened by WHOi marine geo-chemists Ken Buesseler and scott Doney, and Hauke Kite-powell of the WHOi Marine policy center. in talks and wide-ranging discussions, participants raised serious doubts about the practicality, efficacy, and safety of large-scale iron fertilization. Yet many also seemed to accept that more sci-ence—in the form of carefully designed and conducted ex-periments—is the best way to resolve those doubts, one way or the other.Not as simple as it soundsMartin made his pronouncement jokingly because he knew that he was glossing over several hindrances to us-ing iron fertilization to sequester carbon in the ocean. Op-ponents to the idea are quick to point out the three major ones: it may be less efficient than it at first seems; it raises a host of new, worrying consequences; and its effec-tiveness is difficult for anyone to measure.in certain regions, including the equato-rial and north pacific and the entire south-ern Ocean, a simple iron addition does cause phytoplankton to grow rapidly. But tiny zooplankton, known as “grazers,” eat much of the bloom almost as soon as it starts. This begins a chain of recycling that ensues from the sea surface to the seafloor as grazers, krill, fish, whales, and microbes eat, excrete, and decom-pose. Much of the im-mense carbon prize won by iron addition Atmospheric carbon dioxide levels have increased precipitously since the 1850s, and continue to rise.Jack Cook, WHOI1 Plants absorb CO2 from air to grow, and decomposeto release CO2.CO2CO22 Iron-rich dust is blown by windsinto the ocean and stimulatesphytoplankton blooms.8 Over millions of years, carbon is incorporatedinto rocks or turned into hydrocarbons.5 Zooplanktoneat phytoplanktonand respire CO2.3 Air and seaexchange CO2.Dust6 Some carbon sinks to the depths in the form of decaying biota and fecal pellets.9 Rocks are eventually uplifted onto land and weathered to release carbon to soils andthe atmosphere.THE CARBON CYCLE—Carbon moves naturally through ground, ocean, and sky in a slow cycle over millions of years. People have short-circuited this cycle by quickly transferring hydrocarbons from ground to air. Iron fertilization proposes to accelerate the transfer of carbon from air back to ocean.4 Phytoplanktontake up CO2 to grow.7 But only