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It's the science fiction equivalent of being buried 20,000 leagues under the sea. Deep near the ocean floor, where the quiet secrets of an alternate marine world sleep, scientists are talking about trapping and locking large amounts of carbon dioxide for millennia. Like fertilizer used to grow crops on land, researchers have been fertilizing swaths of the ocean with iron dust, a micronutrient that stimulates plankton blooms, which in turn absorb heat-trapping CO2. A man named John Martin is widely credited for planting seeds for the idea in 1988 at an oceanography conference, where he quipped, "Give me a tanker of iron, and I'll give you an ice age." Little did he know that that single, snappy remark would be repeated ad nauseum by proponents of ocean iron fertilization to epitomize its potential. According to the Woods Hole Oceanographic Institution (WHOI) in Massachusetts, early climate models have suggested that intentional iron fertilization across the Southern Ocean, which encircles Antarctica, could absorb one to two billion tonnes of carbon emissions a year -- 10% to 25% of the world's annual total. Ice-core records also showed natural iron fertilization had drawn as much as 60 billion tonnes of carbon out of the air during glacial periods. Private companies are pushing ahead with plans to sow the sea, hoping to enter the carbon trading market: The value of ocean fertilization has been estimated to be $100 billion. But scientists are ringing alarm bells and saying the scheme hasn't yet been proven effective on a large-scale basis. This month, 16 global oceanographers penned an open letter to the journal Science, calling any move to issue carbon credits from ocean fertilization "premature." More research needs to be done to verify the scheme's efficiency at capturing and storing CO2, and not enough is known about the potential side effects, the letter said. "I would agree that it's premature to issue any carbon offsets with the present amount of knowledge we have," added John Cullen, a noted oceanographer at Dalhousie University. While plankton blooms may absorb carbon dioxide, for example, the process could also produce other greenhouse gases like nitrous oxide and methane to even more devastating effect, Cullen points out. "If nitrous oxide came into contact with the atmosphere, it has 300 times the greenhouse gas potential of carbon dioxide." Conversely, at a WHOI conference last year, a gathering of policymakers and scientists including Cullen heard that more plankton could produce dimethylsulfide, a chemical that would promote cloud formation and help cool the atmosphere. But plankton blooms could also rob the waters of nutrients such as nitrate, phosphate and silica from neighbouring plankton growth, while oxygen-depleted waters could cause fish kills. Blankets of plankton would also block sunlight needed by corals and warm surface temperatures. And while forests can be monitored and its effects quantified, the ocean is fluid, Cullen added. "If you plant a hundred square kilometres of forests you can go back every day for the next 100 years and see what happens. But you can't go back to the same part of the ocean because it moves. ... each layer of the ocean is moving at different directions and different speeds." That means companies could shirk liability because any negative results would be difficult to trace. Ocean seeding would also only be effective on a large-scale, long-term basis. But if activity consists of little more than a few private companies penetrating the carbon market, the debate changes from combating global warming to profiteering, Cullen said. "There has to be international policy developed on this," he said. "But there's not enough scientific consensus to develop a firm policy." --- THE OCEANIC CARBON PUMP 1. Proposal: To fertilize large swathes of the ocean with tonnes of artificial iron dust, dissolved in a slurry. 2. Effect: Increase phytoplankton, which will draw more CO2 from the atmosphere. Plankton is also the basis of the marine food chain. 3. Some hope that increased plankton will translate into increased fish stocks and other marine life. Other scientists warn plankton-choked waters will deplete oxygen and cause fish kills. 4. Sedimentation: Organic carbon aggregates with waste products and other solids to sink to ocean floor. 5. Organic carbon gets buried in sediments and ultimately turns into rock. It's hoped that excess carbon can be removed from the Earth's atmosphere this way. 6. Most organic carbon remains in the water (increasing its acidity) and returns to the surface during upwelling. 7. Some carbon dioxide does return to the Earth's atmosphere, but overall the seas are huge, natural carbon sinks. |