If we ever hope to put the brakes on global warming, we're going to have to find a way to prevent carbon dioxide from wafting up to the atmosphere. To that end, researchers have proposed a new type of trap that stashes the greenhouse gas beneath the bottom of the sea. Although other locations have been suggested, deep ocean sediments have a major advantage: Carbon dioxide trapped here is much less likely to leak out.
Trapping carbon dioxide, also known as carbon sequestration, has gained popularity in recent years. Pilot projects are injecting CO2 into a saline aquifer in the Black Sea and off the coast of Norway. Other projects are using CO2 to squeeze extra oil out of wells in Algeria and Canada with the hope that the carbon dioxide will remain trapped within the rock. But neither approach has a sure-fire way to make sure the CO2 stays put. And research published earlier this year has uncovered some worrying subterranean side-effects (ScienceNOW, 28 June)
An alternative, self-sealing CO2 trap is described online this week in Proceedings of the National Academy of Sciences. Kurt Zenz House of Harvard University and colleagues propose that carbon dioxide be collected at a major source near the coast, such as a power or chemical plant, borrowing techniques already in use by natural gas companies to separate CO2 from other gases. The CO2 would then be pressurized into a liquid and shipped about 10 kilometers offshore, where the ocean is at least 3 kilometers deep. Finally, engineers would drill a hole into the ocean floor at least 500 meters deep and inject the carbon dioxide through a pipe. The pressure from 3 kilometers of water combined with the cold temperatures of the deep sea squeeze the liquid CO2 so that it's denser than water. When the CO2 mixes with the water in the sea sediments, recent studies suggest it should form hydrates, a sort of water/CO2 ice mixture that will form a cap over the rest of the injected carbon dioxide.
"It's a clever idea--a lot of water and a little bit of rock," says Robert Socolow, the co-director of the Carbon Mitigation Initiative Field at Princeton University in New Jersey. He adds that the strategy might be particularly useful in places where drilling on land is impractical for other types of carbon sequestration, such as Japan or the northeast coast of the United States.
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