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澳门金沙有几个网站:Into the abyss

作者:郝鹂迨    发布时间:2019-03-08 01:02:03    

By Noreen Parks in Santa Cruz INJECTING carbon dioxide directly into deep ocean waters might help put a brake on the greenhouse effect, the first field test of the idea suggests. Some environmental engineers already dispose of CO2 by pumping it into empty oil wells or water-bearing rocks below the seabed. Statoil, the Norwegian state-owned petroleum company, has been pumping 1 million tonnes of liquefied CO2 annually into an aquifer below the seafloor since 1996. But there are not enough suitable aquifers for this to make a significant dent in the greenhouse effect. If the gas could be put out of harm’s way simply by pumping it into the ocean, however, the potential for disposal would be huge. To test that possibility, Peter Brewer and his colleagues at the Monterey Bay Aquarium Research Institute used a robotic submersible to inject liquid CO2 into a 4-litre glass beaker 3627 metres below the surface of the Pacific Ocean off the coast of central California. Below about 2700 metres, liquid CO2 is denser than sea water. And at low temperatures and high pressures, it reacts with water to form a solid, ice-like hydrate. Based on lab results and previous experiments at shallower depths, Brewer thought he knew what was going to happen. “We expected to see a stable pool of liquid CO2 form, with a skin of solid hydrate over it, like ice on a winter pond.” Instead, the CO2 expanded to several times its original volume as sea water invaded the liquid to form hydrate, which accumulated at the bottom of the beaker. As the hydrate mass grew, it forced the remaining liquid to overflow from the beaker in globules that bounced along the seabed and were swept away by the current, like tiny, transparent tumbleweeds (Science, vol 284, p 943). “The dynamics at great depths are different,” says Brewer. “The hydrate that formed was dense enough to fall into itself and constantly renew a surface at which the reaction between sea water and CO2 could continue.” Although this was not what he predicted, Brewer says that it augurs well for efforts to dispose of CO2 in the deep ocean—although he stresses that it is still not clear whether the strategy would be economically viable. “We have shown that at these depths CO2 will rapidly form hydrates,” he says. “Deep-sea disposal could form very large `icebergs’ at the ocean bottom that, while not permanent, would endure for a very long time.” How long? Gas hydrates dissolve very slowly in deep water, and under existing circulation patterns the turnover of water between surface and deep layers ranges from an average of 250 years in the Atlantic Ocean to about 550 years in the Pacific. So CO2 that would otherwise contribute immediately to global warming could be locked up for centuries. One concern is that CO2 hydrates could acidify the seawater as they dissolved. But given the deep ocean’s vast capacity for dilution,

 

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