WASHINGTON — Scientists are still trying to account for what happened to all of the oil from the BP blowout in the Gulf of Mexico, but they now know what happened to the even greater amounts of natural gas that gushed from the broken well.
Bacteria ate just about all of it by August.
The discovery was released on Thursday in report for the journal Science by John D. Kessler, an oceanographer at Texas A&M University, and his colleagues.
One of the reasons scientists are interested in methane, the main component of the natural gas that flowed from the broken BP well, is that it's a very potent heat-trapping gas. A huge reservoir of methane lies under the ocean floor, especially near continents.
In the BP disaster, there was no measurable loss of methane to the atmosphere. The methane remained trapped in a deep-water layer until the bacteria finished it off within about four months after the spill began on April 22.
"Here we had a massive release of methane handed to us, thanks to this man-made disaster," Kessler said. Part of the scientific motivation to study it was to get some insight into what would happen in a massive natural release, he said.
The scientists concluded that other releases of methane in the deep ocean also would probably set off a rapid response by bacteria.
Still, a single study is "only a piece of evidence in a scientific puzzle," Kessler said. Other factors could change the outcome in a natural release of methane — it could be much larger, or occur in colder water where organisms that decompose methane are less prevalent, or it could occur in shallower water where the chance of reaching the atmosphere is greater.
Scientists have reached a strong consensus that global warming is mainly caused by the accumulation of heat-trapping gases from fossil fuel burning. A natural release of methane from the ocean could make the changes happen faster.
"Some have put it as a wild card, if you will, on climate change scenarios," Kessler said.
"This at least gives us some insight to what might happen in deep water, especially in subtropical waters," he said. It's not known what might happen if a methane release came in colder waters, say off Alaska, he added. "That's an exciting area of research."
Kessler and his colleagues discovered the methane layer in a research cruise in June. He said they were surprised when they went on a second trip to the area in August and found the methane gone. They'd expected it to remain much longer.
The conclusion that bacteria broke down the methane was based on a series of measurements and tests during three research expeditions from mid-August to early October. The team found no dead zones as a result of oxygen use by the bacteria.
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