Where did BP's methane clouds end up?
In the bellies of zillions of hungry microbes, A&M scientist says
As black, murky oil fulminated from the Gulf of Mexico sea floorlast summer some scientists were more concerned about large amounts of unseen hydrocarbons gushing forth.
They worried this methane, as much as half the flow from the wellhead, would spread in large clouds that would eventually leave sizable areas of the Gulf hypoxic, starving marine life of oxygen.
Some environmentalists went much further, warning that a massive methane bubble could rise to the surface of the Gulf and trigger a cascade of tsunamis.
In June, before the Macondo well was capped, scientists did find evidence of low-oxygen levels deep in the Gulf due to high levels of methane, an odorless, colorless gas that can be toxic in high concentrations.
Was this, they wondered, the sign of large plumes of methane forming in the deeps of the Gulf? They got their answer upon returning for another survey in late August.
"The methane was gone," said Texas A&M University oceanographer John Kessler.
"When we went back out we were just seeing the last breath of a once great methane plume. It went away much faster than we expected, and it's kind of the inspirational story of the oil spill."
Kessler and the co-authors of a paper published today by the journal Science believe large amounts of bacteria bloomed rapidly as the methane levels rose and metabolized the natural gas as food.
It must have been quite a feast.
No 'dead zone' found
During the height of the spill, the scientists measured levels of dissolved methane in the area around theDeepwater Horizon site at 10,000 to 100,000 times above normal. An estimated 200,000 tons of methane gushed into the Gulf from the spill.
Yet only about 120 days after the initial well blowout, the levels of methane surveyed across wide areas of the Gulf were actually a tad lower than what scientists characterize as "normal" levels.
"It does appear the microbes licked their plates clean," Kessler said.
There was also no evidence of hypoxia, a condition annually found as a "dead zone" along the Louisiana and Texas coasts.
The concern was that, as the microbe populations bloomed, they would also gobble up the oxygen deep in the sea, creating areas with very low levels of it.
During their initial cruise in June, Kessler said the survey, which was funded by the National Oceanic and Atmospheric Administration, found oxygen levels as much as 25 percent below normal in waters around the blow-out site.
That's far below the threshold of hypoxia, which is 67 percent below normal levels of oxygen. But the later cruise, from late August to early October, found that oxygen levels were only about 3 percent below normal.
The microbes had done their work and then apparently died off.
"When you look at how fast it must have decomposed from when we left the water in June to September, those rates, while they are in the realm of possibilities, are higher than anything that's ever been measured," Kessler said.
"What we found is that the ocean, in this capacity at least, had a remarkable ability to take care of itself."
No all-clear yet
Although the Gulf of Mexico has recovered significantly since last summer's oil spill, scientists cautioned that it's too early to signal an all-clear.
What concerns scientists like Paul Montagna, chairman of ecosystems and modeling at Texas A&M-Corpus Christi's Harte Research Institute, is the effect on breeding of larger fish species, many of which spawn just once a year.
"If their spawning seasons occurred during the oil spill there could have been a real big wipeout," Montagna said. "But we don't know yet. When will we find out? I
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