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Study: Bubble plumes of methane escaping warming ocean

"What we’re seeing is possible confirmation of what we predicted from the water temperatures," said researcher H. Paul Johnson.
By Brooks Hays   |   Oct. 15, 2015 at 10:10 AM

SEATTLE, Oct. 15 (UPI) -- The most infamous and abundant greenhouse gas is carbon dioxide. But though less prolific, methane actually packs a meaner climate-warming punch.

To the dismay of climate scientists (and anyone concerned by global warming), there appears to a new and growing source of methane -- the deep sea.

In analyzing instances of bubble plumes, columns of rising methane gas bubbles, researchers found a growing number have been measured at a transition zone. The transition zone, beginning a third of a mile below the surface, is significant to stability of methane hydrates -- an area where warming water temperatures could encourage sublimation.

Researchers at the University of Washington looked at data on 168 bubble plumes observed in recent years, recorded by the sonar of fishing boats and scientific expeditions. Fourteen were measured in the transition zone, a higher concentration than were measured on the seafloor off the coast of Washington and Oregon.

The new analysis was detailed in a paper published this week in the journal Geochemistry, Geophysics, Geosystems.

"What we're seeing is possible confirmation of what we predicted from the water temperatures: Methane hydrate appears to be decomposing and releasing a lot of gas," lead study author H. Paul Johnson, a professor of oceanography with Washington, said in a press release. "If you look systematically, the location on the margin where you're getting the largest number of methane plumes per square meter, it is right at that critical depth of 500 meters."

Most methane plumes don't make it all the way to the surface. They're converted to CO2 by methane-eating microbes, encouraging low-oxygen, highly acidic pockets of deep sea water. Upwelling can bring these anoxic pockets to the surface, suffocating sea life.

More bubble plumes could lead to more frequent dead zones and allow more decomposed methane to reach the surface and enter the atmosphere.

For now, the researchers work is only proof of a growing number of bubble plumes in the transition zone. Their work can't confirm that the rising methane bubbles are the product of thawed methane hydrates.

"The results are consistent with the hypothesis that modern bottom-water warming is causing the limit of methane hydrate stability to move downslope, but it's not proof that the hydrate is dissociating," explained co-author Evan Solomon, an associate professor of oceanography at Washington.

Solomon and his colleagues are now analyzing the chemical composition of bubble plumes release by seafloor sediments to better understand the likely source of new methane plumes.

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