Climate Change: Warming Ocean is Causing Bubbling Plumes to Release Methane

Scientists have uncovered methane plumes in a warming ocean. They've found bubble plumes off of the Pacific Northwest that could support the idea that gradual ocean warming at about a third of a mile down may be releasing frozen methane in the seafloor.

"We see an unusually high number of bubble plumes at the depth where methane hydrate would decompose if seawater had warmed," said H. Paul Johnson, lead author of the new study, in a news release. "So it is not likely to be just emitted from the sediments; this appears to be coming from the decomposition of methane that has been frozen for thousands of years."

Methane has largely contributed to sudden swings in Earth's climate in the past. It's unknown what role it might contribute to contemporary climate change. With that said, recent studies have revealed that there are warming-related methane emissions in Arctic permafrost and off the Atlantic coast.

In all, the researchers examined 168 methane plumes in the new study. Of these, about 14 were located at the "transition depth" in the ocean; there, there were more plumes per unit area than on surrounding parts of the Washington and Oregon seafloor.

If methane bubbles rise all of the way to the surface, they enter the atmosphere and act as a powerful greenhouse gas. Most of the deep-sea methane, though, becomes consumed on the journey up by marine microbes. These microbes convert methane to carbon dioxide, producing low-oxygen, more-acidic conditions in the deeper offshore water which then wells up along the coast.

"Current environmental changes in Washington and Oregon are already impacting local biology and fisheries, and these changes would be amplified by the further release of methane," said Johnson.

Another possible consequence could be the destabilization of seafloor slopes where frozen methane acts as the glue that holds the steep sediment slopes in place.

Currently, methane hydrate appears to be decomposing and releasing a lot of gas; in fact, the margin where there are the greatest number of plumes is at the critical depth of 500 meters.

The findings reveal a bit more about methane release, and show that it's certainly a phenomenon scientists want to keep their eyes on as warming continues.

The findings are published in the journal Geochemistry, Geophysics, Geosystems.

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