Warming Ocean May Be Releasing Frozen Methane

You hear a lot about carbon dioxide’s role in climate change. But methane, which is emitted by both natural sources and human-caused ones such as natural gas production for energy, is actually 25 times more potent as a greenhouse emission than C02, according to the U.S. Environmental Protection Agency.

That’s why it’s a particularly ominous sign that rising deep ocean temperatures are thawing ancient frozen deposits of methane beneath the sea floor, which are bubbling up toward the surface.

A study by University of Washington scientists, which appears in a journal published by the American Geophysical Union, reports that numerous bubble plumes observed off the Washington and Oregon coast come from levels where methane hydrate, the frozen stable form of the gas, would decompose because of warming seawater.

The release “appears to be coming from the decomposition of methane that has been frozen for thousands of years,” UW oceanographer H. Paul Johnson said in a university press release.

Although methane is a powerful greenhouse gas, the liberated deep deposits may not be quite as much of a climate threat as it might seem. The scientists say that most of the deep-sea methane is consumed by marine microbes as it rises, which convert it to carbon dioxide. Even so, it still has a harmful impact. The extra C02 results in water with a lower oxygen content and higher acidity, which is less hospitable to aquatic life. That water eventually wells up along the coast and surges into waterways.

“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,” Johnson said.

Another problem is that the release of methane takes it out of seafloor slopes where it acts as a sort of glue, holding the sediment in place.

The study confirms the scenario described in a 2014 study, in which thawing deposits release about 100,000 metric tons of methane per year.That’s close to the amount released by the 2010 Deepwater Horizon blowout in the Gulf of Mexico.

From Discovery News