Seabed Methane: Warm Pacific Releases Powerful Greenhouse Gas off US West Coast

Summary: Thawing seabed methane deposits at critical solid-to-gas conversion depths in the warm Pacific release powerful greenhouse gas off the U.S. west coast.

sonar image of methane bubbling from seafloor off Washington coast; column base at depth of 1/3 mile (500+ meters); top of plume at depth of 1/10 mile (180 meters): Brendan Philip/University of Washington, usage restrictions: credit required, via EurekAlert!

Seabed methane deposits, thawed by warming Pacific waters, are bubbling to the surface and releasing plumes of the super powerful greenhouse gas off the west coast of the United States.

The Environmental Defense Fund (EDF), a New York City-based, global nonprofit environmental advocacy group, identifies methane emissions as 84 times more potent than carbon dioxide within the first two decades of release. Methane emissions cause about 25 percent of today’s man-made global warming.

The bubbling phenomenon, which is not recent and is taking place globally, is particularly obvious along Pacific Northwest coastlines, where biologically rich waters and strong geologic activity along the underwater Cascadia fault account for the area’s extremely large deposits of methane hydrate, methane’s crystal, or solid, state. Warming is occurring in intermediate-depth waters, about one-third of a mile (500 meters) below the surface, which is the critical depth where methane changes from its temperature-sensitive solid state into a gas.

Research co-authored by University of Washington (UW) and Oregon State University (OSU) professors and published in December 2014 reveals that, between 1970 and 2013, an estimated 4 million metric tons of methane has been released off the Washington coast. The total breaks down to a yearly average of 220 million pounds, which equates to 500 times its natural release rate from the seafloor.

Evan Solomon, co-author and UW assistant professor of oceanography, notes the huge scale of yearly released methane: “We calculate that methane equivalent in volume to the Deepwater Horizon oil spill is released every year off the Washington coast.”

Worrisome concerns about methane plumes percolating up to the water surface are not restricted to releasing of the powerful greenhouse gas into the atmosphere. As methane bubbles up through the water column, the food chain, literally, takes bites that significantly reduce the amount of surfacing gas. Paul Johnson says that microbes consume about 95 percent of methane bubbles in Pacific Northwest waters.

The methane consumed by microbes is converted into carbon dioxide and released back into the water, creating a low-oxygen, more-acidic environment. Pacific Northwest fishermen, who alerted Paul Johnson over a decade ago to mysterious seafloor bubbles mistaken on their sonar for schools of fish, see reduced catches as a result of ocean acidification.

The Sea of Okhotsk, a sea partially enclosed by coastal Far Eastern Russia and Japan’s Hokkaidō Island, is responsible for the warming of Pacific Northwest coastal waters. With rising temperatures for more than five decades, the Okhotsk sends its dense, warm surface water eastward across the Pacific, reaching Pacific Northwest coastlines within one or two decades.

Over the past 44 years, the temperature of Pacific Northwest waters has warmed 0.3 degrees Celsius (0.6 degrees Fahrenheit).

H. Paul Johnson, co-author and UW adjunct professor of oceanography, describes the warming rate as: “In the deep ocean, that is a big deal.”

Climatologist Gavin Schmidt, who directs NASA’s Goddard Institute for Space Studies, minimizes the significance of seabed methane plumes within the larger context of global warming.

“These are interesting but they are minor issues. People have detected methane seeps all over the place off the continental shelves and mostly they are in equilibrium with what is going on,” Schmidt explains.

University of Washington measurement locations -- yellow dots show ocean temperature measurements off Washington coast from 1970 to 2013; green triangles are places where scientists and fishermen have seen columns of bubbles; stars are sites of measurements to check whether warming water is responsible for plumes: Una K. Miller/University of Washington, usage restrictions: with credit, via EurekAlert!

Acknowledgment

My special thanks to talented artists and photographers/concerned organizations who make their fine images available on the internet.

Image credits:

sonar image of methane bubbles: Brendan Philip/University of Washington, usage restrictions: credit required, via EurekAlert! @ https://www.eurekalert.org/multimedia/pub/83785.php?from=284201

University of Washington measurement locations -- yellow dots show ocean temperature measurements off Washington coast from 1970 to 2013; green triangles are places where scientists and fishermen have seen columns of bubbles; stars are sites of measurements to check whether warming water is responsible for plumes: Una K. Miller/University of Washington, usage restrictions: with credit, via EurekAlert! @ https://www.eurekalert.org/multimedia/pub/83786.php

For further information:

Casey, Michael. "Those Plumes of Methane Leaking Off the Coast of Washington Are Really Bad News for the Oceans." VICE News > Tipping Point. Oct. 26, 2015.
Available @ https://news.vice.com/article/those-plumes-of-methane-leaking-off-the-coast-of-washington-are-really-bad-news-for-the-oceans

CGTN America. "Researchers Find Warmer Ocean Waters Cause Increasing Methane Emissions." YouTube. Jan. 29, 2015.
Available @ https://www.youtube.com/watch?v=i_bFmFSinIM

Hamburg, Steve. "Methane: The Other Important Greenhouse Gas." EDF Environmental Defense Fund.
Available @ https://www.edf.org/methane-other-important-greenhouse-gas

Hautala, Susan L., et al. "Dissociation of Cascadia margin gas hydrates in response to contemporary ocean warming." Geophysical Research Letters, vol. 41, issue 23 (Dec. 16, 2014). DOI: 10.1002/2014GLO61606
Available @ https://catalyst.uw.edu/workspace/file/download/b98d3d3d2584da71135d8cc833a48eff4f70bf779532217a1e368aa1c7951bff

Hickey, Hannah. "Warmer Pacific Ocean Could Release Millions of Tons of Seafloor Methane." University of Washington > UW News. Dec. 9, 2014.
Available @ http://www.washington.edu/news/2014/12/09/warmer-pacific-ocean-could-release-millions-of-tons-of-seafloor-methane/