Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Bubble plumes off Washington, Oregon suggest warmer ocean may be releasing frozen methane

15.10.2015

Warming ocean temperatures a third of a mile below the surface, in a dark ocean in areas with little marine life, might attract scant attention. But this is precisely the depth where frozen pockets of methane 'ice' transition from a dormant solid to a powerful greenhouse gas.

New University of Washington research suggests that subsurface warming could be causing more methane gas to bubble up off the Washington and Oregon coast.


Sonar image of bubbles rising from the seafloor off the Washington coast. The base of the column is 1/3 of a mile (515 meters) deep and the top of the plume is at 1/10 of a mile (180 meters) depth.

Credit: Brendan Philip/University of Washington

The study, to appear in the journal Geochemistry, Geophysics, Geosystems, shows that of 168 bubble plumes observed within the past decade, a disproportionate number were seen at a critical depth for the stability of methane hydrates.

"We see an unusually high number of bubble plumes at the depth where methane hydrate would decompose if seawater has warmed," said lead author H. Paul Johnson, a UW professor of oceanography. "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 contributed to sudden swings in Earth's climate in the past. It is unknown what role it might contribute to contemporary climate change, although recent studies have reported warming-related methane emissions in Arctic permafrost and off the Atlantic coast.

Of the 168 methane plumes in the new study, some 14 were located at the transition depth - more plumes per unit area than on surrounding parts of the Washington and Oregon seafloor.

If methane bubbles rise all the way to the surface, they enter the atmosphere and act as a powerful greenhouse gas. But most of the deep-sea methane seems to get consumed during the journey up. Marine microbes convert the methane into carbon dioxide, producing lower-oxygen, more-acidic conditions in the deeper offshore water, which eventually wells up along the coast and surges into coastal 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 potential consequence, he said, is the destabilization of seafloor slopes where frozen methane acts as the glue that holds the steep sediment slopes in place.

Methane deposits are abundant on the continental margin of the Pacific Northwest coast. A 2014 study from the UW documented that the ocean in the region is warming at a depth of 500 meters (0.3 miles), by water that formed decades ago in a global warming hotspot off Siberia and then traveled with ocean currents east across the Pacific Ocean. That previous paper calculated that warming at this depth would theoretically destabilize methane deposits on the Cascadia subduction zone, which runs from northern California to Vancouver Island.

At the cold temperatures and high pressures present on the continental margin, methane gas in seafloor sediments forms a crystal lattice structure with water. The resulting icelike solid, called methane hydrate, is unstable and sensitive to changes in temperature. When the ocean warms, the hydrate crystals dissociate and methane gas leaks into the sediment. Some of that gas escapes from the sediment pores as a gas.

The 2014 study calculated that with present ocean warming, such hydrate decomposition could release roughly 0.1 million metric tons of methane per year into the sediments off the Washington coast, about the same amount of methane from the 2010 Deepwater Horizon blowout.

The new study looks for evidence of bubble plumes off the coast, including observations by UW research cruises, earlier scientific studies and local fishermen's reports. The authors included bubble plumes that rose at least 150 meters (490 feet) tall that clearly originate from the seafloor. The dataset included 45 plumes originally detected by fishing boats, whose modern sonars can detect the bubbles while looking for schools of fish, with their observations later confirmed during UW research cruises.

Results show that methane gas is slowly released at almost all depths along the Washington and Oregon coastal margin. But the plumes are significantly more common at the critical depth of 500 meters, where hydrate would decompose due to seawater warming.

"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," Johnson said. "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."

Still unknown, however, is whether these plumes are really from the dissociation of frozen methane deposits.

"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," said co-author Evan Solomon, a UW associate professor of oceanography.

Solomon is now analyzing the chemical composition of samples from bubble plumes emitted by sediments along the Washington coast at about 500 meters deep. Results will confirm whether the gas originates from methane hydrates rather than from some other source, such as the passive migration of methane from deeper reservoirs to the seafloor, which causes most of the other bubble plumes on the continental margin.

###

The research was funded by the National Science Foundation and the U.S. Department of Energy. Other co-authors are Marie Salmi, a UW doctoral student in oceanography with Johnson, and Una Miller, a former UW undergraduate who is now a research assistant in Johnson's group. Miller will present the results at the American Geophysical Union's annual fall meeting in San Francisco.

For more information, contact Johnson at 206-543-8474 or paulj@uw.edu, Solomon at 206-221-6745 or esolomon@uw.edu, and Miller at 206-579-6047 or unam@uw.edu.

Media Contact

Hannah Hickey
hickeyh@uw.edu
206-543-2580

 @UW

http://www.washington.edu/news/ 

Hannah Hickey | EurekAlert!

Further reports about: bubble bubbles deposits methane gas methane hydrate methane plumes seafloor sediments

More articles from Earth Sciences:

nachricht Global study of world's beaches shows threat to protected areas
19.07.2018 | NASA/Goddard Space Flight Center

nachricht NSF-supported researchers to present new results on hurricanes and other extreme events
19.07.2018 | National Science Foundation

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Future electronic components to be printed like newspapers

A new manufacturing technique uses a process similar to newspaper printing to form smoother and more flexible metals for making ultrafast electronic devices.

The low-cost process, developed by Purdue University researchers, combines tools already used in industry for manufacturing metals on a large scale, but uses...

Im Focus: First evidence on the source of extragalactic particles

For the first time ever, scientists have determined the cosmic origin of highest-energy neutrinos. A research group led by IceCube scientist Elisa Resconi, spokesperson of the Collaborative Research Center SFB1258 at the Technical University of Munich (TUM), provides an important piece of evidence that the particles detected by the IceCube neutrino telescope at the South Pole originate from a galaxy four billion light-years away from Earth.

To rule out other origins with certainty, the team led by neutrino physicist Elisa Resconi from the Technical University of Munich and multi-wavelength...

Im Focus: Magnetic vortices: Two independent magnetic skyrmion phases discovered in a single material

For the first time a team of researchers have discovered two different phases of magnetic skyrmions in a single material. Physicists of the Technical Universities of Munich and Dresden and the University of Cologne can now better study and understand the properties of these magnetic structures, which are important for both basic research and applications.

Whirlpools are an everyday experience in a bath tub: When the water is drained a circular vortex is formed. Typically, such whirls are rather stable. Similar...

Im Focus: Breaking the bond: To take part or not?

Physicists working with Roland Wester at the University of Innsbruck have investigated if and how chemical reactions can be influenced by targeted vibrational excitation of the reactants. They were able to demonstrate that excitation with a laser beam does not affect the efficiency of a chemical exchange reaction and that the excited molecular group acts only as a spectator in the reaction.

A frequently used reaction in organic chemistry is nucleophilic substitution. It plays, for example, an important role in in the synthesis of new chemical...

Im Focus: New 2D Spectroscopy Methods

Optical spectroscopy allows investigating the energy structure and dynamic properties of complex quantum systems. Researchers from the University of Würzburg present two new approaches of coherent two-dimensional spectroscopy.

"Put an excitation into the system and observe how it evolves." According to physicist Professor Tobias Brixner, this is the credo of optical spectroscopy....

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Leading experts in Diabetes, Metabolism and Biomedical Engineering discuss Precision Medicine

13.07.2018 | Event News

Conference on Laser Polishing – LaP: Fine Tuning for Surfaces

12.07.2018 | Event News

11th European Wood-based Panel Symposium 2018: Meeting point for the wood-based materials industry

03.07.2018 | Event News

 
Latest News

A smart safe rechargeable zinc ion battery based on sol-gel transition electrolytes

20.07.2018 | Power and Electrical Engineering

Reversing cause and effect is no trouble for quantum computers

20.07.2018 | Information Technology

Princeton-UPenn research team finds physics treasure hidden in a wallpaper pattern

20.07.2018 | Materials Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>