Researchers found that water off the coast of Washington is gradually warming at a depth of 500 meters, about a third of a mile down. That is the same depth where methane transforms from a solid to a gas. The research suggests that ocean warming could be triggering the release of a powerful greenhouse gas.

“We calculate that methane equivalent in volume to the Deepwater Horizon oil spill is released every year off the Washington coast,” said , a 91̽»¨assistant professor of oceanography. He is co-author of a to appear in Geophysical Research Letters.

While scientists believe that global warming will release methane from gas hydrates worldwide, most of the current focus has been on deposits in the Arctic. This paper estimates that from 1970 to 2013, some 4 million metric tons of methane has been released from hydrate decomposition off Washington. That’s an amount each year equal to the methane from natural gas released in the 2010 Deepwater Horizon blowout off the coast of Louisiana, and 500 times the rate at which methane is naturally released from the seafloor.

“Methane hydrates are a very large and fragile reservoir of carbon that can be released if temperatures change,” Solomon said. “I was skeptical at first, but when we looked at the amounts, it’s significant.”

Methane is the main component of natural gas. At cold temperatures and high ocean pressure, it combines with water into a crystal called methane hydrate. The Pacific Northwest has unusually large deposits of methane hydrates because of its biologically productive waters and strong geologic activity. But coastlines around the world hold deposits that could be similarly vulnerable to warming.

“This is one of the first studies to look at the lower-latitude margin,” Solomon said. “We’re showing that intermediate-depth warming could be enhancing methane release.”

Co-author Una Miller, a 91̽»¨oceanography undergraduate, first collected thousands of historic temperature measurements in a region off the Washington coast as part of a separate research project in the lab of co-author , a 91̽»¨professor of oceanography. The data revealed the unexpected sub-surface ocean warming signal.

“Even though the data was raw and pretty messy, we could see a trend,” Miller said. “It just popped out.”

The four decades of data show deeper water has, perhaps surprisingly, been warming the most due to climate change.

“A lot of the earlier studies focused on the surface because most of the data is there,” said co-author , a 91̽»¨associate professor of oceanography. “This depth turns out to be a sweet spot for detecting this trend.” The reason, she added, is that it lies below water nearer the surface that is influenced by long-term atmospheric cycles.

The warming water probably comes from the , between Russia and Japan, where surface water becomes very dense and then spreads east across the Pacific. The Sea of Okhotsk is known to have warmed over the past 50 years, and other studies have shown that the water takes a decade or two to cross the Pacific and reach the Washington coast.

“We began the collaboration when we realized this is also the most sensitive depth for methane hydrate deposits,” Hautala said. She believes the same ocean currents could be warming intermediate-depth waters from Northern California to Alaska, where frozen methane deposits are also known to exist.

Warming water causes the frozen edge of methane hydrate to move into deeper water. On land, as the air temperature warms on a frozen hillside, the snowline moves uphill. In a warming ocean, the boundary between frozen and gaseous methane would move deeper and farther offshore. Calculations in the paper show that since 1970 the Washington boundary has moved about 1 kilometer – a little more than a half-mile – farther offshore. By 2100, the boundary for solid methane would move another 1 to 3 kilometers out to sea.

Estimates for the future amount of gas released from hydrate dissociation this century are as high as 0.4 million metric tons per year off the Washington coast, or about quadruple the amount of methane from the Deepwater Horizon blowout each year.

Still unknown is where any released methane gas would end up. It could be consumed by bacteria in the seafloor sediment or in the water, where it could cause seawater in that area to become more acidic and oxygen-deprived. Some methane might also rise to the surface, where it would release into the atmosphere as a greenhouse gas, compounding the effects of climate change.

Researchers now hope to verify the calculations with new measurements. For the past few years, curious fishermen have sent 91̽»¨oceanographers sonar images showing mysterious columns of bubbles. Solomon and Johnson just returned from a cruise to check out some of those sites at depths where Solomon believes they could be caused by warming water.

“Those images the fishermen sent were 100 percent accurate,” Johnson said. “Without them we would have been shooting in the dark.”

Johnson and Solomon are analyzing data from that cruise to pinpoint what’s triggering this seepage, and the fate of any released methane. The recent sightings of methane bubbles rising to the sea surface, the authors note, suggests that at least some of the seafloor gas may reach the surface and vent to the atmosphere.

The research was funded by the National Science Foundation and the U.S. Department of Energy. The other co-author is at Oregon State University.

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For more information, contact Solomon at 206-221-6745 or esolomn@uw.edu and Hautala at 206-543-0596 or hautala@uw.edu. Solomon will be at the American Geophysical Union meeting in San Francisco Dec. 15-17 and best reached via e-mail.

It’s a landmark trip for the vessel that has spent almost 30 years taking people from the 91̽»¨and elsewhere out to the Sound, the Olympic Peninsula and nearby coasts to make discoveries about chemistry, currents and marine life.

All this from a boat that even its biggest fans admit has serious drawbacks.

The boat was never built to go into open seas, and adding 10 tons of scientific equipment to the stern did nothing to help with stability issues.

“It’s safe; it’s just miserable,” said Ray McQuin, the ship’s captain and supervisor. “Everyone gets seasick.”

(McQuin has a naturally strong stomach, he said, and suffers from seasickness only a couple of times each year.)

The scientists’ berths, two sets of triple bunks that hang from chains, make the undergraduate dorms seem plush by comparison. There’s only one bathroom and shower. And a 100-square-foot room serves as kitchen, dining room, common area and recreational room for up to six researchers (15 for short trips) and a two-person crew.

But most noticeable are the small scientist quarters, which were squeezed on after the fact. The small room is jam-packed during cruises with people, laptops and science equipment.

“It’s very — personal,” said , professor and director of the UW’s School of Oceanography. Others describe it as “crowded” or even “controlled chaos.”

Still, Armbrust has fond memories. “It’s fun working on the Barnes. It’s very hands-on. You can get to your first station in five minutes, in contrast to when you’re working offshore and it takes you a day to get to your first station.”

The vessel was built in 1966 as a U.S. Coast Guard inland harbor tug that spent years towing boats, quenching fires and doing light ice-breaking out of Bellingham and Alaska.

The 91̽»¨acquired the 65-foot boat at a bargain price in 1983 and converted it, replacing the original transmission with one that will go at the slower speeds needed for research, attaching a winch to lower instruments into the water, and adding a science cabin.

“It’s not a purpose-built research boat. There are a lot of compromises, but we get the job done,” McQuin said. “It’s a work boat, and that’s what we need.”

show that in recent years, the Barnes has been out studying nitrogen near Neah Bay, algal blooms, marine food webs, effects of the Elwha Dam removal, and oxygen levels in Hood Canal.

The 1000th cruise will be a series of half-day trips May 7-9 from Shilshole Marina for , an introductory lab course that lets students take oceanographic measurements.

“For oceanography majors, getting out on the water early is really important,” said instructor , a 91̽»¨associate professor of oceanography. “It gives students an idea of both what oceanographers do, and of why oceanography is so challenging: It’s taking limited measurements in a highly variable environment, and trying to piece together bits of evidence.”

The boat’s namesake, , was a 91̽»¨alumnus and professor of oceanography from 1947 to 1973 whose publications include “Circulation near the Washington Coast” and “An Oceanographic Model of Puget Sound.”

The millennial cruise will be one of the last for the vessel, which is nearing the end of its lifetime. The National Science Foundation will decommission the boat in 2016.

“You reach a point – and we’re getting there with this boat – where you can’t afford to keep it running. There are too many repairs,” McQuin said.

Plans are already under way to find a replacement. The School of Oceanography is looking for grants and private donations to fund a new vessel. Jensen Maritime Consultants created a custom design for an 86-foot vessel that would have more than four times as much lab space, carry twice as many people, and include modern navigation capabilities.

“The Barnes has been an incredible resource both for monitoring and understanding Puget Sound, and for giving our students an opportunity to do hands-on research, which is a core part of our program,” Armbrust said. “We’re looking forward to getting a new ship that will allow us to do this and more.”

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For more information, contact Hautala at 206-543-0596 or susanh@ocean.washington.edu.