Scientists are continually working to improve estimates of just how much methane, a potent greenhouse gas, is being emitted from the Arctic.

A new study led by researcher Natalia Shakhova of the University of Alaska, Fairbanks, and the Russian Academy of Sciences' Far Eastern Branch reports that methane releases from one part of the Arctic Ocean are more than twice what scientists previously thought.

Shakhova and her colleagues investigated releases of methane from permafrost underneath a shallow part of the Arctic Ocean called the East Siberian Arctic Shelf, which sits in the ocean north of Siberia and east of the Lena River Delta.

There, the underwater permafrost serves as a cap over methane in the seafloor. The permafrost is thawing, though and losing its ability to hold in the methane.

"Thus, methane could release in large amounts," Shakhova said.

In deeper parts of the ocean, the methane released from the ocean floor would likely never make it up to the atmosphere, since it would get used up by microbes before it reached the surface.

However, on the shelf where Shakhova measured methane releases, the shallowness of the sea and the fact that methane is released as bubbles mean that it rises quickly to the surface and escapes into the atmosphere.

Storms bring up more methane
Pulses of the methane bubbles are often triggered by storms, which churn up the water and allow the bubbles to quickly make their way up to the surface, the study found. Storms are already common in the area and may increase with climate change, leading to more methane pulses.

Shakhova's research team used sonar to target bubbles of methane rising up from the seafloor. They calculated the amount of methane being released from the bubbles to the atmosphere at 17 teragrams per year, which is close to the amount being released from the Arctic tundra.

"This means that the East Siberian Arctic Shelf is at least as significant a source of methane to the atmosphere as Arctic tundra, which is thought to be one [of the] major sources of methane in the Northern Hemisphere," Shakhova said.

Another recent study also pointed to ponds in the Arctic tundra as a possible important source of methane (ClimateWire, Nov. 22).

While the quantity of methane being released may sound alarming, scientists are not sure whether this methane escape is new, or whether it has been happening for a long time. Until 2003, when Shakhova's team started studying this part of the Arctic Ocean, no one had measured how much methane was being released from it.

Researchers do believe that climate change contributes to more thawing of the ocean floor permafrost in the Arctic because they have measured increases in seafloor temperatures in recent years.

The research adds another number to the effort to quantify just how much methane is being released from the Arctic. Knowing that is key to understanding how climate change is affecting methane releases in the polar region, said Shakhova.

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC., 202-628-6500