Methane bubbles collect under the ice. Natalia Shakhova

The Arctic seafloor off the coast of Northern Siberia is releasing more than double the amount of methane as previously estimated, a new research has found.

According to the results of the research published Sunday in the journal, Nature Geoscience, the East Siberian Arctic Shelf, or ESAS, which encompasses more than two million square kilometers of seafloor in the Arctic Ocean, is releasing at least 17 teragrams of methane into the atmosphere each year, compared to previous estimates of eight teragrams of methane. A teragram is equal to 1 million tons.

“It is now on par with the methane being released from the arctic tundra, which is considered to be one of the major sources of methane in the Northern Hemisphere,” Natalia Shakhova, one of the paper’s lead authors and a scientist at the University of Alaska Fairbanks, said in a statement. “Increased methane releases in this area are a possible new climate-change-driven factor that will strengthen over time.”

Methane, a greenhouse gas considered to be an important factor in global climate change, is over 30 times more effective than carbon dioxide. On land, methane is released when previously frozen organic material decomposes, and on the seabed, it is found as a pre-formed gas or as methane hydrate, a solid compound that traps a large amount of methane within a crystal structure of water, forming a solid similar to ice.

As long as the subsea permafrost, ground that remains at or below 0 degree celsius for at least two consecutive years, remains frozen, it forms a cap that effectively traps the methane underneath. But, as the permafrost melts, it develops holes, allowing the methane to escape. According to researchers, these releases can be larger and more abrupt than those that result from decomposition.

The findings are part of the twice-yearly Arctic expeditions by Shakhova and Igor Semiletov, a researcher at the UAF International Arctic Research Center, which have revealed that subsea permafrost in the region has melted much more extensively than previously thought, in part due to warming water near the bottom of the ocean.

As a result, subsea methane is allowed to escape in much greater amounts than earlier models estimated. In addition, frequent storms in the area also speed up its release into the atmosphere.

“We believe that the release of methane from the Arctic, and in particular this part of the Arctic, could impact the entire globe,” Shakhova said. “We are trying to understand the actual contribution of the ESAS to the global methane budget and how that will change over time.”