Siberian seabed methane more than double previous estimates

Ongoing international research led by scientists from the University of Alaska indicates that the East Siberian Arctic Shelf is releasing 17 millions tons of methane into the atmosphere each year, more than twice the amount previously estimated. Because it is so efficient at trapping heat, methane is a much more potent greenhouse gas than carbon dioxide.

The East Siberian Arctic Shelf is a methane-rich area that encompasses more than 2 million square kilometers of seafloor in the Arctic Ocean. Previous estimates suggested that the area was releasing 8 million tons of methane into the atmosphere yearly.

In the seabed, methane can be stored as a pre-formed gas or as methane hydrates. As long as the subsea permafrost remains frozen, it forms a cap, effectively trapping the methane beneath. However, as the permafrost thaws, it develops holes, which allow the methane to escape.

The researchers behind the new methane estimates say the subsea permafrost in the area has thawed much more extensively than previously thought. Their work, appearing in the journal Nature Geoscience, suggests this is in part due to a previously overlooked warming water layer near the bottom of the ocean.

Lead researcher Natalia Shakhova said the warm water layer has created conditions that allow the subsea methane to escape in much greater amounts than her team’s earlier models suggested. “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,” she noted. “Increased methane releases in this area are a possible new climate-change-driven factor that will strengthen over time.”

The new study is based on work carried out on field expeditions using a variety of techniques – including sonar and visual images of methane bubbles in the water, air and water sampling, seafloor drilling and temperature readings – to determine the conditions of the water and permafrost, as well as the amount of methane being released.

“Results of this study represent a big step forward toward improving our understanding of methane emissions from the East Siberian Arctic Shelf,” said Shakhova. “I believe that all other arctic shelf areas are significantly underestimated and should be paid very careful attention to. We believe that the release of methane from the Arctic, and in particular this part of the Arctic, could impact the entire globe.”

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Source: University of Alaska Fairbanks

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