Methane From Arctic Ocean

Far more of the greenhouse gas methane is seeping from seabed deposits in the Arctic shelf into the atmosphere than previously thought, a new study shows.

The finding not only adds to growing evidence that Arctic oceanic outgassing is an important source of atmospheric methane but also adds a new variable for climate-change modelers as they consider the potential effects of oceanic warming.

Natalia Shakhova and Igor Semiletov, research professors at the International Arctic Research Center at the University of Alaska, Fairbanks, and their colleagues spent more than five years monitoring dissolved methane in the water column of the East Siberian Arctic Shelf, as well as methane venting from the ocean to the atmosphere. They found that the amounts of outgassed methane are greater than was thought to be emitted by the entire world’s oceans (Science 2010, 327, 1246).

Methane is the third most prevalent greenhouse gas and has been known to seep from seabed deposits accumulated in the East Siberian Arctic Shelf. Those methane deposits were previously protected by a thick layer of frozen permafrost. But after that permafrost was submerged by shallow Arctic seas due to sea-level rises at the end of the last ice age, it has been continuously, slowly warming. As a result, the permafrost is losing its ability to preserve the methane deposits.

Whether oceanic warming due to climate change might hasten thawing of the permafrost and thus methane flux into the atmosphere is an important, as yet unanswered question. Shakhova notes that to learn whether the rate of oceanic methane venting is increasing, scientists need to continue monitoring the area.

Ted Schuur, ecosystem ecology professor at the University of Florida, Gainesville, calls the work an “important advance,” because it extends findings that have been made on land out into the ocean.

The discovery doesn’t change the current methane budget of Earth but rather changes the gas’s distribution picture, Schuur notes. But “anytime you have a lot of carbon coming from a place that nobody expected,” that affects climate science conceptually and affects how models work, he adds.