Stores of Methane in Arctic Seabed Being Released into Atmosphere
08.03.2010 - Atmosphere & Space, Water & Oceans, Ice & Snow, Arctic
New results from an international study published in the journal Science show that the permafrost under the East Siberian Arctic Shelf is perforated and releasing huge amounts of methane, a powerful greenhouse gas, into the atmosphere. Three times as large as the Siberian wetlands, the East Siberian Arctic Shelf is a methane-rich area that encompasses more than 2 million km2 of seafloor in the Arctic Ocean. Already releasing some 7 teragrams (some 7.7 million tons) of methane per year, the area leaks the greenhouse gas in two ways:
- When the organic material thaws and begins to decompose;
- When the subsea permafrost thaws.
While earlier studies focused on methane escaping from thawing terrestrial permafrost, this one goes beyond the coast. From 2003 to 2008, the researchers sampled seawater at various depths and sampled the air 10 metres above the ocean surface. In 2006, a helicopter made it possible to take samples up to 2,000 metres in the atmosphere over the same area. In 2007, researchers conducted a winter expedition on the sea ice.
The findings show that more than 80% of the deep water and more than half the surface water had methane levels over eight times that of normal seawater, with saturation levels reaching at least 250 times that of background levels in the summer and 1,400 times higher in the winter. Corresponding results were found in the air directly above the ocean surface. The team found methane levels to be elevated overall and that the gas was not only being dissolved in the water, but also bubbling up into the atmosphere from more than 100 hotspots in the ocean.
The East Siberian Arctic Shelf raises particular concern because of its shallow depth. While methane leaking from deeper waters has time to oxidize into carbon dioxide before reaching the surface, methane being leaked from the East Siberian Arctic Shelf does not, which means more is being released into the atmosphere.
This process, paired with the concentrated amounts of methane in the region, might add a variable unaccounted for in current climate models.
