Methane releases in arctic seas could wreak devastation

Massive releases of methane from arctic seafloors could create oxygen-poor dead zones, acidify the seas and disrupt ecosystems in broad parts of the northern oceans, new preliminary analyses suggest.

Such a cascade of geochemical and ecological ills could result if global warming triggers a widespread release of methane from deep below the Arctic seas, scientists propose in the June 28 Geophysical Research Letters.

Worldwide, particularly in deeply buried permafrost and in high-latitude ocean sediments where pressures are high and temperatures are below freezing, icy deposits called hydrates hold immense amounts of methane (SN: 6/25/05, p. 410). Studies indicate that seafloor sediments beneath the Kara, Barents and East Siberian seas in the Arctic Ocean, as well as the Sea of Okhotsk and the Barents Sea in the North Pacific, have large reservoirs of the planet-warming greenhouse gas, says study coauthor Scott M. Elliott, a marine biogeochemist at Los Alamos National Laboratory in New Mexico.

Many oceanographic surveys have already discovered plumes of methane rising from the ocean floor, particularly in the Arctic, Elliott notes. The climate warming expected in coming decades will likely extend even into the deep sea, melting or destabilizing hydrates and releasing their trapped methane, he explains. Some scientists estimate that increased temperatures across some swaths of ocean floor between 300 and 600 meters deep — where methane hydrates are now stable but may not be in the future — could eventually release as much as 16,000 metric tons of methane each year.

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