AGU: Geophysical Research Letters

 

Editors' Highlight

Decomposing methane gas hydrates on the Arctic Shelf?

More than 8000 years ago, parts of the Arctic Shelf were an unglaciated coastal plain covered with thick permafrost. As sea levels rose, this permafrost became submerged and is currently inundated by relatively warm seawater. Permafrost is known to contain gas hydrates, a solid phase composed of water and gases that formed under low-temperature, high-pressure conditions. Because disturbances to permafrost may outgas methane, a potent greenhouse gas, Paull et al. (2007) sought to determine whether venting was occurring on the Arctic's submerged Beaufort Sea Shelf. They focused on underwater features similar in shape to terrestrial pingos, which are conical, ice-cored hills. Data collected from eight pingo-like formations (PLFs) revealed systematically elevated methane concentrations and streams of methane-rich gas bubbles coming from the formations' crests. On the basis of this, they hypothesized that pressure generated by methane gas hydrate decomposition within subsurface permafrost layers helped to push ice-rich sediment above the surrounding seafloor, forming PLFs. They expect that after degassing, the seafloor subsides around the PLFs, forming moat-like depressions that have also been observed in bathymetric surveys.

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