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Arctic Methane Bubbling Up From Beaufort Sea

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.

Origin of pingo-like features on the Beaufort Sea shelf and their possible relationship to decomposing methane gas hydrates

Charles K. Paull

Monterey Bay Aquarium Research Institute, Moss Landing, California, USA

William Ussler III

Monterey Bay Aquarium Research Institute, Moss Landing, California, USA

Scott R. Dallimore

Natural Resources Canada, Sidney, British Columbia, Canada

Steve M. Blasco

Natural Resources Canada, Dartmouth, Nova Scotia, Canada

Thomas D. Lorenson

U.S. Geological Survey, Menlo Park, California, USA

Humfrey Melling

Fisheries and Oceans Canada, Sidney, British Columbia, Canada

Barbara E. Medioli

Natural Resources Canada, Ottawa, Ontario, Canada

F. Mark Nixon

Natural Resources Canada, Ottawa, Ontario, Canada

Fiona A. McLaughlin

Fisheries and Oceans Canada, Sidney, British Columbia, Canada

Abstract

The Arctic shelf is currently undergoing dramatic thermal changes caused by the continued warming associated with Holocene sea level rise. During this transgression, comparatively warm waters have flooded over cold permafrost areas of the Arctic Shelf. A thermal pulse of more than 10°C is still propagating down into the submerged sediment and may be decomposing gas hydrate as well as permafrost. A search for gas venting on the Arctic seafloor focused on pingo-like-features (PLFs) on the Beaufort Sea Shelf because they may be a direct consequence of gas hydrate decomposition at depth. Vibracores collected from eight PLFs had systematically elevated methane concentrations. ROV observations revealed streams of methane-rich gas bubbles coming from the crests of PLFs. We offer a scenario of how PLFs may be growing offshore as a result of gas pressure associated with gas hydrate decomposition.

Full Article (No subscribers may purchase for $9.00, Includes print PDF, file size: 230987 bytes)

Index Terms: 0702 Cryosphere: Permafrost (0475); 1630 Global Change: Impacts of global change (1225); 3002 Marine Geology and Geophysics: Continental shelf and slope processes (4219); 3004 Marine Geology and Geophysics: Gas and hydrate systems; 9315 Geographic Location: Arctic region (0718, 4207).

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