Methane Emissions at the Continental Shelf Edge of the Northern Cascadia Margin

What is it about?

Recognizing individual components of the global carbon cycle is critical to understand both past and present future climates. The sediments that accumulate on continental margins are an underappreciated part of this cycle, containing 40% of the oceanic reservoir of free carbon. Methane plumes issuing from the seafloor are an unquantified leakage of carbon from this giant reservoir. The current inventory of methane plumes on the northern Cascadia margin now approaches 500 emission sites, or an average of one a bubble emission site every 500 m. The majority of these methane emission sites are grouped within a north‐south band that follows the continental shelf edge and uppermost margin. The geological process for producing such a narrow band of emissions appears related to the megathrust earthquakes that occur episodically on the Cascadia Subduction Zone that underlies the Washington coast. During these earthquakes, the Juan de Fuca plate is thrust eastward beneath the overlying North American plate. The overlying plate that includes the Washington continental shelf extends rapidly westward during the fault motion. This rapid westward extension of the overlying plate produces faults and diapirs beneath the outer continental shelf, which become pathways for the methane fluid and gas from the margin sediments.

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Why is it important?

http://www.washington.edu/news/2019/03/21/hundreds-of-bubble-streams-link-biology-seismology-off-washingtons-coast/