In a study published online Sunday in the journal Nature Geoscience, European researchers report that an underwater quake off Pakistan nearly 70 years ago likely fractured seafloor sediments and created pathways for methane, a potent greenhouse gas, to bubble up from below.

 

Methane, which is formed by the decomposition of organic material, seeps from reservoirs under the seafloor in many places around the world. But under certain conditions it mixes with seawater to form icy compounds, called gas hydrates, in the top layers of sediments. The hydrates act almost like cement, creating a barrier that prevents more free methane from coming up from below.

 

The researchers analyzed sediment cores taken in 2007 from two locations in the northern Arabian Sea where hydrates were present and seepage was occurring. They found chemical signatures in the cores suggesting that the methane flow greatly increased sometime in the mid-20th century which corresponds with a magnitude 8.1 quake that occurred in the area in 1945. The quake broke open gas-hydrate sediments and the free gas underneath migrated to the surface. The hydrates themselves did not dissolve.

 

The upward flow of methane is continuing today, and the researchers do not know when it might stop. All told, they estimate that nearly 10 million cubic yards of methane have been released from the core sites over the years.

 

Other scientists are less certain of the potential impact on climate studies. Unless the rate of flow is fast enough, methane that bubbles from the seafloor usually dissolves in the seawater before reaching the surface.