Ocean Floor Reveals Clues To Global Warming

In a paper published Jan. 8 in the journal Nature, UW Department of Geology and Geophysics graduate student Matthew Hornbach and professors Demian Saffer and Steve Holbrook propose that the source of the carbon is methane gas found beneath methane hydrate -- an ice-like substance consisting of frozen methane and water. Methane hydrate exists in vast quantities beneath the ocean floor and is believed to constitute the largest reservoir of organic carbon on Earth.

Hornbach, Saffer and Holbrook contend that a rise in ocean temperatures can convert the methane hydrate into methane gas. "Since methane is a greenhouse gas, substantial amounts of it released from beneath these hydrate deposits can contribute to global warming," Hornbach says.

For decades climate researchers have recognized that global warming events correspond with rapid spikes in atmospheric methane concentrations. But the UW scientists' discovery of widespread critically pressurized volumes of methane gas below continental margins may answer the often debated question of where the methane comes from and how it gets into the atmosphere so quickly.

Critically pressurized volumes of methane gas exist below many methane hydrate deposits, resulting in a potentially unstable ocean floor that is highly sensitive to changing conditions. Hornbach says any change in temperature or pressure at these critically pressured gas sites can cause hydrate to convert into methane gas. The highly pressurized gas can cause faults in the ocean floor to break apart, allowing the gas to escape.

"It's like a cork in a champagne bottle," he says. "If you shake up the champagne and build up enough pressure, the champagne bubbles can pop the cork."

Because these critically pressured gas volumes are found worldwide, Hornbach says large quantities of methane could be released during a global warming event.

"It is well documented that bottom-water temperatures in the ocean increase by approximately 5 degrees centigrade during periods of global warming," Hornbach says. "Our study indicates that perhaps as much as 2,000 gigatons (a single gigaton is one billion tons) of methane gas might escape from the ocean into the atmosphere during such warming events."

The UW scientists also contend that massive underwater landslides -- the relics of which sprawl across continental margins -- may be the direct result of ocean floor failures caused by overpressured methane gas.

Much of the project's data was collected at Blake Ridge in the Atlantic Ocean, located 300 miles off the coast of North Carolina. The scientists used soundwave technology to image beneath the ocean floor, Hornbach says, and dove some three kilometers below the surface of the Atlantic to find samples of methane gas leaks.

The research was funded jointly by the U.S. National Science Foundation and the U.S Department of Energy.