Los Angeles ? Scientists have discovered an undersea deposit of frozen methane just off the Southern California coast, but whether it can be harnessed as a potential energy source is unknown.

In recent years, there has been a growing interest in tapping methane hydrates, ice-like crystals that form at low temperatures and high pressure in seabeds and in Arctic permafrost.

Scientists estimate the methane trapped in previously known frozen reservoirs around the globe could power the world for centuries. But finding the technology to mine such deposits has proved elusive.

The ecosystem surrounding the methane hydrate site was unlike any of the other vast hydrate deposits around the world. Scientists found seashells and clams with unique chemical characteristics, suggesting the area experiences an extreme flux of methane gas mixing with water, said Jim Hein, a marine geologist at the U.S. Geological Survey in Menlo Park.