Making a prisoner out of methane.

Deep in the ocean, intense pressure and cold temperatures can trap methane gas inside a cage of water molecules, forming an icy white substance called methane hydrate. Hiding under the seafloor, vast deposits of this solid methane represent the largest remaining source of fossil fuel known. Despite the potential economic importance of these molecules, oceanographers know few details about methane hydrates and their deep-sea behavior (SN: 11/9/96, p. 298).

A team of California researchers is trying to unlock the secrets of this substance by fabricating methane hydrates in a natural setting. Peter G. Brewer of the Monterey Bay Aquarium Research Institute in Moss Landing, Calif., and his colleagues used a remote-controlled submersible to carry acrylic cylinders 910 meters below sea level. They then pumped methane gas into the cylinders in an attempt to coax seawater and methane to form the hydrate cage.

"The folklore is that these things are very difficult to make," says Brewer. In past laboratory experiments, researchers found that hydrates formed slowly and required as much special care as an infant. Sometimes, investigators had to rock the experiments to get the hydrates to develop.

In the deep ocean, however, methane hydrates are not so temperamental. As the scientists bubbled methane gas into the cylinders, the hydrates formed within minutes, sometimes seconds, Brewer and his colleagues report in the May Geology.

Some cylinders contained straight seawater. Others held a layer of sand or mud through which the gas had to seep--a situation much closer to the natural process of hydrate formation in seafloor sediments.

The team is now conducting follow-up experiments, such as testing how long methane hydrates survive when left on the ocean floor. Initial results suggest that they can last for months.