Bacteria Keep Undersea Methane Out of the Atmosphere

Today, researchers at the University of California-Santa Barbara said they have discovered that only one percent of the dissolved methane escapes into the air - a finding that is good news for the climate.

Methane heats the Earth 23 times more than the most prevalent greenhouse gas, carbon dioxide, when averaged over a century, scientists have found.

The potency of methane and the fact that thousands of seep fields exist in the sea floor around the world makes fate of methane bubbles from seeps an important environmental question.

David Valentine, associate professor of Earth Science at UC Santa Barbara who led the study, said the one percent finding enabled the authors to conclude that most of the methane is transported below the ocean's surface - away from the seep area.

Then it is oxidized by microbial activity. "We showed that the currents control the fate of the gas and supply it to bacteria in a way that allows them to destroy the methane," said Valentine.

Coal Oil Point, COP, one of the world's largest and best studied seep regions, is located along the northern margin of the Santa Barbara Channel.

Methane escapes from the Coal Oil Point seep near Santa Barbara. (Photo by David Valentine)

The amount of methane released from COP seeps is around two million cubic feet per day, according to Valentine. About 100 barrels of oil oozes out of this area as well.

"We found that the ocean has an amazing capacity to take up methane that is released into it - even when it is released into shallow water," said Valentine.

"Huge amounts of gas are coming up here, creating a giant gas plume. Until now, no one had measured the gas that dissolves and moves away, the plume," he said.

Valentine hypothesized that the methane is oxidized by microbial activity in the ocean, thus relieving the ocean of the methane "burden."

To confirm this hypothesis, Valentine and lead author Susan Mau, a postdoctoral fellow in Valentine's lab, tracked the plume down current from the seeps at 79 surface stations in a 280 square kilometer study area. They found that the methane plume spread over 70 square kilometers.

By boat, the authors sampled the water on a monthly basis. They found variable methane concentrations that corresponded with changes in surface currents. They also found that more wind releases more methane into the atmosphere.

This research effort is the first time that the gas plume that dissolves and moves away from Coal Oil Point has been studied.

The results will soon be published as a cover story in the journal "Geophysical Research Letters."

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