ShareThisBy MATT WEISER
Research on ocean sediments near Santa Barbara suggests that climate change could be accelerated by methane gas stored in oil deposits on the seafloor.
The work by Tessa Hill, an assistant professor of geology at the University of California-Davis, documents a new source of methane gas that has not yet been factored into previous analyses of historic climate change.
The findings are potentially troubling because methane is at least 20 times more potent as a greenhouse gas than carbon dioxide, so it has the potential to make the planet hotter faster if released to the atmosphere.
Hill is the lead author of the research, published online Monday by the Proceedings of the National Academy of Sciences, a peer-reviewed journal.
She cautioned, however, that more study is needed before her findings can be applied globally. For instance, it isn't clear how the methane would be released during climate change, and it is far from certain that similar methane stores worldwide would be freed up as sea temperatures rise.
"We need to learn more about this process, about how globally widespread it is," said Hill, who did the research for her doctoral dissertation at UC Santa Barbara. "But I think we can certainly say this methane seepage out of this source clearly responds to climate warming."
Climate researchers have long been concerned about methane hydrate, a form of frozen methane widespread on the seafloor. If ocean temperatures rise enough to thaw this methane, it could have devastating effects on the climate. But methane stored as a gas in natural offshore petroleum deposits has not yet been figured into climate change.
Hill theorizes that melting methane hydrate could free up the second supply of methane in oil deposits by causing underwater landslides and sinkholes as it melts. But she said this theory requires more research.
Hill and her co-authors looked at ocean sediments in the Santa Barbara Channel, and measured the amount of tar left behind after methane seepage. They compared this with global temperature records, obtained by analyzing oxygen isotopes in the shells of tiny fossilized sea animals.
They found that methane emissions from natural offshore petroleum sources peaked between 16,000 and 14,000 years ago, and again between 11,000 and 10,000 years ago. Both were periods when glaciers melted and the ocean became warmer.
Keith Kvenvolden, a retired geochemist for the U.S. Geological Survey in Menlo Park, also has studied methane seepage. He praised Hill's work for connecting the phenomenon to periods of historic climate change.
But like Hill, he cautioned that more research is needed.
"Their basic observations are unique and very interesting," he said. "But I don't think you can tie it into what's happening over the whole world. Maybe in time it will be shown to be true. But right now it's a big leap in faith."
Petroleum deposits and methane gas are locked together in sediments all over the Santa Barbara Channel _ a fact well-known to area surfers and beach lovers.
As the oil rises to the ocean surface, it releases methane bubbles locked in the gooey mass. On the surface, the petroleum degrades and leaves behind tar, which falls back to the ocean floor.
This happens in many other locations around the world. But the present rate of methane emissions by this natural process is unknown, and it's also unknown how this rate would change if ocean temperatures increased.
"It appears as though this source of methane reacts dynamically to climate change in the past, and we would expect that it might in the future as well," Hill said. "I can't tell you how big the problem is, because this is the first time anyone has ever reconstructed petroleum seepage over time."
