Some of the largest natural oil and gas leaks in the United States lie off the coast of Santa Barbara, producing tar on the beaches and work for professors.

Professors in the geological sciences and geography departments have spent the last six years studying the origin of the seeps. Using research from the past 25 years, they have also studied how the seeps have changed.

The seeps may have global effects. Methane, or natural gas, makes up about 90 percent of the gas coming out of the ocean floor and is one of the greenhouse gases that contribute to global warming.

“How much of the global methane budget is coming from these seepages? It could be up to 10 percent of that budget,” Geological Sciences Dept. Chair Bruce Luyendyk said. “Once we have a good model, then we can start estimating for other places around the world.”

“[The methane] is very important in the county and at the local level because we have to meet certain air quality standards,” geological sciences professor James Boles said. “And the amount contributed by natural seepage and the and the amount contributed by man, e.g. cars, oil production, etc., is important and we need to know how much each contributes.”

Seeps can be found in the Gulf of Mexico, all along coastal California, the North Sea, the west coast of Africa and in the Caspian Sea, which are all areas rich in oil.

Though it is rare for an offshore oil field to seep, faults off the central coast of California run through the oil and gas deposits and fracture the rocks containing the oil. There is also a lot of oil off the Santa Barbara coast, Luyendyk said.

“The leakages or seepages from this area are larger than any other in the U.S.,” he said, “and could be larger than any other in the world.”

To study the seeps they have used sonar as well as data from special devices called seep tents, which the oil industry uses to collect the leaking gas.

Platform Holly and other offshore platforms around the world drill into large oil and gas deposits under the sea floor, which in this case are the same ones causing the seeps. “A lot of people think the seepage is because of the [oil] production, but it’s not,” Boles said. “In fact, it’s just the opposite.”

The amount of oil and gas seeping from underground during the nineties was less than in the seventies, Luyendyk said. The researchers attribute the drop-off in seepage to the offshore oil drilling, which may reduce the pressure that drives oil and gas to the surface.

The reduced seeps are also due to a change in the amount of the gas and oil.

“It’s like taking something out of a bucket,” Boles said, “so eventually the bucket’s not going to be able to leak as much because there’s not as much in the bucket.”

Local marine life seems to have adjusted over time to live around these seeps, which have likely persisted for thousands of years.

“There’s a lot of evidence that marine ecosystems adapt to this phenomenon,” Luyendyk said. “There’s no reason to think these seepages haven’t been going on for hundreds of thousands of years.”

The gas disperses by mixing with oil, which accounts for the oil slicks in the Santa Barbara Channel.

“Bubbles of methane coated with the oil float to the surface and burst, dispersing crude oil and air and methane,” Luyendyk said.

Although oil slicks are a local phenomenon, other effects of the seeps are more widespread.

“Some of the gas dissolves in the water. In the winter it migrates south toward Baja and then in the summer it migrates north,” Bren School of Management and Environmental Science graduate student Misty Gonzales said. “It’s speculated that 50 percent of the tar all the way to Santa Monica comes from these seeps.”

Geological sciences assistant professor Jordan Clark, geography professor Libe Washburn, chemical engineering postdoctoral fellow Ira Leifer and graduate students Kris Broderick, Thor Egland and Derek Quigley have also helped with the research.