USGS Chemists Analyze Monterey Tarballs....Most Oil Residues In Monterey BayProbably From Natural Seeps

February 11, 1998

Many of the tarballs washing up on the shores of Monterey Bay are most likely from natural seeps from the floor of Monterey Bay and the continental shelf, rather than from ruptured oil tankers and other man-made occurrences, according to scientists from the U.S. Geological Survey in Menlo Park, Calif.

Although the investigation and analyses of petroleum residues from Monterey Bay is in its early stages, USGS geochemist Keith Kvenvolden said that many of the samples match the known isotopic compositions of crude oils from inland and offshore sources in the Miocene Monterey Formation of California.

Kvenvolden presented the USGS analyses at the American Geophysical Union's Ocean Sciences meeting in San Diego, Thursday, February 12.

His poster session illustrated that a detailed organic geochemical study of petroleum residues in Monterey Bay indicated that the samples have unusually heavy carbon isotopic compositions, which are characteristic of crude oils emanating from the Miocene Monterey Formation. "Because the coastal petroleum residues apparently are extensively distributed within Monterey Bay National Marine Sanctuary, we believe their source is likely natural and not spilled petroleum products," Kvenvolden concluded.

Kvenvolden's study of the Monterey Bay tarballs is similar to one he and colleagues conducted on residues collected on the beaches of southern Alaska, following the Exxon Valdez oil spill of 1989. That study, which was published in 1993, concluded that some of the tarballs carried an isotopic "fingerprint" that traced them to California oil that had spilled from on-shore tanks that ruptured during the 1964 Alaska earthquake.

"These carbon isotopes are the fingerprints of petroleum," Kvenvolden said, "and identifying them gives investigative earth scientists forensic tools similar to those used by criminal investigators in their work."

As the nation's largest water, earth and biological science and civilian mapping agency, the USGS works in cooperation with more than 2000 organizations across the country to provide reliable, impartial, scientific information to resource managers, planners, and other customers. This information is gathered in every state by USGS scientists to minimize the loss of life and property from natural disasters, to contribute to the conservation and the sound economic and physical development of the nation's natural resources, and to enhance the quality of life by monitoring water, biological, energy, and mineral resources.
Editors: Dr. Kvenvolden will be back in his Menlo Park office and available for interviews on Feb. 13. To arrange for interviews, call the USGS Public Affairs Office at (650)329-4000.

This press release and in-depth information about USGS programs may be found on the USGS home page: To receive the latest USGS news releases automatically by email, send a request to <>. Specify the listserver(s) of interest from the following names: water-pr; geologic-hazards-pr; biological-pr; mapping-pr; products-pr; lecture-pr. In the body of the message write: subscribe (name of listserver) (your name). Example: subscribe water-pr joe smith.

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