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NOAA Researchers Investigate Shipwrecks and 'Mystery Oil Spills'

Part 2: Long-sunk secrets rise slowly to the surface

December 12, 2011
S/S Montebello

Six miles off the California coast, a Japanese submarine sank the American oil tanker S/S Montebello, shown here at sea, on December 23, 1941 – barely two weeks after Pearl Harbor.

In Part 1 of this feature, NOAA researcher Doug Helton explained how he and his co-investigators began studying shipwrecks as the source of mysterious oil spills. His interview resumes with a case study of one of those vessels.

What is the ‘Montebello Mystery’?

ROV being launched to investigate the Montebello

In October 2011, NOAA partner Global Diving & Salvage launched a remotely operated vehicle (ROV) to conduct an underwater assessment of the S/S Montebello, which lies 900 feet deep just south of the Monterey Bay National Marine Sanctuary. Photo Courtesy California Department of Fish and Game.

For the past two-and-a-half-years, NOAA’s Office of Response and Restoration and Office of National Marine Sanctuaries have assisted the U.S. Coast Guard (USCG) and the California Office of Spill Prevention and Response in evaluating the potential pollution threat from the American oil tanker S/S Montebello. A Japanese submarine sank the tanker off the California coast early on the morning of December 23, 1941 – barely two weeks after Pearl Harbor. At the time, it carried 3 million gallons of crude oil.

Today, the wreck of the Montebello still rests in 900 feet of water just south of the Monterey Bay National Marine Sanctuary. It’s one of the shipwrecks we’ve been investigating to make sure that the oil still on board hasn’t leaked into the surrounding environment.

No significant oil releases were reported when it sank, and investigations in 1945, 1996, 2003, and 2010 found the hull and cargo tanks to be remarkably intact. But the question remained: Did the ship still hold the 3 million gallons of crude oil it was carrying when it went down?

In October 2011, we finally got some answers. NOAA worked with the State of California, the USCG, and the marine salvage company Global Diving and Salvage to assess the wreck’s condition with a remotely operated vehicle (ROV). A special ultrasound device was used to measure the thickness of the ship’s hull and detect which tanks might contain oil. The ROV also drilled access points into the tanks to visually test for oil.

After two weeks of testing, the salvors determined that no crude oil remained in the tanker. The fate of the oil may never be known, but sometime during the past 70 years, the oil seeped out.

Who pays for the cleanup of “mystery” oil spills?

The Oil Pollution Act of 1991 authorizes the use of the federal Oil Spill Liability Trust Fund for the payment of claims for uncompensated costs associated with oil removal and for natural resource damage assessment, restoration, and compensation in cases where there is no financially viable responsible party (as in mystery spills). The Fund is managed by the USCG’s National Pollution Funds Center.

What are the results of your research to date? And future plans?

We know that there are approximately 20,000 shipwrecks in U.S. waters. Most are probably too old or too small to contain substantial amounts of oil. Others lost their cargo when they sank, decayed on the sea floor, or were intentionally destroyed as hazards to navigation.

We also know that some wrecks still have oil onboard. I and my co-investigators in the Office of National Marine Sanctuaries are identifying which of these vessels, based on age, size, type, and condition, have the highest potential still to contain oil. We are doing additional archival research on the highest-priority vessels to estimate how much oil may have been onboard when they sank. We are also looking for clues as to how the wrecks have decayed over time.

For the wrecks that have high potential for oil, we are using computer modeling to look at the environmental implications of potential spills. We are preparing a summary report on our findings that should be published next year.

Is there anything else you’d like to share about your research?

Researching shipwrecks is fascinating. Every ship has a story, and that story is partially revealed through the accounts of survivors, old newspaper articles, insurance investigations, accident records, and cargo reports. Salvage reports and survey records from NOAA charts add to the picture, but these old documents provide incomplete clues. Sometimes these silent wrecks at the bottom of the sea end up keeping some secrets down there with them. We hope to uncover a few of them!


Doug Helton is the Incident Operations Coordinator in the Emergency Response Division of NOAA’s Office of Response and Restoration. The Division, based in Seattle, provides scientific and technical information and on-the-ground expertise when the U.S. Coast Guard responds to spills of oils, chemicals, and other hazardous materials.