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Environment: Researchers still tracking oil leaks from the Deepwater Horizon disaster in the Gulf of Mexico

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A massive slick from the Deepwater Horizon oil spill spreads across the Gulf of Mexico in July 2010. Photo courtesy NASA.

Oil ‘fingerprinting’ technique shows the oil is likely from the wreckage of the sunken drill rig

By Summit Voice

FRISCO — Chemical fingerprints show that oil sheens in the Gulf of Mexico are probably from pockets of oil trapped within the wreckage of the sunken Deepwater Horizon drilling rig. Both the Macondo well and natural oil seeps common to the Gulf of Mexico were confidently ruled out by researchers from Woods Hole Oceanographic Institution and the University of California, Santa Barbara. The study was published online this week in Environmental Science & Technology.

The oil sheens were first reported to the United States Coast Guard by BP in mid-September 2012, raising public concern that the Macondo well, which was capped in July 2010, might be leaking.

“It was important to determine where the oil was coming from because of the environmental and legal concerns around these sheens. First, the public needed to be certain the leak was not coming from the Macondo well, but beyond that we needed to know the source of these sheens and how much oil is supplying them so we could define the magnitude of the problem,” said WHOI chemist Chris Reddy.

Together with UCSB’s Dave Valentine, Reddy has been investigating multiple aspects of the Deepwater Horizon spill for the past three years, including the detection of subsurface plumes, the biodegradation of the oil, the fate of the dispersants, and the chemical transition from floating oil slicks to sunken tar balls.

“Because of our ongoing funding from the National Science Foundation, we were prepared to interrogate the source of mysterious oil sheens in the Gulf of Mexico,” Valentine said. “We’ve been exploring new ways to do this for several years in the context of natural seeps and this event provided us an opportunity to apply our fundamental advances to a real-world problem. This is a classic case where fundamental science finds a real world application.”

Using their recently patented oil fingerprinting technique, the scientists first confirmed that the sheens included oil from the Macondo well. But they also found trace amounts of industrial chemicals used in drilling operations, leading to the conclusion that the sheens may be originating from mechanical equipment from the drilling platform.

“The occurrence of these man-made olefins in all of our sheen samples points to a single main source which contains both Macondo oil and lesser amounts of the drilling fluids that harbor the olefins,” said Valentine. “This pointed us to the wreckage of the rig, which was known to have both, as the most likely source for the sheens.”

To try and make the final link, the researchers compared oil from the sheen with other samples, including two pieces of debris from the Deepwater Horizon, found floating in early May 2010, as well as oil collected by BP in October 2012 during an inspection of the 80-ton cofferdam that had been abandoned at the sea floor after its use in a failed attempt to cover the Macondo well in 2010.

When Reddy and Valentine compared the chemical makeup of the sheens with Deepwater Horizon debris found floating in 2010, they found a match. That debris, which came from the rig itself, was coated with oil and contaminated with drilling mud olefins.

“We had a fruitful exchange and developed a collegial relationship with both BP and the government. Both provided us with data, and in turn we gave them a preview of our findings with no strings attached,” said Valentine.

This research was funded by the National Science Foundation, the Gulf of Mexico Research Initiative DEEP-C Consortium, Woods Hole Oceanographic Institution, and the Swiss National Science Foundation Postdoctoral Fellowship.

 For more information, visit www.whoi.edu.

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