Scientists Map Large Hydrocarbon Plume in Gulf

Scientists have detected a plume of hydrocarbons at least 22 miles long and more than 3,000 feet below the surface of the Gulf of Mexico, a residue of the BP Deepwater Horizon oil spill.

The 1.2-mile-wide, 650-foot-high plume of trapped hydrocarbons was detected by scientists funded by the National Science Foundation (NSF) and affiliated with the Woods Hole Oceanographic Institution (WHOI) during a ten day subsurface sampling effort from June 19-28 near the wellhead.

The results provide a snapshot of where the oil has gone as surface slicks shrink and disappear.

"These results create a clearer picture of where the oil is in the Gulf," said Christopher Reddy, a WHOI marine geochemist and one of the authors of a paper on the results that appears in this week's issue of the journal Science.

The study confirms once again that a continuous plume was found "at petroleum hydrocarbon levels that are noteworthy and detectable," Reddy said.

The researchers measured petroleum hydrocarbons in the plume and, using them as an investigative tool, determined that the source of the plume could not have been natural oil seeps but had to have come from the Deepwater Horizon blowout at the Macondo well.

They reported that deep-sea microbes were degrading the plume relatively slowly, and that it was possible that the plume had and could persist for some time if the rate of microbial degradation or the dilution of the plume does not accelerate.

"These findings confirm what NOAA and our federal partners have reported about the presence and concentration of subsurface oil, and provide an additional piece of the puzzle as we continue to aggressively monitor the fate of the oil in the Gulf," said Steve Murawski, NOAA's chief scientist. "Our collaborations with Woods Hole and other academic and private research institutions are critical to the ongoing response and recovery efforts."

"This research illustrates the value of NSF's long-term investment in state-of-the-art technology like Sentry so that it can be deployed not only to advance basic knowledge but also in national emergencies," said David Conover, director of NSF's Division of Ocean Sciences.

"Similarly, the NSF RAPID award program enables scientists to quickly arrive on the scene and begin rigorous study of episodic events like this oil spill."

NSF has so far issued a total of 90 RAPID grant awards to investigators; the grants to date are worth $10.2 million for study of the spill. NSF has invested an additional $3 million in ship-related operating costs.

"The payoff occurs when peer-reviewed results like these reported today are made public," said Conover.

The research team based its findings on some 57,000 discrete chemical analyses measured in real time during a June 19-28, 2010, scientific cruise aboard the R/V Endeavor, which is owned by NSF and operated by the University of Rhode Island.

"We've shown conclusively not only that a plume developed, but also defined its origin and near-field structure," said Richard Camilli of WHOI's Applied Ocean Physics and Engineering Department, chief scientist of the cruise and lead author of the paper.

"In June, we observed the plume migrating slowly [at about 0.17 miles per hour] southwest of the source of the blowout," said Camilli.

The researchers began tracking it about three miles from the well head and out to about 22 miles (35 kilometers)--until the approach of Hurricane Alex forced them away from the study area.

The levels and distributions of the petroleum hydrocarbons show that "the plume is not caused by natural [oil] seeps" in the Gulf of Mexico, Camilli said.

The plume has shown that the oil "was persisting for longer periods than we would have expected," Camilli said.

Whether the plume's existence poses a significant threat to the Gulf is not yet clear, the researchers say. "We don't know how toxic it is," said Reddy, "and we don't know how it formed, or why. But knowing the size, shape, depth, and heading of this plume will be vital for answering many of these questions."

(C) NewsRoom America 2010