The persistence of a giant plume of oil in the Gulf of Mexico suggests that the long-term impact of the BP Deepwater Horizon spill may be worse than earlier assumed, a new scientific study has revealed.

In the latest issue of Science magazine, researchers at the Woods Hole Oceanographic Institution (WHOI) discussed their investigations of a plume of hydrocarbons at least 22 miles long and more than 3,000 feet below the surface. According to Christopher Reddy, a WHOI marine geochemist and oil spill expert, “The plume was not a river of Hershey’s Syrup... But that’s not to say it isn’t harmful to the environment.”

Doubts on earlier claims

Their discovery has cast doubt upon earlier claims by government agencies such as the National Oceanic and Atmospheric Administration (NOAA), which said that 74 per cent of the oil that gushed into the Gulf between April and August was either captured directly at the Macondo well site, had naturally evaporated or had been dispersed by operations at the surface and dissolved into microscopic droplets.

According to the most recent study, the 1.2-mile-wide, 650-foot-high plume of trapped hydrocarbons provided at least a partial answer to recent questions asking where all the oil had gone as surface slicks shrank and disappeared. Mr. Reddy said, “These results indicate that efforts to book-keep where the oil went must now include this plume.”

The WHOI study also disputed official estimates of the speed at which deep-sea microbes were degrading the plume. The plume has shown that the oil already “is persisting for longer periods than we would have expected”, according to Richard Camilli, Chief Scientist at WHOI and lead author of the paper. He added, “Many people speculated that subsurface oil droplets were being easily biodegraded. Well, we didn’t find that. We found it was still there.”

The WHOI study was based on approximately 57,000 discrete chemical analyses undertaken during a June 19-28 scientific cruise. The expedition entailed the use of two highly advanced technologies: the autonomous underwater vehicle and an underwater mass spectrometer.

While the WHOI scientists noted that they had found no “dead zones”, or regions of significant oxygen depletion within the plume where marine life could not survive, WHOI geochemist Benjamin Van Mooy, said this finding could have significant implications.

“If the oxygen data from the plume layer are telling us it isn’t being rapidly consumed by microbes near the well,” he said, “the hydrocarbons could persist for some time. So it is possible that oil could be transported considerable distances from the well before being degraded.”