Gulf reveals 22-mile plume of oil

Reports of the “death” of millions of gallons of spilled oil in the Gulf of Mexico might be greatly exaggerated, as scientists have found an underwater plume of hydrocarbons that’s at least 22 miles long, more than a mile wide and 3,000-plus feet deep.

That finding flies in the face of assertions from US federal officials on 4 August that the “vast majority” of the estimated 4.9 million barrels of spilled oil had been evaporated, burned, recovered or dispersed. Just 26 per cent of the oil that gushed into the Gulf in the wake of the Deepwater Horizon drill rig disaster remained, most of it on or just below the water’s surface or washing onto shore, according to the National Oceanic and Atmospheric Administration.

In a new study published today in the journal Science, scientists with the Woods Hole Oceanographic Institution describe the plume as 1.2 miles wide and 650 feet high. At a depth of more than 3,000 feet, the hydrocarbon plume was being degraded by deep-sea microbes “relatively slowly,” with researchers noting the residue is likely to persist for some time.

“We’ve shown conclusively not only that a plume exists, but also defined its origin and near-field structure,” said Richard Camilli, chief scientist of the cruise that tracked the plume and the study’s lead author. “Until now, these have been treated as a theoretical matter in the literature.”

The plume’s presence shows the spilled oil “is persisting for longer periods than we would have expected,” Camilli said. “Many people speculated that subsurface oil droplets were being easily biodegraded.

“Well, we didn’t find that. We found it was still there.”

Camilli and his research colleagues are now considering a new research proposal to look for additional residual oil plumes from the spill, which began April 20 when the drill rig conducting work for the oil giant BP exploded, burned and sank, killing 11 workers and setting off a gush of oil that continued through July 15.