Florida researchers said Friday that they had for the first time conclusively linked vast plumes of microscopic oil droplets drifting in the Gulf of Mexico to the Deepwater Horizon disaster.
The scientists, from the University of South Florida, matched samples taken from the plumes with oil from the leaking well provided by BP. The findings were the first direct confirmation that the plumes were linked to the spill, although federal scientists had said there was overwhelming circumstantial evidence tying them to BP’s well.
The discovery of the plumes several weeks into the oil leak alarmed scientists, who feared that clouds of oil particles could wreak havoc on marine life far below the surface. Plumes have been detected as far as 50 miles from the wellhead, although oil concentrations at those distances are extremely low, about 750 parts per billion.
This is well below the level considered acutely toxic for fish and marine organisms, but could still affect eggs and larvae, the scientists fear.
“There are a lot of things that are potentially at risk,” said David Hollander, an oceanographer with the University of South Florida who is studying the plumes. “There’s not a lot known of the toxic effects of oil on organisms living in deeper waters.”
The announcement by the Florida researchers came as federal scientists released their own report on the oil formations. The multiagency report describes the presence of large plumes of microscopic oil droplets within several miles of the wellhead at a depth of 3,280 to 4,265 feet. Oil concentrations there are as high as 10 parts per million, or the equivalent of one tablespoon of oil in 130 gallons of water.
The plumes closest to the well may be concentrated enough to pose a threat to nearby deepwater coral reefs, which host a diversity of ocean life, said Steve Murawski, the National Oceanic and Atmospheric Administration’s chief scientist for the spill response. “We know that even low concentrations can be harmful to the eggs and larvae of the deep coral,” he said.
The federal report also described a drop in dissolved oxygen levels in deep water near the well, which it said probably resulted from the rapid reproduction of oil-eating microbes. Yet the reduction did not signal conditions that could cause a die-off in sea life, the report concluded.
The ultimate impact of the oil plumes on sea life in the gulf remains open to debate. A plume has been found near DeSoto Canyon, an underwater valley south of the Florida Panhandle where ocean currents push nutrient-rich water up onto the continental shelf. Some scientists fear that oil, even in the low concentrations found in the plumes, could be driven into the shelf’s life-rich shallow waters and cause harm.
“It’s almost an express route up there,” Dr. Hollander said. “That’s what raises the concerns of the biologists.”
Yet federal scientists say they believe that the oil concentrations in the deepwater plumes are too low to have much of an effect on the gulf’s commercially valuable fisheries.