In the weeks after BP's blown well began gushing oil into the Gulf of Mexico, scientists wondered about what would happen to all that crudewhether it would pool at the surface, or somehow spread underwater. This wasn't a tanker spill like the Exxon Valdez disaster, in which the oil was lost on the surface of the water and stayed there. It was a deep underwater well, in which oil gushed a mile down. Early groups of researchers theorized that some of the oil might spread in underwater plumesperhaps aided by the liberal application of chemical dispersants at the wellhead. But then-BP CEO Tony Hayward wouldn't hear of it. "They're aren't any plumes," he said at the end of May. "The oil is on the surface."
Well, Hayward is long gone, but it still kind of feels good to say it: he was wrong. Earlier this month, the National Oceanic and Atmospheric Administration (NOAA) released a report saying that 74% of the spilled oil had evaporated or been been skimmed, dispersed, burned or consumed by microorganisms. That sounds like great news but there's a big loophole, and it's in that word "dispersed." Oil that's broken up into fine droplets is still oil, after all, and a new study published in the August 19 issue of Science contains the best evidence yet that a 22 mi-long underwater plume of oil exists more than 3,000 ft. below the surface and that the crude definitely came from BP's well. More worrying, the oil inside the plume is breaking down much slower than it would at the surface, meaning it's likely to linger for a long time, posing a potential threat to marine life.
"The chemistry of this plume clearly shows that it comes form the Deepwater Horizon spill," says Richard Camilli, a researcher with the Woods Hole Oceanographic Institute's Applied Ocean Physics and Engineering Department and the lead author of the paper. "This is something that is really unexpected."
It's unexpected for a simple reason oil is supposed to float on water, so it's reasonable to believe that even if it's released 5,000 ft. below the surface of the Gulf, it would eventually make its way to the top. But the Science paper shows that that simple premise isn't so simple after all, and that at least some of the oil stayed in the middle depths. The study relied on some 57,000 chemical analyses conducted during a research cruise in the Gulf between June 19 and 28, using an autonomous underwater vehicle and a mass spectrometer capable of detecting chemical signatures. The entire study was suggested and funded in just a few days by the National Science Foundation (NSF), as part of the NSF's rapid response to the spill. "That's lighting speed for research," says Camilli.
The mass spectrometer detected chemicals found in hydrocarbons, like benzene and toluene the signature of an oil spill. The researchers estimated that the plume, found near the site of the BP well, was growing by more than 12,120 lbs. (5,500 kg) a day while the spill was underway. That was proof that the plume couldn't be the result of oil seeping naturally from the floor of the Gulf of Mexico. The Science team calculated that even if all of the oil naturally leaking from the seafloor were to be added to the plume, it would account for less than half of the total.
And now that the oil plume has formed under the water, it could stay there for some time. While oil can evaporate or be broken down by microbes rather quickly on the surface, the colder temperatures of the depths significantly slow down that decomposition. In fact, the Science researchers estimate that the temperatures found 3,000 ft. below the ocean surface could mean decomposition will happen ten times slower than it would on the surface. How long the oil will remain in some fashion is anyone's guess right now, but Florida State University scientist Ian MacDonald told Congress today that the "imprint of the BP discharge will be detectable in the marine environment for the rest of my life."
At the same time, it's important to understand what the Science study doesn't say. Camilli and his fellow researchers at Woods Hole can't say how toxic the underwater oil may be or may not be. Because their research is based only on a short snapshot from late June, they can't say whether the plume is still there, whether it's grown larger or smaller or exactly what will happen to it in the future. They don't know what effect the application of subsea dispersants have had on the underwater spread of the oil. (Federal scientists have said that the underwater oil plume may have broken up into smaller clouds but that may not change their potential toxicity.) "We don't live in a CSI world," said Chris Reddy, a Woods Hole scientist and co-author of the Science paper. "It's going to take a long time but we'll know as more and more data comes out."
Certainly the Science paper provides convincing evidence that the oil spill is far from over, at least in terms of its ecological effects, and that those effects will linger long after the media have gone home and the politicians have moved on. That was also the message at an unusual hearing held by Representative Edward Markey (D-MA) Thursday on the potential health impacts of the spill on seafood. "The oil has not gone away, and it is important for the Gulf of Mexico residents to know that the attention on this issue has not gone away," Markey said.
Indeed, BP's well has not even been fully, officially killed yet and that may not happen for some time. Today retired Coast Guard Admiral Thad Allen ordered BP to carry out additional pressure tests on the well, to prepare for the possibility of removing the Deepwater Horizon's original blowout preventer and replacing it with a tougher one, so the last stages of the bottom kill can finally go forward. That could mean the procedure will stretch out past Labor Day, long after the original target date of mid-August. "We're doing this out of an overabundance of caution," Allen said today. We'll need more of that going forward.