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Oceanographers announced today the discovery of a wispy oil plume at least 22 miles long and 1.2 miles wide floating beneath the surface of the Gulf of Mexico, a sign that plenty of the oil from BP’s Deepwater Horizon leak remains in the environment. It’s the first conclusive proof that a deep-sea plume from the leak exists, which at least partially explains what happened to the oil in the three months since the Deepwater Horizon rig exploded. It also casts doubt on the federal government’s statement earlier this month that most of the oil has dispersed or disappeared.

But the new study is merely a rough snapshot of what is happening in the depths. Wide disagreement persists among scientists who study the Gulf and oil spills, and they say it could take generations to fully understand the leak’s scope. The best minds in marine science and geology can’t say yet how bad it will be.

Woods Hole Oceanographic Institution researchers Richard Camilli and Chris Reddy followed the plume starting about three miles from the wellhead of the deep-sea Macondo well. Using autonomous submersibles, they took samples for 22 miles, until the approach of Hurricane Alex forced them to turn back.

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As of now, they don’t know how much oil (of the estimated 4.9 million barrels leaked) is in the plume, and they can’t be certain how diffuse it is until they analyze more water samples, Reddy said. The researchers say the levels of dissolved oxygen within the plume had not dropped to levels that would suggest bacteria were breaking down the oil in significant volumes.

The report comes two weeks after a government study that most researchers said was widely misinterpreted. Other scientists dismissed the report as inaccurate or incomplete. That report, from the National Incident Command (NIC), said the majority of the oil had evaporated, been recovered or been dispersed — but dispersed does not mean gone.

Rick Steiner, a retired professor at the University of Alaska and marine conservationist who worked on cleaning up the Exxon Valdez oil spill, called that report fatally flawed.

“The estimate that chemical dispersants were successful at dispersing 8 percent of the leaked oil [as stated in the NIC report] is, quite frankly, ludicrous,” he said in an e-mail message.

Many others agree, and at least two studies emerged this week that appear to directly contradict the government’s findings. But none of them proves anything conclusively. Reddy said government scientists, along with those at universities and private institutions, are trying to account for all the oil like balancing a checkbook. But a checkbook is difficult to balance when none of the numbers being used are firmly accurate.

“This data that we’re waiting for, as it becomes available, they will be able to put it into their calculations,” he said. “When we have analyzed those samples, we’ll be able to constrain what the inventory of those compounds was in there. And at that point, we may be able to see whether it’s a penny in a big checking account, or maybe it’s bigger.”

Submarine Explorer

Woods Hole researchers used unmanned submarines to track the extent of the plume.

The problem is that every variable is couched in terms of estimates. Without a firm grasp on where the oil settled — at the surface, in the middle, or at the bottom of the sea — it’s nearly impossible to say what happened to it. The Woods Hole study uses oxygen as a proxy for microbial degradation, for instance. But scientists don’t have good baselines for pre-existing oxygen concentrations, so it’s hard to tell what has changed.

“In truth, no one really has any idea whatsoever of how much oil has gone where,” Steiner said.

Some estimates suggested 80 percent of it went to the surface, and if that’s so, then it’s reasonable to assume much of it is gone, according to Louisiana State University emeritus professor Ed Overton. Oil at the surface would quickly evaporate and be consumed by naturally present bacteria, he said.

Overton reviewed the NIC report and generally accepts its findings, though he believes the government may have underestimated how much oil remains below the surface. He said the visible evidence looks promising — surface slicks are disappearing, and things seem to be returning to normal. He went swimming off the coast of Alabama last week and said it was wonderful, though he did find a few tar balls. Work, not oil, forced him to return home.

“I could still be swimming if there wasn’t so much work to do associated with the spill,” he said.

Others don’t seem quite as eager to dive in. Ron Kendall, chair of the department of environmental toxicology at Texas Tech and director of the university’s Institute for Environmental and Human Health, believes the oil’s persistence, as well as the profligate use of dispersants, could lead to entirely new environmental effects. He compared the dispersants to mineral spirits used to clean up oil spots in a garage.

“If you pour mineral spirits on your skin, it’ll burn. You breathe it, it’ll be very antagonistic to your sinuses. You drink it, it’ll be very harmful,” he said. “There were a lot of organisms that came into contact with the use of dispersants deep in the ocean, and on the surface.”

He thinks dispersants probably contributed to the plume’s presence. If the oil had not been dissipated into microdroplets as it was spewing from the well, more of it would have floated to the surface, he said.

“A lot of that oil, and the toxic constituents in that oil, has probably been dispersed into the water column, and that is what these scientific discoveries are finding out — there appear to be these plumes,” he said.

Adding to the confusion is the tricky element of politics. Plenty of research will be wrapped up in lawsuits, and scientists who are being hired by BP and legions of attorneys are being caught in the middle. Last month, NPR reported that BP is essentially buying the silence of prominent Gulf researchers. The public radio network quoted University of South Alabama’s Bob Shipp, who said BP’s lawyers tried to hire his whole Department of Marine Sciences to do research for them. Under the deal, the scientists could only disclose their findings if BP gave them a green light. Otherwise, they’d have to keep it secret for three years, NPR said.

“A lot of this event has been politicized, versus letting the scientists do their jobs and get the best science possible,” Kendall said. “It’s really hard for the science to rise to the top when everybody is getting ready for a big lawsuit, including the government.”

There’s at least one area in which scientists can agree: The impact on Gulf ecosystems will not be clear for years to come.

Kendall believes most of the leaked oil remains in the environment, and said it will take years to understand its impacts on wildlife like sea turtles, whales and bluefin tuna.

“It takes 10 years before those female (turtles) come back to nest, in the case of the coast of Texas, so we won’t know for a decade. So let’s not race to judgment. This is a time for good science,” he said.

Overton said more work is still needed to at least determine where the oil went.

“As soon as that damn oil quit coming into the Gulf, the amount of oil at the surface nearly disappeared. Now that doesn’t mean there is zero oil. There’s still oil on the marshy grass, some buried a foot or so down … coastal erosion changes those beaches a lot. There’s tar balls out there like the ones I found.

“But what if, instead of 20 percent being spread at the bottom, what if 80 percent was down there, and all we were seeing at the surface was 20 percent? If that’s the case, then 80 percent of that oil is still down there, minus what is being degraded.”

Overton said he would not be surprised if there is still plenty of diluted oil beneath the surface — which the Woods Hole study suggests is plausible.

“The question is, can the dilute oil cause environmental impacts? We don’t know. We can’t know, because we don’t know very much about deepwater environments,” Overton said. “This is a question that may never be answered.”

If all this uncertainty indicates anything, it’s that much more data is needed before anyone — scientists or policymakers — attempts anything resembling declarative statements. Science is incremental, as Reddy said in today’s conference call. Individual studies are usually designed to address narrow questions, such as today’s glimpse at the plume’s size and spread. Further studies will address its toxicity, density and impacts on fish and other wildlife. It will be a long time before everything is tied together to paint a complete picture of this disaster.

Kendall said that research is only just beginning.

“To me, we’re still in the very early phases of this,” he said. “Quite frankly, we may not fully figure out the ultimate impact of this for many years to come.”

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