msnbc.com staff and news service reports
updated 8/19/2010 10:07:48 PM ET 2010-08-20T02:07:48

Scientists on Thursday reported results from the first detailed study of a giant plume of oily water near the blown-out BP well — stating that it measured at least 22 miles long, more than a mile wide and 650 feet tall.

While other scientists earlier found evidence of plumes in the area, the new data is the first peer-reviewed study about oil lurking in the water, in this case at some 3,000 feet below the surface. It's also the first to offer some details about the size and characteristics of a plume not only vast in size but which remained stable and intact during a 10-day survey last June.

Moreover, the study adds to the controversy over how much oil is still in the Gulf ecosystem from the spill. The U.S. government earlier this month estimated that 75 percent of the oil that spewed from the Macondo well had been skimmed, burned or broken up by chemical dispersants and natural microbes in the water.

The plume, which scientists said came from the busted Gulf well, shows the oil "is persisting for longer periods than we would have expected," lead researcher Rich Camilli said in a statement issued with the study. "Many people speculated that subsurface oil droplets were being easily biodegraded. Well, we didn’t find that. We found it was still there."

How significant a threat to the Gulf's ecosystem the plume might be is still not clear, but further analysis of collected water samples could shed light on that.

"We don’t know how toxic it is," said Chris Reddy, who like Camilli works for the Woods Hole Oceanographic Institution. "And we don’t know how it formed, or why. But knowing the size, shape, depth and heading of this plume will be vital for answering many of these questions."

The collected water samples had no odor of oil and the plume is mostly water mixed with some hydrocarbons that include oil. "The plume was not a river of Hershey’s syrup," said Reddy. "But that’s not to say it isn’t harmful to the environment."

The levels and distributions of the petroleum hydrocarbons show "the plume is not caused by natural (oil) seeps," Camilli added.

Reddy said study data and more samples yet to be analyzed eventually could refine estimates about the amount of the spilled oil that remains in the Gulf. The U.S. government estimates 4.9 million barrels spilled, and that only a quarter remains in the water or along marshes.

Jane Lubchenco, head of the National Oceanic and Atmospheric Administration, told a White House briefing on Aug. 4 that "at least 50 percent of the oil that was released is now completely gone from the system. And most of the remainder is degrading rapidly or is being removed from the beaches."

On Tuesday, however, two new scientific reports raised fresh fears about the environmental fallout from the world's worst offshore oil spill and questioned government assurances that most of the oil was already gone.

In one report, researchers at the University of Georgia estimated that about three-quarters of the oil was still lurking below the surface of the Gulf. In the other, University of South Florida scientists said they found oily clouds of water inside an underwater canyon. The oil was at levels toxic to critical marine organisms.

Submarine crisscrossed plume
The plume researchers based their findings announced Thursday on some 57,000 chemical analyses during a June 19-28 cruise.

A robotic submarine also crisscrossed the plume boundaries to help determine its size, shape and composition, the researchers said.

Previous attempts to define the plume were "like watching the Super Bowl on a 12-inch black-and-white TV and we try to bring to the table a 36-inch HD TV," said Reddy. The paper, fast-tracked for the world of peer-reviewed science, was written on a boat while still in the Gulf, he said.

The researchers tracked the plume about three miles southwest of the wellhead and out to about 22 miles until the approach of Hurricane Alex forced them back to shore. They said Thursday that they did not know what has happened to the plume since then, but assume it has moved with the Gulf currents.

One important finding from water samples was that levels of dissolved oxygen within the plume had not dropped to levels that would suggest bacteria were quickly breaking down the oil.

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If further analysis confirms that, then it means "the hydrocarbons could persist for some time," said Benjamin Van Mooy, a geochemist at Woods Hole. "So it is possible that oil could be transported considerable distances from the well before being degraded."

The study, funded by the National Science Foundation, appears in Thursday's issue of the journal Science.

Expect long-term presence, experts say
Monty Graham, a scientist at the Dauphin Island Sea Lab in Alabama who was not involved in the study, praised the work. "We absolutely should be concerned that this material is drifting around for who knows how long," he said. The researchers "say months in the paper, but more likely we'll be able to track this stuff for years."

Florida State University scientist Ian MacDonald, in testimony before Congress on Thursday, said the gas and oil "imprint of the BP discharge will be detectable in the marine environment for the rest of my life."

The oil is at depths of 3,000 to 4,000 feet, far below the environment of the most popular Gulf fish like red snapper, tuna and mackerel. But it is not harmless. These depths are where small fish and crustaceans live. And one of the biggest migrations on Earth involves small fish that go from deep water to more shallow areas, taking nutrients from the ocean depths up to the large fish and mammals.

Those smaller creatures could be harmed by going through the oil, said Larry McKinney, director of Texas A&M University's Gulf of Mexico research center in Corpus Christi.

Some aspects of that region are so little known that "we might lose species that we don't know now exist," said Graham of the Dauphin Island lab.

"This is a highly sensitive ecosystem," agreed Steve Murawski, chief fisheries scientist for NOAA. "The animals down at 3,300 to 3,400 feet grow slowly." The oil not only has toxic components but could cause genetic problems even at low concentrations, he said.

For much of the summer, the mere existence of underwater plumes of oil was the subject of a debate that at times pitted outside scientists against federal officials who downplayed the idea of plumes of trapped oil. Now federal officials say as much as 1 million barrels of oil may be lurking below the surface in amounts that are much smaller than the width of a human hair.

While federal officials prefer to describe the lurking oil as "an ephemeral cloud," the Woods Hole scientists use the word "plume" repeatedly.

While praising the study that ended on June 28, Murawski said more recent observations show that the cloud of oil has "broken apart into a bunch of very small features, some them much farther away." Texas A&M's McKinney said marine life can suffer harm whether it is several smaller plumes or one giant one.

NOAA redirected much of its sampling for underwater oil after consulting with Woods Hole researchers. The federal agency is now using the techniques that the team pioneered with a robotic sub and an underwater mass spectrometer, Murawski said.

msnbc.com's Miguel Llanos as well as The Associated Press and Reuters contributed to this report.

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