http://www.nytimes.com/2010/08/20/science/earth/20plume.html?_r=1&hp

By JUSTIN GILLIS and JOHN COLLINS RUDOLF

New research confirms the existence of a huge plume of dispersed oil deep in the Gulf of Mexico and suggests that it has not broken down rapidly, raising the possibility that it might pose a threat to wildlife for months or even years.

The study, the most ambitious scientific paper to emerge so far from the Deepwater Horizon spill, casts some doubt on recent statements by the federal government that oil in the gulf appears to be dissipating at a brisk clip. However, the lead scientist in the research, Richard Camilli, cautioned that the samples were taken in June and circumstances could have changed in the last two months.

The paper, which is to appear in Friday’s issue of the journal Science, http://www.sciencemag.org/ , adds to a welter of recent, and to some extent conflicting, scientific claims about the status of the gulf. While scientists generally agree that the risk of additional harm at the surface and near the shore has diminished since the well was capped a month ago, a sharp debate has arisen about the continuing risk from oil in the deep waters.

So far, scientific information about the gulf has emerged largely from government reports and statements issued by scientists. Many additional research papers are in the works, and it could be months before a clear scientific picture emerges.

The slow breakdown of deep oil that Dr. Camilli’s group found had a silver lining: it meant that the bacteria trying to eat the oil did not appear to have consumed an excessive amount of oxygen in the vicinity of the spill, alleviating concerns that the oxygen might have declined so much that it threatened sea life. On this point, Dr. Camilli’s research backs statements that the government has been making for weeks.

Dr. Camilli, of the Woods Hole Oceanographic Institution in Woods Hole, Mass., said the plume, at the time he studied it, was dissipating so slowly that it could still be in the gulf many months from now. Assuming that the physics of the plume are still similar to what his team saw in June, “it’s going to persist for quite a while before it finally dissipates or dilutes away,” he said.

Concentrations of hydrocarbons in the plume were generally low and declined gradually as the plume traveled through the gulf, although Dr. Camilli’s team has not yet completed tests on how toxic the chemicals might be to sea life.

In a report on Aug. 4, a team of government and independent scientists organized by the National Oceanic and Atmospheric Administration estimated that 74 percent of the oil from the leak had been captured directly from the wellhead; skimmed, burned, dispersed chemically or by natural processes; evaporated from the ocean surface; or dissolved into the water in microscopic droplets.

The report found that the remaining 26 percent of the oil had mostly washed ashore or collected there, was buried in sand and sediment, or was still on or below the surface as sheen or tar balls.

While the government report expressed concern about the continuing impact of the spill, it was widely viewed as evidence that the risk of additional harm in the gulf was declining.

This week, scientists at the University of Georgia, who in May were among the first to report the existence of the large plume studied by Dr. Camilli’s team, sharply challenged

the government’s assessment. They contended that the government had overestimated rates of evaporation and breakdown of the oil.

“The idea that 75 percent of the oil is gone and is of no further concern to the environment is just incorrect,” said Samantha Joye, a professor of marine sciences at the University of Georgia. She has studied the spill extensively but has not yet published her results.

Responding to the University of Georgia criticism, Jane Lubchenco, the NOAA administrator, said the government stood by its calculations. “Some of those numbers we can measure directly,” she said. “The others are the best estimates that are out there.”

Dr. Lubchenco has noted repeatedly that some of the remaining oil existed in the form of undersea plumes and cautioned that this subsurface oil could pose a threat to marine life.

In another report http://usfweb3.usf.edu/absoluteNM/templates/?a=2604&z=120

( also see )
http://green.blogs.nytimes.com/2010/08/18/oil-plumes-may-be-more-toxic-than-thought-scientists-warn/

this week, researchers from the University of South Florida said they had found oil droplets scattered in sediment along the gulf floor and in the water column, where they could pose a threat to some of the gulf’s most important fisheries.

The dispersed oil appeared to be having a toxic effect on bacteria and on phytoplankton, a group of micro-organisms that serves as a vital food for fish and other marine life, the scientists said, although they cautioned that further testing was needed.

Dr. Camilli’s paper tends to support the view that considerable oil may be lingering below the surface of the gulf. He said he was not especially surprised by the slow rate of breakdown, considering that the deep waters of the gulf are cold, about 40 degrees Fahrenheit in the vicinity of the plume.

“In colder environments, microbes operate more slowly,” Dr. Camilli said. “That’s why we have refrigerators.”

For weeks, BP, the company that owned the out-of-control well, disputed claims from scientists that a huge plume of dispersed oil droplets had formed in the gulf, with its chief executive at the time, Tony Hayward, declaring at one point, “There aren’t any plumes.” http://topics.nytimes.com/top/reference/timestopics/people/h/tony_hayward/index.html?inline=nyt-per

NOAA, while initially skeptical, ultimately confirmed the existence of such plumes in two reports. The new paper appears to dispel any lingering doubt, providing detailed evidence that one major plume and at least one minor plume existed and that they contained large quantities of hydrocarbons, albeit dispersed into tiny droplets.

Dr. Camilli’s team measured the main plume at roughly 3,600 feet below the surface; it extended for more than 20 miles southwest of the well. It was more than a mile wide in places and 600 feet thick, traveling at about four miles a day.

At the time his team studied it in June, the plume appeared to have narrowed from measurements reported early in the spill by a team that included Dr. Joye and Vernon Asper, a marine scientist from the University of Southern Mississippi, but Dr. Camilli’s results otherwise matched their report.

The slow breakdown of the plume, if verified by additional research, suggests that scientists may find themselves tracking the toxic compounds from BP’s well and trying to discern their impact on sea life for a long time.

“I expect the hydrocarbon imprint of the BP discharge will be detectable in the marine environment for the rest of my life,” Ian MacDonald, an oceanographer at Florida State University, told Congress in prepared testimony on Thursday. “The oil is not gone and is not going away anytime soon.”

Special thanks to Richard Charter