Vast underwater concentrations of oil sprawling for miles in the Gulf of Mexico from the damaged, crude-belching BP PLC well are unprecedented in "human history" and threaten to wreak havoc on marine life, a team of scientists said today, a finding confirmed for the first time by federal officials.

Researchers aboard the F.G. Walton Smith vessel briefed reporters on a two-week cruise in which they traced an underwater oil plum 15 miles wide, 3 miles long and about 600 feet thick. The plume's core is 1,100 to 1,300 meters below the surface, they said.

"It's an infusion of oil and gas unlike anything else that has ever been seen anywhere, certainly in human history," said Samantha Joye of the University of Georgia, the expedition leader.

Bacteria are breaking down the oil's hydrocarbons in a massive, microorganism feeding frenzy that has sent oxygen levels plunging close to what is considered "dead zone" conditions, at which most marine life are smothered for a lack of dissolved oxygen.

Such low-oxygen conditions were noticed farther from the spill site, although Joye said she did not think the process would immediately produce a dead zone, since low nutrient concentrations in the water would limit the rate of the bacterial consumption.

Joye said her team also measured extremely high levels of methane, which is also spewing from the gushing BP well at up to 10,000 times background levels in Gulf waters.

"I've been working in the Gulf of Mexico for 15 years," Joye said. "I've never seen methane concentration this high anywhere in the water."

Less clear to researchers like Joye are what role the unprecedented deployment of oil-dispersing chemicals are having on the undersea gathering of oil. She said dispersants likely played a role in keeping the oil underwater but that they are "certainly not required" to produce such an effect, given the deep-water -- as opposed to surface -- injection of oil and gas.

Also still unclear, she said, are the long-term effects of oil and dispersant use on fisheries.

"The primary producers -- the base of the food web in the ocean -- is going to be altered. There's no doubt about that," Joye said. "We have no idea what dispersants are going to do to microorganisms. We know they are toxic to many larvae. It's impossible to know what the impacts are going to be."

A full understanding and the full impact to the Gulf's fishery may be years away, she said.

"It's a very, very complicated problem, and there are a lot of people doing fisheries work to try to get a handle on this, but it's going to be months or years probably before we realize the full consequences of this spill," Joye said.

Asked to react to BP officials earlier assertions that the Gulf of Mexico was a large enough body of water to absorb the impact of an oil spill under way, Joye bristled.

"The solution to pollution is not dilution," she said. "It's an excuse, and it's arm-waving, and it takes away from the important things that we should be thinking about," she said, such as measuring the scope of the spill and its effects.

Federal confirmation

Federal officials for the first time today confirmed the researchers' findings, although Coast Guard Adm. Thad Allen, who is leading the federal response to the spill, questioned the use of the term "plume" to describe that underwater oil.

"The term 'plume' has been used for quite awhile, [but] I think what we are talking about are concentrations," he said. "'Cloud' is a better term."

Joye's team's results echo the findings of a University of South Florida team aboard the Weatherbird II vessel.

National Oceanic and Atmospheric Administration chief Jane Lubchenco said her agency had finished testing water samples collected by the USF team that confirmed the presence of the oil.

"The bottom line is, yes there is oil in the water columns," she told reporters. "That's confirmed for the sites we've done the analyses."

BP CEO Tony Hayward had disputed the presence of plumes, saying on June 6 that there was "no evidence" of their existence. BP spokesman John Pack said today they would be paying attention to the data that is coming in.

"We will obviously listen to what they have to say," Pack said.

Lubchenco said the test confirms the presence of subsurface oil, which she said federal scientists suspected was present.

Lubchenco said that oil was found in "very low concentrations" in the range of less than 0.5 parts per million. NOAA tested samples from three collection sites, confirming the presence of subsea oil 40 nautical miles northeast of the well. She said samples from a site 42 nautical miles northeast were inconclusive and that samples from a site 142 miles southeast "were not consistent with the oil spill."

"That does not mean it doesn't have significant impact. A more complete picture will require additional information, and we're in the process of getting that," Lubchenco said.

"We remain concerned about the location of oil on the surface and under the sea," Lubchenco said. "We are attacking it aggressively to mitigate the harm and understand the impact."

Lubchenco said "there is definitely oil subsurface" and that NOAA would continue to analyze water samples as they were collected.

"We will continue to do research to understand where it is and in what concentrations and what are its impacts," she said.

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