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Gulf oil spill plumes: what is known so far

Scientists have found evidence of at least two undersea plumes from the Gulf oil spill. The plumes appear to be diluted, but still a threat to the foundations of the Gulf food chain.

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In one area, "what we found was a very strong signal" at about 3,300 feet down to about 4,300 feet, he says. In many of the images coming from the fluorescence detector, the field was filled with tiny orange specs, strongly suggesting oil, along with tiny white specs – sometimes looking like clouds – which the team suspects are methane hydrate crystals that can form when methane accompanies oil billowing from an undersea blowout. Some estimates put the methane content of the blowout at about 40 percent of the oil-methane mix spewing from the wellhead – in contrast to roughly 5 percent methane in a typical well.

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The images must be correlated with water samples, which themselves must be analyzed to confirm the presence of oil and to see if the oil's chemical fingerprints match those of samples from the BP blowout.

Day in and day out during a cruise, researchers drop and retrieve this rosette, or "dope on a rope," as Dr. Asper wryly calls it, "as often as we can with the time allotted" for the cruise. A single CTD "cast" can take up to two hours, then the ship moves to its next sampling point.

It's a frustrating pace, Dr. Mayer adds. "We're trying to measure something that varies in space and time over a large area with little dips" of a rosette at a target that's 4,000 feet away, he says.

8,332 animal and plant species in well area

One intriguing find: A cloud sampled by a research team including Asper contained lower concentrations of oxygen than did adjacent waters – in some spots, much lower. This suggests that microbes were feasting on the oil and methane in the water column.

"On the one hand, that's good," he says, because the process is removing oil. "On the other hand, you're removing oxygen from a layer of the ocean that isn't used to having oxygen removed from it."

The water at the depth the team sampled is highly enriched in oxygen to begin with, so researchers don't expect it to approximate the annual oxygen-starved "dead zone" that forms each year where the Mississippi River empties into the Gulf. Moreover, the Gulf region hosts a naturally occurring layer of low-oxygen water at depths of between 300 and 600 feet.

Still, "the question is: What effect is that going to have on the other organisms" living at the depth the team was sampling?, asks Asper.

A newly published catalog of Gulf marine life illustrates just how rich the area around the blowout is – home to 8,332 species of plants and animals, says Thomas Shirley, a marine ecologist with Texas A&M's Harte Research Institute for Gulf of Mexico Studies in Corpus Christi.

The depth range that includes the wellhead is home to more species than anywhere else in the Gulf at that same depth range. "I found that to be very surprising," he says.