A jellyfish is seen trapped in sargassum. Scientists have confirmed the presense of a 22-mile long oil plume in the Gulf of Mexico, which they say will threaten marine life for months or even longer. Press-Register / Ben Raines

The Associated Press
Published: Thursday, August 19, 2010, 1:00 PM     WASHINGTON — A 22-mile-long invisible mist of oil is meandering far below the surface of the Gulf of Mexico, where it will probably loiter for months or more, scientists reported Thursday in the first conclusive evidence of an underwater plume from the BP spill. The most worrisome part is the slow pace at which the oil is breaking down in the cold, 40-degree water, making it a long-lasting but unseen threat to vulnerable marine life, experts said. Earlier this month, top federal officials declared the oil in the spill was mostly “gone,” and it is gone in the sense you can’t see it. But the chemical ingredients of the oil persist more than a half-mile beneath the surface, researchers found. And the oil is degrading at one-tenth the pace at which it breaks down at the surface. That means “the plumes could stick around for quite a while,” said study co-author Ben Van Mooy of the Woods Hole Oceanographic Institution in Massachusetts, which led the research published online in the journal Science. Monty Graham, a scientist at the Dauphin Island Sea Lab in Alabama who was not involved in the study, said: “We absolutely should be concerned that this material is drifting around for who knows how long. They say months in the (research) 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.” … “There’s no visible evidence of oil in the samples; they look like clear water,” study chief author Richard Camilli said. The scientists used complex instruments — including a special underwater mass spectrometer — to detect the chemical signature of the oil that spewed from the BP well after it ruptured April 20. The equipment was carried into the deep by submersible devices. With more than 57,000 of these measurements, the scientists mapped a huge plume in late June. The components of oil were detected in a flow that measured more than a mile wide and more than 650 feet from top to bottom. …

Underwater Gulf oil plume 22 miles long, likely to threaten marine life for months