[MARINE_BIOLOGY_INTERNATIONAL] Scientists describe 'Manhattan' size plume of oil

Scientists describe 'Manhattan' size plume of oil

Thursday, 19 Aug 2010, 4:05 PM EDT

Robert Lee Hotz
WALL STREET JOURNAL via NewsCore

At the height of the Deepwater Horizon spill, oil escaping from the damaged well was trapped underwater in a drifting plume of hydrocarbons the size of Manhattan, scientists who probed the submerged spill region said Thursday.

By confirming the existence of this submerged plume, the new data also challenge government estimates that the vast majority of the 4.9 million barrels of spilled oil is already gone from the Gulf or being rapidly broken down by bacteria, several marine experts said.

Instead, some of that oil may persist deep underwater and in seafloor sediments, at levels thousands of times higher than those caused by the natural oil seeps that dot the Gulf sea floor -- where it can elude conventional detection and clean-up efforts, scientists said.

Even so, the chemicals are not concentrated in these depths at levels high enough to be directly toxic to marine life, several ocean experts who study the Gulf said.

Other researchers earlier detected hints of other such plumes. No one knows yet how long these plumes will last or what their long-term impact will be.

"This plume is moving along in a very regular manner," said Richard Camilli, from the Woods Hole Oceanographic Institution in Massachusetts, who was chief scientist on the research cruise through the oil spill region. "These hydrocarbons may well show up somewhere else, running undetected below the surface."

Researchers suggest the submerged plume may last for a year or more but no knows yet whether the oil has dissipated since the Woods Hole researchers last measured it at the end of June.

An independent research group from the University of Georgia is expected to launch a month-long cruise to the Gulf spill area on Friday to pick up the study of the plume.

Reporting their preliminary findings Thursday, they confirmed that oil from the well had been caught below the surface of the Gulf in pools of microscopic oil drops and petroleum-based trace chemicals, which were degrading more slowly than many had expected.

In its essence, this plume resembled a mist of trace chemicals largely invisible to the eye, rather than a river of oil.