By Alec Liu & Jeremy A. Kaplan

Published August 19, 2010

| FoxNews.com

Science/AAAS

Based on measurements taken in June, scientists have recreated the shape and distribution of oil in a massive plume in the Gulf of Mexico -- evidence the spill may not vanish as quickly as hoped. Blue indicates low methane concentrations, red high.

Is the Gulf getting cleaner? Or does oil there pose a long-term hazard? It seems to depend mostly on whom you ask.

Scientists have discovered an oil plume at least 22 miles long, 3,000 feet deep in the Gulf of Mexico -- suggesting that the tens of millions of gallons of oil that leaked from a broken BP well could persist far longer than expected.

Whether the plume’s existence poses a significant threat to the Gulf ecosystem and sea life is not yet clear, the researchers say. 

“We don’t know how toxic it is,” said Christopher Reddy, a Woods Hole Oceanographic Institute (WHOI) marine geochemist and oil spill expert and one of the authors of the study. “But knowing the size, shape, depth, and heading of this plume will be vital for answering many of these questions.”

The existence of the plume, which was concretely pinned to the blown-out well, seems to contradict a five-page report released August 4 by the National Oceanic and Atmospheric Administration (NOAA), which claimed "a vast majority" of the BP oil spill is now completely gone. The remaining 25% consists of residual oil buried in sediments and sand, the report claimed. 

Researchers and scientists as well as environmental groups and Gulf residents immediately disagreed with the report, calling it "misleading if not totally inaccurate." Yet despite the seeming contrast between the government report and their new findings, Reddy refused to describe this new evidence as a contradiction.

"What the government has done and other universities are trying to do is constrain a budget," he said, arguing that it was too early to determine whether this finding was a smoking gun or just "a penny in a very big checking account."

"I can't tell you how much oil is in the plume," he noted, so it doesn't contradict the government's report that only 26% of the leak remains. And the picture will change as more chemical analysis is done, Reddy pointed out. 

But one thing is clear: There's definitely still oil down there. 

“We’ve shown conclusively not only that a plume exists, but also defined its origin and near-field structure,” said Richard Camilli the other lead researcher from WHOI, of the 1.2 mile wide, 650 foot high plume.

The team's observations were made during a June 19-28 scientific cruise aboard the National Science Foundation owned ship Endeavor. It was halted by the onset of hurricane Alex. Since measurements ended nearly two months ago, the scientists admit they are unsure what has happened to the plume.

"We don't know where these hydrocarbons are. We saw them in June," Reddy said.

The findings were based on two technologies: an autonomous underwater vehicle called Sentry and an underwater mass spectrometer. By integrating the two, researchers were able to detect even minute quantities of petroleum as well as other chemical compounds, something previous investigators were unable to achieve using conventional profiling.

They discovered consistent concentrations of hydrocarbons throughout the plume. Given the makeup and concentration -- in excess of 50 micrograms per liter -- the researchers concluded that the plume could not have developed from natural seepage. Further analysis of the samples will provide a clearer picture of the plume structure as well as a better estimate of the total amount of spilled oil. It will also give insight into what sort of threat the plume poses.

“The plume is not pure oil,” Camilli said. “But there are oil compounds in there.” It may require a few months of laboratory analysis and validation, Reddy said. Both researchers were surprised by the size and concentration of the plume. 

“[The plume] is persisting for longer periods than we would have expected,” Camilli said. “Many people speculated that subsurface oil droplets were being easily biodegraded."

The underwater oil was also remarkably stable, hanging at around 3,000 feet beneath the surface. "We don't have any indications as to why it's set up at that water depth," he said, an area meriting additional research. 

Another unexpected result was the lack of "dead zones," regions of significant oxygen depletion as a result of microbe metabolism.

“The oxygen data from the plume layer are telling us it isn’t being rapidly consumed by microbes near the well,” said Benjamin Van Mooy, a geochemist on the research team. “The hydrocarbons could persist for some time. So it is possible that oil could be transported considerable distances from the well before being degraded.”