USF scientist: oil plumes from BP well
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07/26/10 Kate Bradshaw
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As we reported Friday, a team of Florida researchers has confirmed that two gigantic oil plumes beneath the surface of the gulf are indeed the result of the Deepwater Horizon blowout. Scientists are now trying to see what threat the plumes pose to sea life.

At first getting BP to cough up an oil sample from its broken well wasn’t easy. When they finally did the researchers compared it to microscopic droplets of oil they’d found floating in enormous clusters dozens of miles away from the blown out site. Through a process called fingerprinting, the scientists found the subsurface plumes of oil came from the same place as the oil sample BP reluctantly handed over. University of South Florida chemical oceanographer David Hallander said that this turns the common conception of an oil spill on its head.

"The samples that we've been analyzing to the northeast and the east of the wellhead, on the order of 45 miles to the northeast, again, changes this whole concept that an oil spill is related to the surface processes and the damage potentially, the disaster that oil at the surface can cause. I think you have to compound that problem by then adding the sub surface component of oil to the disaster and perhaps at that point it turns into a three dimensional catastrophe."

Hallander said with oil gushing a mile below the surface, factors like variations in temperature and water pressure cause crude to chemically break down before it can make it to the surface, and the unprecedented use of chemical dispersants isn’t helping. Hallander said his team found plumes 45 miles northeast of the blown out well.

"Essentially we found two layers. The first layer was two miles long by six miles wide, by about 100 feet deep. The second layer, that we found at about 1,000 meters, was more diffuse. It actually was between 1,000 and 1,200 meters. It extended for about 20 miles, and was diffuse on its sides as well."

He said the top of the two layers of subsurface oil is 22 miles long, six miles wide and 100 feet thick at a depth of 400 meters. The bottom layer, occurring at a thousand meters, is smaller and more diffuse. But Hallander did say they have yet to determine the plumes’ precise dimensions.

"We're hoping that we can come back in within a week or so to synthesize the data so we can at least get a formulation of its eastern extent, where the front of the subsurface oil is, how far it has moved, and ultimately we should be able to get the physical dimensions using our shift board sensors."

Confirmation that the plume is a result of the BP blowout came the same day the federal government released a report confirming similar findings. Hallander said concentrations of broken down oil, which is not visible to the naked eye, are as high as 750 parts per billion. He said that concentration was not technically toxic, but could become so for organisms exposed to it over long periods of time.

"Time and concentrations can be interchangeable. You can have a high concentration for a low amount of time and have a very strong toxic effect, or you can have a lower concentration for a longer time and still have that same toxic effect. And this is where the danger for the environment lies."

Also unknown is the direction the plumes are headed. Hallander said there’s concern over the possibility that oil might creep onto the continental shelf by way of De Soto Canyon, which he called an express route between the blowout site and the shallow waters off Florida.

"The De Soto Canyon itself is a conduit, where deeper waters that are rich in nutrients commonly make their way up onto the continental shelf. And those nutrients are used to support some really important aspects of primary production, which then go into the spawning, which then lead to the production and the effect of spawning ground."

Hallander said this could be hazardous to sensitive fisheries in the eastern Gulf.

"These micro droplets essentially are 100% hydrocarbon, and can easily coating the gills of fish. They can be ingested by larval fish as food particles. So the fact that these are not diluted in the water, but they are actually droplets within the water, changes the dynamics of how they interact with the environment."

Hallander’s research team will head back out into the gulf in early August. He said they plan on assessing the plumes in relation to De Soto Canyon.

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