Science & Environment

Oil leak's spread predicted by simulation

Detailed simulations of the Gulf of Mexico oil leak show that crude is likely to start spreading into the Atlantic Ocean soon.

Once oil becomes caught in the Gulf of Mexico's fast moving Loop Current, it could be carried thousands of miles, around Florida, up the Atlantic coast of the US, and then out into the open ocean.

An animation by the US National Center for Atmospheric Research (NCAR) suggests that concentrations of oil in the water south of Florida will start to become detectable around 70 to 90 days after a leak starts. The Deepwater Horizon rig sank on the 22nd April.

The animation, given to the BBC World Service's Science in Action programme, is based on a computer model of ocean currents and eddies, and assumes that conditions will be similar to those found in a typical year.

"In the Atlantic Ocean there is a Western Boundary Current System, and the Gulf of Mexico's Loop Current is part of this system," explains NCAR scientist Synte Peacock.

"So what happens is the current comes up through the Yucatan [Channel, the strait between Mexico and Cuba], and it does a clockwise loop within the gulf, and then shoots out and joins the Gulf Stream proper.

"So when something in the gulf gets caught up within that current, it can get out of there."

So with that definitely happen? Dr Peacock says: "At some time in the next six months it's highly highly likely that it will escape from the Gulf."

The Atlantic Ocean Gulf Stream carries water towards Europe, but the simulations show it is unlikely that oil will be detected that far away.

"Even a year after the spill start date, in our simulations we don't see any detectable quantities of oil hitting Europe," says Dr Peacock.

"It's very diluted within the Atlantic Ocean."

'Food colouring'

To create the dramatic video, the scientists modelled what would happen if they were to release a coloured tracer dye into the water at the site of the leak.

Image caption The situation in the gulf is worse than that on which the simulation is based

"It's like a food colouring. You inject it into the ocean and watch it disperse," explains Dr Peacock.

The virtual dye then shows the path that the water - and therefore the oil - could take.

The researchers repeated the experiment several times, using slightly different scenarios, to arrive at a likely spread pattern for the oil.

There are still some aspects to the Gulf of Mexico leak, and the behaviour of oil released at great depth, which are not fully understood.

The scientists say that could have an influence on the accuracy of the model.

"Oil is a little bit different, for several reasons; it undergoes a number of transformations," says Synte Peacock.

"There is a lot of evaporation in the first few hours, so it changes form.

"People are also skimming it like crazy, and trying to contain it as it comes up from the flow head. So it's not a perfect analogy by any means, but it's the closest thing we have right now."

The model assumes an oil leak lasting just 60 days, so already the reality is worse than the model scenario.

The eventual outcome will be complicated, as the southern US heads further into hurricane season. The scientists are now trying to add simulations of storms' possible effects to the model.

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