Published online 1 June 2010 | Nature 465, 532-533 (2010) | doi:10.1038/465532b

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Researchers track path of oil from rig spill

Officials desperately seek answers on where the slick will head.

An ocean-monitoring sensor package is about to be dropped from a plane.M. Schrope

With no end in sight for the oil gushing from the explosion site at the Deepwater Horizon drilling rig, anxious US officials are looking to researchers who study the Gulf of Mexico and its idiosyncratic currents to help determine where all the oil is and where it might be heading. Long-term efforts to understand the movement of Gulf waters because of their effect on hurricanes are now being used to address the more immediate question of which regions and ecosystems outside the immediate spill zone are most likely to bear the brunt of a non-stop river of oil.

"This is where a lot of the action is," says Lynn 'Nick' Shay, a physical oceanographer at the University of Miami in Florida. Shay is referring to an expanse of open water visible from the window of the National Oceanic and Atmospheric Administration (NOAA) 'hurricane hunter' research plane that routinely carries him on 9-hour-long sweeps of the Gulf. At this particular spot, some 460 kilometres southeast of the spill, the Gulf's hairpin-shaped Loop Current is pinching off to form a circular eddy about the size of Ireland.

The eddy, a temporary detour from the current's normal path, could well be a lucky break. As the oil spreads, it is gradually becoming entrained in the Loop Current, an offshoot of the Gulf Stream that flows south and east of the spill site off the Louisiana coast towards the opening between Cuba and Florida. The prospect of large amounts of oil moving towards coastlines in that region is a dire one for communities and fisheries, as well as for the sensitive coral reefs. By contrast, oil pulled into the eddy could be sequestered there for months as the vortex drifts westward at "about the speed of Miami traffic", says Shay. Although it would still threaten marine life, the effects on coastal ecosystems would be lessened, because there would be more time for evaporation and microbes to help break down the oil. "The question is how much goes each way," says Shay.

Shay's team is helping to answer the question by gathering detailed information on the state of the Loop Current and eddy on its research flights. Every few minutes during a flight, a sensor package about the size of a poster tube is dropped through a hole in the floor of the plane. Depending on which sensor is used, the tube will radio back information on temperature, salinity or current movement as it plunges into the depths.

The deep-water data are important because so little is known about what the currents are doing below the surface — and that's exactly where much of the oil may be hiding, in the form of vast underwater plumes (see Nature 465, 274–275; 2010). As Shay and his team criss-cross the Gulf by air, scientists aboard the F. G. Walton Smith research ship are tracking the subsurface spread of layers of what seems to be an oil plume at multiple depths west of ground zero. And two other research groups have just returned from studying other areas of apparent deep oil.

James Cowan, a fisheries biologist at Louisiana State University in Baton Rouge, has been aboard a small charter fishing boat about 120 kilometres northwest of the main spill deploying a remotely operated vehicle to examine water down to about 120 metres. In one large area beneath visible surface oil, says Cowan, "we saw oil all the way down as far as we could go. It was thick enough so that it pretty much covered our camera globe and the lights."

The challenge now is to predict where all that oil will go. Ruoying He, an oceanographer with the ocean observing and modelling group at North Carolina State University in Raleigh, works with an ocean-circulation model that takes data such as temperature and wind measurements and tries to forecast the behaviour of the currents in the Gulf and the adjacent portion of the Atlantic. Having built up expertise over years, He's ocean modelling group is one of several teams running ocean-circulation forecast models used by NOAA's Emergency Response Division. NOAA, the lead agency for scientific issues relating to the spill, is using these modelling results to generate its prediction of the oil's movement and so guide local, state and federal responses.

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But He acknowledges that lack of data from the deep water makes the entire situation murky. The stricken oil well lies 1,500 metres down, and no one really knows how the oil is distributed at such depths or how well the numerical models of ocean circulation can perform there. "Information from only the surface might be misleading," He says. Yonggang Liu, a physical oceanographer at the University of South Florida in St Petersburg, agrees that the observations are sparse. "We need more data," he says. "Without it, our models are very limited."

In the coming weeks, some of those data will start to trickle in. They will do nothing to stop the oil, but they will be essential in revealing what happens next. 

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