On board a Gulf oil spill science ship

A look at the work of the RV Cape Hatteras

The massive, floating drilling rig Deepwater Horizon was around 50 miles off the coast when it sank on the 22 April.

Now the area where it was once positioned in the Gulf of Mexico is comparable to a floating town, with around 60 vessels involved in the efforts to capture and clean up the oil, and to drill relief wells to seal the leak.

Supporting them is a flotilla of supply ships bringing in groceries and taking away rubbish every day, as well as refilling water supplies and providing other essential services.

The RV (research vessel) Cape Hatteras, a science ship, is orbiting that nucleus of activity - held at a distance of five nautical miles. That is close enough to the leak site to make it clearly visible from aboard the ship; the clouds of smoke and steam, generated by flaring off escaping gas, dominate the skyline.

RV Cape Hatteras Research vessel, Cape Hatteras, is orbiting a "floating town" of clean-up ships

"It's not been as bad as I was fearful it would be" says captain Dale Murphy.

"We've had a few days where the VOCs [volatile organic compounds] were high enough that we had to wear masks on deck, and of course all the intakes on the ship have been closed off or special filters put over them," he explains.

The ship has been modified to meet the needs of the scientists studying this leak, with the installation of equipment, and piping, tubing, and power cords all fighting for the limited space.

Spill site in the Gulf of Mexico (BBC) The spill site is clearly visible from the ship

The researchers are hoping to answer some basic questions about how much crude is flowing and where it is going. Although usually referred to as an "oil spill", the leak also contains large quantities of natural gas.

"About half of the total flow is probably gas. The estimates out there now indicate that about 40% of the total mass flowing out is composed of methane.

"There's also a lot of ethane and propane and those three together make up a large fraction of natural gas," says Professor David Valentine from the University of California, Santa Barbara, one of the scientists on the RV Cape Hatteras.

Oil in the wake of a powerboat in the Gulf of Mexico Oil is visible on the surface but there is methane trapped in the water

Much of the methane in particular seems to be trapped in the water, rather than rising to the surface.

Atmospheric measurements just above the water do not show elevated readings of the gas, so the scientists believe it is held at depth, and spreading in what they are calling "plumes" - horizontal layers of gas and oil.

The ship is moving slowly around the oil spill site, and the researchers on board are taking regular samples at varying depths to try to map the plumes.

"We're collecting samples for molecular and atomic analyses" explains lead scientist Professor John Kessler from Texas A&M University.

"We're doing as many of those on the ship as we can, because we then don't have to transport those samples back to the laboratory.

Also, simply taking a sample out of its natural environment for a long period of time means there's a greater probability of the sample being altered, and then getting a false result."

Mapping the plumes of methane could help scientists map undersea plumes of oil, to enable a better understanding of how this deep water spill is behaving and where the oil is travelling. And by calculating the quantity of trapped methane, scientists could also better estimate the total volume of oil that is leaking.

"The basic idea is that methane is the bulk gas component that is coming out of the pipe, and because it's trapped in the water we can develop a sampling plan to measure methane regionally" says Professor Valentine.

Booms on a beach in Louisiana, US Booms are being used in an effort to protect miles of coastline

"We can go out and measure methane in a very detailed fashion throughout the area. We can then figure out how much is residing in the deep water. Because it's trapped there and we know the proportion to oil, we can get a very on basic constraint on the total amount of oil that has been released."

The scientists are working to get firm results as soon as possible.

It is a busy time for the RV Cape Hatteras. Captain Dale Murphy expects to be out on the waters of the Gulf of Mexico until the end of the year. As soon as this scientific mission ends, he is ready to support another one.

"We'll get a quick turnaround, and be right back out here to put some sediment traps overboard; and when I say quick turnaround I mean we go in one day and back out the next," he says.

"A lot of people are scrambling to get their stuff ready, to get funding, to try to get out here."

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