Dana Yoerger/Woods Hole Oceanographic Institution
The Sentry automated underwater vehicle, shown aboard the research vessel Endeavor at the Deepwater Horizon oil spill site, was used to track the underwater oil plume.
The Sentry automated underwater vehicle, shown aboard the research vessel Endeavor at the Deepwater Horizon oil spill site, was used to track the underwater oil plume. Dana Yoerger/Woods Hole Oceanographic Institution
Scientists have mapped out, for the first time, the underwater path that some petrochemicals took after gushing from BP's oil well in the Gulf of Mexico. It's an important new piece in a huge scientific puzzle.
Researchers are trying to figure out where as much as half of the spilled oil has gone.
Christopher Reddy, a co-author of the study released Thursday by the journal Science, says it was a big surprise when scientists first reported that large amounts of oil and oil compounds were staying underwater rather than rising to the surface.
"If you’d asked me — and I've been studying oil spills for 15 years — whether or not you would see oil in the subsurface, I would have said, 'No — doesn't oil float?' " he said at a news conference Thursday.
The phenomenon is fascinating but also troublesome, he says, because if scientists don't know where the oil is, they also don't know what harm it may be causing.
In June, Reddy and his colleagues from the Woods Hole Oceanographic Institution took a research ship to the scene of the spill. They lowered a sensor deep into the water and towed it in a large circle around the blown-out well, looking for particular hydrocarbons that are easy to detect.
The sensor picked up a hydrocarbon signal southwest of the well, in a layer of water 3,000 feet below the surface.
Richard Camilli, another researcher from WHOI, says they then sent down a new device — a small unmanned submarine called Sentry.
"We had Sentry fly at a constant depth in kind of a zigzag pattern, moving out from the well site, tracking the plume," he said.
The hydrocarbons, including benzene and toluene, were highly diluted in the water. They were coming from the gushing well, but they weren't spreading out in all directions. Instead, they followed an invisible underwater channel just over a mile wide and 650 feet thick. The researchers tracked that channel southwest for 22 miles, until bad weather forced them to stop.
They looked for signs that microorganisms are feasting on those petroleum products and breaking them down, but they didn't see any. Reddy says they don't know exactly why.
"Microbes are a lot like teenagers," he says. "They work on their own time, at their own scale. They do what they want when they want."
There are many other unknowns. Reddy and his colleagues don't yet know how much of the oil from the well is in this plume. They hope to arrive at an estimate in a few months, after analyzing all of their water samples. They also don't know how toxic the plume may be to wildlife.
Yet this is the best-documented case so far of oil flowing underwater.
"This is a big piece of the puzzle," says Steven Murawski, science adviser for fisheries at the National Oceanic and Atmospheric Administration.
Murawski is trying to put the whole puzzle together. He is in touch with many of the research vessels — as many as seven on any given day — that are working in the Gulf of Mexico.
Murawski says additional scientific reports about oil in the deep sea around the well will be released in the coming weeks. But he'd like to see more scientists working in other places, such as on the continental shelf, the wide shallow area close to shore where most fish live. Murawski says he's drafting plans to expand such research.