Oil released during the Deepwater Horizon disaster and suspended deep underwater appears to be breaking down more slowly than expected, suggests a new study. The greatest damage to the Gulf may ultimately be in the deep sea, rather than the shorelines -- a catastrophe in a black box.
During the last two weeks of June, researchers from the Woods Hole Oceanographic Institute tracked a mile-long, 650-foot-thick plume of crude oil hydrocarbons as it oozed southwest of the blown well at a depth of about 3,000 feet. It was not the only such plume, nor necessarily the largest, but its behavior may give some indication of what is happening elsewhere. Much of the spilled oil, perhaps most, may share a similar fate.
Though unable to gauge precisely how quickly oil was breaking down, the researchers were able to measure the activity of microbes responsible for its decomposition. It's slow. And though the researchers autioned that the findings are just "a snapshot," a "first chapter," the results suggest that lots of oil is still in the Gulf, and will be there for a long time.
Published August 19 in Science, the findings come as the Deepwater Horizon's still-evolving legacy is a matter of both political and scientific controversy.
Not long after the blown well was capped on July 15th, after nearly five million barrels of oil had leaked, journalists were able to pose questions like, "Where is all the oil?" Hundreds of square miles of ocean surface had been covered, and hundreds of miles of shoreline fouled, but it still amounted to less than was expected.
Most of the public, however, interpreted the spill through a lens formed by shallow-water oil drilling, where spills float right to the surface. The dynamics of deep-sea spills, where hot oil shoots out into frigid water at extraordinary depth and pressure, are different.
For reasons still unknown, but hinted at in an obscure 2003 study and now made painfully clear, much of that oil doesn't float. It rises a bit, and hangs there. Hence reports during the disaster of giant, underwater oil plumes, which ultimately received less general attention than shoreline pollution, but was no less real.
In the disaster's aftermath, with the Obama administration announcing tight restrictions on deep-sea drilling and the oil industry fighting them, the federal National Oceanic and Atmospheric Administration released a report declaring that almost three-quarters of oil spilled into the Gulf was already gone (pdf). That conclusion was promptly attacked by oceanographers from the University of Georgia. Based on the same data, they said almost three-quarters of the oil was still there.
The difference was drastic, but relatively easy to explain. NOAA considered oil dissolved into the water or chemically dispersed as being gone. To the Geogia researchers, it was no more gone than sugar stirred into iced tea. Georgia ecologist Charles Hopkinson called the government "absolutely incorrect," saying "the oil is still out there, and it will likely take years to degrade. Soon after the Georgia team's declaration, researchers from the University of Florida reported finding oil in critical deep-water fish spawning grounds.
The WHOI team's Science data is the latest entry to this fight. Though they are careful to note the limitations of the data, gathered during two weeks in June by a remote vehicle programmed to follow oil, the findings are not encouraging.
Measurements of water oxygen levels -- a proxy for the respiratory activity of microbes expected to decompose oil -- found more activity than would be expected in oil-free water, but far less than would be found amidst surface oil. Some of the difference is expected because chemical reactions happen more slowly in the deep sea's colder environment. But even taking that into account, it was slower than predicted.
"Petroleum hydrocarbons did not fuel appreciable microbial respiration on the temporal scales of our study," wrote the researchers in Science. "It may require many months before microbes significantly attenuate the hydrocarbon plume."
The exact composition of the plume remains to be determined, but it does contain benzene, toluene, xylene and other compounds responsible for oil's toxicity.
"There is a huge unknown on the impact of these undersea plumes," said Carys Mitchelmore, a University of Maryland aquatic toxicologist. "We do not know what organisms are there," nor their tolerance to different concentrations of oil, nor how long those concentrations will remain, she said.
"It's easy to relate to an oiled pelican. It's harder to relate to an oiled copepod," said Georgia Aquarium ecologist Al Dove, who studies whale sharks in the Gulf of Mexico. "People get used to seeing images of oiled wildlife, birds on beaches, and that's a tragedy -- but it's not what's going to keep the ecosystem from returning to what it was."
The Gulf's deep sea ecosystems have been studied far less than its shorelines, but it's possible that effects will ripple from one to the other.
"My experience is that what goes on in shallow water affects what goes on in the deep sea, and vice versa," said Craig McClain, a deep sea ecologist at the National Evolutionary Synthesis Center. "The interconnection is going to be really important, and we're only now getting a handle on it."
Studies of the oil's deep sea effects are just starting, and will continue for years. McClain said that data on deep sea life is far harder to gather and interpret than on coastlines, where animals can be easily counted and solid baseline data already exists.
"Those lower subsurface plumes could hang around for a while," said Mitchelmore. "There will be a black box of organisms dead out there."
Images: 1) Water visibility at descending depths./R. Camilli, WHOI. 2) Topographical map of plume location./R. Camilli, WHOI.
See Also:
- Gulf Coast May Be Permanently Changed by Oil Spill
- No Progress on Better Chemicals for Oil Disaster Cleanup
- Tracked From Space: Gulf Oil Slick Approaches Land
- BP's 'Nightmare' Well: Internal Documents Uncover Negligence
- Citizen Science: Count the Gulf's Ghost Crabs
Citation: "Tracking Hydrocarbon Plume Transport and Biodegradation at Deepwater Horizon." By R. Camilli, C. Reddy, D. Yoerger, B. Van Mooy, J. Kinsey, C. McIntyre, S. Sylva, M. Jakuba, J. Maloney. Science, Vol. 329 No. 5994, August 19, 2010.
Brandon Keim's Twitter stream and reportorial outtakes; Wired Science on Twitter. Brandon is currently working on a book about ecological tipping points.
