Thursday, August 19, 2010

Plumes Happen

Scientists from the Woods Hole Oceanographic Institution (WHOI) have taken what they characterize as a major step toward establishing that the Deepwater Horizon disaster created underwater plumes of oil in the Gulf of Mexico.

In a study appearing in the August 19 issue of the journal Science, the researchers gave measurements for a plume they studied in June, before Hurricane Alex forced them to abandon the work. They described it as about 1,100 meters below the Gulf's surface, over 35 kilometers long, 200 meters high and up to 2 kilometers wide. It also contained about 6 to 7 percent of all the BTEX hydrocarbons -- the variously toxic benzene, toluene, ethylbenzene, and xylenes -- which leaked from the Macondo well. In addition, quantities of dissolved oxygen the WHOI team found around the plume had not dropped to levels that would suggest bacteria were breaking down the oil.

The plume might be hard to discern with the naked eye. "It looks like spring water," said Chris Reddy, one of the study's co-authors, describing the samples taken from the plume area. Photos of the water column, however, show a change in water color and turbidity at the level of the plume. In addition, it was clearly detectable using mass spectrometry from an autonomous underwater vehicle which traversed the plume area and found abnormally high levels of hydrocarbons which could be tracked back to BP's Macondo Well.

Remotely operated vehicle (ROV) still images taken during descent through the water column from a location less than 500 meters southwest of the well site on June 1, 2010. Still images were recorded from a forward looking video camera on the ROV. A highly turbid oil-emulsion layer was evident in the depth region between 1065 and 1300 meters, with small oil droplets temporarily collecting on the camera lens within this depth interval.
[Credit: R. Camilli, Woods Hole Oceanographic Institution]

The picture painted by WHOI scientists at a press conference today suggest that while the Macondo well might now be sealed, the story of the massive leak's effects is far from over. In answer to questions from journalists, researchers spent as much time detailing what they don't know as what they do. They don't know whether the plume they measured in June still exists, or where it might now be. They don't know its level of toxicity, or how it might be affecting fisheries in the Gulf or consumers eating seafood at NOLA restaurants. They don't know whether its existence might contradict recent government estimates that 75% of the oil spewed out of the shattered Deepwater Horizon rig has somehow been removed from the Gulf.

Given, however, that the very existence of these plumes had initially been denied by BP or had been attributed to natural seepeage, researchers considered this study a very significant scientific step.

"One of the most important aspects of this is to document that these plumes do exist," said Richard Camilli, the study's lead author. "To understand other ecological complications, we have to first establish a base case, plume or no plume."

This research, Camilli added, was able to "document using a fairly rigorous approach not only that the plume did exist but it was stable at a particular depth interval, and that it was not produced by natural seeps."

The study team hopes to learn more about the nature of the plume as they continue analyzing samples over the next several months.

For a series of commentaries on the Gulf oil disaster please visit