Science Report Describes Deepwater Horizon Oil Plume as of June
Filed under: Discovery,Gulf Oil Spill,News & Resources
(Click to enlarge) Slow burn. To help dissipate the plume, crews in May burned floating oil from the Deepwater Horizon spill in the Gulf of Mexico. (Public domain image by John Kepsimelis, U.S. Coast Guard)
In mid-June, two months after the 20 April blowout of BP’s Deepwater Horizon drilling rig, the resulting oil plume had reached huge proportions, peer-reviewed research published 19 August on the Science Express Web site suggests.
(From AAAS / by Kathleen Wren and Ginger Pinholster) — The research also shows that levels of dissolved oxygen within the plume had not dropped enough by mid-June to suggest bacteria were breaking down the oil, according to Richard Camilli of the Woods Hole Oceanographic Institution (WHOI), who directed the study.
As of June, water samples suggested that the plume “had and will persist for some time,” according to a WHOI news release.
Between 19 and 28 June, Camilli and his colleagues concluded, the plume measured approximately 22 miles long and 1.2 miles wide. It had by then reached a height of more than 650 feet and depths in excess of 3,600 feet below the Gulf of Mexico, the researchers reported in their Science Express paper.
The team sent the automated underwater vehicle Sentry on a 10-day reconnaissance of the plume that erupted from the Macondo Prospect oil field following the Deepwater Horizon disaster. The Sentry vehicle, funded by the U.S. National Science Foundation, zigzagged through the plume, recording information about the water’s chemical composition and biological activity at various depths. The researchers also took deep-water measurements using a set of instruments cabled to a ship.
According to the WHOI news release, the researchers began tracking the plume three miles from the Deepwater Horizon well head, extending 22 miles, until the approach of Hurricane Alex forced them out of the area. “We’ve shown conclusively not only that a plume exists, but also defined its origin and near-field structure,” said Camilli, chief scientist of the research cruise and lead author of the Science Express paper. “In June, we observed the plume migrating slowly [at about 0.17 miles per hour] southwest of the source of the blowout.”
In addition to measurements of the size of the plume as of mid-June, the researchers reported that about 6% or 7% of all the so-called BTEX hydrocarbons leaked from the well—benzene, toluene, ethylbenzene and xylenes—were in the plume. These volatile hydrocarbons make up a small fraction of all the compounds in the oil but are relatively easy to measure.
Since the WHOI researchers have concluded that the plume still exists, the public may wonder whether it poses a significant ongoing threat to the Gulf. In the WHOI news release, co-author Christopher Reddy, a marine geochemist and oil spill expert, said: “We don’t know how toxic it is, and we don’t know how it formed, or why. But knowing the size, shape, depth, and heading of this plume will be vital for answering many of these questions.”
Nick Wigginton, associate editor with Science, said: “The authors of this paper have taken an innovative approach to identifying and sampling part of a deep hydrocarbon plume, including measuring the critical oxygen levels in the water column. These levels are obviously important biologically but also reveal the extent of natural degradation of the oil by microorganisms.”
The presence of such a plume shows that hydrocarbons can move into deep marine ecosystems, the authors say. They noted that more research will be needed before scientists know the eventual fate of this material and the full extent of the chemical compounds in the plume.
The 19 August Science Express paper is entitled “Tracking Hydrocarbon Plume Transport and Biodegradation at Deepwater Horizon.” The research was funded National Science Foundation. Additional authors on the Science Express paper, in addition to Camilli and Reddy, were Dana Yoerger, Benjamin Van Mooy, James Kinsey, Cameron McIntyre, and Sean Sylva of the WHOI; Michael Jakuba of the University of Sydney; and James Maloney of Monitor Instruments Company, LLC.
