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Gulf Oil Plume Tracked

Oil Spill: First journal report to characterize deep-sea oil plume

by Elizabeth K. Wilson
August 19, 2010 | A version of this story appeared in Volume 88, Issue 34

Credit: Richard Camilli/WHOI
Images taken by Sentry during its descent through an oil plume near the Deepwater Horizon well show a highly turbid oil-emulsion layer at a depth of 1,065 to 1,300 meters.
Credit: Richard Camilli/WHOI
Images taken by Sentry during its descent through an oil plume near the Deepwater Horizon well show a highly turbid oil-emulsion layer at a depth of 1,065 to 1,300 meters.

The first peer-reviewed report in a major journal to focus on the catastrophic BP oil spill in the Gulf of Mexico describes an enormous, persistent plume of hydrocarbons more than 3,000 feet deep moving southwest from the site of the spill to sites up to 22 miles away. In addition, measurements of oxygen levels in the plume show that oil-feeding microbes are not degrading oil as quickly as experts thought.

Ocean scientist Richard Camilli, marine chemist Christopher M. Reddy, and colleagues at Woods Hole Oceanographic Institution (WHOI), in Massachusetts, and in Australia collected 57,000 data points during their investigation of the plume, one of several such plumes in the Gulf. The researchers used instruments on a ship and on the submersible automated vehicle Sentry, including a mass spectrometer that tagged a number of easily identifiable components of oil: benzene, toluene, ethylbenzene, and xylenes (Science, DOI: 10.1126/science.1195223).

The oil spill, which is now recognized as the largest in history, began on April 20 and dumped an estimated 200 million gal of oil into the ocean until BP engineers stopped the flow with a temporary cap on July 15. Scientists and government officials have issued conflicting reports on the scope of the disaster, most notably regarding the existence and size of underwater plumes.

Scientists at the National Oceanic & Atmospheric Administration have characterized several oil plumes in the Gulf, and recently researchers at the University of South Florida announced that samples from the plumes match those from BP’s oil (C&EN, Aug. 2, page 12). The published WHOI study adds credibility to those reports.

During its 10-day mission in June, WHOI’s Sentry zigzagged through the plume, providing definitive boundary information and measuring the rate at which the plume was migrating from the well site. Measurements showed no significant drops in dissolved oxygen, implying that oil is not being quickly degraded by microbes, which consume the gas.

Although the NOAA work mainly focused on dispersed oil near the wellhead, the WHOI researchers found “a river of oil in deep water and the current moving surprisingly quickly southwest from the wellhead,” notes Jeffrey Short, an oil spill expert and consultant for Oceana, an environmental advocacy group. The paper’s estimate of the migration rate of dispersed oil in the plume “is the first rate I’ve seen or heard about,” he says.

The amount, location, and form of remaining oil from the spill continue to be hotly debated. The federal government’s National Incident Command released a report on Aug. 2 that was widely interpreted to suggest that 75% of the oil had already degraded. However, experts with the University of Georgia, Athens, immediately responded with their own interpretation, saying that almost 80% of the oil persists in the environment.



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