500K tons of hydrocarbons released during Gulf of Mexico oil discharge

Monday, February 14, 2011

LONDON - Up to 500,000 tons of gaseous hydrocarbons were emitted into the deep ocean, according to a new University of Georgia study.

The authors conclude that such a large gas discharge-which generated concentrations 75,000 times the norm-could result in small-scale zones of “extensive and persistent depletion of oxygen” as microbial processes degrade the gaseous hydrocarbons.

The Macondo Well blowout discharged not only liquid oil, but also hydrocarbon gases, such as methane and pentane, which were deposited in the water column. Gases are normally not quantified for oil spills, but the researchers note that in this instance, documenting the amount of hydrocarbon gases released by the blowout is critical to understanding the discharge’s true extent, the fate of the released hydrocarbons, and potential impacts on the deep oceanic systems.

Samantha Joye, UGA Professor of Marine Sciences who led the study, team examined samples from 70 sites around the leaking wellhead during a research cruise aboard the R/V Walton Smith during late May and early June of 2010.

They combined their data with estimates of the volume of oil released to arrive at a figure that allows scientists to quantify, for the first time, the gas discharge in terms of equivalent barrels of oil. They calculated a gas discharge that’s the equivalent of either 1.6 to 1.9 or 2.2 to 3.1 million barrels of oil, depending on the method used.

Although the estimate reflects the uncertainty still surrounding the discharge, even the lowest magnitude represents a significant increase in the total hydrocarbon discharge.

“These calculations increase the accepted government estimates by about one third,” co-author Ian MacDonald of Florida State University said.

The study appears in the online edition of the journal Nature Geoscience. (ANI)

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