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Sunday, November 18, 2018

Deepwater Horizon oil plume consumed by bacteria, say scientists

Article reproduced from The Times, 25 August 2010.


The vast plume of oil that spread from the Deepwater Horizon oil spill in the Gulf of Mexico has disappeared, say marine scientists. The team was investigating new bacteria that, together with other microbes, were breaking down the oil faster than expected. "We've been out there continuously and we've not been able to detect [the plume] for three weeks," said Terry Hazen, head ecologist at the Lawrence Berkeley National Laboratory in California.


Several groups have been monitoring the 22-mile long, mile-wide plume of oil as it drifted southwest of the accident site at a depth of around 1,000 metres. Dr Hazen said that his instruments were sensitive to hydrocarbon concentrations in the "parts-per-billion" range and that the research vessel searched more than 100km (62 miles) down-current of the accident site. "All we could find was a slight dip in the amount of dissolved oxygen and flocks — bacterial debris and the remains of oil degraded by the biomass," he said. Dr Hazen's team — whose work was supported by a USD 500 million Gulf science fund established by BP following the accident — published evidence yesterday that the plume was being consumed by bacteria between May 25 and June 2.


Some experts had feared that a sudden boom in populations of oil-eating microbes fuelled by the oil would rapidly consume the oxygen available in deep water and create a "dead zone", but the growth of bacteria found by Dr Hazen's team appears to have been restrained, perhaps by the lack of essential minerals such as iron.


Last week a group from the Woods Hole Oceanographic Institute in Massachusetts announced that they had mapped a 22-mile oil plume in June but had found little evidence of the oxygen depletion expected if there was a surge in oil-consuming bacteria within the oil "cloud".


The latest study of the plume – to be published in the Journal Science— revealed a new species thriving on the oil. The microbe, similar to the Oceanospirillales family, is a "gamma proteobacteria" that flourishes in the cold waters (5C) found a kilometre beneath the surface where the plume had spread.


Half of the oil in the plume degraded within between 1.2 and 6.1 days, say the authors. Although the rate was surprisingly high for such cold water, it was likely to have been aided by the light nature of the crude from the well, the tiny size of the oil droplets, the low concentrations within the plume and the presence of naturally occurring hydrocarbon seeps in the Gulf.


"This bacteria has always been there at background levels. It will thrive, destroy the oil and then go back to being in the background," said Simon Boxall, of the National Oceanography Centre, Southampton. "An oil spill is a bad thing but nature is incredibly good at dealing with this kind of natural compound."


Using chemical dispersants, such as those deployed by BP, disrupts this natural process, said Dr Boxall. Studies of the 1992 Arctic spill of the Exxon Valdez, he continued, had shown that "the worst areas were where dispersants had been applied".


Contact: Bill Box