Bacteria degrades oil faster in deep, cold water, study finds

A new species of bacteria found in the Gulf of Mexico degrades oil faster at deeper and colder depths than expected, according to scientists in a study that could explain how the BP oil spill has mostly disappeared.

The bacteria not only speeds up the bio-degradation of crude oil, but does it without depleting vital oxygen levels in the water, said the scientists who analysed in May a plume of oil at a depth of 1,000-1,200 meters, extending 16 kilometres out from the broken BP wellhead.

“Our findings, which provide the first data ever on microbial activity from a deepwater dispersed oil plume, suggest that a great potential for intrinsic bioremediation of oil plumes exists in the deep-sea,” said Terry Hazen, a microbial ecologist with Berkeley Lab’s Earth Sciences Division and lead author of the study.

“These findings also show that psychrophilic (cold temperature) oil-degrading microbial populations and their associated microbial communities play a significant role in controlling the ultimate fates and consequences of deep-sea oil plumes in the Gulf of Mexico,” he added.

The bacteria live in waters as cold as 5 C in a relatively unexplored microbial habitat in the Gulf of Mexico, where the pressure is enormous and there is normally little carbon present.

Once the BP wellhead was plugged on July 15, nearly three months after an explosion unleashed the worst oil spill in US history, US government investigators said 74 per cent of the more than four million barrels of oil that leaked had evaporated, biodegraded or was recovered by mechanical means.

The Berkeley study attributed the faster than expected oil degradation in such cold water, in part, to “the nature of Gulf light crude, which contains a large volatile component that is more biodegradable”.

Other accelerating factors, the scientists added, may have been the chemical dispersant Corexit used by BP at the source of the leak – at 1,500 metres – which broke up the oil into smaller particles, as well as the low overall concentrations of oil in the plume studied.

“In addition, frequent episodic oil leaks from natural seeps in the Gulf seabed may have led to adaptations over long periods of time by the deep-sea microbial community that speed up hydrocarbon degradation rates,” they said.

The study also dispelled some oceanographers’ fear that the oil bio-degradation would deplete oxygen levels in the water, creating so-called “dead-zones” where life cannot be sustained.

The Berkeley study found that oxygen saturation outside the plume was 67 per cent while within the plume it was 59 per cent.

It also appears to refute a University of Georgia study from a week ago that said 80 per cent the oil leaked into the Gulf was still drifting beneath the surface of the Gulf posing and slowly decomposing, posing a significant threat to ecosystems in the area.