Now you see it, now you don’t: Less than one week after reporting a 22-mile-long, mile-wide plume of hydrocarbons deep underwater in the Gulf of Mexico, researchers now say they can’t find a trace of it.

The plume, a remnant of the months-long Deepwater Horizon oil disaster, has apparently been degraded by deep-water microbes, in particular a “new and unclassified” species that might have evolved to devour the oil that emerges from natural seeps in the Gulf. That species appears to have degraded oil from BP’s failed well much faster than anticipated, report scientists from the Lawrence Berkeley National Laboratory. They also report that degradation seems to have taken place without significantly depleting oxygen levels, a concern for marine life in a region that already sees a large, low-oxygen “dead zone” develop every summer.

“Our findings, which provide the first data ever on microbial activity from a deep-water 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 who led the Berkeley Lab 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.”

The three-month-long gusher, set off after an April 20 explosion on the Deepwater Horizon drilling rig, spewed nearly 4.9 million barrels of oil into the Gulf.

A DNA-based analysis of microbes in and around the plume reported last week found that the dominant species was a new one closely related to members of Oceanospirillales family. These microbes live in a habitat that has been relatively unexplored, a  realm deep underwater marked by crushing pressure, temperatures of around 5 degrees C and typically low carbon content.

“The oil escaping from the damaged wellhead represented an enormous carbon input to the water column ecosystem and while we suspected that hydrocarbon components in the oil could potentially serve as a carbon substrate for deep-sea microbes, scientific data was needed for informed decisions,” said Hazen.

While microbial degradation of oil is a good thing, researchers had been concerned that the process would also see microbes consuming large volumes of oxygen from the water. However, the Berkeley Lab study found that oxygen saturation inside the hydrocarbon plume was 59 per cent, compared to a saturation of 67 per cent outside the plume.

“The low concentrations of iron in seawater may have prevented oxygen concentrations dropping more precipitously from biodegradation demand on the petroleum, since many hydrocarbon-degrading enzymes have iron as a component,” Hazen speculated. “There’s not enough iron to form more of these enzymes, which would degrade the carbon faster but also consume more oxygen.”

Ironically, the Berkeley Lab study was funded through a $500 million partnership grant funded by BP well before the Gulf oil disaster occurred.

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