'Methanotroph' bacteria feasted on blown BP rig's methane belch

Deepwater Horizon upsets climate-change assumptions

Scientists believe they have solved the mystery over what happened to the hundreds of thousands of tons of methane that belched into the Gulf of Mexico following the Deepwater Horizon oil rig explosion last April.

According to a study published in Science Xpress, the gas served as a feast for methanotrophs: bacteria able to use natural gas as food.

A team of US researchers found that the level of dissolved oxygen in a 36,000-square-mile are surrounding the rig had plummeted, a tell-tale sign of a boom in the methanotroph population. They made measurements that ruled out the possibility that the escaped methane had simply bubbled into the atmosphere.

"What we observed in June was a horizon of deep water laden with methane and other hydrocarbon gases," said UC Santa Barbara oceanographer David Valentine.

"When we returned in September and October and tracked these waters, we found the gases were gone. In their place were residual methane-eating bacteria, and a one million ton deficit in dissolved oxygen that we attribute to respiration of methane by these bacteria."

The scientists were particularly surprised at the speed with which the bacteria consumed their enormous meal. Earlier studies elsewhere in the world suggested methane levels around Deepwater Horizon would be well above normal for years ahead.

Valentine's co-author, John Kessler of Texas A&M, said the study has major implications for our understanding of how methane releases affect the climate. There are vast stores of the powerful greenhouse gas trapped on the sea floor, and it had been supposed that occasional large releases have a significant impact on global temperatures.

"What the Deepwater Horizon incident has taught us is that releases of methane with similar characteristics will not have the capacity to influence climate," Kessler said.

The question of what happened to the more than four million barrels of crude oil spilled after the blow out, which also dissipated sooner than expected, remains under debate. Factors including high winds, natural breakdown, evaporation and the clean-up operation have all been suggested. ®

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