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Methane's hidden impact in Gulf oil spill

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Yet gas data represents the largest gap in efforts to take the full measure of the blowout, Dr. Joye says. That gap results from "the perception that it doesn't really matter; the focus is on oil, oil, oil."

Oil clearly has its own set of serious environmental effects. But the gas's behavior and fate at depth also is relevant to gauging the blowout's full ecological impact.

"It's not the same as the oil, but it's a big number," Joye says. "We have to get a handle on it, and we don't have a handle on it right now."

As with the undersea oil clouds researchers have been hunting, the main concern regarding methane is the possibility that the action of methane-munching microbes could exhaust oxygen in the affected layers.

That low-oxygen condition would threaten small marine organisms – plankton, fish larvae, and other creatures that can't roam large distances and form a vital link in the marine food chain. If a low-oxygen plume were to glide across the bottom on the continental shelf, it could have a similar effect on corals and shellfish.

"We've never dealt with a situation like this before," Joye says. The closest analogues appear in the paleo-oceanographic record, "when there have been these methane burps over geologic time scales."

There, she says, the evidence is strong for a run-up in microbe populations that feed on the methane and for the significant draw-down of oxygen that accompanies their feast. But the paleo record is silent on the fall-out for higher levels of the food chain.

That most of the leaking methane is hunkering down at depth is evident in measurements researchers have been taking in the Gulf.

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