Researchers suggest that the huge release of potent greenhouse gas from the ocean must have been accilarated the ends of past ice ages. Kieran O'Hara of the University of Kentucky in Lexington carried out the research.
According to a report in Discovery News, the signals of sudden methane releases during ice ages were extracted from 400,000 years-worth of ice drilled out of Antarctica's Lake Vostok.
The pattern suggests that there have been spikes in methane releases over and over - right at the times when things are coldest, driest, and the most common modern source - wetlands - are the scarcest.
O'Hara modeled methane releases seen in the ancient ice to try and find out their source.
What he found was that the methane releases happened relatively suddenly and then the methane persisted - which is weird because methane breaks down rather quickly in the atmosphere. This means that wherever the methane came from, it kept coming for a while, replenishing the methane that was being destroyed in the atmosphere.
That suggests there was a really big methane source. The biggest source that was available in those dry, icy times would be the frozen gas hydrates that exist throughout the world in the cold depths of the oceans.
"The gas hydrates would have been vulnerable because the ice age sea level was close to 120 meters lower, which would expose shallower gas hydrates to lower pressures that that would make them unstable," said O'Hara.
While sea levels are not lower today, another factor - warming ocean temperatures - may be making gas hydrates similarly vulnerable.
"A reduction in pressure by lowering sea-level, or an increase in ocean temperature, via global warming, can lead to hydrate destabilization, converting generally immobile and innocuous methane hydrate (a solid), into more buoyant and mobile methane gas," explained gas hydrate researcher Matthew Hornbach of the University of Texas at Austin.
"There's also the danger that the warming of hydrates could weaken undersea slopes and cause massive submarine landslides that belch huge amounts of methane into the atmosphere," he added.
According to Hornbach, two studies back in 2003 and 2004 indicate that near-critical gas pressures may exist at many gas hydrate provinces, indicating that many are at the brink of instability, and only very minor changes in temperature or pressure could lead to structural failure, and methane gas release.