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Last Updated: Friday, 11 April, 2003, 14:15 GMT 15:15 UK
Methane theory gets frosty response
Molly Bentley, BBC
By Molly Bentley
BBC News Online in Nice

A hot theory about how the Ice Age ended has got a frosty response at a meeting of the leading European and American geoscience societies in France.

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A climatologist says the idea that bursts of methane from deep-sea reservoirs jolted the planet out of its chilly state does not match the geologic record.

This idea, popularly dubbed the "hydrate gun hypothesis", was first proposed a decade ago, but has gained momentum through the work of James Kennett, a paleo-oceanographer from the University of California - Santa Barbara.

Hydrates are a frozen mixture of water and methane and form under the cool temperatures and high pressures found in ocean sediment.

The idea that methane escaping from these hydrates explains a pattern of rapid warmings in the climate record has caught on among scientists.

Burping cows

But Mark Maslin, from the Environmental Change Research Centre at University College London, UK, claims he has shot the "hydrate gun theory" full of holes.

Methane was the result - not the cause - of a more temperate climate, he says, and the vast majority came from tropical wetlands - swamps. He says the sums for the alternative hypothesis do not add up.

Hydrate, USGS
Energy source: Some would like to drill for hydrates (Image by USGS)
Methane is most familiar as natural gas, or the by-product of burping cows.

It is also a hydrocarbon and a more potent greenhouse gas than carbon dioxide. A voluminous amount is bound in gas hydrates - approximately 3,000 times the amount currently found in the atmosphere.

Its sudden release would be a tremendous "shot" to trigger global warming, according to Dr Kennett. The hydrates depend on high pressure and cold temperatures to keep their form.

Change either of these, and "then the gun shoots off," he said. A reversal in ocean circulation, a warming of the sea floor, or a drop in ocean depth, releasing the pressure, are all possible triggers.

Accelerated warming

Dr Maslin says his calculations are the first to quantify the amount of methane present in the atmosphere at the end of the last Ice Age.

"Hydrate is only about 10% of all the methane released," he told the European Geophysical Society (EGS), the European Union of Geosciences (EUG) and the American Geophysical Union (AGU). The rest comes from swamps, and was a response to climate change, not the cause.

Dr Kennett has yet to check the numbers, but points out that geological evidence says that there were no wetlands at the very times when methane increased in the atmosphere.

Where Drs Kennett and Maslin agree is on the need for more hydrate research - particularly because deposits on the sea floor today may respond to current climate change.

"We want to know how they react to warmer ocean temperatures," Dr Maslin told BBC News Online. "Will they stabilise or is there going to be lots of methane release in the future that will make global warming worse?"

Hydrates and microbes

Scientists have only recently discovered that hydrates support rich and diverse microbial life. Some consume methane, others release it as a metabolic by-product.

Hands, Geomar
Don't try this at home: Water drips away from the burning methane (Image by Geomar)
"These gas hydrates are really the food and faeces of deep-Earth microbes," said Charles Paull, a senior scientist at the Monterey Bay Aquarium Research Institute in California, who believes the bugs are some of the "same critters" that feed on hydrothermal vents.

And they protect land critters as well.

"They sit there like a filter on the sea floor and retain as much of the methane as they can," said Erwin Suess from the Geomar Research Centre in Germany.

"If you took this filter away, that methane would escape into the ocean, then of course, into the atmosphere."

Highly pressurised drilling devices have only recently allowed scientists to bring the delicate hydrate structures to the ocean's surface.

Party trick

They have to work quickly - the hydrate chunks, which resemble crystallized snow and smoke like dry ice, deteriorate rapidly once they are brought to the surface.

As they melt, they release methane gas. For amusement, scientists can hold burning hydrate in their palms while the remaining water drips down their hands.

First time analysis of still-frozen samples has allowed them to discover bubbles of free methane gas trapped within the solid hydrate.

"This is not supposed to happen," said Dr Suess. "Methane, when combined with high pressure and water, should be converted to gas hydrate."

He adds that the discovery of free gas may have implications for the overall stability of the hydrate system. The bubbles make the hydrate more porous, and might make it easier for the methane gas to escape.

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