Wetlands likely source of methane from warming event 11,600 years ago

Malaysia Sun (ANI) Sunday 26th April, 2009

Washington, April 24 : A new research by an international team of scientists has determined that an expansion of wetlands and not a large-scale melting of frozen methane deposits is the likely cause of a spike in atmospheric methane gas that took place some 11,600 years ago.

The international research team was led by Scripps Institution of Oceanography at UC (University of California) San Diego.

The finding is expected to come as a relief to scientists and climate watchers concerned that huge accelerations of global warming might have been touched off by methane melts in the past and could happen again now as the planet warms.

By measuring the amount of carbon-14 isotopes in methane from air bubbles trapped in glacial ice, the researchers determined that the surge that took place nearly 12,000 years ago was more chemically consistent with an expansion of wetlands.

Wetland regions, which produce large amounts of methane from bacterial breakdown of organic matter, are known to have spread during warming trends throughout history.

"This is good news for global warming because it suggests that methane clathrates do not respond to warming by releasing large amounts of methane into the atmosphere," said Vasilii Petrenko, a postdoctoral fellow at University of Colorado, Boulder, who led the analysis while a graduate student at Scripps.

The research team, overseen by Scripps geoscientist and study co-author Jeff Severinghaus, collected what may be the largest ice samples ever for a climate change study.

The researchers cut away 15 tons of ice from a site called Pakitsoq at the western margin of the Greenland ice sheet to collect the ancient air trapped within.

Methane exists in low concentrations in this air and only a trillionth of any given amount contains the carbon-14 isotope that the researchers needed to perform the analysis.

Levels of carbon-14, which has a half-life of 5,730 years, were too high in the methane to have come from clathrates, the researchers concluded.

"This study is important because it confirms that wetlands and moisture availability change dramatically along with abrupt climate change," said Severinghaus.

"This highlights in a general way the fact that the largest impacts of future climate change may be on water resources and drought, rather than temperature per se," he added.