Study Ties Methane Spike to Melting Ice Age Permafrost

A sudden increase in atmospheric methane at the end of the last ice age might have come from arctic lakes that sprung up as permafrost melted, according to new research published in this week's issue of Science magazine.

An international team of researchers found that the formation of new lakes in the arctic coincided with a spike in atmospheric methane that took place between 11,500 and 14,000 years ago. These thermokarst lakes were created as the climate warmed, thawing arctic permafrost and causing meltwater to pool aboveground in regions that were once dry grasslands. As the lakes formed, organic matter previously locked into the permafrost became food for methane-producing bacteria at the lake bottoms.

The team of researchers developed their hypothesis after studying lakes in northern Alaska and Siberia that are now releasing methane. They also took samples of permafrost to see how much methane it would produce when thawed in the lab.

"We found that it produced a lot very quickly," said Katey Walter, a researcher at the University of Alaska Fairbanks (UAF) and lead author of the Science report.

Scientists had previously linked the post-ice age methane spike to wetlands or gas hydrates, which are ice-like crystals of water and methane that can occur in the pores of buried sediments and rocks. The new research indicates newly formed arctic lakes might have also contributed to the spike significantly, possibly accounting for anywhere from 33 to 87 percent of the methane increase.

"All that carbon that had been locked up in the ground for thousands of years is converted to potent greenhouse gases: methane and carbon dioxide," Walter said.

Methane is believed to be anywhere from 25 to 72 times as powerful a greenhouse gas as carbon dioxide. Scientists studying climate change are concerned that sudden influxes of methane from melting permafrost or other sources could accelerate global warming already being driven by rising carbon dioxide levels.

"We estimate that as much as 10 times the amount of methane that is currently in the atmosphere will come out of these lakes as permafrost thaws in the future," Walter said. "The timing of this emission is uncertain, but likely we are talking about a time frame of hundreds to thousands of years, if climate warming continues as projected."

Co-authors of the Science paper include Mary Edwards of the University of Southampton and the UAF College of Natural Science and Mathematics, Guido Grosse of the UAF Geophysical Institute, Sergey Zimov of the Russian Academy of Sciences and Terry Chapin of the UAF Institute of Arctic Biology.

University of Alaska, Fairbanks, "Study Reveals Lakes a Major Source of Prehistoric Methane." URL:(http://www.uaf.edu/news/news/20071024130833.html)