Thermokarst lakes a major source of prehistoric methane

November 14th, 2007 - 2:53 am ICT by admin  
The team focused their research on areas of Siberia and Alaska, which were dry grasslands atop ice-rich permafrost during the last ice age.

As the climate warmed, that permafrost thawed, forming thermokarst lakes.

As part of her study, lead author Katey Walter and her team examined lakes in Siberia and northern Alaska that still released methane.

In addition, they gathered samples of permafrost and thawed them in the laboratory to study how much methane permafrost soil could produce immediately after thawing.

Finally, the researchers studied when existing lakes and lakes in the past formed, and found that their formation coincided with the early Holocene Period northern methane spike.

“We came up with a new hypothesis. Thermokarst lake formation is a source of atmospheric methane today, but it was even more important during early Holocene warming. This suggests that large releases from lakes may occur again in the future with global warming,” Walter said.

Ice cores from Greenland and Antarctica have shown that during the early Holocene Period - about 14,000 to 11,500 years ago - the levels of methane in the atmosphere rose significantly.

“They found that an unidentified northern source (of methane) appeared during that time,” said Walter.

Previous hypotheses suggested that the increase came from gas hydrates or wetlands.

But the new study indicates that methane bubbling from thermokarst lakes, which are formed when permafrost thaws rapidly, is likely a third and major source for that spike.

Walter said methane emissions from arctic lakes could have been responsible for up to 87 percent of that increase.

“Lakes really flared up on this icy permafrost landscape, emitting huge amounts of methane,” said Walter.

“It tells us that this isn’t just something that is ongoing now. It would have been a positive feedback to climate warming then, as it is today. 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. 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,” she said.

The study appears in the October 26 issue of the journal Science. (ANI)

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