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Tundra exhales methane when winter comes

By Bart B. Van Bockstaele     Dec 9, 2008 in Environment
When the summer ends, Greenland's tundra freezes up again. That leads to an enormous release of methane gas, contrary to expectations.
Although not much CO2 comes from uninhabited regions of the planet, these regions most definitely help a lot with increasing the amount of greenhouse gases in the atmosphere. Measurements in Greenland's grass lands have shown that they release very large amounts of methane, a greenhouse gas that is rather more potent than CO2.
The tundra starts to release methane in the spring. This release increases rapidly to a climax, and then slowly decreases to practically zero. However, new research shows that this is only part of the story.
Noorderlicht, a leading science blog in The Netherlands, reports that Swedish researchers discovered an interesting phenomenon when they decided to continue their measurements for two months longer than they normally do. They were able to do that because, thanks to the international polar year, research station Zackenberg in the north-east of Greenland. THis station normally closes in the beginning of September, but in 2007, it closed at the end of October.
The results of the continued research were surprising. At the end of September, the amounts of methane released by the tundra started to increase rapidly until they reached a peak that was twice as high as the summer maximum. The amounts decreased rapidly the week after the peak. The amount of methane released during this short period was about as large as the amount released during the entire summer.
The reason for this seemingly paradoxical release of methane is unknown, but the researchers are hypothesizing that freezing is the cause. When the tundra starts to freeze, ice crystals force the methane out of the way, and because of the permafrost, the methane can only go in one direction: the atmosphere.
Sander Houweling, a researcher of the Dutch space institute for space research SRON, uses data from satellites, land stations and sea measurements to construct simulations of methane flows around the planet. He doesn't know if this refreezing of the ground causes methane peaks everywhere around the North Pole. This is still unknown. Houweling thinks it is quite likely however, since the presence of such a peak seems to correspond quite well with observations.
Houweling does caution that there are still a lot of uncertainties as permafrost is still poorly understood. He has tried to compare the autumnal release of methane in the northern hemisphere between 2002 and 2005 with the numbers of 10 years ago. It looks as if these amounts have not increased. However, it is not impossible that this will change in the coming years, because the North Pole is warming up rather quickly.
This phenomenon could strengthen the greenhouse effect and is therefore something that must be carefully observed. SRON is currently testing an instrument that is much better suited to look at methane than current satellites. It is called TROPOMI and it will be launched in 2014 at the earliest. However, it will still be necessary to take field measurements, since the instrument can't detect methane in the darkness of the arctic winter.
More about Greenland tundra, Methane greenhouse gas, Winter
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