for National Geographic News
Arctic ponds that have hosted diverse ecosystems for thousands of years are now disappearing because of global warming, according to a new study.
These ponds, which lie atop bedrock, freeze solid in the winter and then melt for a few months each summer, becoming hot spots of activity in the forbidding Arctic terrain. (Related: "Arctic Ice Isn't Refreezing in the Winter, Satellites Show" [March 17, 2006].)
"If you fly over, you see them everywhere," said study leader John Smol of Queen's University in Kingston, Canada.
The ponds brim with moss, algae, fairy shrimp, and other organisms that need liquid water to live during the summer.
The ponds vary in size, with some reaching three feet (a meter) deep and around several hundred feet across. But now these ponds have reached a tipping point, according to a study that appears in the journal Proceedings of the National Academy of Sciences this week.
Some of these ponds are going bone dry in the summer or shrinking to tiny puddles, while others are a fraction of their former size, because of global warming believed to be caused by humans.
The wetlands around some of the ponds are also disappearing, threatening the creatures that inhabit these areas, Smol added.
"Now they're so dry you can put a match to it and they'll burn," he said.
Drying Out, Dying Out
Smol and Marianne Douglas at the University of Alberta in Edmonton have spent more than two decades tracking about 45 ponds on Canada's Ellsmere Island, which is located just off the northwest coast of Greenland (see a map of Canada).
In earlier studies the researchers searched sediments in these ponds and dug out the shells of diatoms—microbes that grow protective mineral sheaths around themselves.
The record of diatoms revealed that the ponds had been relatively stable for several thousand years—until the 1800s. Then new kinds of diatoms and mosses took over the ponds, the first signs of warming's effects.
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