Ponds in Canada's High Arctic are drying up because of global warming, two researchers say.
"The final ecological threshold for an aquatic ecosystem is loss of water," said biology Prof. John Smol of Queen's University. "These sites have now crossed that threshold."
"A key 'tipping point' has now been passed: Arctic ponds that were permanent water bodies for millennia are now ephemeral," Smol and co-author Marianne Douglas, professor of earth and atmospheric sciences at the University of Alberta, said in an article in the online edition of the Proceedings of the National Academy of Sciences.
The two scientists have been studying shallow ponds on Cape Herschel on Ellesmere Island since 1983.
When they went back last year, after an absence of a year, permanent ponds which previously had been up to a metre deep were drastically shrunken or even dry.
Their measurements had shown the water had been going down, but they were taken aback to find that about 40 well-studied pools — among themCamp Pond,Cape Herschel Lagoon andBeach Ridge Pond — were fractions of their former size, or totally gone.
These ponds were substantial bodies of water; Cape Herschel Lagoon, once 160 metres by 35 metres and a metre deep, "had only a small shallow puddle" (23 metres by 11 metres and 10 centimetres deep) in one basin when the scientists sampled it on July 13, 2006. Camp Pond, 20 metres by 40 metres, and Beach Ridge Pond, 100 metres by 60 metres, were completely dry.
They had not been to the site in 2005, but had left devices called thermistors in 2004. The devices — two per pond, one in the water and one on land nearby — suggested some ponds had dried up in 2005 because the temperatures on land and in the former ponds were the same.
While other research has suggested some Arctic ponds are shrinking because the permafrost is melting, allowing the water to seep away, that was not the case in Cape Herschel.
The ponds there had existed for millennia — ice for 10 months of the year and liquid in July and August — in depressions in the bedrock, so the water could only have evaporated as temperatures rose, they believe.
Environment Canada has reported that Arctic temperatures have been rising, and 2006 was the warmest year on record for that part of the Arctic.
The researchers also measured the concentration of salts in the water remaining in the ponds. It has risen sharply, in much the same way that a pot of soup left to simmer on the stove will become saltier as the volume of liquid falls, Smol said.
The authors also saw that nearby wetlands were drying up. Areas that once required hip waders to study could be set on fire with a lighter. Where once the wetlands had absorbed carbon as the plants grew, they now may release carbon as the vegetation decomposes.
Ponds provide habitat, drinking water, food source
The ponds are the most common source of surface water in many polar areas, and part of the Arctic ecosystem. They provide habitat for waterfowl, drinking water for animals and homes for tiny invertebrates like shrimp, which are a food source for larger animals.
"We don't really know how this cascades through the whole system," Smol said, but "if you're an eider duck, you're not so happy."
The authors attracted sharp criticism in 1994 when they published a paper suggesting the ponds were undergoing ecological changes consistent with global warming.
"In the past, researchers like us have sometimes been accused of being alarmist when we discussed climate warming," Smol said in a news release.
"We now think we have been overly optimistic — the speed and magnitude of environmental changes are worse than even we imagined."
The two scientists used identical techniques to collect detailed data on the water in the ponds in the summers of 1983, 1984, 1986, 1987, 1995, 1998, 2001, 2004, and 2006.
The research was mainly paid for by the Natural Sciences and Engineering Research Council of Canada and the Polar Continental Shelf Project.