Arctic lakes show signs of global warming

Posted: 21 April 2005

Author: J.R. Pegg

A major study of Arctic lake sediments provides new evidence of human-induced climate change and concludes it may soon be impossible to find "pristine Arctic environments untouched by climate warming."

Arctic lakes have undergone dramatic ecological change in the past 150 years, the study finds, and the timing of these changes mirrors the warming trend that commenced when humans began the widespread burning of fossil fuels.

The Mackenzie River Delta of the western-Canadian arctic. Photo: Simon Fraser University
The Mackenzie River Delta of the western-Canadian arctic. Photo: Simon Fraser University
The Mackenzie River Delta of the western-Canadian arctic. Lakes are abundant in the Arctic and scientists say the hold ample evidence of global warming.(Photo courtesy SF University)
The findings, which represent the largest study of its kind, were published in the "Proceedings of the National Academy of Sciences."

Co-author Alexander Wolf said the new research provides key data on a region that is on the frontlines of climate change but can be difficult to study.

"Polar regions are expected to show the first signs of climatic warming, and are therefore considered sentinels of environmental change," explained Wolf, an earth scientist from Queen's University in Canada. "Unfortunately, long term monitoring data are generally lacking in these areas, which makes it difficult to determine the direction and magnitude of past environmental changes."

But microfossils of aquatic organisms preserved in lake sediment offer an archive of the lake's history - and lakes are abundant in the Arctic.

"If you look at one lake at a time, you still get important information, but it is hard to make large scale, regional assessments," said lead author John Smol, an Arctic lake expert from Queen's University. "Once you compile the larger dataset of all these lakes and ponds, striking and consistent patterns become evident. Taken together, it is a very powerful message."

Warming impact

To determine that message, the international team of 26 researchers analyzed lake sediment from 46 Arctic lakes in four polar nations.

They produced 55 historical profiles of algal and invertebrate animals, covering an area that extends halfway around the world and 30 degrees of latitude spanning boreal forest to high arctic tundra ecosystems.

Changes in the community composition of freshwater algae, water fleas and insect larvae in the majority of lakes reflect the impact of warming, the researchers said.

The study reports little change in these communities until the mid-1800s, with dramatic shifts occurring in the past three decades.

These organisms make up the base of most aquatic food webs, the researchers said, and impacts are likely to trickle up the food chain and affect larger animals.

Arctic lake expert John Smol. Photo: Canada Research Chairs
Arctic lake expert John Smol. Photo: Canada Research Chairs
Arctic lake expert John Smol is the Canada Research Chair in Environmental Change and 2004 winner of Canada's top science award, the Gerhard Herzberg Gold Medal.(Photo courtesy Canada Research Chairs)
The findings are consistent with data that show climate change has lengthened summers and reduced lake ice cover across much of the Arctic.

These changes in turn prolong the growing season available to highly sensitive lake organisms, the researchers said, and opens up new habitats for others.

Wakeup call

The researchers also found the most intense population changes occurred in the northernmost study sites, where the greatest amount of warming appears to have taken place.

Changes in the Arctic are considered bellwethers of what is to come further south, the study's authors said, and should sound an urgent environmental wakeup call.

It shows that "human interference is affecting ecosystems on a profound scale," Smol said.

"We are crossing ecological thresholds here, as shown by changes in biota associated with climate related phenomena like receding ice cover in lakes," he added. "Once you pass these thresholds it is hard to go back."

Findings from one area in the Canadian sub-Arctic did not show similar patterns of biological change.

But this area appears not to be warming to the same extent as other areas, the researchers said, and this actually boosts the overall conclusions of the study.

The region represents an important control region, according to researcher Reinhard Pienitz from Université Laval in Quebec City.

It supports the determination that the changes observed in lakes where warming has occurred "have not been primarily caused by, for example, atmospheric deposition of contaminants," Pienitz explained.

Smol noted that an earlier lake sediment study he co-authored, published in the journal Science in 1994, caused controversy with its interpretation of climatic warming in three high Arctic ponds.

But now "the tide has turned," Smol said, "and some of the strongest skeptics of that 1994 study are co-authors on this paper."

Source: Environment News Service (ENS), March 3, 2005