Fading blue: Mountain lakes are losing their unique color due to climate change, study says

According to new research, the unmistakable milky turquoise of the mountain lakes follows the path of the glaciers that feed them.

“Many of the turquoise glacial lakes in the Canadian Rockies are clearing up,” says Rolf Vinebrooke, who studies such lakes at the University of Alberta. “They take on more of the blue color people think are normal lakes.”

The delicate, translucent celadon, which mountain lovers everywhere say “alpine”, comes from the meltwater of the glaciers. Even small glaciers are huge ice rivers that can pulverize rock into flour-fine particles, and it is these particles that color the lakes.

“Sunlight reflects off these white particles,” said Vinebrooke, who published his findings in the latest State of the Mountains report for the Alpine Club of Canada. “Because the light is scattered when it hits these particles, the lake takes on this turquoise color.”

However, glaciers are severely affected by climate change. And not just the big ones.

“Between the 1970s and 1990s, when no one was talking about global warming, many of these smaller glaciers had already melted and disappeared.”

Vinebrooke took stock photos of many lakes taken in the middle of the last century and compared them to modern day images. Even in the black and white of the earlier images, the change was evident.

The researchers then removed sediment cores from the bottom of the lakes. Sediment cores reveal the history of a lake in a similar way to the growth layers of a tree trunk.

“We were looking for clear blue mountain lakes,” said Vinebrooks. “We found them, and when we took these sediment cores, we found that they had only been a clear blue color for the past few decades.

“We found many lakes that are clear today, but were still turquoise a few decades ago. Their little glacier had melted.”

The color change didn’t happen everywhere, but it happened frequently. It also seems to have happened pretty quickly.

“In a few years it’ll shift and the lake will clear,” Vinebrooke said.

He said it’s happening right now in places like Geraldine Lakes, a series of alpine lakes in Jasper National Park.

“We have several lines of evidence that show all of this pretty convincingly.”

Vinebrooke said a clear blue lake lets in a lot more sunlight than a lake tarnished with glacial powder. That will likely bring about a very different local ecology, he said

“They increase the potential for this lake to be more productive because there is more microscopic algae growth in these lakes.”

But there are winners and losers.

Organisms that are adapted to the weak light of milky water are unlikely to survive, which would be a bright new glow from ultraviolet radiation to them. The problem is particularly acute because of the speed of the transition.

“If you take that sunscreen off, some organisms may not be able to tolerate this increase in UV radiation. It does not give the organisms time to adapt. “

Vinebrooke suspects that some lakes may remain “biologically impoverished”, at least temporarily – especially since so many are remote and in barren environments.

Ultimately, he said, this is another example of climate change already working to change familiar touchstones.

“It captures the effects of global warming in the here and now.”

This report from The Canadian Press was first published on September 24, 2021

– Follow Bob Weber on Twitter at @ row1960

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