New study investigates threat of 'watermelon snow' to mountain glaciers

The colourful algae colonize thousands of North American snowfields each summer

The Rocky Mountains conjure up images of grey rugged peaks capped with white. But within the upper reaches of the harsh mountain landscapes, a rosier hue often blooms.

Watermelon snow, also known as glacial blood, is caused by algae that turns the snow a startling shade of red.

The algae blooms in summer, forming on the snowfields that linger on glaciers, frozen lakes, rugged peaks and icy valleys in the upper reaches of mountain terrain.

The darker the snow, the faster it melts — and new research sheds light on the threat snow algae poses to shrinking glaciers across northwestern North America.

Snow algae researcher Lynne Quarmby, lead author of a study recently published in Science Advances, said the findings serve as a warning about our changing climate.

'Canary in the mine'

"We don't really need any more canaries in this mine, but they're yet another canary in the mine," said Quarmby, a professor of molecular biology and biochemistry at Simon Fraser University.

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"Losing the algae is just an indicator that we're losing snowpack and glaciers, and these will impact our lives and the lives of lots of other organisms."

The study mapped the presence of snow algae on mountains in Alberta, British Columbia and Canada's north along with Alaska, Idaho, Montana and Washington state.

The researchers developed a machine learning program to analyze more than 6,100 satellite images of glaciers captured between 2019 and 2022.

The study found that the red-pigmented algae blooms contribute to glacial melt. However, global warming poses a far greater threat to mountain glaciers and to the surprisingly complex microscopic ecosystems that allow snow algae to colonize them.

"We set out on this study to look at the impact of climate change on these blooms and their impact on climate change," said Quarmby.

"And I think the impact of climate change on them is clear and dramatic."

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A red survival mechanism

Supported by a vast ecosystem of bacteria and fungi, snow algae flourish when water and nutrients are released from melting snow.

The phenomenon is the result of blooms of Chlamydomonas nivalis, which thrives at near-freezing temperatures. Relying on photosynthesis, the blooms act as carbon sinks, absorbing carbon dioxide from the atmosphere.

"The red pigment means that when they bloom they give the snow this red hue," she said. "It gets called watermelon snow because it looks like the colour of watermelon."

The blooms darken the surface of summer snowfields, making them less reflective against the sun, causing the snowpack and the ice beneath the bloom to melt faster.

The red pigment creates a "positive feedback loop," Quarmby said: the algae feeds on water released by the added heat.

The darker hue also acts as a "shade umbrella," protecting the algae from being damaged by the sun, she said.

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Quarmby and fellow SFU researcher Casey Engstrom set out to draw a large-scale map of the microscopic ecosystems.

They found that between 2019 and 2022, red snow covered more than 4,214 square kilometres of glacier landscape, equivalent to 4.5 per cent of the total study area.

The researchers estimate that the red snow contributed an average of three centimetres of snow meltwater per season.

"The impact of [the algae] is discernible, it's real," Quarmby said. "But of all the things we have to worry about that are amplifying climate change, it's not one we have to worry about."

Snow algae was found on 4,552 of 8,700 glaciers studied.

Some had just a patch but many had vast blooms. For example, in 2020, algae covered nearly two-thirds of the surface area of Alberta's Bow Glacier in the Wapta Icefield.

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Glaciers along the Pacific Northwest coast are usually teeming with algae but during the heat dome of 2020, the ice melted so fast, the blooms did not have a chance to develop.

Quarmby said as snow begins to disappear amid rising temperatures, the algae will also vanish. It will mean the loss of a valuable ecosystem that scientists are just beginning to understand.

Watermelon snow/Lynne Quarmby via CBC

A unique ecosystem of microorganisms like algae and fungi are responsible for sometimes giving snow an unusual reddish hue. (Submitted by Lynne Quarmby)

"For me, it's one more little sadness that we're losing it. If you see these things under the microscope, they're spectacular. Even if you see them just on the landscape, it's awe-inspiring."

Scott Hotaling, a Utah State University ecologist who studies biodiversity in cold and high altitude environments, said the scope of research is impressive. Hotaling was not involved with the SFU study.

By relying on satellite images, the researchers were able to study glaciers previously inaccessible to science and gather data on a massive scale, he said.

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Hotaling said the work provides an important baseline for the impact of snow algae on retreating glaciers.

"As the snowpack dwindles, these blooms are going to become increasingly concentrated and smaller and smaller.

"The melting characteristics of that snow algae are going to become increasingly important. When there's only a small amount of snow left, anything that affects that matters more."

WATCH: Hear glaciers pop and crack in the fastest-warming place on the planet

Thumbnail courtesy of Lynne Quarmby via CBC.

The story was originally written by Wallis Snowdon and published for CBC News.