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News / Northwest

Algae blooms that cause pink snow could accelerate melting as Earth warms

By Sandi Doughton, , The Seattle Times (TNS),
Published: July 23, 2023, 6:05am

IN MARCH 1875, readers of The American Naturalist were treated to a discourse on the curious phenomenon of red snow.

“Truly a beautiful sight,” the periodical opined, “in direct contrast with the expanse of white, whether appearing in thinly scattered patches, or crimsoning the hills and plains for miles around.”

The earliest recorded observation was from Aristotle, who spotted reddish patches on Mount Olympus in the 4th century B.C. The Greek philosopher suspected hairy worms were somehow involved.

British explorer Sir John Ross brought back samples of red snow from Greenland after his disappointing search for a northwest passage in 1818, setting off a lively debate among Europe’s gentlemen scientists as to what the stuff actually was.

The Times of London described it as meteorite detritus. Other authorities argued for fungus or lichen. Upon learning of a red snowfield in the Swiss Alps, the American Naturalist reported that a Mr. Shuttleworth “betook himself thither” with his microscope and declared the color due to tiny animalcules.

Though debate continued for decades, the correct answer came from botanist Robert Brown, for whom Brownian motion was named. He examined Ross’ specimens in 1819 and reported they were brimming with single-celled algae.

“The subject has ever been of the deepest interest,” the American Naturalist enthused — which was hyperbole even in the 19th century. And certainly for the next 120 years or more, snow algae were regarded mostly as a curiosity. Field biologists continued to collect and catalog specimens and puzzle over the cells’ survival in such harsh environments, but mainstream science paid little attention — until recently.

“There never used to be any funding for this kind of work,” says Robin Kodner, a biologist at Western Washington University who’s at the forefront of a new push to understand what folks in the Pacific Northwest call “watermelon snow” — if they’ve heard of it at all. A nickname for it in the French Alps is sang de glacier, or glacier blood. While red and pink are the most common colors, different types of snow algae produce a rainbow of hues, including orange, yellow and green.

THE RESURGENCE OF interest in these tiny organisms is driven by something natural historians of the Victorian era never could have envisioned: global climate change.

As the planet warms, the most extreme transformations are occurring at the poles and in alpine environments, where glaciers, snowfields and icefields are shrinking at a rapid pace. Over the past several years, scientists have come to realize that algae blooms actually can accelerate the melt by darkening snow and ice and absorbing heat like a black T-shirt on a sunny day.

Now, research teams around the world are scrambling to figure out how significant the algae effect might be, and whether the plantlike organisms are likely to flourish and spread as temperatures continue to rise. Kodner has mobilized a small army of citizen scientists to collect specimens through her Living Snow Project.

“Everybody wants to know if these algae blooms will get worse in the future,” she says.

The answer has implications for global climate models, which might need to be tweaked to incorporate melting caused by algae and its contribution to sea-level rise. In the western United States, where more than 50% of water supplies come from snowpack, shifts in the speed and timing of the melt could disrupt irrigation, hydropower and salmon runs.

Microscopic organisms might seem a trivial factor compared to rising temperatures. But research on snowfields and glaciers across Iceland, Greenland and Scandinavia found red algae increases heat absorption by 13%. In Alaska, researchers estimate algae accounts for almost one-fifth of the annual melt across a large ice field.

“That result was kind of eye-popping,” says Scott Hotaling, assistant professor of watershed studies at the University of Utah. “We’re not talking about fractions of a percent. We’re talking about big chunks, and you can’t ignore that.”

Warming also threatens the algae’s own existence, along with the weird and wonderful assortment of creatures, like ice worms (but not hairy ones), tardigrades and rotifers, that thrive in one of the planet’s least-understood ecosystems.

“These are places the world thinks of as ecological dead zones,” says Hotaling, who’s part of a multiyear study of snow algae across Washington, Oregon, Montana, Idaho and Utah. “There’s a whole universe up there, but it’s kind of like the deep sea. There’s so much we don’t know.”

FRESH SNOW IS the Earth’s most reflective natural surface. Up to 99% of the sunlight that strikes it bounces back into space. Anything dark on the surface — dust, soot or algae — reduces that reflectivity and increases melting.

The effect is obvious at Upper Bagley Lake, in a small basin near the Mount Baker Ski Area where Kodner has been monitoring blooms for nine years. On a sunny morning in late May, the surface of the snow is scalloped by depressions, each cupping a patch of pink. By absorbing sunlight, the algae warm and melt the snow, creating the depressions, Kodner explains.

Using drones equipped with special cameras, WWU professor and environmental engineer Alia Khan surveyed algae around the lake and estimated it increases snowmelt by 20% — the first such measurement in the Pacific Northwest. Khan also works in Antarctica, where she found multicolored algae blooms can reduce the reflectivity of snow 20% to 40%.

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The pink blush at Upper Bagley Lake usually appears at the end of May or early June, Kodner explains as she and her team unpack gear and prepare to check eight monitoring stations across the lake surface. This year, in the midst of a record-breaking spring heat wave, the bloom started almost a month early.

“I was shocked,” says postdoctoral fellow Brooke Weigel, who was the first to spot it on a reconnaissance trip.

But the researchers don’t have enough data yet to show a clear correlation between temperature and the size and timing of blooms in the North Cascades. In fact, during really hot years, algae cells are more stressed than during cooler springs.

“I think there’s a lot of other factors at play,” Kodner says.

While it’s reasonable to hypothesize blooms will become bigger and more frequent as temperatures and atmospheric carbon dioxide levels rise, there’s no historic data to compare against what’s happening now, Kodner cautions. And so little is known about the many types of snow and ice algae around the world that it’s hard to know how they will react to future warming. “The blanket assumption that algae blooms are increasing bothers me, because we don’t really know,” she says.

“We still don’t know from a genetic point of view, from a metabolic point of view, what kicks them off — what triggers the blooms,” adds Liane Benning, a biogeochemist at GFZ German Research Centre for Geoscience in Potsdam who studies multiple species. “They turn on very quickly, the moment they have a little bit of water.” The concern is the runaway effect that occurs as the algae absorb heat and melt more snow, which in turn intensifies the bloom.

“They melt their own house, so to speak,” says Benning, co-leader of Deep Purple, a $12 million European initiative to unravel the impact of the purple algae that grow on bare ice in Greenland. She and her colleagues are also collaborating with Kodner and other North American researchers to look for local adaptations in a species that grows worldwide.

WORKING AT MULTIPLE sites in the North Cascades, Kodner’s group hopes to identify factors that control the algae’s growth and productivity. At Upper Bagley Lake, that means collecting a lot of data.

“We characterize each station and take a bunch of samples,” Weigel says, kneeling in the snow and inserting an avalanche probe to measure its depth. Then she weighs a cylinder packed with snow to estimate density, while Kodner and students AG Camara and Honu Pata measure air temperature and pack plastic tubes with pink snow.

Back at the lab, they’ll examine the samples under a microscope and analyze their genetic makeup. But any experimentation has to happen in the field, because most species can’t survive when removed from their chilly habitat.

“Studying them in the field is so critical because they don’t like to be warm, and we can’t grow them in the lab,” Weigel says, laying out tubes in the snow for an hourlong incubation to measure photosynthesis rates. Nearby, Kodner loads samples into a boxy black device that gauges photosynthetic efficiency. A new instrument will enable them to expose algae to varying temperatures and levels of carbon dioxide and see how they react — mimicking future climate scenarios.

One surprise from Upper Bagley Lake is that the species of algae growing here is new to science — even though thousands of skiers and hikers pass through every year. “This site is not exotic or remote,” Kodner says. “It just happens to be a new species because no one’s studied it.” Camara analyzed a sediment core from the lake with layers dating back almost 3,000 years, and found algae have been living there all that time.

Its full life cycle remains a mystery, but it probably includes a cyst stage that hibernates on the lake bottom until it’s triggered to divide and release new cells. Some have flagella and swim up through the snow in spring, when temperatures warm and enough meltwater is present for the cells to photosynthesize and explode in numbers.

The red color comes from a carotenoid pigment that acts as a sunscreen, protecting the cell’s machinery from UV radiation. Cosmetic companies have figured out how to grow a few types of snow algae by the tankful, because the pigment is also a powerful antioxidant prized for face cream. Others contain so much lipid, they might be useful as biofuels.

HOTALING AND HIS colleagues also are experimenting this spring at Oregon’s Mount Hood and the Powder Mountain ski area in Utah, using hula hoops to lay out a gird of circular plots in the snow. They’re studying nutrients such as phosphorus and nitrogen, which can blow in from agricultural fields and factories and might act as fertilizer to spur algae growth.

Each plot is sprayed with a mix of chemicals, then the researchers monitor algae populations. “It’s pretty simple,” says Hotaling, who’s running the tests in Utah. “It’s just a lot of work because it’s in the middle of nowhere.”

Studying snow algae is also challenging because it’s hard to predict when blooms will start, and how long they will last, says Trinity Hamilton, an environmental microbiologist at the University of Minnesota and co-leader of the five-state project.

“They’re ephemeral, and they disappear at rates that don’t always make sense,” she says. On Powder Mountain, the snow melted away much faster this spring than expected, cutting the studies short. And the window is already brief — basically a few months between snowmelt and snowfall.

To expand the researchers’ reach, Kodner launched The Living Snow Project, recruiting volunteers to report algae blooms and collect samples. Since 2017, more than 500 participants have submitted more than 800 specimens, mostly from the Pacific Northwest, but some from as far away as Alaska and the Italian Alps. The collection tubes contain a DNA preservative, so even though samples are melted when they reach the lab, researchers can analyze the mix of species and their genetic properties. (For more, see The Backstory on Page 2.)

The Deep Purple project is the most ambitious snow algae initiative ever attempted. The idea is to gather chemical, genetic and biological information from algae in the field and laboratory and correlate it with the physical properties of snow and ice, along with measurements of solar radiation and bloom size from drones and satellites, Benning says.

And yes, she adds: The name was chosen with the pioneering heavy metal band in mind. Its biggest hit, “Smoke on the Water,” calls to mind the Greenlandic algae, which for a long time were mistaken for dust or soot. And Benning and other project leaders got to hear Deep Purple in concert before the research began.

COMPUTER MODELS USED to predict the impact of rising temperatures and greenhouse gas levels on snow, ice and sea levels already account for the extra melting caused by dust and soot deposits. Factoring in algae makes sense — but first, biologists need to identify key factors that control the size and distribution of blooms, says Joseph Kennedy, a computational glaciologist at the University of Alaska Fairbanks.

Impacts at the local and regional scale could be especially significant in the western United States, Hotaling says. If algae blooms cause the snowpack to melt even a few weeks earlier, that could cause problems for agriculture, hydropower generation and species such as salmon that depend on cool freshets at critical points in their life cycles. “The timing of the snowpack runoff is really, really important, and I’ve never heard of a snowpack runoff model that includes snow algae,” he says.

This spring, parts of Washington’s snowpack melted as much as four weeks earlier than usual, says Scott Pattee, a water supply specialist with Washington’s Snow Survey.

But the main drivers were record high temperatures and an unseasonable amount of sunshine. Pattee isn’t convinced snow algae is a big player.

“I don’t see that’s a huge problem for us here in the Northwest at this point in time.”

Hotaling is more concerned with the coming decades.

“The key to me is not what is happening right now, but whether a component of that is going to change in a way that we aren’t expecting,” he says. “If we can predict that, I think it’s a real contribution, not just to basic science but to water management in the U.S.”