A Colgate biologist copublishes the comprehensive review of snow algae research.

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During spring and summer, colors bloom throughout the snowfields of the world’s alpine and polar regions. It happens when the snow has begun melting, sending films of liquid water down the snowpack and onto the barren ground beneath. As the sunlight filters down through inches of snow, it awakens tiny, desiccated resistant algal cells from their hibernation. Their progeny swim upward through snow crystals; along the way, they stain the melting snow in green, orange, golden brown, pink, or blood red. These algae form new resistant cells before the snow melts. Then they settle back to the soil, where they hibernate until the cycle repeats.

Sometimes the phenomenon is called blood snow, green snow, or watermelon snow. The organisms responsible — snow algae — are the focus of a new review by Colgate University Professor of Biology Emeritus Ron Hoham, cowritten with Daniel Remias of the University of Applied Sciences Upper Austria and published in the April 2020 Journal of Phycology. Including glacial ice algae within its purview, the article provides an update on Hoham’s chapter in Snow Ecology, published in 2001.

Snow algae, which are found on every continent, are a subset of green algae, a diverse group with unicells, colonies, filaments, and, occasionally, seaweed-like organisms. However, most snow algae are single-celled and use little whip-like appendages (flagella) to move through the water surrounding snow crystals to access nutrients, get better light, and even avoid predators. And, while most green algae live in freshwater, snow algae inhabit a remarkably inhospitable environment, where temperatures usually hover close to freezing. In alpine snowfields and glaciers, exposure to harsh sunlight and radiation is common, or algae might end up in low light beneath deep drifts or tree canopies. Snow is also acidic and nutrient poor — when it melts, organisms living in it are left on dirt and rock for long stretches of time and are at risk of drying out completely.

“This is one of the most extreme habitats on the planet,” Hoham says. “How are these things surviving?”

It turns out that algae have some tricks to help them survive deep freezes. They use ice-binding proteins and polyunsaturated fatty acids to lower the freezing point of their cells, and their pigments — the pools of golden brown, red, pink, or orange — act like sunscreen to help them block out damagingly high doses of ultraviolet radiation.

It’s those pigments that tend to attract the surprise and attention of passing hikers like Hoham. A botanist by training, Hoham became interested in snow algae more or less by accident: as a graduate student at the University of Washington, he went on a hike with a friend in Washington’s Cascade Mountains and was enthralled by the colors he saw staining the snow. He began isolating them from the snow, to the point that he started ignoring his intended research on marine red algae. “When my professor came back from teaching at Stanford’s Marine Station, I told him I was into snow algae now. He was pretty upset at first,” Hoham recalls, laughing. “But it did eventually work out.”

Colleagues at the 2018 International Snow Algae Meeting (SAM) in Potsdam, Germany, encouraged Hoham and Remias to draw together the new research on the subject. “Daniel has been to the glaciers in Antarctica, Austria, and Norway, and to snow fields in European mountain ranges. Whereas my snow algal research occurred in western and eastern North America including upstate New York — our backgrounds were very complementary,” Hoham says.

Work began in 2019, and the pair logged 1,000 hours writing the 19-page document. They drew heavily from research Hoham coauthored through the years with 37 of his Colgate students. “The ones in particular who worked in my research lab really made all of this happen.”

“This is one of the most extreme habitats on the planet,” Hoham says. “How are these things surviving?”

Ron Hoham, Colgate University Professor of Biology Emeritus

Studying snow and glacial ice algae is increasingly important to understanding the loss of glaciers, Hoham notes. To understand why, you have to understand the albedo effect: the tendency for snow to reflect solar radiation. The higher the albedo effect, the more sunlight is bounced away from Earth, keeping temperatures relatively cool. The lower the albedo, the more sunlight gets absorbed by the Earth, raising temperatures.

Since the colors of snow algae are all dark, they absorb heat when sunlight hits them and lower the albedo. (Put your hand on a black object that’s been sitting in the sun versus a white one, and you’ll get an immediate sense of what this means.) The more heat the algae absorb, the faster the surrounding snow and ice melts. Melting, in turn, spreads the algae, leading to yet more warming, meltwater, and blooms.

With increased temperatures from global warming putting more liquid water into the glaciers and snowfields, algal growth has been shown to accelerate the melting of glaciers by approximately 16–17%. One of the papers the team analyzed as part of the review pointed out that, when comparing one section of a glacier with dust particles to another with algae, the algae caused a 15% increase in melting versus the dust. (The results of these blooms can be dramatic, as in the media-famous “blood snow” incident: Antarctic glaciers that seemed to bleed in great pools and streaks of red.) Researchers now monitor these algal blooms through satellites and have tracked blooms like a 700-square-kilometer explosion of algae streaking an Alaskan glacier. The growth of these blooms is a troubling indicator of climate change.

Snow algae have attracted research interest for commercial reasons as well: selected strains produce astaxanthin, an antioxidant compound that produces the red color. “It’s one of the hottest things in the vitamin industry,” Hoham says. “There aren’t enough sources to grow it — these red-colored snow algae can’t be cultured yet.” Some types of snow algae also produce glycerol, a type of alcohol, and components of vitamin E. In addition, the cosmetic industry is looking at cultivating snow algae for use in skin creams, ostensibly to reduce wrinkles and restore collagen, though as yet no peer-reviewed research has come out on this.

More than anything, however, research on snow algae is helping us understand how life can thrive even in remarkably extreme environments. Thanks to new tools in molecular biology, it is apparent that “there are a lot more life forms in snow and ice than we knew even a few years ago,” Hoham says. Sometimes, all it takes to find them is tramping out across the white slopes when the snowpack starts melting, looking for the colors that blush and run beneath the blue sky.