by The Rocky Mountains conjure up images of craggy, gray peaks covered in white. But in the upper reaches of harsh mountain landscapes, a pinker hue often blooms.
Watermelon snow, also known as glacial blood, is caused by algae that turns the snow a striking shade of red.
Algae bloom in summer and form in snowfields that persist on glaciers, frozen lakes, steep peaks, and frozen valleys in the upper parts of mountainous terrain.
The darker the snow, the faster it melts, and new research sheds light on the threat snow algae poses to shrinking glaciers in 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.
“We don’t really need more canaries in this mine, but they are another canary in the mine,” said Quarmby, a professor of molecular biology and biochemistry at Simon Fraser University.
“The loss of algae is just one indicator that we are losing snow and glaciers, and this will affect our lives and the lives of many other organisms.”
The study mapped the presence of snow algae in the mountains of Alberta, British Columbia and northern Canada, 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 blooms of red-pigmented algae contribute to the melting of glaciers. However, global warming poses a much greater threat to mountain glaciers and the surprisingly complex microscopic ecosystems that allow snow algae to colonize them.
“We started this study to look at the impact of climate change on these blooms and their impact on climate change,” Quarmby said.
“And I think the impact of climate change on them is clear and dramatic.”
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 the flowering of Chlamydomonas nivalis, which thrives at temperatures close to freezing point. Relying on photosynthesis, blooms act as carbon sinks, absorbing carbon dioxide from the atmosphere.
While closely related to the blue-green algae often seen in lakes, snow algae have a red pigment that allows them to survive in harsh mountain environments.
“The red pigment means that when they bloom they give the snow this red hue,” he said. “It’s called watermelon snow because it looks like the color of watermelon.”
A hiker holds a handful of watermelon snow, caused by snow algae. A new study examines the presence of blooms in North American glaciers. (Rick Bowmer/Associated Press)
The flowers darken the surface of summer snowfields, making them less reflective of the sun, causing the layer of snow and ice under the flowers to melt faster.
The red pigment creates a “positive feedback loop,” Quarmby said: The algae feed on the water released by the added heat.
The darker shade also acts as a “sunshade,” protecting the algae from sun damage, he said.
Quarmby and fellow SFU researcher Casey Engstrom set out to draw a large-scale map of microscopic ecosystems.
They found that between 2019 and 2022, red snow covered more than 4,214 square kilometers of glacial landscape, equivalent to 4.5 percent of the total study area.
Researchers estimate that the red snow contributed an average of three centimeters of meltwater per season.
“The impact of [the algae] “It’s 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 of the things we need to worry about.”
Snow algae were found on 4,552 of the 8,700 glaciers studied.
Some had just a spot, but many had huge flowers. For example, in 2020, algae covered nearly two-thirds of the surface of Alberta’s Bow Glacier in the Wapta Icefield.
Glaciers along the Pacific Northwest coast are typically filled with algae, but during the 2020 heat dome, the ice melted so quickly that blooms didn’t have a chance to develop.
Quarmby said as the snow begins to disappear amid rising temperatures, the algae will disappear as well. It will mean the loss of a valuable ecosystem that scientists are only beginning to understand.
“To me, it’s just another little sadness that we’re losing control. If you see these things under the microscope, they’re spectacular. Even if you just see them in the landscape, it’s impressive.”
A hiker walks through pink-hued snow at Tony Grove Lake on Wednesday, June 28, 2023, near Logan, Utah. (Rick Bowmer/Associated Press)
Scott Hotaling, an ecologist at Utah State University who studies biodiversity in cold, high-altitude environments, said the scope of the research is impressive. Hotaling was not involved in the SFU study.
Relying on satellite images, researchers were able to study glaciers that were previously inaccessible to science and collect large-scale data, he said.
Hotaling said the work provides an important basis for the impact of snow algae on retreating glaciers.
“As snow cover decreases, these blooms will become increasingly concentrated and smaller and smaller.
“The melting characteristics of those snow algae are going to become more and more important. When there’s only a small amount of snow left, anything that affects that matters more.”
