The French Alps are covered in austere white snow from winter to spring. As summer arrives, it seems as if the slopes start to take a blush color. Parts of the snow take on bright colors: deep red, rusty orange, lemonade pink. Locals call this “sang de glacier,” or “glacier blood.” Visitors sometimes go with “watermelon snow” or “glacier blood.”
As one hopes that it is magic, it’s not, it comes from an alarming amount of algae. In recent years, the alpine habitats have experienced an increased spike of snow algae blooms. They’re normally invisible, but there has been a dramatic, strange hue to them.
Although snow algae blooms are not as well researched, signs of them is most likely not a good sign. Researchers have begun surveying the algae of the Alps to better grasp what species live there, how they survive and what might be pushing them over the bleeding edge.
So small yet powerful, algae are plantlike organisms that we refer to as “the basis of all ecosystems,” said Adeline Stewart, an author of the study who worked on it as a doctoral student at Grenoble Alpes University in France. Thanks to algae’s photosynthetic prowess, they are able to produce a large amount of the world’s oxygen, and form the foundation of most food webs.
However, algae may overproduce and keep multiplying until things go out of balance. As a result, it can cause toxic red tides, scummy freshwater blooms or unsettling glacier blood. Although it is unclear what exactly caused the blooms and the color, the hue of the algae absorbs a lot more sunlight which causes the snow to melt more quickly. If the snow is melting more quickly, it can change the dynamic of the ecosystem and quicken the shrinking of glaciers around the world.
Inspired by the growing reports of the algae bloom, researchers at several alpine institutes decided to turn their attention from algae species in far-away habitats to those “that grow next door,” said Eric Maréchal, the head of a plant physiology lab at Grenoble Alpes University and a leader of the project.
Because so many different types of algae can live and bloom in the mountains, the researchers began with a census in parts of the French Alps to determine which algae grows where. They took soil samples from five different peaks, spread over various altitudes, and searched for algal DNA. They found that many species tend to prefer particular elevations, and have most likely evolved to thrive in the conditions found there. One key genus, called Sanguina, grows only above 6,500 feet.
The researchers brought some species as well back to the lab to investigate their potential bloom triggers. Algae blooms occur naturally. The first written observation of glacier blood came from Aristotle, who hypothesized that the snow had grown hairy red worms from lying around too long.
Human-generated factors can worsen such blooms and make them more frequent. Extreme weather, unseasonably warm temperatures and influxes of nutrients from agricultural and sewage runoff all play a part in freshwater and ocean algae blooms. To see if the same was true for glacier blood, the researchers subjected the algae to surpluses of nutrients, like nitrogen and phosphorus. While they have not found anything significant so far, they plan to continue this line of testing, Dr. Stewart said.
The limits of DNA sampling mean that even this study gives an incomplete picture of what’s living in and under the snow, said Heather Maughan, a microbiologist and research scholar at the Ronin Institute in New Jersey. However, it revealed the “incredible diversity” of alpine algae and underscoring how little we know about them, as well as their potential to “serve as beacons of ecosystem change,” she said.
As time continues, researchers will keep track of how species distributions shift over time, which may shed light on the overall health of the ecosystem, Dr. Stewart said. They will also try to establish whether temperature patterns correlate with blooms, and begin to compare species compositions in white versus colorful snow. Eventually, they hope to determine the meaning behind the blood-red message.