French scientists have recorded a rise in Alpine snow turning from white to pinkish red, warning the colour shift could be a marker of accelerating climate change.
The Alps are covered with a thick mantle of white snow from winter to spring but as the slopes warm with the approach of summer, some mysteriously shift to turn various shades of orange, red and red.
Locals call the phenomenon “sang de glacier”, or “glacier blood”, while others dub it “watermelon snow”.
It has been observed for centuries, with Aristotle believing it was the work of "red and hairy worms" under the snow.
In fact, the pinker shade of white is caused by blooms of normally invisible algae.
French researchers say they change colour to protect themselves from ultraviolet light and that they may be proliferating due to global warming.
They have just published their preliminary findings in Frontiers in Plant Science.
“When you ski, you slide over these micro-algae,” said Eric Maréchal, the head of a plant physiology lab at Grenoble Alpes University and a leader of the project.
Algae are the foundation of most food webs
Credit: WILLIAM WEST/AFP
“But you don’t notice them because they are green and less numerous,” he told The Telegraph.
“They live off carbon dioxide and light. Then come bacteria that eat them.
“It’s when the sun’s rays become very strong, starting in May, that they create a shield of red molecules that play the same role as sun cream.”
He and experts from CNRS, CEA, Meteo France and Inrae, decided to try and work out how they survive and why blood glaciers have thrived in recent years.
To do so, they took samples from soil found in five peaks at various altitudes to create a snow bloom map.
“To date, and to our knowledge, no such systematic investigation has been attempted,” they said.
After studying their DNA, they found a variety of algae including one key blood-red type appropriately named Sanguina, which only grows above 2,000m (6,500ft).
Algae produce a large amount of the world’s oxygen through photosynthesis, and are present at the root of most food chains. However, in certain conditions they multiply wildly, causing toxic sludge, for example.
Here, the experts believe that the snow algae may be a marker of climate change for three reasons.
"The first is that the algae are photosynthetic and live off carbon dioxide, which is positive for them but causes an imbalance in nature," said Mr Maréchal.
"Second, all other blooms in nature, such as algae in lakes, are linked to human activity and emissions of nitrates and phosphates. We believe this is the case here and that they reach the snow in high altitude rather like acid rain."
"The third reason is that all mountain residents have noticed that whereas these blooms were pretty rare in the past, they are now observable every year."
The red algae’s rise could also hasten the shrinking of glaciers and snow caps, he said.
A swimmer heads towards a red algae bloom in Sydney
“Unfortunately, the red coloration favours the melting of glaciers by getting rid of the snow’s ‘albedo’ effect; it reflects the sun’s rays less, and heats up and melts more quickly,” said Mr Maréchal.
“In areas without glaciers, it shortens periods of snow cover with cascading consequences on (water) supply to dams, farming irrigation in the plains.
“It’s a paradox,” he went on. “The more the micro-algae multiply, the more they contribute to the disappearance of their own environment."
He said that his aim was not to scaremonger or dramatise the situation.
"Climate change is underway and as scientists, there is no point crying about it. Our job is to try and understand it as we are observing huge change in our lifetimes. I personally find these red blooms marvellous as it’s nature’s way of adapting."
The researchers have taken some species back to the lab to deepen their investigation into what triggers the blood-red blooms.
Mr Maréchal’s team is about to take fresh findings to see how they have been affected by large quantities of sand blown from the Sahara onto Alpine peaks due to particularly strong sandstorms this year.
There may be, however, a silver lining to the rise of such bloody snow algae, according to the researchers.
“Sanguina molecules are rich in antioxidants and could interest the health sector to fight against the ageing of cells or even energy to synthesise new fuels,” said Mr Maréchal.