The secrets of the Alps’ strange red snow – BBC News

The secrets of the Alps' strange red snow

(Image credit: Bob Gibbons/Alamy)

Growing patches of coloured snow in the French Alps could be a sign of the impact climate change is having in the mountains.

It is a shocking, garish sight to come across on a peaceful mountainside. Hike high enough in the French alps during the late spring and early summer, and there is a good chance thatyou will come across some rather strange patches of snow among the grey limestone and stunted clumps of vegetation. This snow isn't white it's blood red.

The peculiar phenomenon sometimes known as blood snow is the result of a defence mechanism produced by microscopic algae that grow in the Alpine snow. Normally these microalgae have a green colour as they contain chlorophyll, the family of pigments produced by most plants to help them absorb energy from sunlight.However, when the snow algae grow prolifically and are exposed to strong solar radiation, they produce red-coloured pigment molecules known as carotenoids, which act as a sunshield to protect their chlorophyll.

While red snow algaehas been known for a long time (it is mentioned in a book published in 1819 as having been discovered during an expedition to the Arctic in 1818) it is still steeped in mysteries that scientists are attempting to unravel.

Just two years ago, botanists at Charles University, Prague, in the Czech Republic, identified an entirely new genus of microalgae that is responsible for causing red and orange snow in different parts of the world, which they named "Sanguina" in reference to the blood-red colour they produce. The researchers found forms of Sanguina algae that cause red snow samples from Europe, North America, South America along with both polar regions. A species of Sanguina that causes an unusual orange snow was also found in Svalbard.

Researchers discovered a new genus of algae called Sanguina that is responsible for the red snow in the French Alps above 2,400 metres (7,874ft) (Credit: ALPALGA)

It isn't the only type of microalgae responsible for red snow though. Several other types, such as Chlamydomonasnivalis and an algae found growing close to Antarctic penguin colonies called Chloromonas polyptera, also produce pigments to create red and pink stained snow.

But understanding more about red snow algae carries a significance far greater than simply explaining the existence of strange-coloured patches in the Alps and near the poles. Its appearance and disappearance are important markers of climate change and how it is affecting the delicate ecosystems where the algae are found.

According to Liane G Benning, professor of interface geochemistry at the German Research Centre for Geosciences in Potsdam, red snow is becoming more common due to global warming. "The rise in the atmospheric carbon dioxide levels increases the temperature, which leads to more snow melting," she says. "The moment there is liquid water on the snow, the algae start growing."

This increasing abundance of red snow algae may also be contributing to climate change too. The red pigment turns the snow surface dark, reducing the amount of light and heat it reflects back into space something known as the albedo effect. By trapping more of the Sun's heat, the snow melts even faster, allowing the algae to proliferate further. "There is a runaway effect in which the algae melt their preferred habitat," says Benning. "Its as if they are destroying their own house."

On a wider scale, the extra heat absorbed by the tinted snow can alter the temperature in the wider environment, speeding up the melting of snow packs and glaciers. One study estimated that over a single melt season, red pigmented algal blooms could reduce the snow albedo by 13%, suggesting it plays an important role in how the effects of climate change can be amplified within mountain environments.

Studies have shown red algal blooms occur on glaciers all over the world, from Antarctica to the Himalayas and in the Arctic. So one question that scientists like Benning and Eric Marchal, director of the Cell and Plant Physiology Laboratory in Grenoble, France, are keen to answer is whether red snow algal blooms are becoming more widespread and occurring more often.

One way of doing this would be to use satellite imagery to study the albedo-reducing effect of the red snow. A study using satellite imagery of snow fields on Fildes Peninsula on King George Island, off the coast of Antarctica, revealed that in January 2017, 26% of the snow was darkened by algae.

Although there is little widespread data to show if red algae are becoming more common globally, both Benning and Marchal believe they will occur more often as our planet warms, and this will need to be taken into account as scientists try to estimate what the impacts will be.

But even laying aside their role in climate change, scientists are unpicking other mysteries surrounding red snow.