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An unexpected force may be speeding up glacier melt across the globe: colorful algae blooms


  • Pink, red, purple, and green algae blooms are growing on glaciers all over the planet.
  • Scientists who study snow and ice algae fear the blooms are a symptom of climate change.
  • Algae blooms can induce ice melt, hastening the catastrophic disappearance of the world’s glaciers.

Glaciers around the world are turning beautiful but menacing shades of pink, red, purple, and green.

Eric Maréchal has seen it firsthand in the European Alps.

About 20 years ago, as he trekked through the mountains, he would occasionally run into other scientists who were giddy about finding rare “blood snow” — an overgrowth, or “bloom,” of red algae that stains the glacier’s surface.

Maréchal said the blood snow started becoming more common about 10 years ago. Now he sees bright pink and red algae blooms every year.

alps pink snow italy glacier algae

Pink snow at the Presena glacier, in the Italian Alps, due to colonies of algae.


Miguel Medina/AFP/Getty Images



Much like soil, snow and ice are thriving with microorganisms.

Colorful blooms of microscopic algae have been documented on glaciers in nearly every continent. The “blood snow” algae has also been found in the Arctic, Antarctica, and mountains in both Americas.

Maréchal suspects snow and ice algae are on every glacier — vestige of a time when ice covered the planet, 20,000 years ago.

eric marechal smiling in the mountains holding up a sample tube of pink snow

Eric Maréchal shows a sample of microalgae near the Galibier peak, in the French Alps.


Philippe Desmazes/AFP/Getty Images



“It’s like the memory of the Ice Age, when the Earth was a snowball,” Maréchal, who studies algae at the French National Centre for Scientific Research, told Insider.

“We have the chance when they are blooming, that everybody who goes hiking can experience them. So it’s a wonder. At the same time, it’s a marker of environmental change, because when they are blooming, it means that there is a strong disturbance of the ecosystem.”

Algae may be accelerating the disappearance of Earth’s glaciers

man with pole stands next to bloom of green in a snowy field next to antarctica water mountains in background

Andrew Gray surveys blooms of green algae in Antarctica.

Dr. Matt Davey



Scientists like Maréchal think these algae blooms are getting larger and more frequent as rising global temperatures melt glaciers worldwide. This is still a hypothesis, as there is no historical data on glacier algae and scientists haven’t pinpointed exactly which nutrient or environmental condition is fueling the blooms.

But the researchers believe microalgae thrive in warmth and moisture.

hand scoops pink snow with tube

A researcher takes a sample of Sanguina nivaloides algae at the Brevent in Chamonix, France.


Denis Balibouse/Reuters



“The moment you have melting, the algae just are happy,” Liane Benning, who leads a research project called Deep Purple, funded by the European Research Council, told Insider.

Her team is working to build a historical record of Greenland’s purple ice algae, including how much it bloomed before humans began changing the climate.

helicopter flies over black snow

A helicopter flies above a purple algae bloom darkening the ice sheet in Greenland.

Dr. Pamela E. Rossel/GFZ German Research Centre for Geosciences, Potsdam



“They just need a little bit of water,” she added. “And they have a party. They go and bloom.”

liane benning blonde woman wearing disposable gloves holds up inspects a cylinder of ice against blue sky

Liane Benning examines an ice core in Greenland.

Courtesy of Katie Sipes



It may be a party for the algae, but it’s a slow funeral for the glacier.

Instead of the blinding white that reflects sunlight away from a glacier, algae blooms create vast patches of pink, red, purple, or even green.

Studies in the Himalayas, Greenland, Alaska, and across the Arctic have found that these colorful blooms darken the surface of glaciers, causing them to absorb more sunlight and leading to new ice melt.

satellite image shows snowy antarctica island with green algae blooms along coast

Satellite imagery shows green blooms of algae lining the coast of Robert Island in Antarctica.


Landsat/Copernicus/Maxar Technologies/Google Maps



“It’s like a runaway effect,” Benning said. “You make more algae; they bloom more; they melt more. They melt more; there is more blooms.”

They’re still gathering data to prove it, but if that runaway loop hypothesis is real, it’s probably accelerating as Earth’s glaciers disappear.

Already, the catastrophic impacts of ice loss are creeping across the planet — like sea-level rise and the dwindling of water sources that are usually replenished by glaciers. Those dangers could worsen faster than scientists have predicted, since their models don’t account for microalgae.

Glacier algae seems to be booming, but scientists have a lot to learn

man in winter clothes sinks pickaxe into green patch of ice

Researcher Matt Davey samples snow algae at Lagoon Island, Antarctica.

Sarah Vincent



The first written record of snow algae appears in writings from Aristotle, the ancient Greek philosopher, who described seeing the red snow on Mount Olympus.

It was another two millennia before someone took a sample of glacier algae for scientific research, Maréchal said.

two scientists squat in a field of pink snow on a mountain and take samples

Maréchal’s colleagues, Stephane Ravanel and Lucie Liger, take samples of red snow algae on Mount Olympus.

Eric Maréchal/AlpAlga



The algae species turning the Alps pink didn’t get a scientific name until 2019. Before that, it was mistaken for a different species.

“We are incredibly late. We are maybe 50 years behind the ocean sciences,” Maréchal said.

aerial image shows tents set up on dark grey black ice glacier

A Deep Purple research camp in Greenland, surrounded by an algae bloom, as seen from a drone.

Courtesy of Rey Mourot



But in the last couple of decades, as the algae have seemed to boom, so has research on them. Ice algae and snow algae are different types of microorganisms, and different fields of study, but they both affect glaciers.

“Most people when they go on a glacier and they look at that, they think it’s just dirt,” Benning said. “Only when we looked at them under the microscope, we realized: ‘Wait a moment, this dirt is moving.'”

purple algae microscope image little filaments

Purple algae from Greenland, imaged through a microscope.

Courtesy of Katie Sipes



Scientists have learned that the algae take on their colorful pigments in order to protect themselves from UV damage from the brilliant glare of sunlight reflecting off white snow.

But there’s still much to learn about these vibrant microalgae.

pink snow strip in the middle of black snow

A strip of “blood snow” filled with red algae cuts across a dark bloom of purple algae in Greenland.

Dr. Pamela E. Rossel/GFZ German Research Centre for Geosciences, Potsdam



“We still don’t know much about the fundamental ecology of snow algae,” Andrew Gray, who studies snow algae in Antarctica, told Insider in an email.

He added that the biggest snow algae mysteries include “where they are, why they are where they are, and how they’re likely to respond to warming.”

As glaciers disappear, so might this ancient algae

Both Greenland and the Alps saw record ice melt this summer.

melting glacier in valley between mountains aerial view

An aerial photograph shows the melting Sermeq glacier in Greenland.


Hannibal Hanschke/Reuters



In May, Maréchal’s team hiked up to the glaciers to take samples of the snow while it was still white. They needed a baseline to compare against later in the summer, once the red algae started blooming.

But when they reached their sampling site, expecting blankets of pure white snow, they found it was already pink with algae. When they returned a week later, all they found was bare earth. The snow had already melted away.

bare mountaintop with small remnants of snow in little crevices

A research site atop Mont Brévent, usually covered in seasonal snow through early July, lost most of its snowpack in May.

Eric Maréchal/AlpAlga



The trend continued later in the year.

“This summer proved to be extremely difficult, because the snowpack and glacier proved to melt at an accelerated pace,” Maréchal said.

The disappearance of glaciers is a compounding global catastrophe, with dire implications for our climate, sea levels, and water supplies.

Beneath all of that, if you zoom in to microscopic levels, global ice melt could also spell the disappearance of these ancient algae, which are likely the foundation of an under-researched ice ecosystem.

antarctica snow slope colored green yellow pink with algae

Multi-colored snow algae on Anchorage Island in Antarctica.

Dr. Matt Davey



Ice and snow are full of “bacteria, fungi, virus, cyanobacteria, algae,” and even insects, Gray said. Scientists don’t know enough about those ecosystems yet to understand what that loss could mean.

What if ice and snow microbes play a role in keeping glaciers stable, or pulling carbon from the atmosphere?

In some places, like one Italian ski resort, covering the glacier with reflective white material can slow its melt and counteract the snow’s color change. But that’s a Band-Aid solution.

mountain snow glacier covered in white sheets beneath ski lift

Large white geotextile sheets cover northern Italy’s Presena glacier in order to delay snow melting on skiing slopes and reflect sunlight during summer months.


Flavio Lo Scalzo/Reuters



“What can we do about these pesky algae? Everybody asks that question,” Benning said. “We should bloody stop changing the climate.”



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