Resilient algae may speed up Greenland ice melt

The snow starts to melt. Flowers and plants break through the ice gasping for light. And the algae living on the ice sheet blooms, darkening the ice.

It's been like that for thousands of years.

But soon this may change. Spring comes earlier and earlier each year because of climate change and this could enable the algae to colonize larger and larger areas of the ice.

The algae contains brown pigment which darkens the ice. This, in turn, makes the ice melt faster, as its ability to reflect the sun diminishes when it's darkened.

This has been known by polar researchers for quite some time. But it was believed that the algae has limited capabilities of colonizing the ice, because of the lack of nutrients in this ice desert.

Until now.

New results published in Nature Communications show the algae are able to live off very few nutrients. And that they are able to store and save up energy. This makes it possible for them to colonize much more of the ice sheet than previously thought.

Laura Halbach, who recently got her ph.d.-degree at the Department of Environmental Science at Aarhus University, together with her research team is behind the discovery. Now a postdoc at the Max Planck Institute in Bremen, she continues unravelling the mysteries of the arctic ecosystems.

"My main goal with the trip to Greenland was to understand the mechanisms of the algae bloom formations. With new methods I was able to, as the first researcher ever, to measure the activity of single algae cells from the Greenland Ice Sheet. This led to the discovery of their ability to live off very few nutrients and to store up energy," she says.

The life of an ice alga

Ice algae are small single celled organisms. Elongated, brownish and ellipse shaped.

They thrive on ice surfaces around the world. They have been found on the Greenland ice sheet, in the Alps as well as on glaciers in the Himalayas and Alaska.

Like plants the ice algae releases oxygen through photosynthesis and produces organic molecules. It needs sunlight, water and CO2 as well as small amounts of phosphorus, nitrogen and carbon to survive.

During spring and summer the ice algae blooms creating large patches of darkened ice.

The ice sheet is teeming with life

Not that many years ago the Greenland ice sheet was thought of as a frozen desert. Desolate and almost devoid of life. But since the first researchers from Aarhus University and GFZ Helmholtz Center for Geosciences in Germany arrived in 2020, this has gradually changed.

Now we know that the ice is teeming with microbial life.

Expedition after expedition has revealed more and more of the secret life of the ice algae. One major breakthrough was the discovery that the algae is not alone. A whole ecosystem of microorganisms live on the ice: Bacteria, fungi and even viruses.

But this made it hard to do specific studies of the algae. When researchers scrape off samples of blackened ice, the petri dishes are filled with whole ecosystems. Until now the researchers have only been able to manipulate and test hypotheses on all of the microorganisms at once. And that was what Laura Halbach set out to change.

"If you melt a piece of the surface ice, you see these dark pigmented algae. But there are many organisms in the sample as well as snow-algae, other eukaryotic algae, bacteria and fungi. What is commonly done is to incubate the whole community. You give them a nutrient and measure the uptake in the whole community. But then it remains unclear what role the different organisms play."

Zooming in on single cells

Because Laura Halbach was interested in understanding the role of the ice algae in the ecosystem on the ice, she couldn't just isolate them. Instead, she fed the whole ecosystem marked nutrients. Minuscule isotopic traces that can be recognized by a machine called a mass spectrometer.

"You could say that we kind of labeled the food we gave them. This enabled us to see who ate what. Combined with a machine called SIMS, which is extremely precise, we were able to measure the nutrient uptake of single cells," Laura Halbach explains.

The data from the machine showed that the algae effectively consumed the small amounts of nutrients available -- and that they had some stored as well. Something that was completely unknown to the researchers.

"They are very efficient in taking up the limited nutrients on the ice. Furthermore we discovered that they have the capability of storing phosphorus, which is crucial for their metabolism.

Phosphorus is very limited on the ice. Some research suggests that it comes from local rocks containing minerals with phosphorus in them. When the rocks are turned into mineral dust by erosion, it's scattered across the ice and becomes available to the algae."

A game changer in understanding ice algae

Because the ice algae are able to store phosphorus, they can potentially colonize areas of the ice with very limited amounts of these nutrients. Thus the darkening of the ice might spread to larger areas than was previously thought possible.

"New ice is being exposed on Greenland every year, because the snow melts earlier and earlier. There used to be a thick snow cover all year round, but now large new areas of ice are being exposed to the sun. This opens up these areas for the algae to colonize and as they can live on very limited amounts of nutrients it might happen sooner than later."

Laura Halbach's discoveries are not only fascinating but also important, because the knowledge on the algae's nutrient requirements can help us to better predict their future role in the melting of the Greenland Ice Sheet. Today microbes are not yet integrated into most Earth climate models.

These new discoveries will hopefully be included in the climate models, making them more precise in predicting the melting of the ice in the years to come -- and how it will impact the global climate.