algae black Greenland ice

The algae blackens the ice. When that happens the ice reflects less sunlight and melts faster. Several areas in Greenland are covered with black algae. (Photo: Laura Perini)

Scientists believe snow algae blooms could actually be protecting Arctic ice from melting

AARHUS, Denmark — The Arctic is a vast, icy landscape that’s shrouded in darkness for months at a time. As spring arrives, the Sun’s warm rays breach the horizon, signaling a grand awakening of the local wildlife. However, there’s another, less visible stirring happening right beneath the ice — one that could have a profound impact on our planet’s future. Scientists say they have discovered “giant” viruses infecting snow algae on the Greenland ice sheet. While this may sound disturbing, researchers from Denmark say it may actually protect this region from melting away!

A team from Aarhus University explains that as the spring sun intensifies, algae that have been dormant through the long, dark winter begin to bloom. However, this isn’t your typical spring bloom. These algae, known as snow algae, are turning large swaths of the pristine white Greenland ice sheet into a disconcerting black.

Why is this a problem? Well, the study published in Microbiome explains that it all comes down to a concept called albedo — the ability of a surface to reflect sunlight. White ice is excellent at reflecting the Sun’s rays back into space, helping to keep our planet cool. But when algae bloom and darken the ice, it absorbs more heat, causing it to melt faster. This accelerated melting contributes to global warming, creating a vicious cycle: more warmth leads to more algae, which leads to darker ice, which leads to more melting, and so on.

But nature, in its infinite wisdom, may have provided a solution in the most unexpected of places: viruses. Not just any viruses, though — we’re talking about giants.

Discovering the black ice virus

Laura Perini, a postdoctoral researcher at Aarhus University’s Department of Environmental Science, has been studying the Arctic ice alongside her colleagues. What they’ve discovered is astonishing: giant viruses living right alongside the algae. These aren’t your run-of-the-mill viruses; they’re behemoths in the microbial world.

“We don’t know a lot about the viruses,” Perini explains in a media release, “but I think they could be useful as a way of alleviating ice melting caused by algal blooms. How specific they are and how efficient it would be, we do not know yet. But by exploring them further, we hope to answer some of those questions.”

One of the samples in which Laura Perini found giant viruses. At first glance it looks like dirty water, but the bag is teeming with microorganisms, one of those being the ice algae that darkens the ice.
One of the samples in which Laura Perini found giant viruses. At first glance it looks like dirty water, but the bag is teeming with microorganisms, one of those being the ice algae that darkens the ice. (CREDIT: Laura Perini)

So, what exactly are these giant viruses? Typically, viruses are incredibly tiny — about 1,000 times smaller than bacteria. A regular virus measures between 20 to 200 nanometers (a nanometer is one-billionth of a meter), while a typical bacterium is two to three micrometers (a micrometer is one-millionth of a meter).

These massive viruses, known as nucleocytoplasmic large DNA viruses (NCLDVs), however, break all the rules. They can grow up to 2.5 micrometers in size — larger than most bacteria! It’s not just their physical size that’s impressive; their genetic makeup is equally gigantic. While bacteriophages (viruses that infect bacteria) have between 100,000 and 200,000 letters in their genome, giant viruses boast around 2.5 million. That’s a lot of genetic information!

These oversized viruses were first discovered in 1981 in the ocean, where they specialized in infecting green algae. Since then, they’ve been found in soil, and even in humans. But this is the first time they’ve been spotted in the Arctic’s icy realm.

‘Viruses are living and active on ice’

So, how did Perini and her team find these viruses if they’re too small to see with the naked eye? The answer lies in DNA analysis. Researchers collected a variety of samples from the Greenland ice sheet during two field campaigns in 2019 and 2020. These samples included cryoconite (tiny granules of rock and microbial life), dark ice, ice cores, and colorful patches of red and green snow. The team also analyzed genomic data from five cultivated snow algae species.

Using state-of-the-art sequencing techniques and bioinformatics tools, the researchers meticulously searched for the presence of NCLDV marker genes in the collected samples. These genes serve as unique identifiers for giant viruses and provide insights into their diversity and evolutionary relationships.

The results of the study were nothing short of remarkable. NCLDV marker genes were found in almost all the samples, with the highest abundance in red snow, followed by genomic data from snow algae, green snow, and dark ice. The researchers discovered an impressive variety of active algae and protists in these habitats, suggesting that giant viruses have the potential to infect a wide range of eukaryotic hosts.

“We analyzed samples from dark ice, red snow, and melting holes (cryoconite),” Perini says. “In both the dark ice and red snow we found signatures of active giant viruses. And that is the first time they’ve been found on surface ice and snow containing a high abundance of pigmented microalgae.”

Laura Perini hasn't seen a giant virus in the microscope yet. But it's not impossible. Here it's some of the other microorganisms from Greenland.
Laura Perini hasn’t seen a giant virus in the microscope yet, but it’s not impossible. Here are some of the other microorganisms from Greenland. (Photo: Laura Perini)

To ensure these weren’t just remnants of long-dead microorganisms, they also looked for mRNA — a type of genetic material that breaks down quickly and is a sign of current activity. “In the total mRNA sequenced from the samples, we found the same markers as in the total DNA,” Perini says. “It means that the viruses are living and active on the ice.”

Biological climate shield

Not long ago, scientists thought this part of the world was lifeless. Now we know it’s teeming with microorganisms, including these giant viruses.

“There’s a whole ecosystem surrounding the algae,” Perini explains. “Besides bacteria, filamentous fungi, and yeasts, there are protists eating the algae, different species of fungi parasitizing them, and the giant viruses that we found, infecting them.”

Part of the Greenland Ice sheet with blackened ice caused by algae
Part of the Greenland Ice sheet with blackened ice caused by algae. (Credit: Shunan Feng)

This discovery in the Greenland ice sheet is groundbreaking because giant viruses are quite different from their smaller cousins. Normal viruses can’t transcribe their DNA into mRNA — the “recipes” for making proteins — on their own. Instead, they hijack a host’s cellular machinery to do it for them. Giant viruses, however, can handle this task independently, making them unique in the viral world.

The presence of giant virus signatures in snow algae genomic data indicates that these viruses have likely co-evolved with their algal hosts over time. This close relationship raises intriguing questions about the potential impact of giant viruses on the growth and survival of algae in these extreme habitats.

While there’s still much to learn about these giant viruses — like which specific hosts they infect — the implications are exciting. If these viruses naturally feed on the snow algae, they could act as a biological control, keeping the algal blooms in check. This, in turn, could help maintain the ice’s reflectivity, slowing its melt rate and mitigating some effects of global warming.

StudyFinds Editor Chris Melore contributed to this report.

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