Every spring, as the Arctic sun breaks months of darkness, life stirs in Greenland. Polar bears emerge, arctic terns return, and musk oxen migrate. And, amidst this awakening, algae on the ice begin to bloom, darkening the surface and accelerating ice melt. This phenomenon exacerbates global warming by reducing the ice’s ability to reflect sunlight.

But a team of researchers may have found a natural solution. Giant viruses discovered on the ice — at least 1,500 times larger than your typical cold-causing variety — could control these algae blooms, offering a potential way to mitigate ice melting. Postdoc Laura Perini from Aarhus University led this groundbreaking research.

A New Ally in the Arctic Ecosystem

Giant viruses can measure up to 2.5 micrometers, surpassing even some bacteria in size. Their genomes are also extensive, containing about 2.5 million base pairs, significantly more than the 100,000-200,000 found in bacteriophages (bacteria-targeting viruses). Despite their relatively large size, these viruses cannot be seen with the naked eye or even with a light microscope.

These viruses were first discovered in the ocean in 1981, infecting green algae. Later, they were found in soil and even humans. However, this is the first time they’ve been found in ice and snow environments dominated by algae. Researchers led by postdoc Laura Perini from the Department of Environmental Science at Aarhus University analyzed samples from dark ice, red snow, and melting holes, finding signs of active giant viruses in the dark ice and red snow.

Ice Melt Acceleration

Greenland’s ice sheet is the second-largest ice mass on Earth, after Antarctica, and plays a critical role in regulating global sea levels. Unfortunately, the ice sheet is experiencing significant melting due to rising global temperatures. A recent study published in the journal Nature revealed that the rate of ice melt is 20% higher than previously estimated.

One of the most affected areas is the Petermann Glacier in northwest Greenland. Research led by the University of California, Irvine and NASA’s Jet Propulsion Laboratory found that warm ocean water penetrating the glacier’s underside has significantly increased its melting rate. This phenomenon, occurring since the early 2000s, has resulted in the glacier thinning by about 140 meters (460 feet) over the past two decades.

The situation is equally dire at other major glaciers. For instance, the 79° North Glacier has been losing ice at unprecedented rates, with melt rates measured at 130 meters per year. Overall, the retreat of Greenland’s glaciers is happening “everywhere and all at once,” exacerbating global sea level rise. This widespread retreat is not merely a consequence of surface melting but is increasingly attributed to the complex interactions between ocean water and glacier bases. These interactions reduce the resistance glaciers face as they flow toward the sea, accelerating their disintegration​.

Ice Teeming with Microbes

The algae that darken the ice further accelerate melting by absorbing more sunlight. However, if these giant viruses indeed infect and regulate the snow algae, they could serve as a natural mechanism to control algae blooms, thus potentially reducing the rate of ice melt.

Perini and her team discovered these viruses by analyzing DNA and mRNA from ice samples. The presence of specific marker genes and the transcription of these genes into mRNA confirmed that the viruses are active. This indicates that the giant viruses are not only present but also functioning in the ice environment.

That’s highly remarkable — only a couple of years ago, the consensus was that this icy part of the world was barren and largely devoid of life.

Future Research and Questions

Many questions remain about the exact role and functioning of these giant viruses. Their ability to transcribe DNA into single-stranded mRNA makes them unique compared to regular viruses. However, the specific hosts they infect and their precise impact on the ecosystem are still unclear.

Perini’s ongoing research aims to uncover more about these interactions. Later this year, more findings on giant viruses and their role in the Greenland ice ecosystem will be published. The microbial ecosystem there is rich, including bacteria, filamentous fungi, yeasts, algae-eating protists, and of course giant viruses.

Understanding the biological controls on algal blooms is crucial for mitigating ice melt and, by extension, combating global warming. This discovery of giant viruses on Greenland’s ice sheet offers a promising avenue for future research and environmental management.

The findings appeared in the journal Microbiome.