If you found yourself in the unlikely position of diving beneath the Arctic ice pack, you may notice what looks like a layer of dirt lining the frozen undersurface. Despite appearing lifeless, this green film is in fact very much alive – and not only that, but it’s also moving, a new study has found.
The colouration is caused by vast communities of microscopic algae known as diatoms. The new research, published in Proceedings of the National Academy of Sciences, reveals that despite previous assumptions, these organisms are not dormant when trapped inside ice.
Instead, the algae remain active and mobile, able to move at temperatures as low as –15°C, the lowest temperature ever recorded for movement by a eukaryotic cell – the complex cell type shared by plants, animals and fungi.
The researchers say that knowing the algae are mobile within the ice supports the theory that they help transfer resources through the Arctic food web, making them a vital component of one of the most hostile environments on Earth.
Moving through a frozen world
The research was carried out on a 45-day expedition through the Chukchi Sea – a marginal sea of the Arctic Ocean, located between Russian and Alaska.
With the aid of the research vessel Sikuliaq, the team collected ice cores from 12 research stations throughout the summer of 2023, then took them back to their on-board lab to take a closer look under custom-built microscopes. The samples revealed that the algae were indeed active within the ice.
The scientists then recreated icy environments with thin layers of freshwater and saltwater, replicating the micro-channels that form naturally as seawater freezes. Astonishingly, even under these controlled subzero conditions, the diatoms continued to glide.
“This is not 1980s-movie cryobiology. The diatoms are as active as we can imagine until temperatures drop all the way down to –15 C, which is super surprising,” says Manu Prakash, associate professor of bioengineering at Stanford University and senior author of the new research.
Lead author Qing Zhang, a postdoctoral scholar at Stanford, described the moment she saw them in motion: “You can see the diatoms actually gliding, like they are skating on the ice.”
Further experiments showed that their movements are powered by a secretion similar to mucus. “There’s a polymer, kind of like snail mucus, that they secrete that adheres to the surface, like a rope with an anchor,” says Zhang. “And then they pull on that ‘rope’ and that gives them the force to move forward.”
This mechanism relies on actin and myosin, the same proteins that drive human muscle contraction. Exactly how these molecular motors function in extreme cold is something the researchers want to study further.
The team also observed that these Arctic algae glide faster than their temperate relatives, suggesting an evolutionary adaptation to polar environments.
Engine of the Arctic food web
During their time in the Arctic, the team also sent a drone under the ice so see if they could learn any more about the algae.
“The Arctic is white on top but underneath, it’s green – absolute pitch green because of the presence of algae,” say Prakash. “In some sense, it makes you realise this is not just a tiny little thing, this is a significant portion of the food chain and controls what’s happening under ice,” adds Prakash, who says the algae could be fuelling ecosystems that support everything from fish to polar bears.
Researchers warn that shrinking sea ice and looming cuts to polar science budgets could undermine efforts to understand exactly what's going on.
“Many of my colleagues are telling me, in the next 25 to 30 years, there will be no Arctic,” says Prakash. “When ecosystems are lost, we lose knowledge about entire branches in our tree of life.”
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