Scientists at Stanford have discovered that single-celled Arctic algae can actively move at temperatures as low as –15 degree Celsius (5 °F), the coldest motion ever recorded in a eukaryotic cell.
The finding challenges long-held assumptions that these diatoms lie dormant when locked in sea ice and suggests they may play a more dynamic role in polar ecosystems than previously understood.
“This is not 1980s-movie cryobiology. The diatoms are as active as we can imagine until temperatures drop all the way down to -15 degree Celsius, which is super surprising,” said Manu Prakash, associate professor of bioengineering and senior author of the study.
Diatoms, algae encased in glass-like shells, have long been seen as a faint, dirt-colored line in Arctic ice cores. Their presence was known, but they appeared trapped and immobile, and so drew limited attention. The new work overturns that picture.
“You can see the diatoms actually gliding, like they are skating on the ice,” said lead author Qing Zhang, a Stanford postdoctoral scholar who collected samples during an Arctic expedition.
The team showed that this gliding persists down to –15 degree Celsius, setting a new benchmark for cellular motility in complex, nucleus-bearing organisms.
Coldest-known motion in complex cells
The discovery stems from a 45-day expedition in the Chukchi Sea aboard the research vessel Sikuliaq in the summer of 2023. Researchers from the Prakash Lab and the lab of Kevin Arrigo, professor of Earth system science, extracted ice cores from 12 stations and used a suite of microscopes developed by the Prakash Lab to image inside the ice.
Back in the lab, they recreated the diatoms’ environment with a thin layer of frozen freshwater over very cold saltwater, mimicking the natural micro-channels that form because sea ice expels salt as it freezes. To approximate those strand-sized pathways, the team fashioned channels in ice using human hair.
Using a special sub-zero microscope, the researchers watched the algae slip through these ice highways without thrashing, scrunching, or using visible appendages. In complementary tests, they embedded fluorescent beads in gels to track movement “footprints,” confirming directed gliding rather than passive drift.
Compared with temperate relatives observed gliding on glass, the Arctic species moved much faster, hinting that cold-adapted motility could offer an evolutionary advantage in polar ice.
How “skating” works in extreme cold
The motion is powered by a well-known diatom strategy. Gliding on self-secreted mucus. “There’s a polymer, kind of like snail mucus, that they secrete that adheres to the surface, like a rope with an anchor,” said Zhang. “And then they pull on that ‘rope’ and that gives them the force to move forward.” The “rope-and-winch” mechanism depends on actin and myosin, the same molecular motors that drive human muscle contractions.
That this machinery remains functional in subzero conditions raises new biophysical questions the team is now pursuing, including how proteins and polymers maintain flexibility and force generation when water is largely frozen.
Implications for a changing Arctic
Beneath the seemingly white Arctic surface lies “absolute pitch green because of the presence of algae,” Prakash said, highlighting how widespread these organisms are under the ice. If diatoms are actively moving at extreme cold, they may be redistributing nutrients and energy in ways that ripple through the food web, from microbes to fish and, indirectly, to top predators like the polar bears.
The team also points to speculative but testable possibilities, such as whether mucus trails could serve as nucleation points for new ice formation, much as pearls form around grains of sand. The stakes for understanding these processes are high. “In some sense, it makes you realize this is not just a tiny little thing, this is a significant portion of the food chain and controls what’s happening under ice,” Prakash said.
He added that “in the next 25 to 30 years, there will be no Arctic,” and noted that severe projected budget cuts to the National Science Foundation are predicted to reduce polar research funding by 70 percent. “I feel a sense of urgency in many of these systems, because, at the end of the day, the infrastructure and capacity to be able to operate is critical for discovery.”
The study has been published in Proceedings of the National Academy of Sciences.