If you pull an ice core from the outer edges of the Arctic polar cap, you might spot what looks like a faint line of dirt. Those are diatoms - single-celled algae with outer walls made of glass. Their presence in ice isn't new, but because they seemed trapped and dormant, few bothered to study them.
But new research from Stanford, published Sept. 9 in Proceedings of the National Academy of Sciences, revealed Arctic diatoms aren't immobile or entombed. They're not just surviving either - they're gliding into the record books.
"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," said Manu Prakash, associate professor of bioengineering in the Schools of Engineering and Medicine and senior author of the paper.
That temperature (5 F) is the lowest ever recorded for movement by a eukaryotic cell - the type of complex cells in plants, animals, fungi, and more, defined by having a nucleus inside a membrane.
"You can see the diatoms actually gliding, like they are skating on the ice," said lead author and Stanford postdoctoral scholar Qing Zhang, who collected the samples during an Arctic research expedition. She and her colleagues demonstrated not only motility at such low temperatures, but also that their gliding - or skating - relies on a combination of mucus and molecular motors.
Navigating a bustling 'berg
The diatoms featured in this research resulted from a 45-day Arctic expedition in the Chukchi Sea aboard the research vessel Sikuliaq, which is owned by the National Science Foundation and operated by the University of Alaska Fairbanks. Researchers from the Prakash Lab and the lab of Kevin Arrigo, professor of Earth system science in the Stanford Doerr School of Sustainability, collected ice cores from 12 stations throughout the summer of 2023. Using a range of on-ship microscopes that the Prakash Lab has been developing for years, the team was able to image inside ice and document the secret lives of these incredible arctic diatoms.
Back in the lab, the team extracted diatoms from the ice cores and recreated their environments in a petri dish containing a thin layer of frozen freshwater and a layer of very cold saltwater. When ice forms in the Arctic, it kicks out salt, leaving freshwater ice with small microfluidic channels in it - so the lab also made channels in their ice, using their own hair.
Even as they lowered the temperatures of a special sub-zero microscope below freezing, the diatoms slipped through the strand-sized highways. Further experiments, using gels seeded with fluorescent beads, tracked their movements like footprints in sand.
The researchers developed and used special microscopes and experimental environments to track how the diatoms move through ice. | Prakash Lab
What's so surprising is the diatoms cruised along without wiggling, scrunching, or use of any appendages. Instead, they practice the art that many diatoms display: gliding.
"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 mucilage rope mechanism depends on actin and myosin - the same biological system that drives human muscle movements. How that machinery still works in subzero conditions is now a key research question the lab is pursuing. When the team compared Arctic diatoms with temperate relatives gliding along glass, the polar species moved much faster, hinting at an evolutionary advantage.
The bigger picture
The Prakash Lab made the most of their time in the Arctic and gathered an abundance of data on multiple projects, in addition to diatoms. That includes drone footage, taken under the ice, that vividly displays the potential of this work.
"The Arctic is white on top but underneath, it's green - absolute pitch green because of the presence of algae," said Prakash. "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."
The diatoms were gathered during an expedition aboard the research vessel Sikuliaq. During this trip, the researchers visited a dozen research stations and saw several polar bears. | Lexi Arlen, Stanford University
Knowing the diatoms are active raises broader questions about adaptation to a changing polar environment. Could they be moving resources through the Arctic food web, nourishing everything from fish to polar bears? Could their mucus trails even seed new ice formation, the way pearls form around grains of sand?
Normally, Prakash wouldn't show his hand when it comes to these kinds of nascent ideas, but the stakes this time are different, he said.
"Many of my colleagues are telling me, in the next 25 to 30 years, there will be no Arctic. When ecosystems are lost, we lose knowledge about entire branches in our tree of life," he said, noting 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."
