Frosty the Snowman famously came to life one day with the help of a magical silk hat. As recent research suggests, however, he and other snowmen might already be more "alive" than most people realize — even if they aren't dancing around with broomstick canes. That's because, regardless of how it's sculpted or adorned, snow itself is often surprisingly full of microbial life.
That includes snow that's been lying on the ground for weeks or months, but freshly fallen snow can teem with tiny creatures, too. Some microbes even play key roles in the formation of snowflakes long before they fall.
Although life generally depends on liquid water, a variety of organisms have evolved impressive techniques for surviving in snow and ice. They may wait for seasonal thaws, slow their metabolisms, produce antifreeze proteins or encourage the snow around them to melt. A few have been known to science for a long time, but many have only been discovered in recent years.
There is "watermelon snow," for example, whose pink or red color was documented centuries ago by Aristotle. It wasn't until the 19th century, though, that scientists realized it was caused by something alive in the snow. We now know it can be caused by a few kinds of algae, including Chlamydomonas nivalis, which is often found in mountains, polar regions and other places where snow lasts all year. The algae themselves are green, but they produce a red pigment as a defense against UV radiation. The pigment also reduces the albedo of snow, helping it melt and support more algae. The algae help other life inhabit snow, too, by serving as prey for creatures like ice worms, nematodes, rotifers and tardigrades.
Even if snow is pristinely white, it may still host a wealth of microbial life. That's what researchers recently found after looking for microbial DNA in snow samples from Northern Europe and North America. Published earlier this year in the journal Microbial Ecology, their findings reveal a hidden empire of bacteria, fungi and algae in seemingly lifeless snow. "I was just blown away by the biodiversity," co-author Shawn Brown, a professor of biology at the University of Memphis, told New Scientist.
Snow often carries microbes before it even reaches the ground, and in some cases it may not have formed without them. Like raindrops, snowflakes develop in the sky when water molecules cluster around some kind of nucleus. That could be a particle of dust or soot, but research suggests many snowflakes form around a bacterium of the species Pseudomonas syringae.
These bacteria float into the sky as moisture evaporates from foliage and soil, or they can just be whisked into the atmosphere by wind. Their surfaces have proteins that are highly effective at prompting water to freeze, so once they're up in a cloud, water molecules cluster around them, freeze and fall as precipitation. P. syringae is so helpful for snow formation that it's often used to create artificial snow for ski slopes, according to Micropia, a museum in Amsterdam dedicated to microbes.
There are also algae that live in glaciers and sea ice, as well as other ice-adapted microbes that remain shrouded in mystery or have yet to be discovered. Scientists have found intriguing hints of bacterial life in Antarctica, for example, in surface snow as well as in dark lakes sealed deep below an enormous ice sheet.
Many snow and ice microbes may play important ecological roles, but we still have a lot to learn about where they live, what they do and how they work. Unfortunately, some of these cold-adapted microbes may soon see their habitats transformed by human-induced climate change, which is widely melting ice and scrambling snowfall patterns.
Snow and ice would be beautiful even if they were lifeless, so their support of mysterious microbial communities is yet another reason not only to appreciate the world we've inherited, but also to do what we can to protect it. An extinction crisis increasingly threatens species around the planet, and unlike Frosty, vanishing wildlife can rarely promise to "be back again someday."