A still, quiet winter morning. Everything is asleep, on pause. I wish I could accompany this article with the smell and sound of that winter morning I’m talking about. Not the smell of brown snow and the sound of cars in town, I’m not that mean! No, rather the smell of a country morning, when a foot of fresh snow has fallen overnight. It’s an indescribable smell of cold and emptiness that tickles the nostrils. There’s a slightly mineral, even metallic touch, and the air seems dry, prickly, as if ice crystals were suspended in the air we breathe.
And the sound this morning! It’s a melody I can’t get enough of. At first sight, everything is silent, nothing moves. The silence seems deeper than any silence, as if the carpet of snow could absorb the slightest sound. Then you realize that this hushed ambience is actually made up of echoes. For the snow echoes the tiniest, most distant sounds, creating a soothing hum of air currents and the rustling of dry oak leaves still on the branches. It’s like resting your ear against a shell.
But this apparent tranquility hides a fascinating truth: under the snow, it’s a party! A silent, invisible party, of course, but a party nonetheless!
An Igloo For The Little Ones
Before we introduce you to our microscopic stars, it’s important to understand why snow is the perfect winter habitat. Contrary to what you might think, the temperature under the snow remains surprisingly stable, around 0°C (32°F). It’s like a natural igloo for animals and microbes.
Snow is full of little pockets of air that act as insulation, a bit like the layers of air we stack on top of our sweaters, jackets and coats. Even if it’s cold to the touch, snow and ice are so insulating that they create habitats that are well protected from the coldest weather. These are even heated naturally, either by the body heat of animals, or by other natural activities such as decomposition.
People living in the Far North have known this for millennia: even when it’s -40°C (-40°F) outside, the inside of an igloo can remain relatively comfortable. Why should a shrew’s tunnel be any different? There’s a good reason why many winter-active animals dig their habitats in the snow: it can be a “warmer” refuge than a natural cavity in rocks or tree trunks. In short, in your backyard, under the snow, there’s an active world, even in winter.
I’ve mentioned igloos and tunnels of small animals, but what I’m getting at is the even smaller life that affects the environment in winter. Organisms that you can’t even see with the naked eye, but which are essential to the balance of the ecosystem and the health of your flowerbeds.
Cold Weather Champions
Let’s start with psychrophilic fungi. Psychro means “cold-loving”, and these organisms don’t just tolerate freezing temperatures, they need them to thrive! Most of them grow best between 0°C and 10° (32 and 50°F), and some species can even remain active down to -20°C (-4°F).
The role of these fungi is to continue decomposing organic matter, even when everything is frozen. To achieve this, they have developed remarkable adaptations: their cell membranes contain more unsaturated fat than saturated fat, which keeps them supple even in the cold. Think of butter, which is a solid fat at room temperature, compared to oil, which is liquid. Proteins, too, are different: their entire composition is adapted to winter temperatures.
These champions of the cold are found everywhere: in the soil, on fallen leaves, even on conifer needles. Their work is essential: by decomposing organic matter throughout the winter, they release nutrients that will be immediately available to plants in spring.
Bacteria, Not To Be Outdone!
Some soil bacteria have developed adaptations worthy of the best science-fiction films. They produce antifreeze molecules similar to those found in the blood of Arctic fish… or in car windshield washer fluid! In the case of bacteria, these are antifreeze proteins that bind to the beginnings of ice crystals, preventing them from growing and tearing their cells apart.
Other bacteria enter a state of “active dormancy” (yes, I know, it sounds contradictory!). In this state, their metabolism slows down considerably, but doesn’t stop completely. They maintain just enough activity to repair cellular damage caused by the cold, and to quickly resume growth as soon as conditions improve. This strategy enables them to survive at temperatures that would kill most other organisms.
Like fungi, these bacteria are useful for winter decomposition.
Algae That Color The Snow
But my personal favorites are the algae that colonize the snow. These microscopic organisms live ON, not UNDER, the snow, so they’re exposed to the elements head-on. But the reason I find them so extraordinary is that these algae can literally color snow pink, green or even red! Colorful winter strips in sight?
These microalgae can not only survive on snow, but actively multiply in it, resulting in the coloration of large surfaces. These colors come from specialized pigments: carotenoids that protect their cells from the intense UV rays reflected by the snow, and modified chlorophylls that enable them to photosynthesize even at freezing temperatures. Depending on the species and pigment concentration, snow appears in different colors.
The life cycle of these microalgae is particularly well adapted to extreme conditions. In summer, they survive as spores in the soil. When winter arrives, these spores germinate and the algae migrate to the snow surface, where they multiply rapidly. They can even create their own micro-environment: their dark pigments absorb the sun’s heat, slightly melting the snow around the colony, and releasing the water they need.
Unfortunately, don’t expect to color your snowbanks with these algae, as they only live in very cold regions where snow is present for most, if not all, of the year. They can be found in the Arctic, Greenland, the Alps… In short, not really in the suburbs!
A Complex Ecosystem
These microorganisms don’t live alone. They form a veritable network under the snow. Fungi break down organic matter, releasing nutrients that bacteria use to decompose matter that the fungus does not. Algae produce oxygen and sugars, which also contribute to the cycle of winter species. It’s an icy mini-city where everyone has a role to play, and where exchanges are just as important and complex as in summer.
This microbial activity is crucial to our gardens. Without it, the nutrient cycle would come to a complete halt in winter, and our plants would have far less food available in spring. This tiny world is being extensively studied, and new species and adaptation mechanisms are constantly being discovered.
Even More
Recently, scientists have even discovered that microorganisms living on the surface of snow can significantly influence its melting speed. This phenomenon is particularly visible with coloured algae, but also with certain coloured bacteria and fungi (even if you can’t see them with the naked eye!). By multiplying on the surface, these organisms form colonies that modify the snow’s albedo, i.e. its ability to reflect light.
So what? Fresh, clean snow reflects up to 90% of sunlight. But when colonized by microorganisms, this reflectivity can drop to as little as 40%. The organisms’ dark pigments absorb the sun’s heat rather than reflect it back into space, creating warmer microzones on the ground that accelerate melting. This phenomenon can have a significant impact: in some Arctic regions, the presence of snow algae can accelerate melting by 13% to 21% compared with uncolonized snow. Think about it for a moment: that’s a huge effect for such tiny organisms!
Conclusion
The next time you’re looking at a snowy, calm, sleepy, still landscape… remember that underneath, it’s party time! (And now I feel bad every time I shovel or plow my car… S’cuse me, mushrooms!!)
I gad the pleasure of seeing “pink” snow in Antarctica just recently.
Wow! What were you doing in Antartica?
Fascinating.
Beautifuland poetic Audrey! And so interesting!
Fascinating, Audrey, thank you for this!