Aspen, Chamonix, Zermatt, Kitzbühel, Whistler – there’s a long list of places it would be great to be having a winter holiday right now. Up there on the highest ski slopes, you wouldn’t think that those banks of pure, white, frozen snow would support anything much in the way of life. But come back in a few months for a trek among the melting snowfields and you could be in for a bizarre experience.
Walking across the snow, you might be alarmed to see behind you a trail of blood-red footprints. It’s not an omen of an impending appointment with the Grim Reaper, nor is it evidence that iron-bearing meteorites had landed here, as was once supposed. This is your first encounter with red snow.
The culprit is Chlamydomonas nivalis, a micro-alga that thrives in a brutal environment that is acidic, cold, contains few nutrients and is subject to repeated freezing and thawing. But the greatest danger it faces is scorching ultraviolet radiation, which explains the alga’s colour. It produces a red carotenoid pigment that acts as a sunscreen, filtering out light that could damage the cell, while letting in the wavelengths needed for photosynthesis. On top of that, the organism produces powerful phenolic antioxidants that help to neutralise damage caused by the UV.
Advertisement
The red algae spend most of their lives as metabolically active spores. You are most likely to see them in spring, when spores buried beneath the snow produce new cells which use their whip-like tails to migrate to the surface. Once there they quickly turn into bright-red spores to protect themselves from the UV radiation in the summer and the cold of the next winter.
Are snow algae more than a curiosity? Thanks to their ability to survive intense UV bombardment, they might one day provide us with a unique source of new medicines. The compounds such as carotenoids and phenolic antioxidants they produce for protection may prove a valuable source of pharmaceuticals targeted at anti-cancer, anti-microbial, anti-coagulant and anti-inflammatory treatments. Brian Duval of the Massachusetts Department of Environmental Protection in Worcester, Massachusetts, and a team from Australia collected snow algae in Antarctica last winter, and are now analysing them for potential drugs.
Even more unexpectedly, snow algae might be one of the missing sinks in the planet’s carbon budget. Bill Williams of St Mary’s College of Maryland and colleagues have hiked up into the Rockies in Wyoming in early July for the past three years. There they have measured light levels, carbon dioxide exchange and algae concentrations in the snow. Their conclusion: a square metre of snow can soak up as much as 5 grams of carbon each year.
Although this is only a small fraction of what fast-growing green plants can lock up, it’s important because summer snowfields cover large areas of the planet. So if you encounter those blood-red stains on the snow, remember it’s a healthy sign of life.