The blame lies with an alga that turns red when it emerges on the surface and absorbs the Sun's heat: the last snow on earth could therefore be red
With the cold weather, the first snow is coming to the Alpine areas. We will have to wait until spring for it to melt. And that may reveal a surprise: red-colored snow. The culprit is algae, or specifically three genera of algae: Coenochloris, Chloromonas, and Chlamydomonas.
The role of algae
This is a natural phenomenon, found as far back as Aristotle's time. These types of green algae live in the deepest layers of the snowpack, where there is ice. When in summer the snow and ice melt and move downstream, the algae emerge on the surface: in the meantime, as plants, they activate the process of photosynthesis.
When they reach the surface they turn red, coloring even the snow. This is because it activates a molecule called astaxanthin, similar to the one that makes carrots orange: the algae produce it because it serves to protect them from sunlight. In fact, it absorbs UV light, warming organisms and melting the surrounding snow.
Why Red Snow is a Problem
Although a completely natural phenomenon, now that glaciers are melting red algae are becoming problematic. In short, the algae are causing glaciers to melt faster: last year they reduced the amount of light (and therefore heat) reflected from some glaciers in Scandinavia by 13%. That means the glaciers warmed up a full 13% more, because unreflected light is absorbed.
The same is true in the Arctic, where the permafrost is already obscured by dust, soot and ash, which speeds up melting, plus leaves nutrients for algae on the surface, which in turn reduces the amount of ice. "It spreads faster than people realize, once it settles in," said Roman Dial, a biologist at Alaska Pacific University.
Recently, Dial and his colleagues conducted an experiment on these algae: they set up a large plot on a layer of ice, dividing it into squares. They flooded some squares with normal water, which increased algae growth by half, and others with nutrient-rich water, which increased growth fourfold. Then they assessed the density of snow in each square, measured how much the ice surface had subsided, and calculated how much snow the algae were melting. The more algae there was, the more the ice melt increased: seventeen percent of all the water that was melting came from snow with algae, a pretty high number.
Scientists have been studying these algae for years because they could make life develop on other icy planets. In cold ecosystems, they become a food source for certain microorganisms: in Iceland, tardigrades; in Chile, stoneflies; in the Himalayas, wingless midges; and in Alaska, ice worms.