‘Glacier blood’ in the Alps
Atop the French Alps, thousands of feet above sea level, the normally white snow sometimes appears stained with blotches of dark red blood, some of which extend for miles. The red stains, known as “glacier blood,” actually come from microalgae that live in the snow.
Much like the microalgae that inhabit oceans, lakes and rivers, snow-borne microalgae help form the base of the food web of a mountainous ecosystem and likely react to pollution and climate change in a similar fashion. In general, microalgae cells measure only a few ten-thousandths of an inch (thousandths of a millimeter) across, and they can exist as either isolated single-cell organisms or colonies. They produce sugars through photosynthesis, “and all the ecosystem eats that, directly and indirectly,” whether the algae grows in the liquid ocean or in compacted snow in the mountains.
The algae that turn snow red are technically green algae, as they belong to the phylum Chlorophyta and contain a specific form of chlorophyll, the green pigment that enables photosynthesis. However, in addition to chlorophyll, these algae also contain carotenoids, the same orange and red pigments that appear in vegetables like carrots. Carotenoids act as antioxidants and likely shield the algae from the damaging effects of intense light and ultraviolet radiation found at high elevations.
Studies suggest that the reddish snow reflects light less effectively than untarnished white snow and therefore melts fasterIt’s unclear whether, as with ocean-borne algal blooms, climate change and pollution will cause red snow to appear more frequently, potentially to the detriment of other organisms in the environment.
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