No, It Doesn’t Taste Like Watermelon
At some point or another, we have all probably been cautioned against consuming tainted (ahem, yellow) snow. It may be pretty, but it’s not tasty. Apparently, though, snow can take on other unexpected hues as well. In some snowy mountain regions, there have been reports of people sampling bites from patches of neon pink snow that they happen upon during hikes. These spots are commonly referred to as “watermelon snow.” Apparently, it does not taste like watermelon, and has nasty gastrointestinal side effects.
What is even more fascinating than the mere existence of pink snow is that it is caused by a green algae, most commonly Chlamydomonas nivalis. So how does a green algae turn white snow pink?
The algae are tiny, single-celled organisms that lie dormant during the winter months. When spring arrives, they germinate, which means that the dormant cells activate and release small, mobile green cells capable of propelling themselves through the snow with their flagella. These little guys make their living near the surface of the snow layer, consuming organic matter such as dead leaves.
Living near the crust of the snow pack at high altitudes means that C. nivalis cells are exposed to intense UV radiation. The higher the altitude, the less atmosphere to filter mutation-inducing UV. To protect themselves from harmful rays, C. nivalis secretes a mucosal substance as a kind of home-made sunscreen. This goo contains a red carotenoid, astaxanthin, in addition to the typical green chlorophyll found in most algae. (Interestingly, astaxanthin is the same pigment found in crustaceans, which provides flamingos with their brilliant plumage coloration).
So the pink color results from the algae’s endogenous UV protection mechanism, as the secretions leach into the surrounding snow and stain it a brilliant pink/red color. Apparently the pigment is so strong that it can stain your hands and hiking boots if you decide to play around in it.
It may seem to be awkward timing to discuss colored snow as we move towards summer, but C. nivalis and other “watermelon snow” species are cryophilic (cold-loving), and only inhabit areas that are cold enough to maintain snow cover all year round, such as the high peaks of the Sierra Nevadas. So, if you are planning a high-altitude vacation this summer, keep an eye out for pink snow! Pretty awe-inspiring to consider that the same substance that produces this alpine phenomenon is also responsible for the plumage of the flamingo, an icon of the tropics. From algae eking out a living in thin-aired, frozen landscapes to equatorial flocks of jewel-like birds, endless forms most beautiful.
Milius, S. 2000. Red snow, green snow. Science News 157: 328-330.
Mosser, J. L., A. G. Mosser, T. D. Brock. 2008. Photosynthesis in the snow: the alga Chlamydomonas nivalis (Clorophyceae). Journal of Phycology 12: 22-27.
Williams, W. E., H. Surface gas-exchange processes of snow algae. PNAS 100: 562-566.
(Image 1 via Wikipedia, Image 2 by Peter and Jackie Main)