Snow alga may be sizable carbon sink. (Earth Science).

A common microorganism that adds color to some patches of snow may be a significant consumer of planet-warming carbon dioxide, researchers say.

The single-celled alga Chlamydomonas nivalis lends a reddish tinge to what's known as watermelon snow (SN: 5/20/00, p. 328). The microbe appears to be global. It's been found in New Zealand, Australia, Europe, and North America, says Thomas C. Vogelmann, a plant physiologist at the University of Vermont in Burlington.

C. nivalis often makes its living in an environment that's unusually harsh for photosynthetic organisms. It's typically found in snowfields above 2,500 meters, where levels of ultraviolet radiation are much higher than they are at sea level. Also, when the microbe is in a snowbank and thus illuminated from every direction, it can receive about three times the light that the upper surface of a leaf might get, says Vogelmann. Finally, temperatures in a snowbank, which don't rise much above 0[degrees]C, typically stifle photosynthesis.

Yet field experiments in the Rocky Mountains of Wyoming show that the organism can sop up significant amounts of carbon dioxide. Although gas-absorption rates varied greatly from one patch of watermelon snow to another, some snowfields with particularly high concentrations of the microbe consumed carbon dioxide about 10 percent as voraciously as green plants do. Because they're so widespread, these microbes could be significant players in the planet's overall carbon dioxide cycle. Vogelmann and his colleagues report their findings in the Jan. 21 Proceedings of the National Academy of Sciences.--S.P.