Watermelon snow

Watermelon snow on Mount Ritter in California

Watermelon snow, also called snow algae, pink snow, red snow, or blood snow, is a phenomenon caused by Chlamydomonas nivalis, a species of green algae containing a secondary red carotenoid pigment (astaxanthin) in addition to chlorophyll. Unlike most species of fresh-water algae, this species appears to be cryophilic (cold-loving) and thrives in freezing water.[1]

This type of snow is common during the summer in alpine and coastal polar regions worldwide, such as the Sierra Nevada of California. Here, at altitudes of 10,000 to 12,000 feet (3,000–3,600 m), the temperature is cold throughout the year, and so the snow has lingered from winter storms. Compressing the snow by stepping on it or making snowballs leaves it looking red. Walking on watermelon snow often results in getting bright red soles and pink trouser cuffs.

Snow algae dominates glacial biomass immediately after the onset of melting, and its pigmentation can significantly darken the surface of a glacier. This plays a substantial role in glacial melt.[2]

  1. ^ William E. Williams; Holly L. Gorton & Thomas C. Vogelmann (January 21, 2003). "Surface gas-exchange processes of snow algae". Proceedings of the National Academy of Sciences of the United States of America. 100 (2): 562–566. Bibcode:2003PNAS..100..562W. doi:10.1073/pnas.0235560100. PMC 141035. PMID 12518048.
  2. ^ Lutz S, Anesio AM, Raiswell R, et al. The biogeography of red snow microbiomes and their role in melting arctic glaciers. Nature Communications. 2016 Jun;7:11968. DOI: 10.1038/ncomms11968.