Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Dr. Jeff Havig and Professor Trinity Hamilton, researchers in Plant and Microbial Biology and Earth and Environmental Sciences at the University of Minnesota.

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Most guests to Yellowstone National Park visit during the summer, enjoying meadows hosting herds of bison and bounded by dense stands of Lodgepole Pine, and strolling boardwalks to see thermal features that are teaming with microorganisms thriving in the high temperature water that would cook other forms of life. Fewer guests are able to see the perennial snow fields that persist through the summer at the high elevations in and around the park. For those lucky few, they may notice colorful patches of pink to crimson on the surface of the snow. These colors are due to pigments produced by snow algae—single-celled organisms related to algae that live in lakes and oceans, but that have adapted to thrive in temperatures near freezing.

Cold-adapted microorganisms aren’t limited to just pink snow algae. There are also species of cyanobacteria (photosynthetic bacteria) that have adapted to the cold.  Cold-adapted snow algae and cyanobacteria can be found on glacial ice surfaces and can have colors of orange, green, brown, and grey—all the result of photosynthetic pigments used by the algae and cyanobacteria to harvest energy from the sun. In the ice and snow of alpine and polar regions, the primary limiting factor for the growth of the algae and cyanobacteria is the presence of liquid water. When temperatures are consistently below freezing, the algae and cyanobacteria go into hibernation to wait until warmer temperatures return. Thus, when visiting snowfields or glaciers during the winter, one will not see patches of pigmented colors, but late spring through to early fall are ideal times to watch for “blooms” on glacier and snow field surfaces.

One particularly good place for visitors to see patches of pink snow algae blooms is in the Beartooth Mountains located northeast of the Northeast Entrance of Yellowstone National Park, near Silver Gate, Montana. It is worth a drive to visit Beartooth Pass on Highway 212, which, at an elevation of 10,947 feet (3,368 meters), hosts many perennial snow fields (as well as beautiful alpine flowers, marmots and mountain sheep, and amazing vistas). Other places in Yellowstone National Park that visitors might catch glimpses of pink snow include snowfields on Mount Washburn/Dunraven Pass and the remote peaks in the northwest part of the park stretching from the White Peaks to Electric Peak.

Scientific research focused on cold-adapted algae and cyanobacteria has increased in recent years, driven in part because little was known about what was causing these blooms: what nutrients (such as phosphorous, nitrogen, and carbon) are feeding the blooms, and why do blooms happen in different places and vary in intensity in different years? Furthermore, the pigments generated by the algae and cyanobacteria are darker than the white snow, and thus absorb most of the energy from the sun (this is why dark paved surfaces get incredibly hot in the summer).

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With increasing temperatures, there has been a precipitous increase in the melting of glaciers—from smaller alpine glaciers that serve as critical water sources through dry summers, to the massive polar ice caps in Antarctica and Greenland. Thus, any darkening of snow and glacier surfaces can further increase the amount of melt occurring. This effect has been documented for both alpine glaciers as well as the Greenland ice cap. As an example, one study of seasonal melt on alpine glaciers in Alaska found that snow algae contributed 11% of total melt. If we can better understand what drives blooms of cold-adapted algae and cyanobacteria, we can better understand the effects of blooms on melting of snow and ice.

Another interesting area of active research of cold-adapted algae and cyanobacteria is their presence and impact during times of global glaciation events, like the last glacial period that ended about 12,000 to 14,000 years ago and that had a strong expression in the Yellowstone region. Instead of being inhospitable for life, did cold-adapted cyanobacteria and/or algae thrive during glacial periods? Perhaps if visitors had come to Earth during those times, instead of a white planet, they may have seen a planet covered in patches of pink! Furthermore, Mars is currently a frozen planet covered with ancient glaciers. If life ever developed on the red planet, perhaps cold-adapted microorganisms became dominant as the surface cooled, and there might yet be evidence for such life locked away in the glaciers that still remain. Certainly fun possibilities to think about!

So, the next time you pass a field of snow or go skiing in the spring/summer, look for patches of pink (or green or orange) and marvel at the unique community of algae and cyanobacteria adapted to life hovering near the freezing point of water.