What goes on under the snow?

Photo by Chuck Lindsay, National Park Service Iceworms in the Harding Icefield are one of several organisms that thrive in ice and snow on the Kenai Peninsula.

Subzero temperatures and a blanket of snow can make the Kenai landscape appear to be biologically quiet during the winter, aside from highlights such as the appearance of animal tracks across a frozen lake, or the swoop of an owl in the trees. Just above and beneath the snow surface, however, is a hotbed of winter activity. Physical processes, such as freezing, thawing, compaction, melting, and erosion, are referred collectively as nivation, derived from the Latin word for snow, nix. The snow surface right down to the subnivean base contains an active biological community with some unique and complex life processes.


Within each layer of snow or ice, from the surface, to sub-surface layers, down to the ground level, various creatures find their niche to function throughout the winter. Snow is coldest in the 18 inches near the surface, and warmer closer to the ground. Snow may be cold, but it has impressive insulation properties. Snow that falls and remains on unfrozen soil can prevent the soil from freezing, and the subnivean temperature remains around 32 degrees regardless of air temperatures once the snow pack exceeds six inches.

Snow mold is a fascinating organism that lives below the snow layer on frozen ground. These cold-loving fungi feed on remnant plant material, and flourish under prolonged snow cover. Snow molds are active just above freezing temperatures in moist conditions. The insulating effect of persistent snow cover facilitates growth and survival of fungal colonies. Optimal conditions for snow mold activity occur when snow falls suddenly and remains on ground that has not yet frozen, so we may see a lot of it on lawns when the snow melts this spring.

The gray snow mold, white to gray in color, is most common in Alaska, but there are also pink snow molds. In summer, snow molds survive under the ground as sclerotia, a thick protective fungal mass. In some areas, damage from snow molds cause serious agricultural or horticultural problems on lawns and commercial crops. Here in Alaska, they tend to be minor spidery threads that disappear soon after the snow does.

A common phenomenon around the Kenai is the appearance of red snow or watermelon snow, caused by the presence of snow algae. Despite the pink color, snow algae is actually a species of green algae which contains a secondary red carotenoid pigment. Described as having the scent of fresh watermelon, red algal blooms can extend to 10 inches beneath the snow surface. The reddish pigments absorb heat from the sun, which melts snow to provide water to the algae. Blooms tend to occur in the spring, when light (and meltwater) increase.  

In the depths of winter, the algal cells lie dormant under thick snow until the right light and temperature cues cause them to release smaller green flagellate cells that travel with their whip-like appendages to the snow surface. Once at the surface, the algal cells multiply and create large colonies, sometimes visible from the air. Nematodes, springtails, and iceworms are all known to feed on snow algae.

One of the biological treasures of the north is the iceworm — which is a real creature. Don’t feel bad if you thought the iceworm was the stuff of legend because, as Robert Service notes, “It is not strange that you should fail to know, since ice-worms are peculiar to the Mountain of Blue Snow.” Iceworms are annelid worms (just like earthworms) that spend their entire lives in glacial ice. They were first described on the Muir Glacier in southeast Alaska in 1887. Iceworms avoid the sun and will retreat under the ice before dawn.  If exposed to temperatures above 41 degrees, the worm’s membrane structures will liquefy.

Iceworms are only a few centimeters long and can be black, blue, or white. Iceworms have been found more than six feet below glacial ice surfaces.  How they tunnel through the ice is unknown. The leading theory is that they are able to detect microscopic fissures in ice sheets. Alternatively, they may secrete some kind of chemical which can melt ice by lowering its freezing point, like antifreeze. In addition to red algae, iceworms feed on pollen and other plant debris.

Snow fleas are another interesting bit of biota that can be seen jumping around the snow surface on warm winter days. These insects are not actually fleas, but are a springtail species with anti-freeze proteins that allow them to live in cold environments. Although they are present all year round, they are only really obvious when they cluster in large patches, often at the base of trees or on melt patches along streams, as they crawl out of their preferred leaf litter and moss habitats looking for food. They feed on bacteria, fungi, algae, pollen, and other plant matter, playing an important role in nutrient cycling in forests.

While winter time is far from the biological riot that is our Alaskan summertime, plenty of interesting and unique stuff is going on. The next time you find yourself out adventuring in the snow, see if you can find any of our nivean-dependent friends lurking about the frozen patches.

Dr. Elizabeth “Libby” Bella is an ecologist at Kenai National Wildlife Refuge. You can find more information about the Refuge at http://kenai.fws.gov or http://www.facebook.com/kenainationalwildliferefuge.