Think Snow for the Supercoolers

Sometimes it seems a little odd to curse the sky for being cloudless, but I do. High-pressure systems hanging over the Interior have made for beautiful clear orange sunrises and sunsets lately, but I'm a snow fan, and we don't have enough to play on yet without transforming new skis into "rock skis."

Some organisms living in Alaska have greater concerns with a lack of snow than trashed ski bottoms. Snow's insulating capacity allows some life forms to survive life in the north.

Pat Holloway, an associate professor of plant sciences at the University of Alaska Fairbanks, lists lowbush cranberries and bearberries as examples of Alaska plants that need snow to make it through an Interior winter. She's frosted low bush cranberries in the lab and has found that they die when the temperature drops below about -12 degrees Fahrenheit. Since 12 below could easily be the high temperature during an Interior winter day, lowbush cranberries wouldn't survive without a warm blanket of snow.

Some trees have the ability to stand naked amid 50 below temperatures without dying. Holloway explained that trees are freeze tolerant, meaning they have adapted the ability to force liquid out of their cells so it freezes outside cell walls. Lowbush cranberries are believed to employ the method of supercooling, a process by which an organism has the ability to rid fluids in its body of impurities that trigger the formation of ice. Supercoolers, which are numerous and diverse, still can't live in temperatures under around 40 below. But plants such as lowbush cranberries and bearberries still survive.

"They really shouldn't be here, but they are because of snow," Holloway said.

Many insects and small mammals also have carved a niche in the north with the help of snow. Scott Armbruster, professor of biology with UAF's Institute of Arctic Biology, said Alaska would have many fewer bugs without snow.

"I think our diversity of invertebrates would be much, much lower," he said. "The presence of snow allows insects with an inadequate overwintering physiology to survive."

But what's so warm about snow? Just like a down jacket traps air around a body, snow traps air over the ground. Because air is a poor conductor of heat and cold, snow slowly releases the heat the earth captured in summer. According to Geophysical Institute Professor Emeritus Carl Benson, the ground/snow interface below a good snowpack in Interior Alaska is always about 27 degrees, even when the air temperature is 50 below.

The mechanism that provides the release of summer's heat is called the latent heat of water, Benson said. It seems counter-intuitive, but when water in the ground freezes, heat is released. That heat travels upward, fueling the relative warmth of the ground surface that snow helps trap.

Interior snow is also particularly good at trapping heat because it's a dry mixture of ice crystals and air. The large amount of pore space on each snow crystal--up to 80 percent of the volume--is filled with air. Older Interior snow is characterized by depth hoar, fingernail-sized crystals that form as a result of temperature differences within the snowpack. Brittle depth hoar allows small mammals, such as lemmings and voles, to easily tunnel through the snow and stay hidden from predators, Benson said.

Small mammals, skiers and snowmachiners and other snow worshipers should take heart, however. Murphy's Law dictates that after this column is mailed out, but before it's printed, we'll get dumped on.