Microclimates

Warmth from this plant has increased the ambient temperature, thus melting the snow around it.
Climate varies from place to place across the Arctic. Temperature, especially, alters with ups and downs of the terrain, with time of day, and with varying amounts of sunshine and wind speeds. Get close enough to measure the temperature around individual plants or animals and you will find that the readings differ yet again. On that scale, you would be measuring microclimate, the physical environment of a single plant or animal. Animals change their microclimate whenever they move from one place to another.

Hummocks on the tundra create differing microclimates. Cracks between the humps provide warm shelters to small plants and animals.
In a microclimate, very small changes can make a big difference to survival. Only a few centimetres above the ground, temperature and humidity can vary widely due to the sun's height, exposure to direct rays, and radiation reflected from the ground and atmosphere. Within millimetres of the surface, sheltered plants and invertebrates may not even be affected by a strong wind.

 

Even on a small scale, temperatures can vary with differences in slope, direction, and composition of surfaces.
Sunny Side Up

On the ground or snow surface, just a little more sunshine can alter the microclimate, especially when the temperature is near freezing. In spring, exposed rock and snow surfaces may warm or cool quickly as the sun appears and disappears behind clouds. The melting and evaporation of snowflakes as they land on a rock may also reduce the surface temperature. Sunlight can warm slivers of ice between rocks just enough to melt the ice and allow moss and lichens to grow. A small slope directly facing the sun might be warmer than level ground nearby. In sheltered pockets where air is confined, the rock and the air might both warm more quickly than nearby exposed surfaces.

Snow Sanctuary

A higher albedo (fraction of light that is reflected) makes temperature changes on a snow surface more gradual than on rock. Still, snow offers microclimates for organisms; it is warmest just below the surface, where algae may live in air pockets and even form patches on melting surfaces. Snow that has been windswept into a sastrugi – where the surface has become rippled – can provide more sheltered conditions in the "valleys" between the ridges. Under the snow, temperatures are often higher and more stable than above, even in the High Arctic, where temperatures are well below freezing at the snow surface.

Older snow has a lower albedo than fresh snow. Overwintered snow may absorb enough sunshine and begin melting in early spring before the air temperature has climbed above freezing. Winter snowfields and lake ice may also begin thawing early, allowing algae near the surface to renew its growth. Pockets of frozen sand that thaw early can make tiny areas of meltwater available for algae and soil organisms.


A sastrugi.