Tundra and Permafrost
Arctic Tundra occurs in the far north of the northern hemisphere, north of the Taiga. Characteristically the subsoil to tundra is usually Permafrost, or permanently frozen ground. Any ground remaining at or below 0 C for two or more years is permafrost, it can be from less than one metre to up to 1,000 metres thick. Some of the permafrost in unglaciated Alaska and Siberia is fossil ice, a remainder from when the temperatures were some 11C degrees colder on average than they are now during the great glaciations of the Pleistocene.
The freezing and thawing of the top layers of the tundra give rise to some spectacular land forms, with frost wedges and patterned ground of many types including polygons and stripes, and solifluction where the soil flows slowly over the underlying frozen ground. And then there are Pingos.
Tundra plants
Conditions on the tundra make it particularly hard for trees to grow there, so the vegetation is low growing and capable of managing on the short growing season and the shallow soil of the ‘active layer’. There are tree species growing on tundra, but with the exception of Black Spruce which can tolerate the shallow soil and adverse conditions, they are mostly the dwarf forms of birch and willow. Because the tundra is often windy, the plants are low growing and by being perennial they have many years to build up a good tap root and have many summers to try to set seed, failure to do this in one season can be offset by success in the next. Cushion plants like the highly specialized Polar Poppy have dark green foliage and the temperature within the plant can be up to 20 degrees warmer than the surrounding air. The Arctic Avens has a flower that follows the sun, like a tiny parabolic reflector, ensuring that it makes the most of any sunlight available. The Saxifraga flagellaris doesn’t set seed but sends out spectacularly red radiating stems with new rooting runners on the end.
Winters on the tundra are dark and fairly cold and the summers are above zero C which melts the top layer of the permafrost leaving boggy pools on the surface in some areas, where the water cannot drain away through the frozen ground and evaporation is slow. These pools make perfect breeding grounds for all the insects and the migratory birds arrive as soon as the snows have almost melted. The tundra has a low level of biodiversity, with large numbers of a few species. The soil is low in nutrients with the exception of where it has been fertilized by animal droppings, under bird cliffs or ancient sites used by indigenous hunters where the soil is fertilized with blood and oil from the kills.
Tundra in the future
As our climate warms, larger plants are colonizing the southern edges of the tundra. The tundra is a major carbon sink, it is believed that as much as 1,000 gigatons of carbon could be tied up as plant material in the world’s permafrost, as the permafrost thaws with climate change, these plants will decompose, releasing the carbon dioxide, a greenhouse gas, that they are storing into the atmosphere.
Map of IPY tundra boreholes
Text © B & C Alexander |
