Arctic tundra

• The arctic tundra occupies 8 million km squared in northern Canada, Alaska and Siberia.
• For eight or night months a year the tundra has a negative heat balance, with average monthly temperatures below freezing.
• The ground is permanently frozen with only the top metre or so thawing during the arctic summer.
• Mean annual precipitation is low
• In winter, when for several weeks the Sun remains below the horizon, temperatures can plunge below -40 degrees.
• Long hours of daylight in summer provide some compensation for brevity of the growing season.
• biodiversity is low, and the ecosystem is treeless.
• Low annual precipitation (50 to 350 mm) with most precipitation falling as snow.
• small stores of moisture in the atmosphere owing to low temperatures which reduce absolute humidity.
• Limited transpiration because of the sparseness of the vegetation cover and the short growing season.
• Low rates of evaporation; much of the sun’s energy in summer is expended melting snow so that ground temperatures remain low and inhibit convection. Surface and soil water are frozen for most of the year.
• Limited groundwater and soil moisture stores; permafrost is a barrier to infiltration, percolation, recharge and groundwater flow.
• Accumulation of snow and river/lake ice during the winter months. Melting snow, river and lake ice, and the uppermost active layer of the permafrost in spring and early summer, results in a sharp increase in river flow.
• Extensive wetlands, ponds and lakes on the tundra during summer. This temporary store of liquid water is due to permafrost which impedes drainage.
• the permafrost is a vast carbon sink
• globally it is estimated to constrain 1600 GT of carbon.
• The accumulation of carbon is due to low temperatures which slow decomposition of dead plant material.
• the amount of carbon in tundra soils is fiver times greater than in the above-ground biomass.
• The flux of carbon is concentrated in the summer months when the active layer thaws.
• Plants grow rapidly in the short summer; long hours of daylight allow them to flower and fruit within just a few weeks.
• During the growing season tundra plants input carbon-rich litter to the soil.
• Net Primary Productivity is less than 200 grams per square meter a yea. Consequently the tundra biomass is small, ranging between 4 and 29 tonnes/ha depending on the density of vegetation cover.
• in the past, the permafrost functioned as a carbon sink. But today, global warming has raised concerns that it is becoming a carbon source.
• Even in winter, pockets of unfrozen soil and water in the permafrost act as sources of carbon dioxide and methane.
• snow cover may insulate microbial organisms and allow some decomposition despite the low temperatures.
• the activity of micro-organisms increases during growing season, releasing carbon dioxide to the atmosphere through respiration.
• the tundra biomass is small, ranging between 4 and 29 tonnes/ha depending on the density of vegetation cover.
• Average temperatures are well below freezing for most of the year so that water is stored as ground ice in the permafrost layer. During the short summer active layer (top metre) thaws and liquid water flows on the surface.
• meltwater forms millions of pools and shallow lakes which stud the tundra landscape.
• drainage is poor; water cannot infiltrate the soil because of the permafrost at depth. In winter, sub-zero temperatures prevent evapotranspiration. In summer, some evapotranspiration occurs from standing water, saturated soils and vegetation
• humidity is low all year round and precipitation is sparse
• Permeability is low owing to the permafrost and the crystalline rock which dominate the geology of the tundra in Arctic and sub-Arctic Canada.
• The ancient rock surface which underlies the tundra has been reduced to a gently undulating plain by hundreds of millions of years of erosion and weathering.
• Minimal relief and chaotic glacial deposits impede drainage and contribute to water logging during the summer months
• carbon is mainly stored as partly decomposed plant remains frozen in the permafrost. Most of this carbon has been locked away for at least the past 500000 years.
• low temperatures the unavailability of liquid water for most of the year and parent rocks containing few nutrients, limit plant growth. Thus the total carbon store of the biomass is relatively small.
• Low temperatures and water logging slow decomposition and respiration and teh flow of carbon dioxide to the atmosphere.
• Owing to the impermeability of the permafrost, rock permeability, porosity and the mineral composition of the rocks exert little influence on the water and carbon cycle.
• Melting is associated with construction and operation of oil and gas installations settlements and infrastructure diffusing heat directly to the environment
• melting is associated with the removal of the vegetation cover which insulates the permafrost