Arctic Flashcards
climatic conditions
Climatic conditions in the tundra are severe and become more extreme with latitude. For eight or nine months a year the tundra has a negative heat balance with average monthly temperatures below freezing.
permafrost
Permafrost underlies much of the tundra and is an important feature of the region’s water cycle
In winter, when for several weeks the Sun remains below the horizon, temperatures can plunge below −40 °C.
Long hours of daylight in summer provide some compensation for brevity of the growing season.
Mean annual precipitation is low.
Few plants and animals have adapted to this extreme environment; biodiversity is low and apart from a few dwarf species, the ecosystem is treeless.
In the southern areas – the Low Arctic – conditions are less severe, and vegetation provides a continuous ground cover.
Further north in the High Arctic, plant cover is discontinuous with extensive areas of bare ground.
precipitation in tundr
Low annual precipitation (50–350 mm) with most precipitation falling as snow
water cycle in tundra
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 & 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. Also, 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 of 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.
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 & 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. Also, surface and soil water are frozen for most of the year.
carbon in tundra
The permafrost is a vast carbon sink.
Globally it is estimated to contain 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 five 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.
net primary productivity (NPP) is less than 200 grams/m2/year. consequently the tundra biomass is small, ranging between 4 and 29 tonnes/ha depending on the density of vegetation cover.
During the growing season tundra plants input carbon-rich litter to the soil. The activity of microorganisms increases, releasing CO2 to the atmosphere through respiration.
However, CO2 (and methane (CH4)) emissions are not just confined to the summer. Even in winter, pockets of unfrozen soil and water in the permafrost act as sources of CO2 and CH4.
Snow cover may insulate microbial organisms and allow some decomposition despite the low temperatures.
In the past the permafrost functioned as a carbon sink.
But today, global warming has raised concerns that it is becoming a carbon source. At the moment the evidence is unclear.
While outputs of carbon from the permafrost have increased in recent decades, higher temperatures have stimulated plant growth in the tundra and greater uptake of CO2.
This in turn has increased the amount of plant litter entering store. It is possible therefore, that despite the warming Arctic climate, the carbon budget in the tundra today remains in balance.
human activity effect
Oil and gas production and the carbon and water cycles in Alaska:
The North Slope of Alaska, between the Brooks Range in the south and the Arctic Ocean in the north, is a vast wilderness of Arctic tundra.
Oil and gas were discovered here at Prudhoe Bay in 1968.
From the start the development of the oil and gas industries on the North Slope presented major challenges: a harsh climate with extreme cold and long periods of darkness in winter; permafrost, and the melting of the active layer in summer; remoteness and poor accessibility; and a fragile wilderness of great ecological value.
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Despite the challenges, production went ahead, driven by high global energy prices and the US government’s policy to reduce dependence on oil imports.
Massive fixed investments in pipelines, roads, oil production plants, gas processing facilities, power lines, power generators and gravel quarries were completed in the 1970s and 1980s.
By the early 1990s, the North Slope accounted for nearly a quarter of the USA’s domestic oil production.
Today the proportion is 6 per cent though Alaska remains an important oil and gas province.
Decline in recent years reflects two things: high production costs on the North Slope and the massive growth of the oil shale industry in the USA.
