2. Arctic tundra Flashcards
What area does the Arctic tundra cover?
Occupies 8 million km2 in northern Canada, Alaska and Siberia and extends from the northern edge of the boreal coniferous forest to the Arctic Ocean
What is the climate like in the Arctic tundra?
They become more severe as latitude increases
8/9 months of the year the tundra has a negative heat balance (loss of energy to the atmosphere)
Average monthly temperatures are below freezing and can reach -40
Mean annual precipitation is low
Describe the ground in the tundra:
Permanently frozen with only the top metre thawing during Arctic summer overlying a layer of permafrost
Describe the biodiversity in the tundra:
Biodiversity is low with few plants/animals adapted to the environment
Dwarf tree species present
What are the main features of the water cycle in the Arctic tundra?
- Low annual precipitation
- Small stores of moisture in the atmosphere
- Limited transpiration
- Low rates of evaporation
- Limited groundwater stores
- Sharp increase in river flow in summer
Describe low annual precipitation:
50-350mm per year
Most falls as snow
Describe small stores of moisture in atmosphere:
Leads to low temperatures and reduces absolute humidity
Why is there limited transpiration?
Due to sparseness of vegetation cover and short growing season
Why is there limited evaporation?
In summer the sun’s energy is used to melt snow, not for evaporation + soil is frozen
Why is there limited groundwater stores?
Permafrost is a barrier to percolation, infiltration, and groundwater flow
Why is there a sharp increase in river flow in summer?
The snow that has accumulated over summer melts, as well as the uppermost active layer of the permafrost – creates extensive wetlands that cannot be drained
How much carbon does the permafrost contain?
Globally estimated to contain 1600 GT of carbon
Why is there such high carbon content in permafrost areas?
Low temperatures slow down the decomposition of dead plant material
When is the largest flow of carbon?
Greatest in summer
Why is the flow of carbon greatest in summer x3?
- Active layer of permafrost thaws releasing CO2
- Plants grow rapidly so photosynthesis is concentrated
- Tundra plants input carbon-rich material into the soil which is decomposed and respired by microorganisms – emitting methane and CO2 (can also occur during winter when snow layer insulates microbes)
Describe NPP in the tundra:
NPP = 200 grams/m2/year which is very low
Is the tundra a carbon source or a carbon sink?
In the past can be described as a carbon sink but global warming has made it a carbon source
What evidence is there that the tundra is actually a carbon sink?
Although outputs of carbon from permafrost have increased, higher temperatures have stimulated plant growth and a greater uptake of CO2 + increased plant litter entering store
Perhaps still in balance???
What physical factors affect the flows and stores in the water cycle?
Temperature
Relief
Rock permeability
How does temperature affect the water cycle in the tundra?
- In winter when average temp below freezing :
water is stored as ice in permafrost
evapotranspiration is low - In summer:
the top active layer thaws and liquid water flows on the surface
millions of shallow lakes stud the tundra landscape
water can’t infiltrate the soil as permafrost not fully melted
some evapotranspiration
How does permeability affect the water cycle in the tundra?
Permafrost and crystalline rocks dominate the geology so permeability = low
How does relief affect the water cycle in the tundra?
Ancient rock surface underneath the tundra gently undulates (due to erosion and weathering) so minimal relief prevents drainage and contributes to waterlogging in summer
Where was oil and gas discovered in the Arctic tundra and when?
Discovered at Prudhoe Bay on the North Slope of Alaska in 1968
What challenges were posed by oil/gas extraction on the Northern Slope?
- Harsh climate
- Long periods of darkness
- Melting of permafrost in summer
- Remoteness
- Fragile ecosystem
Why was US so keen to drill from this area?
High global energy prices and govt policy to reduce oil imports
What investments occurred to carry out drilling in 1970s/1980s?
- Roads
- Oil production plants and gas processing plants
- Pipelines
- Power generators
What % of USA’s domestic oil production was supplied by the North Slope in the 1990s?
25%
What % of USA’s domestic oil production is supplied by the North Slope today?
6%
Why has there been a decrease in oil production on the northern Slope?
High production costs and massive growth of the oil shale industry in the US
What particular oil industry processes have resulted in the melting of the permafrost?
- Construction of settlements that diffuse heat directly into the environment
- Dust deposition along roadsides creates darkened surfaces that absorb more sunlight
- Removal of vegetation which prevents permafrost insulation
What have been the effects of the oil/gas industry on the carbon cycle?
- Permafrost melting releases CO2 (up to 40 million tonnes per year) and methane (up to 114,000 tonnes)
- Gas flares input carbon into the atmosphere
- Removal of tundra vegetation reduces photosynthesis and uptake of CO2
- Thawing soil increases microbial activity and CO2 emitted
Can’t be recovered from as slow-growing nature of tundra vegetation makes it difficult
What have been the effects of the oil/gas industry on the water cycle?
- Melting of snow/permafrost increases run-off and discharge increasing flooding = extensive wetlands and increased evaporation
- Strip mining of aggregates creates artificial lakes and disrupts drainage
- Roads disrupt drainage networks
- Water abstracted from rivers for industrial use reduces localised run-off
