Arctic tundra case study Flashcards
Where is the arctic tundra located? Give some general information
8 million km2 area in northern Canada, Alaska and Siberia
Climatic conditions severe and become more extreme with latitude
8-9 months a year - negative heat balance (average monthly temperatures below freezing)
In winter for several weeks there is no sun (polar night) - temperatures reach below -40°C
Ground permanently frozen (permafrost) - only top meter thaws during during the summer - permafrost underlies much of the tundra and is an important feature of its water cycle
Low mean annual precipitation (50-350mm)
Low biodiversity as few plants and animals are adapted to such extreme conditions - apart from a few dwarf species the ecosystem is treeless - low vegetation provides continuous ground cover in southern arctic, very discontinuous plant cover and extensive areas of bare ground in northern Arctic
Describe the water cycle in the arctic tundra
Low annual precipitation (50-350mm) - low humidity due to low temperatures and limited evapotranspiration - sparse vegetation and short growing season
Low rates of evaporation - much of the sun’s energy is used to melt snow - ground temperatures remain low and inhibit convection - surface and soil water frozen for most of the year
Low groundwater and soil water storage - permafrost is very largely impermeable - barrier to infiltration, percolation, throughflow, groundwater recharge
Sharp increase in river flow (streamflow) in summer due to river/lake ice, snow and uppermost layer of permafrost melting
Extensive wetlands, ponds and lake during summer due to permafrost impeding drainage
Describe the carbon cycle in the arctic tundra
Permafrost is a vast carbon sink - globally estimated to contain 1600 gigatonnes of carbon - due to low temperatures slowing decomposition - amount of carbon in tundra soils 5 times greater than above-ground biomass
Flux of carbon is concentrated in summer months when the active layer thaws - plants grow rapidly - long hours of daylight allow flowering and fruiting within a few weeks
Very low NPP - 200g/m2/year - small biomass between 4 and 29 tonnes/ha depending on cover
During the growing season plants input carbon rich litter into the soil, leading to microorganism activity, releasing CO2 into the atmosphere through respiration - some in winter due to pockets of unfrozen soil and water and microorganisms insulated by snow cover (allowing decomposition to still occur)
In the past the permafrost has acted as a carbon sink - global warming raised concerns that it is becoming a carbon source - as permafrost melts stored CO2 and CH4 (greenhouse gases) are released into the atmosphere - positive feedback. Evidence of this is unclear - higher temps may also stimulate plant growth - greater uptake of CO2 via photosynthesis and more littering entering store - carbon budget in tundra may remain in balance
How does temperature influence the water and carbon cycles in the tundra?
Av temps well below freezing for most of year - water stored as ground ice in permafrost layers. During summer top layer thaws - meltwater forms many pools and shallow lakes. Drainage is poor and water cannot infiltrate frozen soil. Sub-zero temperatures prevent evapotranspiration. Humidity low all year round. Precipitation sparse.
How does rock permeability and composition influence the shit?
Permeability low due to permafrost and crystalline rocks that dominate arctic tundra geology. Due to impermeability of permafrost porosity and mineral composition of rocks has little influence on both cycles
Relief
Ancient rock underlying tundra has been reduced to gently undulating plain due to millions of years of erosion and weathering - minimal relief and glacial deposits impede drainage - contribute to water logging in summer months
Vegetation type and amount
total biomass relatively low - ps and NPP low, shor growing season - however some compensation from long daylight hours during summer
Organic matter
Carbon mainly stored as partly decomposed plant remains in permafrost (for 500,000 years). Low temps and waterlogging slow decomposition and respiration and therefore flow of CO2
Describe the history of drilling for oil and gas in the arctic tundra
North slope, Alaska - oil discovered 1968 - presented major challenges (extreme cold temps, long periods of darkness in winter, permafrost, remote and poor accessibility, fragile environment with great ecological value) - despite challenges went ahead due to high global energy prices and US government wanting to reduce dependence on oil imports - massive investments into pipelines, roads, oil production plants etc. 1970s-1980s. By 1990s accounted for almost 1/4 of USA’s domestic oil production - now 6% due to several factors including high production costs on the north slope and growth of oil shale industry in USA
What have been the impacts of human activity on the arctic tundra?
Oil and gas exploiting as caused localised melting of permafrost (e.g. oil and gas infrastructure diffusing heat into environment, removal of insulating vegetation cover, dust deposits along roadsides darkening snow and causing more heat absorption) - permafrost melting releases CO2 and CH4. On north slope estimated CO2 losses up to 40 million tonnes a a year, CH4 100,000 tonnes a year
Gas flaring and oil spillages put CO2 into the atmosphere
Destruction or degrading of tundra vegetation for infrastructure reduces uptake of CO2 from ps - slow growing vegetation takes decades to regenerate
Melting of permafrost makes flooding more likely
Drainage networks disrupted by road construction
What have been the management strategies on the North Slope?
More emphasis on protecting permafrost, minimising disruption to water and carbon cycles and wildlife:
- roads built on insulating ice and gravel pads to prevent melting permafrost
- Refrigerated building and pipeline supports
- Buildings and pipelines elevated on piles to allow cold air to circulate beneath
What is it called when there is 24 hours of sunlight?
24 hours of night?
Midnight sun
Polar night
What is that archipelago in Norway called? How much . of it is covered by glacial ice?
Svalbard - 60% covered by glacial ice (30% barren rock, 10% vegetation). Lots of flowers and sudden burst of life in short summer as ice thaws
