4.2 Tundra

• The Arctic Tundra PSD

  - 8 million km^2 of Northern Canada, Alaska and Siberia

  - Extends from northern edge of boreal coniferous forest to the Arctic ocean

  - Southern limit approximates the 10 degree isoutherm climatic tree line

  - Severe climate conditions which become more extreme with latitude

  - Temperatures below freezing for 8-9 months as there is a negative heat balance

  - Ground is permanently frozen, top metre thaws in summer

  - Permafrost underlies much of the tundra and is an important feature of the region water cycle

  - Where sun remains below horizon, temps can drop to -40

  - treeless ecosystem, dwarf species
• Describe the water cycle in the Arctic Tundra

  - Low annual precipitation (50-350mm), mostly as snow

  - Small stores of moisture in the atmosphere owe to low temperatures which reduce humidity

  - Limited transpiration because of the sparseness of the vegetation cover and short growing season

  - Low rates of evaporation

  - Limited groundwater and soil moisture stores. Permafrost is a barrier to infiltration, percolation, recharge and groundwater flow

  - Accumulation of snow and river ice during winter months. Melting of snow and ice in the active layer of permafrost in spring and early summer results in an increase in river flow

  - Extensive wetlands, ponds and lakes on the tundra during summer temporarily stores liquid
• Explain the process of the carbon cycle

  - Permafrost is a carbon sink and holds 1600 GT of carbon, due to low temperatures which is slow decomposition of dead plant material

  - Soils = 5x more than above ground biomass

  - Plants grow rapidly in short summer with the long hours of daylight allowing them to flower and fruit within a few weeks

  - NPP <200

  - Small biomass

  - Tundra plants input carbon rich litter to the soil and the microorganism activity increases, releasing CO2 to the atmosphere through respiration

  Winter - pockets of unfrozen soil and water acts as sources of CO2 and CH4

  - Snow insulates microbial organisms and allow some decomposition

  - Global warming has raised concerns that it is becoming a carbon source which as stimulated plant growth

  - As a result, has increased the uptake of CO2 and amount of plant litter entering the store and remaining in balance
• Describe the physical factors that affect the stores and flows of the water cycle

  - Average temperatures are well below freezing for most of the year so water is stored as ground ice in the permafrost layer. During the short summer, the active layer thaws and liquid water flows on the surface

  - Drainage is poor : water cannot infiltrate soil because of the permafrost

  - In the winter, sub-zero temps prevent evapotranspiration

  - In the summer, evapotranspiration occurs from standing water, saturated soil and vegetation

  - Humidity is low and precipitation is sparse

  - Low permeability due to the permafrost and the crystalline rocks

  - The ancient rock surface which underlies the tundra has been reduced to an undulating plain by erosion over millions of years
• Describe the physical factors that affect the stores and flows of the carbon cycle

  - Mainly stored as a partly decomposed plant remains frozen as permafrost for the last 500,000 years

  - Low temperatures, the unavailability of liquid water for most of the year and limited nutrients result in reduced plant growth

  - Low NPP, growing season lasts for barely 3 months, compensated for long hours of sunlight

  - Low temperatures and waterlogging slow decomposition and respiration and the flow of CO2 to the atmosphere

  - Impermeability of permafrost, rock permeability, porosity and mineral composition exert minimal influence on the cycles
• Explain the oil and gas production in Alaska

  - Oil and gas discovered at Prudhoe Bay in 1968

  - Harsh climate with extreme cold and long periods of darkness in winter, permafrost, melting of the active layer, remoteness and poor accessibility provide great ecological value

  - High global energy prices

  - 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 1990, the North Slope accounted for nearly 1/4 of Usa domestic oil production, today it is 6%
• Impact of gas and oil production on the water cycle

  - Permafrost has been disrupted and caused localised melting of permafrost

  - Construction and operation of oil and gas installations, settlements and infrastructure diffusing heat directly to the environment

  - Dust deposition on roads creating darkened snow surfaces, increasing the absorption of light

  - Removal of vegetation which otherwise insulates the permafrost
• Explain the impacts of permafrost melting on the environment

  - Releases CO2 an Methane

  - The north slope estimates CO2 losses from the permafrost to vary from 7 to 40 million tonnes a year

  - Gas and oil spillages inout CO2 into the atmosphere

  - Destruction or degrading of tundra vegetation reduces photosynthesis and co2 uptake ffrom the atmosphere, also reduces thawing of soil and decomposition of CO2

  - Slow growing nature means there is slow recovery

  -Melting also increases run off, and the risk of flooding

  - In summer, wetlands and lakes have become etensive which increases evaporation

  - Strip mining used for creating artificial lakes expose permafrost by disrupting the drainage which ruins the environment

  - Drainage networks are disrupted for road networks and small seismic activity to prospect for oil and gas which increases run off
• Explain how insulated ice and gravel pads is a strategy to reduce the impact on the water and carbon cycle

  - Roads and other infrastructural features can be constructed on insulated ice or gravel pads thus protecting the permafrost from melting
• Explain how building pipelines elevated on piles is a strategy to reduce the impact on the water and carbon cycle

  Constructing buildings and oil pipelines and other infrastructure on piles allow cold air to circulate beneath these structures.

  -v This provides insulation against heat generating buildings which would otherwise melt the permafrost
• Explain how drilling laterally beyond drilling platforms is a strategy to reduce the impact on the water and carbon cycle

  - New drilling techniques allow oil and gas to be accessed several kilometres from the drilling site.

  - Fewer sites needed for drilling rigs reduces the impact on vegetation and the permafrost due to construction and the permafrost due to construction is greatly reduced
• Explain how more powerful computers detecting oil and gas structures remotely is a strategy to reduce the impact on the water and carbon cycle

  Fewer exploration wells are needed thus reducing the impact on the environment
• Explain how refrigerated supports s is a strategy to reduce the impact on the water and carbon cycle

  Refrigerated supports are used on the Trans Alaska pipeline to stabilise the temperature of the permafrost

  - Similar supports are widely used to conserve the permafrost beneath buildings and other infrastructure