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Arctic Tundra (Water (Ground is frozen year-round in high Arctic -…

- - - - Low C uptake in plants via photosyn. bc
        
        Small veg. store
        
        BD is low
      - Transp. rates are low bc
        
        Only 3-4 months of growth
      - 24 hours of sunlight in summer = rapid plant growth
        
        Plants flower + fruit in a few weeks
        
        NPP is only 200g/m2/year
      - Treeless plain with little veg.
        
        Mosses, lichens, dwarf shrubs
    - - Ground is frozen year-round in high Arctic
      - Uppermost layer of Tundra melts - active layer
        
        = wetlands, + partial floods
        
        Water cannot drain away as permafrost layer below is still impermeable
      - = low infil. rates + high runoff
      - Ground that has been frozen for a year or more
      - Methane trapped in permafrost
        
        Product of anaerobic decay of plants in peat
    - - Evap. rates are low
        
        Bc air temp. is low + most precip. is stored as snow
    - - Soil temps. remain low in summer
        
        Bc most of sun's energy is being used to melt snow
      - Few soil microbes + little decomposition = C cycle is slowed
      - Peat
        
        When there is plant death without O2 = plant matter doesn't decompose fully
        
        Builds up in soil as vast C store
    - - As air + ground temps. increase, methane is being released into the atmosphere
      - *30 the warming factor of CO2
  - - - C is stored in permafrost
      - When permafrost thaws, C can enter ecosys. with either aeorbic or anaerobic soil conds.
        
        Aerobic
        
        CO2 is released by microbial decomposition of soil organic C - occurs in active layer
        
        Anaerobic
        
        CO2 + methane are released from incomplete decomposition
    - - Plant inputs
      - Soil environment
      - Soil depth
      - Water saturation
    - - Organic matter in permafrost thaws as permafrost thaws
      - Aerobic decay = CO2
      - Anaerobic decay = methane
      - Microbial decomposition of soil organic C occurs in:
        
        Active layer - thaws each summer + refreezes in winter
        
        Subsurface - newly-thawed C becomes available for decomposition after emerging from the perennially frozen pool
      - More C can be exposed to aerobic conds. via:
        
        Top-down thawing of permafrost (increasing thickness of active layer)
        
        Lake draining
        
        Erosion
        
        Leaching from upland soils into aquatic sys/sed.
      - Abrupt thaw processes = wetter anaerobic conds.
        
        Ground surface subsides, attracting local water
      - Plant C uptake can be stored in plant biomass or deposited in soil surfaces
  - - - Release much C stored as methane hydrates
      - Increases global warming as methane 20-30 times more effective than CO2
      - Positive feedback
    - - Increase in CO2 + warming temps.
      - Arctic will become a C sink
      - But much plant growth would be needed to counter-act the methane that would be released from permafrost melting
- - - - Extreme cold
      - Long periods of darkness
      - Permafrost
      - Melting of active layer
      - Remoteness + poor accessibility
      - Fragile wilderness of great ecological value
    - - 6% today - but still important
      - Decline in recent years bc of:
        
        High production costs
        
        Massive growth of oil shale ind. in USA
  - - - Permafrost is sensitive to changes in thermal balance
        
        Thermal balance disrupted = localised melting
        
        Construction + operation of installations, infrastructure + settlements diffuse heat to environment
        
        Dust deposition along roadside = darkened surfaces = increased sunlight absorption
        
        Removal of veg. cover that insulates the permafrost
      - Increased atmospheric CO2
        
        Permafrost melting = CO2 + CH4
        
        CH4 losses on N Slope = 24,000 - 114,000 tonnes/year
        
        CO2 losses on N Slope = 7 - 40 million tonnes/year
        
        Gas flaring + oil spillages
      - Industrial development + biosphere
        
        Destruction/degrading of veg. = decreased photosyn. + uptake of CO2 from atmosphere
        
        Thawing of soil = increased microbial activity, decomp. + emissions
        
        Slow-growing nature of tundra veg. = recovery + regeneration = decades
    - - Melting permafrost + snow = increased runoff + river discharge = flooding
      - Summer - extensive wetlands, ponds + lakes = increased evap.
      - Strip mining of aggregates for construction = artificial lakes
        
        Disrupts drainage
        
        Exposes permafrost to additional melting
      - Road construction + seismic explosions
        
        Disrupts drainage
      - Water abstracted from creeks + rivers, + ice roads in winter = reduced localised runoff
  - - - Minimises disruption to water + C cycles + wildlife
      - Melting permafrost = building + infrastructure damage, + increased maintenance costs for infrastructure
    - - Infrastructure constructed on these
      - Protects permafrost from melting
    - - Infrastructure constructed on piles
      - = cold air circulates beneath = protection against heat-generating buildings + pipelines that would otherwise melt the permafrost
    - - New drilling technique
      - = oil + gas accessed several kilometres from drilling site
      - = fewer sites needed for drilling rigs
      - = reduced impact on veg. + permafrost due to construction
    - - Fewer exploration wells needed = reduced impact on environment
    - - Used on the Trans-Alaska Pipeline
      - Stabilises the temp. of the permafrost
      - Similar supports used to conserve permafrost beneath permafrost
- - - - Affects salinity balance
- - - - Water stored as ground ice in permafrost = poor drainage
      - No evap. in winter; some form standing water in summer
      - Active layer melts = runoff + wetlands
      - Low year-round humidity + sparse precip.
    - - Minimal relief + glacial deposits impede drainage = waterlogging in summer
      - Hundreds of years of erosion + weathering of ancient rock surface underlying tundra = now a gently undulating plain
    - - Permafrost = low permeability
      - Permeability + porosity of rock has little effect bc of permafrost
      - Geology dominated by impermeable crystalline rocks
    - - Pressure from vehicle types moves water from its store in peaty wastes to lakes/runoff in oceans
  - - - Limited bc of:
        
        Low temps.
        
        Lack of freshwater
        
        Parent rocks w. few nutrients
      - Small total C store of biomass
      - Growing seasons = 3 months; but long hours of daylight in summer
    - - Where most C is stored for past 500,000 years
      - Low temps. + waterlogging = decreased composition rates
    - - Permafrost = low permeability
      - Permeability + porosity of rock has little effect bc of permafrost
    - - Fishing
        
        Moves living biomass in oceans to land
        
        Transport of fish relies on air freight + shipping - fossil fuels
      - Forestry + Combustion
        
        Warmer Arctic = increased fire risk
        
        Fire released C suddenly into fast C cycle
      - Oil + Gas Exploration
        
        Alaska - over 17 billion barrels of oil
        
        Moves C from slow to fast cycle as fuels are burnt
      - Tourism + Human Habitation
        
        ATVs driver over permafrost = melting + release of CH4
    - - Partly decomposed organic matter frozen in permafrost
      - Locked away for 500,000 years
    - - Slowed bc of
        
        Low temps.
        
        Waterlogging
      - Slows flow of CO2 to atmosphere
- - - - White surface reflect light - 205 of heating is reflected
      - Melting ice = liquid water = clouds - reflect sunlight - negative feedback
      - When sun is scarce, clouds reflect light
    - - Ice acts as buffer between cold air + warm ocean - insulation
      - When ice melts, more warm air escapes = more melting - positive feedback
      - 80% of heating is absorbed
      - Evidence
        
        Records of increasing temps.
        
        Melting glaciers
        
        Reductions in extent + thickness of sea ice
        
        Thawing permafrost
        
        Regional variations bc of winds + ocean currents
        
        Temps. in winter are rising more rapidly than in summer
    - - Increasing atmospheric greenhosue gases
      - Arctic summer sea ice is past its ice-free tipping point
      - All Arctic methane feedback sources are releasing methane
      - Permafrost is thawing + emitting methane, CO2 + nitrous oxide
    - - Atmosphere
        
        Is less deep at the poles
        
        As it gets warmer, it can hold more moisture
      - Ocean
        
        Is colder so more CO2 dissolves
        
        3% of E's oceans
        
        Removes 105 of C uptake
      - Land Plants
        
        Boreal forests store C as plant mat., in the low Arctic - tundra stores less
      - Soil
        
        Tundra stores soil C
        
        Stored in permafrost as dead organic matter + methane