CARBON CYCLE - ARCTIC -

• Permafrost


  A vast carbon sink
• The accumulation and slow decomposition of dead plant matter means overall, carbon stored in the tundra soils is five times greater than that in above ground biomass
• Seasonal changes in carbon flux


  1. Summer: Active top layer of permafrost melts and plants grow rapidly in the long hours of daylight, inputting carbon rich litter to the soil, decomposition via microbial activity increases and releases carbon dioxide through respiration

  2. Winter: Pockets of unfrozen water and soil act as carbon sources, snow insulates microbial organisms and allows some slow decomposition
• In the past


  Permafrost acted as a carbon sink
• Today


  Many are concerned we have crossed a tipping point and permafrost has become a carbon source
• Outputs of carbon from thawing permafrost have increased in recent decades
• There has also been an increase in plant growth, taking in increased CO2 and increasing the amount of litter, entering the store
• It is therefore possible that the carbon budget could once again reach an equilibrium
• Temperature


  • Little vegetation grows therefore there is little carbon stored in biomass and slow decomposition
  • The frozen permafrost is a store of carbon. When it thaws, carbon is released
• Organic matter in soil

  • The largest proportion of organic matter found in soil in the world
  • Slow decomposition so the soil stores five times more vegetation
  • Snow insulates the microbes so there is a small amount of decomposition taking place in the winter
  • Living things remain trapped in the soil
• Mineral composition of rocks

  • Soils are generally frozen gelisols
  • Lot's of frozen freeze thaw occurs leading to cryoturbation (mixing)
  • Mixed rock fragments and sediment left behind by glaciers forms the soil