Carbon

• Carbon cycle


  A system of inputs, outputs, stores and flows (fluxes) of carbon

  
• The amount of carbon in the system is measured in petagrams
• Carbon stores

  • Atmosphere
  • Hydrosphere (water)
  • Lithosphere (rocks, fossil fuels)
  • Biosphere (living and dead organisms)
  • Marine ecosystems

  
• Balanced carbon cycle

  • Sources equal sinks
  • Equilibrium
• Changes in the carbon cycle system

  May result in negative or positive feedback

  
• Sedimentary rocks and fossil fuels were made up to 300 million years ago from the remains of organic material
• Formation of fossil fuels

  1. Organisms sink to bottom of rivers/seas

  2. Covered in silt/mud

  3. Decay anaerobically

  4. Heat and pressure exerted on deposits
• Crude oil


  Formed from the remains of tiny aquatic animals and plants
• Coal


  Formed from the remains of trees, ferns and other plants
• Release of carbon from geological stores

  1. Volcanic outgassing

  2. Weathering

  
• Rainwater is a carbonic acid, absorbing CO2 from the air and reacting with rocks to dissolve them
• Formation of limestone

  1. Transportation of calcium ions by rivers

  2. Combination with bicarbonate ions to form calcium carbonate

  3. Precipitation as minerals like calcite

  4. Deposition and burial turns calcite into limestone
• Subduction leads to some of this carbon rising back to the surface and degassed as CO2 and returned to the atmosphere

  
• Tectonic settings that release CO2

  • Volcanic outgassing
  • Subduction
• Tectonic situations that create the largest releases of carbon dioxide into the atmosphere are those with the most volcanic and subduction activity

  
• Biogeochemical carbon cycle


  Biological and chemical processes determine how much carbon is stored or released

  
• Key processes in the biogeochemical carbon cycle

  • Photosynthesis
  • Respiration
  • Decomposition
  • Weathering

  
• Oceans are the largest store of carbon - 60 times greater than the atmosphere
• Thermohaline circulation

  The global system of surface and deep water ocean currents driven by temperature and salinity differences

  
• As major ocean currents move warm waters from tropics to poles


  The water cools and can absorb more CO2

  
• Biological pump

  Phytoplankton consume CO2 from atmosphere during photosynthesis, storing it in their bodies

  
• Carbonate pump

  Marine organisms use carbon to make shells and skeletons, which sink to seafloor
• Physical pump

  Oceanic circulation of water including upwelling, down-welling and thermohaline circulation moves CO2 between surface and deep ocean

  
• Southern Ocean is an important carbon sink due to its high productivity and deep ocean circulation
• Terrestrial photosynthesis removes CO2 from atmosphere and releases oxygen

  
• Soil health is influenced by stored carbon, which is important for ecosystem productivity
• Net primary productivity (NPP)


  Amount of biomass produced minus energy lost through respiration
• Healthy soils usually contain more organic matter, sequester carbon, and improve resilience to wetter weather and drought
• Organic carbon


  Carbon within soil
• Lack of nutrient-rich organic carbon matter can lead to soil erosion and water insecurity
• Ecosystem productivity


  The rate at which plants produce biomass, also called primary productivity
• Net primary productivity (NPP)


  The amount of biomass produced minus the energy lost through respiration
• About 1% of solar insolation reaching Earth is captured by photosynthesis and used by plants to produce organic material called biomass

  
• Healthy soils

  • Are dark and crumbly
  • Contain many worms and other organisms
  • Provide water, air and nutrients for micro-organisms and plants to thrive
  • Contain more organic matter
  • Sequester carbon
  • Improve resilience to wetter weather, because they enable infiltration and percolation of water reducing soil erosion and flood risk
  • Retain moisture, which regulates soil temperature during heat waves and reduces the effects of droughts
• Carbon is vital in soils. Without carbon, the nutrients and water cycles cannot operate properly

  
• Carbon is passed into the soils by the decay of litter/ leaves and other dead material

  
• Microorganisms act as biological decomposers and feed on this material, breaking down organic matter and transferring nutrients into the soil, and providing pore space for infiltration and storage of water
• The higher the amount of organic matter and moisture, the healthier soils are - enhancing plant growth/ productivity
• Fossil fuels are extremely important long term carbon stores
• Their combustion moves the sequestered carbon from the long term geological store to the atmosphere without any corresponding increases in natural sinks, which is widely believed to be the main cause of rising global temperatures