carbon cycle

• Stores of carbon

  • Lithosphere
  • Hydrosphere
  • Atmosphere
  • Biosphere
• Lithosphere


  Largest store of carbon, long term storage in marine sediment, sedimentary rock, fossil fuels and soil
• Hydrosphere


  Carbon stored in ocean, dynamic store but deep ocean carbon stays longer
• Atmosphere


  Very dynamic store, carbon constantly moving in and out, influenced by human activity
• Biosphere


  Carbon stored in terrestrial plants, mid term store
• The carbon cycle is a closed system
• Stores


  Function as sources and sinks
• Fluxes/flows


  Movement of carbon between stores
• Photosynthesis


  Plants convert CO2 into oxygen, glucose and light energy
• Respiration


  Plants and animals convert oxygen and glucose into water
• Combustion


  Burning fossil fuels and organic matter releases CO2
• Decomposition


  Living organisms are broken down by decomposers which respire releasing CO2, some CO2 released into soil
• Diffusion


  Oceans absorb CO2
• Sedimentation


  Shelled marine life die, become compacted to form limestone which traps CO2
• Weathering and erosion


  Carbonation weathering where rocks like limestone are eroded by rainwater and CO2 creating carbonic acid
• Metamorphosis


  Extreme heat and pressure forms metamorphic rock, during which some carbon is released and some becomes trapped
• Volcanic outgassing


  Pockets of CO2 released through volcanic eruption
• Size of carbon stores is measured in Pg/Gt
• Geological carbon cycle


  1. Mechanical, chemical and biological weathering of rocks on land

  2. Decomposition of plant and animal particles

  3. Transportation of particles to ocean

  4. Sedimentation forming sedimentary rocks

  5. Metamorphosis forming sedimentary rocks
• Carbon fossil fuels are made up of organic matter that builds up faster than it decays
• Geological carbon release


  1. CO2 in atmosphere reacts with moisture to form carbonic acid, dissolving surface material and releasing CO2

  2. Pockets of CO2 in crust released through volcanic eruptions and earthquakes
• Ocean sequestering


  Process of trapping carbon in the sea
• Carbon pump


  Process operating in oceans that circulates and stores carbon
• Types of oceanic carbon pumps

  • Biological pump
  • Physical pump
  • Carbonate pump
• Biological pump


  Moves CO2 from ocean surface to marine plants like phytoplankton through photosynthesis, microscopic plants eaten and sink to deep ocean
• Physical pump


  Moves carbon compounds to different parts of ocean in downwelling and upwelling currents, carbon stays in deep ocean for hundreds of years
• Carbonate pump


  Forms sediment from dead organisms that fall to ocean floor, especially hard outer shells and skeletons
• Thermohaline circulation


  Global system of surface and deep ocean currents driven by temperature and salinity differences
• Terrestrial sequestering


  Trapping of carbon in the biosphere, a short term store
• Terrestrial carbon sequestration


  1. Plants sequester carbon from atmosphere through photosynthesis

  2. Animals consume plant matter and carbon becomes part of their fat and protein

  3. Waste from animals eaten by micro-organisms and detritus feeders

  4. When plants and animals die, carbon released into soil
• Diurnal carbon fluxes


  Positive during day, reverse at night
• Seasonal carbon fluxes


  Increase in winter due to low plant growth, decrease in summer
• Biological carbon stores


  Dead organic matter in soil, stored for many years before breakdown by microbes
• Factors determining amount of carbon stored in soil

  • Climate
  • Vegetation cover
  • Soil type
  • Land use
• Greenhouse effect


  Solar radiation passes through atmosphere, some absorbed by Earth, some reflected back, enhanced greenhouse effect reflects some back again
• Balanced carbon cycle is outcome of different components working in harmony
• Photosynthesis


  Plays essential role in keeping CO2 levels relatively constant and regulating Earth's mean temperature
• Net primary productivity (NPP)

  Amount of organic matter available for humans and other animals to harvest or consume
• NPP is highest in warm, wet parts of world like tropical rainforests and shallow ocean waters, least in tundra and boreal forests
• Soil health


  Determined by balance between inputs (plant/animal remains, nutrients) and outputs (decomposition, erosion, uptake)