Carbon

• Carbon cycle = the biocheochemical cycle by which carbon moves from one sphere to another

  • Overall is a closed system made of subsystems with their own inputs, outputs and transfers
• Stores:

  • Terrestial (land)
  • Atmosphere
  • Ocean
• Petagram of Carbon (PgC) = 1b metric tonnes of carbon
• Flux = rate of movement of carbon from one store to another
• Geologically derived carbon = from sedimentary rocks formed in oeans
• Biologically derived carbon = carbon formed in rocks like shale and coal
• Limestone carbon = 80% of world's carbon, whilst shale carbon = 20%
• Himalayas = biggest store of carbon

  • Weathering + erosion transfers carbon back to seas
• Limestone carbon process: rock is precipitated to ocean floor, forming layers which are cemented together + lithified into limestone
• Fossil fuel process:

  • Dead organisms sink to the bottom of seas and rivers – covered in silt and mud
  • Decays anaerobically
  • Deep waters result in high pressure and temperature
  • Kerogen breaks down into oil and gas
  • Oil and gas move through porous rocks into caprocks, trapping them
• Metamorphosis:

  • Layering + burial of sediment causes pressure to build which causes deep sediment layers to turn to rock
• Weak carbonic acid - in atmosphere, water reacts w/ CO2 which falls to ground w/ it rains which reacts w/ surface minerals
• Calcium ions - transported by rivers into seas. Combines w/ biocarbonate ions and makes calcium carbonate and precipiate out as minerals
• Deposition and burial - turns the calcite in sediments into limestone
• Subduction of sea floor - under continental margins by tectonic spreading
• Carbon in magma - carbon degasses from magma and returns to atmosphere.
• Volcanic outgassing occurs:

  • Volcanic zones
  • Places with no current volcanic activity
  • Emission fromr Earth's fractures
• VOG emits 0.2Gt of CO2 anually. Humans = 35Gt
• Sequestation = the natural store of carbon by physical processes such as photosynthesis
• Thermohaline circulation: ocean currents help circulate carbon

  • Takes 1,000 years for water to travel around system
  • Warm oceans depleted of nutrients + CO2 get enriched again as they travel through conveyor belt (as deep or bottom layers)
  • Main current begins in polar oceans - cold oceans with salty water therefore increased density so sinks
• Biological pump:

  • Sequestation of CO2 by phyoplankton. Located near ocean surface where they photosynthesise
  • Have rapid groth rates and live in shallow waters of continental shelves
  • Carbon passed through food chain via consumer fish and zooplankton.
  • Phytoplankton sequester 2b tonnes of CO2 annually
  • They absorb 10b tonnes of CO2 annually
• Carbonate pump:

  • Relies of iroganic carbon sedimentation. Marine organsims use calcium to make shells and inner skeletons
  • W/ organisms die (oysters, lobsters, coral), they dissolve before reaching seafloor and become part of currents
  • Shells that do not disolve sink to floor and become limestone
• Physical pump:

  • CO2 is mixed slowly in oceans creating spaatial difference in concentrations
  • Cold water absorbs more CO2 and polar ocean store twice as much as warm equitorial waters
  • Tropical waters release more CO2, helped by thermohaline circulation helps this.
  • Cold water sinks (salty) taking CO2 down with it.
• 95% of a tree's biomass is made from carbon dioxide turned into cellulose
• Carbon fixation: turns gaseous carbon into living organic compounds that grow. Amount of carbon depends on balance between respiration and photosynthesis
• Biological carbon = in soil in form of dead organic matter - returned to astmosphere via decomposition
• Ecosystems: rainforest

  • Lots of carbon in plant biomass with high photosynthesis.
  • Carbon stored in organic matter creating topsoil
  • High rates of sequestration (plant growth and photosynthesis)
  • Short storage time (decomposition)
• Ecosystems: Tundra

  • Limited carbon in slow growing plant + mass
  • Large amounts of carbon stored in soil, with permafrost preserving organic matter.
  • Low rates of percolation (0.1/0.2PgC / year) due to cold environment
  • Storage times 1,000-10,000 years
  • Global warming leads to increased carbon release as permafrost thaws.
• Ecosystems: Mangroves

  • Carbon in dense biomass
  • High carbon stored in soil - waterlogged so decomposition is low
  • Waterlogged so sequestration rates high. 0.10PgC / year
  • Storage times 10 -100 years
  • Slow decomposition = high storage time. High storage = efficient at sequestation
• Ecosystems: Boreal Forests

  • Carbon stored in trees and plant biomass
  • Lots of carbon stored in rich soils - peat
  • Slow decomposition as cold surroundings
  • Moderate - high sequestration rates. Lots of carbon in vegetation. 0.5-1PgC /year
  • Storage time of 10 - 100 years
  • Storage time decreasing due to global warming (thawing of permafrost)
• Gas affecting solar insolation: carbon dioxide

  • 89% of GHG
  • Via fossil fuels and deforestation
  • Warming power compared to CO2: 1
  • Increase since 1850: 30%
• Gas affecting solar insolation: Methane

  • 7% of GHG
  • Via gas pipeline leaks, rice farming and cattle
  • Warming power compared to CO2: 21x
  • Increase since 1850: 250%
• Gas affecting solar insolation: Nitrous oxide

  • 3% of GHG
  • Via jet aircraft, cars and fertilisers
  • Warming power compared to CO2: 250x
  • Increase since 1850: 16%
• Gas affecting solar insolation: Halocarbons

  • 1% of GHG
  • Via industry solvents and cooling equiptment
  • Warming power compared to CO2: 3000x
  • % increase since 1850: N/A (not natural)
• Temperature variance on globe:

  • Angle of solar insolation high at equator, but low at the poles (dispersed over a wider area)
  • Snow (white) reflects energy but forests (dark) absorb it
• Precipitation variance on globe:

  • Most intense at equator so convection and low pressure systems dominate. High rainfall
  • At poles, percipitation falls as air cools and is dense
  • Regional variances apply - relief and saeasonal changes
• The anthropocene: current geological era due to human impacting greenhouse effect
• CO2 increased in volume by 40% in last 300 years
• Factors affecting soil storage capacity: climate, soil type, seasonality and time of day
• Artic amplification: artic region warming faster than global rate (due to positive feedback loop).