• CO2 + H2O H2CO3 (carbonic acid)

• H2CO3 H+ + HCO3- (bicarbonate)

• HCO3- H+ + CO3

2- (carbonate)

• Ca2+ + CO32- CaCO3 (calcium carbonate

– used by all shelled marine animals and diatoms)

• Movement in atmosphere: atmospheric C as CO2 (0.04% of troposphere)

• Primary production: photosynthesis (“carbon fixation”) moves C from atmosphere to organic molecules in organisms

• Movement through food web: C moves in organic form from organism to organism

• Aerobic respiration: organic molecules broken down to release CO2 back to atmosphere

• Combustion: organic molecules broken by burning release CO2 back to atmosphere

• Dissolving in oceans: C forms carbonate (CO32–) &

bicarbonate (HCO3–)

• Movement to sediments: C enters sediments, primarily as calcium carbonate (CaCO3)

• How are humans affecting the carbon cycle?

• Which parts of the carbon cycle are considered short-term and which are considered long-term?