CARBON CYCLE
The biochemical carbon cycle
- Biological processes (living plants and animals)
- Geological processes (erosion, deposition, rock formation)
- Chemical processes (reactions under heat and pressure)
Carbon Stores Terrestrial carbon store
- Igneous and metamorphotic rocks do not contain much carbon, HOWEVER sedimentary rocks do have high concentrations (limestone contains 42% calcium carbonate by weight)
- Geological processes have also trapped carbon in the form of coal, oil (85% carbon) and natural gas so the terrestrial store Is the largest
- Calcareous oozes are found under the southern pacific Atmospheric carbon stores
- Volcanic activity, respiration, wildfires and outgassing emit CO2 into the atmospheric store. This store is very small compared with others (only 0.03% of natural unpolluted air is co2)
- 2012-2017 average c02 concentration increased by 3%
- Due to human emissions Ocean carbon store
- Carbon dioxide is dissolved by oceans from the atmosphere, but it only makes up a tiny proportion of the seawater mass
- Most carbon dioxide Is stored in intermediate and deep water, with only about 2.5% in surface water Carbon stores and processes Sedimentary carbonate rocks
- Are formed from calcareous ooze and shells and skeletons that collect at the bottom of the ocean
- Phytoplankton absorb carbon from seawater, and when their remains collect on the seabed the calcium carbonate is compacted by the weight of new layers and cemented together to form an organic limestone rock
- Calcareous oozes are not found where the ocean is too deep as the pressure causes calcium carbonate to dissolve Biologically derived carbon rocks
- Formed by the remains of living organisms deposited in layers within sedimentary rocks (such as shale)
- Organic carbon from tropical coastal swamps is buried to produce coal, the hardness of which depends on the amount of pressure and heat when squashed during rock formation
- Anaerobic reactions may convert organic carbon into a liquid (oil) that moves within rock layers until trapped
- A by-product of coal and oil formation is natural gas, which is also trapped within layers of sedimentary rock Carbon release
- Tectonic forces may bring limestone rocks into contact with extreme heat – this causes chemical changes and releases co2 into the atmosphere
- Volcanic activity at plate boundaries or intra-plate hot spots may release co2 into the atmosphere
- Geothermal areas also release co2 through hot springs or overstimulated pools
- Degassing occurs because co2 is not dissolved easily and so is is released early in eruptions Chemical weathering of rocks
- Limestone rocks are very easily weathered by rain because is becomes a weak carbonic acid as it falls through the air and absorbs some carbon dioxide.
- This acid then dissolves the calcium carbonate of the rock, and dissolved carbon is then carried by water for deposition on the seabed or released by a gas.