1. Topic 4.3 Carbon Cycling

3. Carbon Fixation
Autotrophs convert carbon dioxide into carbohydrates and other carbon compounds
Absorb CO2 from the atmosphere and aquatic envrionments
The mean CO2 concentration in the atmosphere is approximately .039% but is lower above parts of the Earth where photosynthesis rates are high.

4. Carbon Dioxide in a solution
In aquatic habitats carbon dioxide is present as a dissolved gas and hydrogen carbonate ions
CO2 can be a dissolved gas or can combine with water to form carbonic acid(H2CO3)
This can reduce the pH of water
Both of these forms of carbon can be used in the process of photosynthesis.

5. Exchange of Carbon
Photosynthesis – Autotrophs absorb CO2 through diffusion from the atmosphere or water
Reduces the amount of carbon in the atmosphere or water
Cellular Respiration – Autotrophs create CO2 and diffuse it to the atmosphere or water
Increases amount of carbon in the atmosphere or water

8. Methanogenesis
Methane is produced from organic matter in anaerobic conditions by prokaryotes and diffuses into the atmosphere.
3 groups of anaerobic prokaryotes are involved
Bacteria that convert organic matter into a mixture of organic acids, alcohol, H, and CO2
Bacteria that use the organic acids and alcohol to produce acetate, CO2, and H
Archaeans that produce methane from CO2, H, and acetate
CO2 + 4H2  CH2 + 2H20
CH3COOH  CH4 + CO2

9. Archaeans These archaeans are found in many anaerobic environments
Mud along shores and in the beds of lakes
Swamps, mires, mangrove forests and other wetlands where soil and peat deposits are waterlogged
Guts of termites and ruminant mammals such as cattle and sheep
Landfill sites where organic matter is in wastes that have been buried

10. Oxidation of methane
When methane is released into the atmosphere they remain for approximately 12 years
The methane molecules become oxidized in the stratosphere and becomes water
This is why atmospheric concentrations are not high, despite large amounts of production of methane

11. Peat forms when organic matter is not fully decomposed because of anaerobic conditions in waterlogged soils
In many soils all organic matter is digested by saprotorphic bacetria and fungi.
In some envrionments water is unable to drain out of soils
These become very acidic which inhibit saprotrophs and methanogens from breaking down that matter

12. Fossilized organic Matter
This partially decomposed organic matter from past geological eras was converted into oil and gas in porous rocks or even coal
Coal is formed when deposits of peat are buried under other sediments.
Peat is heated and compressed over thousands or millions of years and become coal
Many coal deposits are ancient swamps
Oil and Natural Gas
Formed in the mud at the bottom of seas and lakes.
Compression and heating leads to chemical changes and the production of methane and oil.
Deposits are found where there are porous rocks that can hold them such as shales and impervious rocks above and below the porous rocks.
Fracking

13. Combustion –
Carbon Dioxide is produced by the combustion of biomass and fossilized organic matter
Oxidation reaction at high temperatuers
Some fires are natural and periodic in forests or grasslands.
In these areas trees and other organisms are often well adapted to fires and regenerate communities rapidly afterwards

14. Limestone
Animals such as reef-building corals and molluscs have hard parts that are composed of calcium carbonate(CaCO3) and can become fossilized in limestone
When these animals die their soft parts decompose quickly.
Limestone makes up approx. 10% of all sedimentary rock on earth.

15. Carbon Fluxes
The amount of carbon in each “pool” cannot be preciecely measured but they can be estimated.
The amount of carbon in our world is so large the estimates are in gigatonnes (1x1015 grams)