Topic 4.3 Carbon Cycling

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.

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.

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

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

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

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

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

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

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

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.

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)