A LEVEL - Geography - EDEXCEL The carbon cycle

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sudden release of carbon, such as during a volcanic eruption or major wildfires, can upset the balance of the carbon cycle and it may take a long time for the balance to be restored. Carbon Fluxes occur over different time and spatial periods. Measured in Petagrams (Pg) or Gigatonnes (Gt) of carbon per year Equivalent to 1 billion tonnes of carbon Largest fluxes are between the ocean + the atmosphere or the land + the atmosphere Involve photosynthesis and respiration Photosynthesis/ respiration/ combustion/ decomposition may take only minutes, hours or days to transfer Sequestration takes millenia for carbon found in sedimentary rocks or in the ocean. Most of the earth's carbon comes from sedimentary rocks (e.g: limestone) = 99.9% 1. Formed when dead organic matter gets covered by layers of silt and mud which are compressed over many years where they become shale. 2. Formed when dead animal matter, such as crustaceans and corals, fall to the bottom of the ocean and lithify into rocks (e.g: limestone) over millions of years. Fossil Fuels contain 0.004% of carbon Formed by the deposition of organic material. If this organic matter builds up faster than it can decay then oil, natural gas and coal can be formed. Carbon is released into the atmosphere by geological processes Chemical Weath ing atmospheric carbon reacts with water vapour to create weak carbonic acid. During condensation, acid rain is formed which dissolves the calcium carbonate in the rocks Produces carbon ions which wash into rivers and then get carried out to sea. Outgassing the release of trapped or stored gas often via Volcanic eruptions Combustion →→ transfers carbon stored in living, dead or decomposed biomass to the atmosphere by burning. Releases CO2 and heat which can be used to power turbines and generate electricity. Wildfires rapidly transfer large amounts of carbon from biomass to the atmosphere. The loss of vegetation amplifies the increase in atmospheric carbon as wildfires decrease photosynthesis so less carbon is removed from the atmosphere by plants. Carbon can be Sequestered in Oceans → carbon moves between the atmosphere, the surface water of the ocean and the deep water through 3 interconnected systems known as pumps. Biological Pump 1. CO2 in the atmosphere can be consumed by large numbers of phytoplankton through photosynthesis. 2. Phytoplankton are at the bottom of the food chain so the carbon is transferred up the chain as creatures feed off of eachother. 3. Respiration releases some CO2 back into the atmosphere, but, most respired carbon remains in the surface water and is reabsorbed by phytoplankton 4. When marine animals die, they fall to the ocean floor where the carbon stored in their bodies is transferred to the deep ocean. Store dead animals + Transfer = Deep ocean or Surface Water Carbonate Pump 1. Chemical weathering washes carbon based molecules into the sea through river systems. 2. React with CO2 dissolved in water to form calcium carbonate Calcium Carbonate used by some marine organisms to form shells 3. Marine organisms die, sink to the ocean floor, sedimentation occurs. Physical Pump Cold water has a greater capacity to hold CO2 than warm water as it is denser so it sinks and gets held under pressure by the weight of the water above it. Higher concentration of CO2 in the deep water of the ocean and at higher latitudes where the ocean water is cooler. Thermohaline Circulation moves warm water on the surface into cooler parts of the world means that Downwelling Occurs. To redress the balance, Upwelling Occurs. Carbon can remain in the ocean for hundreds of years while moving around the ocean basin through thermohaline circulation where the ocean acts as a giant conveyor belt moving water and dissolved CO2 around the earth. Carbon can be Sequestered into Plants and Soils 1. Photosynthesis transfers carbon stored in the atmosphere to Biomass 2. Carbon is passed through the food chain via primary and secondary consumers 3. Carbon is released via Respiration and Decomposition Carbon can be stored in dead organic matter Decomposition transfers carbon from dead biomass tissue to the atmosphere and the soil. Rate of decomposition depends on soil type and what is being decomposed. Explain how Carbon can be released into the atmosphere through geological processes [6 marks] Carbonic acid is produced as CO₂ within the atmosphere combined with rainfall, dissolving carbonate rocks through chemical weathering. Rivers transport carbon and calcium sediment to oceans to be deposited. Carbon in shells and skeletons from animals, and organic matter from plants sink to the seabed when animals and plants die, building up a strata of limestone, chalk and coal. Calcium ions combine within bicarbonate ions to calcium carbonate and precipitate, calcite sediment is converted to limestone through deposition. The presence of intense heating along subduction zones metamorphoses sedimentary rocks, creating metamorphic rocks that release CO2. Terrestrial carbon within the lithosphere is released into the atmosphere through volcanic out-gassing, with carbonate rocks being dragged into the mantle by rising magma at subduction zones. Volcanic out-gassing at constructive plate boundaries and at mid-ocean ridges tend to be less explosive with less carbon emitted.