Matching Pairs Carbon Cycle - ProcessesOnline version Carbon Cycle - Processes by Whitney Wikert Kuecker 1 Weathering and run-off 2 Deep circulation 3 Burning 4 Respiration 5 Burning fossil fuels 6 Decay 7 Sinking sediment 8 Photosynthesis 9 Carbon dioxide exchange 10 Phytoplankton 11 Rock formation Plants take up CO2 – they essentially breathe it in and use it to build their physical structures – and phytoplankton are basically teeny tiny microscopic plants that live in the surface of the ocean, so essentially you have in the surface of the ocean these little tiny microscopic plants are taking carbon from the water and using it to build parts of their bodies. Now as the phytoplankton mature, there are a couple of different things that can happen. One thing that can happen is they can be recycled back into the biological processes of the surface ocean – so maybe zooplankton eats them, maybe they die and they are returned to their component minerals by natural processes and that carbon is taken up by some other phytoplankton. But the other thing that can happen is that, when they die, they can precipitate down into the deep ocean and when that happens because ocean circulation is so slow that carbon can be stored or sequestered in the ocean for a very long period of time. There is a constant vigorous exchange that is going two ways between the ocean and the atmosphere. So once the CO2 goes into the ocean then that CO2 forms carbonic acid, bicarbonate and carbonate ion, and it means that the ocean can take up more CO2, so at present, there is about 60 times as much carbon in the ocean as there is in the atmosphere. Sediments containing lots of calcium carbonate from shells can be turned into rock over millions of years. This limestone rock can be pushed up to form land by tectonic Earth movements. Some carbon trapped in the sediments forms gas and oil. In fossil fuels, the carbon is stored in long-chain hydrocarbons, and then through combustion with oxygen in our cars or in factories, the carbon is converted to CO2, which is released to the atmosphere. And in addition, a number of other byproducts are also produced through inefficiencies in combustion like CO which are atmospheric pollutants. When phytoplankton die, many sink and take their carbon (calcium carbonate shells) to form sediments at the bottom of the ocean. This is called a biological pump, removing carbon from the ocean and atmosphere systems for long periods of time. Rain slowly dissolves minerals from rocks – a process called weathering. These minerals eventually get washed into the sea, where some minerals, such as calcium carbonate, add to sediments at the bottom of the ocean. A lot of organic matter from the soil also gets carried to sea by rivers. Plants take in carbon dioxide from the atmosphere during photosynthesis. They use energy from the sun to combine the carbon dioxide and water to form carbohydrates. In the soil, decomposers (such as microbes and soil animals) break down dead plant material. As well as making nutrients available for living plants, this process also releases carbon dioxide into the atmosphere. Plants and animals release carbon dioxide into the atmosphere through the process of respiration. Respiration releases energy from carbohydrates, with carbon dioxide as a waste product. Some carbon from phytoplankton is carried by deep ocean currents that might not return it to the surface for hundreds of years. All the mass of all the trees that you’re seeing around is mostly coming from atmospheric CO2. So when we cut down forests and burn forests, then we are releasing CO2 into the atmosphere.
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