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The carbon cycle
Transcript of The carbon cycle
Exchange of carbon between the atmosphere and the ocean
There are two types of carbon cycle, the biological (fast) and the geological (slow) carbon cycle. The first carbon cycle that is going to be covered is the geological carbon cycle, this carbon cycle takes 100-200 million years for one cycle to be completed and in total transfers 10-100 million tonnes of carbon per year through the cycle. This cycle transfers carbon from the atmosphere to the mantle and back out into the atmosphere via volcanoes, this cycle contains the largest carbon storage. All measurements in gigatonnes of carbon are quite recent. A carbon cycle contains a means of removal, addition and storage. This is shown in the presentation by a carbon dioxide chemical formula (carbon dioxide is commonly used to represent other forms of carbon in the cycle) and an arrow. Addition is shown by an arrow pointing outside the word bubble, storage is shown by the formula inside the word bubble and removal is shown by an arrow pointing inside the word bubble.
The effect of global warming on today's carbon cycle
Due to increased carbon emissions by human activity, there is more carbon added into the atmosphere than removed. Emissions are produced by methods such as fossil fuel use in transport, factories and electrical energy production. The effect of the carbon in the atmosphere is emphasized by deforestation as trees remove and store carbon. The gas that has the largest contribution to climate change is carbon dioxide, other greenhouse gases include methane and nitrous oxide. Carbon dioxide is a greenhouse gas which means it is able to trap and emit the sun's radiation into the atmosphere, this process is called the greenhouse effect. When the sunlight reaches the earth the visible light is converted into infrared or heat, this is then reflected back into space. Although some gases in the atmosphere such as carbon dioxide absorb this heat which is then converted into potential and kinetic energy. These greenhouse gases then re-emit the heat back into the atmosphere. As the amount of carbon dioxide is increased in the atmosphere, from 275 parts per million 200 years ago to over 400 parts per million today, climate change is one of the consequences. The earth has warmed 0.85˚ Celsius in the last 400 years but because of the increasing carbon dioxide emissions it is generally predicted that if nothing is done to prevent increasing emissions the temperature will rise approximately 4˚ Celsius by 2060. A consequence of climate change is the increase of wildfires as the world becomes generally hotter, this results in more carbon dioxide released through combustion and decay of the trees, there is also loss of method of photosynthesis which is effective in removing carbon from the atmosphere. Another consequence of climate change is the melting of the ice in the poles and of permafrost. When the ice melts, it loses it's reflective ability to reflect heat well into space, it becomes dark and more easily absorbs radiation. The land which was covered in permafrost begins to decay and releases carbon into the atmosphere that way. As the oceans become warmer carbon dioxide more easily diffuses into the water and more easily produces carbonic acid which could cause the oceans to become more acidic. The increasing acidity of the ocean begins to dissolve shells and increasing heat begins to kill corals, this would affect the longterm storage of carbon as limestone as the main process of creating limestone is affected by climate change. Overall climate change can greatly unbalance the carbon cycle if left to continue at an increasing rate, emissions have changed the carbon cycle from what it was 200 years ago.
At the surface of the ocean, where the atmosphere meets water, carbon dioxide is steadily exchanged between water and the atmosphere. In the beginning the carbon dioxide is diffused into the ocean. In the ocean the carbon dioxide gas reacts with water molecules to release hydrogen and thus causes the water to become more acidic.When carbon dioxide enters the water, carbonic acid is formed .This hydrogen reacts with carbonate ions from weathering to make bicarbonate ions, the carbon could also become carbonate ions. These reactions of carbonic acid that form carbonate and bicarbonate ions protect the ocean from having an acidic pH.
These ions are stored in the ocean or taken in by calcifying organisms which then adds calcium ions to the bicarbonate and create calcium carbonate which is later stored. The atmosphere stores 766 billion metric tonnes of carbon in total, the ocean stores 38,000-40,000 billion metric tonnes in total. About 90 gigatonnes of carbon are exchanged between water and the atmosphere and 90 gigatonnes are exchanged between the atmosphere and water, so about 180 gigatonnes in total per year. Although the exchange relies on temperature as in cooler climates carbon dioxide more easily diffuses into the ocean while in warmer climates carbon diffuses into the atmosphere more easily. Between 60 and 85% of carbon released into the air is dissolved into the ocean, this process takes 20-200 years.
A diagram of the overall carbon cycle and the amounts of gigatonnes the carbon is transferred or stored per year.
There are different ways carbon could be released into the atmosphere other than volcanoes, the carbon can escape more gradually through seeps, vents and carbon dioxide rich hotsprings. Examples of different places in New Zealand include: the Kotuku gas see or the carbon dioxide vents under lake rotomahana or the volcanic activity in Rotorua.
Volcanoes cause carbon dioxide to be released into the atmosphere. When a volcano erupts they vent the carbon into the atmosphere, this is called degassing. They also cover the ground with silicate rocks (when they undergo the process of weathering, they continue the carbon cycle.) Volcanic activity is usually caused by plate tectonics and usually near a subduction zone (one plate moving underneath another) where the built up magma from the melting rock in the subducting plate is forced to escape. These subduction zones are caused by plate tectonincs, which are caused by convection currents on the mantle. The rock in the subducting crust melts as it is forced under great heat and pressure, some of it then recombines into a silicate mineral, which is later erupted out of the volcano. Part of the melting rock is limestone and this is stored carbon mostly accumulated in the ocean by shell building organisms (calcifying) and by previous processes of the carbon cycle, this means that the carbon is released again into the atmosphere. Volcanoes are now producing between 130-180 million metric tonnes of carbon per year.
Not just volcanoes...
The geological carbon cycle
The carbon cycle
The biological carbon cycle
Plant and animal respiration
Combustion is a process that releases carbon into the atmosphere this process requires fuel and oxygen. Combustion of organic matter is incomplete and leads to the production of carbon dioxide, methane and carbon monoxide. Wildfires release carbon during combustion and also the result of organic matter not combusted decaying adds further to the carbon in the atmosphere. Combustion of biomass adds approximately 1.6 million gigatonnes of carbon into the atmosphere per year.
Carbon can be stored in animal bodies and plant bodies such as trees. This is a type of storage that is not very long term and it is accumulated by ingesting organic molecules or photosynthesizing. In trees the carbon is stored in cellulose, the cellulose is used to form the structure of the tree. Approximately 610 billion gigatonnes of carbon are stored in terrestrial plants such as trees, this storage could last hundreds to thousands of years (the oldest tree is over 2000 years old). Animal storage of carbon is caused by ingesting plant material and storing the carbon in the tissues, carnivores can then ingest the tissues of those that ate plant material and thus transferring the carbon to their own tissues, some of this storage lasts an animal's lifetime.
When plants and animals die or waste is produced, it undergoes a process of decay or decomposition. Fungi and bacteria break down this stored carbon into carbon dioxide if there is enough oxygen or methane if there is not enough oxygen. This carbon is released into the atmosphere, 60 billion metric tonnes are released back into the atmosphere. An example is melting permafrost which is contributing to global warming 21 times more than by carbon dioxide. Partially decomposed matter is also used as a form of carbon storage and stores approximately 1,600 gigatonnes of carbon, in the soil.
The main forms of removal in the biological cycle (aka short term) are either by photosynthesis or chemosynthesis. These processes are managed by autotrophs such as plants, phytoplankton or bacteria (archaea) that live at sea vents. These organisms use sunlight or chemical energy to convert products such as carbon dioxide into organic compounds (eg. glucose). This example uses plants as a method of carbon removal, by photosynthesis in a tree as most carbon removal is by the process of photosynthesis. The plant uses this method to create food for itself so it can carry out it's life processes. Atmospheric carbon enters the leaf through the stomata on the underside of the leaf while oxygen and some water is lost through the stomata. The carbon dioxide then diffuses through the thin leaf and enters the cells in the mesophyll (palisade and spongy) then the carbon dioxide and water is converted in the chloroplasts with the assistance of sunlight is converted to glucose and oxygen. This carbon is then part of glucose and is taken via the phloem to be stored. Photosynthesis removes about 121.3 billion metric gigatonnes per year of carbon from the atmosphere.
this is a bird poo
The biological carbon cycle is the fast carbon cycle, this carbon cycle can be measured in a lifespan as this cycle is the transfer of carbon through organisms in the biosphere. This cycle transfers 1 billion to 10 billion metric tonnes of carbon per year, which is a much larger amount per year than the geological carbon cycle. The storage from this cycle also does not last as long as the geological carbon cycle because it is only short term.
This process is the movement of carbon from the atmosphere to the largest geological carbon store which is deep underground in the lithosphere. In the atmosphere, carbon dioxide combines with with water to form carbonic acid, this acid falls to the surface as rain.
This rain erodes rocks- chemical weathering and releases magnesium, sodium, calcium or potassium ions. All different types of rocks erode at different rates, the rate depends on the reactivity of the rock, minerals such as gold are not very reactive and thus are very hard to weather. Other minerals such as sulphides are very reactive and weather easily and the weathering is shown by a film of often colourful secondary minerals (such as malachite), minerals such as carbonates react with carbonic acid even more quickly. Although most rocks are on the more stable end of the spectrum and the weathering takes millions of years. The weathering occurs by large amounts of weak carbonic acid (pH: 4-4.5) over long periods of time. An example of a rock being chemically weathered is calcium carbonate (on the surface), the process of weathering produces calcium and bicarbonate ions in solution.
Weathering removes about a gigatonne of carbon from the atmosphere per year. All of these ions are transported by streams to rivers and from rivers to the ocean.
These ions are transported by rivers to the ocean.
Calcium carbonate is produced
These dissolved calcium ions combine with the dissolved bicarbonate ions and form calcium carbonate, 80% of carbon containing rock is formed in this way. This creation (reprecipitation) of calcium carbonate is mostly created by calcifying organisms such as corals and plankton (cocolithophores, foraminifera) as these organisms form their shells or skeletons out of calcium carbonate. There is a net loss of carbon in this process, as the process ends with half as much carbon as it began. This carbon is then locked away as calcium carbonate and as these organisms die the calcium carbonate remains locked.
Formation of limestone
After these organisms die, they sink to the seafloor, over a long time layers of shells and sediment are cemented together and turn to rock, which stores the carbon in rocks such as limestone. This part of the process remains for a very long time (insert time), thus labeled long term storage. Both calcium and magnesium play a large part in storing the carbon because of both their abundance and their chemical properties that allow them to store carbon in this way. Only 0.032% of the lithosphere is stored carbon by weight. 150 billion metric tonnes of carbon are stored in sedimentary deposits.
An alternative way of storing carbon is by the death and the layering of dead organisms. 20% of carbon storage is created by this method. The organisms first die, they then sink to the seafloor. Over time more and more layers are created of these dead organisms, as the remains are pushed deeper they become sedimentary rocks such as shale due to the heat and pressure deep underground, these sedimentary rocks are stored as part of a large carbon storage underground. The organic carbon in their bodies is locked in the sedimentary rock. Sometimes dead plant matter accumulates faster than it can decay, the layers of carbon become oil, coal or natural gas instead of a sedimentary rock, during these times the rate of photosynthesis exceeded the rate of respiration. 4000 billion metric tonnes in total are stored as fossil fuel deposits.
Carbon storage through organic matter
All cells carry out respiration in order to produce energy so they can survive and replicate. This can be aerobic respiration (with oxygen) or anaerobic respiration (without oxygen), a product of respiration is carbon dioxide as well as energy, thus this process adds carbon into the atmosphere. In plants carbon dioxide is expelled by the stomata on the underside of the leaf after diffusing through to the underside of the leaf from the cell. In animals the carbon dioxide is diffused into the blood stream at the capillaries, it is then taken by veins to the heart which it enters through the vena cava. The carbon dioxide then exits the heart by the pulmonary artery which takes it to the lungs and then the carbon dioxide diffuses from a capillary into an alveolus, it is then transported through the trachea and out into the atmosphere as the animal exhales. The amount of carbon released by respiration is 60 billion gigatonnes per year. The balance between photosynthesis and respiration is managed by the amount of daylight in a day as photosynthesis stops at night because it needs sunlight for the process but respiration continues. This means at nighttime more carbon is added to the atmosphere than removed. This change in amount of photosynthesis is seen by the increase in atmospheric carbon during the winter where days are shorter and many trees lose their leaves (can't photosynthesize) and decrease in spring and summer while the plants are growing and sprouting new leaves.
At a point where two plates meet, due to seafloor spreading, subduction could occur. One plate that is denser than the other plate (eg. oceanic plate compared to continental plate) begins to move further underneath the less dense continental plate. As the plate is being pushed underneath the other plate the rock in the plate begins to melt as a result of immense heat and pressure, this rock then becomes part of the mantle, it partially melts.
Respiration chemical equation:
production of cement:
Human activity such as burning/consumption of fossil fuels and production of cement adds carbon to the atmosphere. Combustion of fossil fuels is used to produce electricity, for transport etc... Combustion of fossil fuels can either be incomplete combustion or complete combustion. Combustion produces water and carbon dioxide, carbon (soot) and carbon monoxide.
Another process that produces lots of carbon dioxide is the production of cement, large quantities of fossil fuels are used during production. To form lime, a component of cement, calcium carbonate is heated, this produces a large amount of carbon dioxide which is released into the atmosphere. Combustion and cement production combined release about 5.5 million gigatonnes of carbon into the atmosphere per year.
Over 200 years ago New Zealand had a much smaller population compared to today, in total the population was only 100,000-120,000 individuals. Today the population of New Zealand is at approximately 4,500,000. A much smaller population and the technology 200 years ago lead to a more conservative and traditional system of production, the majority of the population was Maori, who upheld their traditional methods of farming root vegetables (they did not keep livestock) and their spiritual beliefs in the forests, as some places were considered Tapu and people were not allowed to harm these places or exploit these places. The Maori also held a belief in Tangata Whenua as they regard themselves as people of the forest, this meant that they co-exist with the forest and respecting living creatures and the environment. For example the Maori believed that fish were the children of Tangaroa- the god of seas and oceans and they sang a karakia to appease Tangaroa so that they can take fish, as it is seen that taking fish is an attack on Tangaroa's children. At this time there were only about a hundred of the British in New Zealand and their less sustainable activities had less of an impact at the time, therefore the carbon emissions from 200 years ago were much smaller than today. They were not negligible though as both the British and the Maori burnt large tracts of forest to make way for grassland, by (beginning of British colonisation) 1840 around 6.7 million hectares of forest has been replaced by grassland. This means that (as about 186 tonnes are stored of carbon dioxide in an acre of mature forest, therefore... 186 x 16,556,060.56-in acres=3,079,427,264 (1 decimal place) about 3,000,000,000 tonnes of carbon dioxide (equivalent) (3079427264/3.666=840,000,000 tonnes of carbon) was lost from storage and some released into the atmosphere by the combustion of the trees and if not combustion, eventually by decay. There is also loss of 6.7 million hectares of photosynthesizing trees. Keep in mind that this is the total deforestation since the Maori came to New Zealand at about 1250-1300 AD.
Today New Zealand has total carbon emissions of 76.048 Gg of carbon dioxide equivalent over the course of 2013. The largest contributor to the total is the agriculture sector, this produces 35,020.1 Gg and is 46% of the total carbon dioxide emitted. This number is caused mostly by the hold of livestock, especially cows. Cows themselves produce (they are the 2nd largest source of carbon emitted) 10,807 Gg of carbon dioxide equivalent in total, there are about 10.2 (6.5 dairy+3.7 beef) million cows in New Zealand. There are also about 30.8 million sheep and 1 million deer. Agriculture is a large part of New Zealand's economy and the increase in agricultural emissions is due to the increasing population and the improvement of the efficiency of these methods. Another large contribution to total carbon emissions is the production of energy; this releases 32,121.3 Ggs of carbon dioxide equivalent and 42% of the total emissions. This sector involves the many small sections of energy related industries, these industries usually use fossil fuels such as natural gas, oil or coal. The largest contributor to this sector is the production of public electricity and heat production this contributor produces 2643.8 Ggs of carbon dioxide equivalent. Public electricity production from coal or gas is approximately a quarter of energy produced in New Zealand, for example, coal energy production is based in the Waikato region and the Huntly power station. Energy production was non existent 200 years ago, the invention of using electricity and the larger population increased the carbon emissions. Deforestation has reduced the native forest area to 6.2 hectares (measured in 2000), but some reforestation and pine forests set the number at 82690 square kilometers (measured in 2013), so there is some forest photosynthesising and storing carbon. The deforestation from 1840-2000 released about (8 million hectares cleared) 3,600,000,000 tonnes of carbon dioxide equivalent. New Zealand has higher emissions today than 200 years ago due to population size and the change of lifestyle which lead to increased carbon emissions.
*LULUCF: Land Use, Land Use Change and Forestry