The sea carbon cycle (or sea carbon cycle ) consists of a process that exchanges carbon between the various pools in the ocean as well as between the atmosphere, the Earth's interior, and the seabed. Carbon is a very important element for all living things; the human body consists of about 18% carbon. The carbon cycle is the result of many interacting forces at different timescales and spaces that circulate carbon around the planet, ensuring that carbon is available globally. The Oceanic carbon cycle is the central process for the global carbon cycle and contains inorganic carbon (carbon not related to living things, such as carbon dioxide) and organic carbon (carbon which, or has been, incorporated into living things). Part of the marine carbon cycle changes the carbon between inanimate and living things.
The three main processes (or pumps) that make up the marine carbon cycle carry atmospheric carbon dioxide (CO 2 ) into the interior of the ocean and distribute it through the oceans. The three pumps are: (1) solubility pump, (2) carbonate pump, and (3) biological pump. Total active carbon on the surface of the Earth for a period of less than 10,000 years is about 40,000 gigaton C (Gt C, gigaton is one billion tons, or weighs about 6 million blue whales), and about 95% (~ 38,000 Gt C) is stored in the ocean , mostly as dissolved inorganic carbon. The dissociation of inorganic carbon dissolved in the marine carbon cycle is the main chemical-acid-base control in the oceans.
Plants and Earth algae (major producers) are responsible for the largest annual carbon flux. Although the amount of carbon stored in marine biota (~ 3 Gt C) is very small compared to terrestrial vegetation (~ 610 GtC), the amount of carbon exchanged (flux) by these groups is almost the same - about 50 GtC each. Marine organisms connect the carbon and oxygen cycle through processes such as photosynthesis. The marine carbon cycle is also biologically bound by the nitrogen and phosphor cycle by nearly constant stoichiometric ratios C: N: P from 106: 16: 1, also known as the Redfield Ketchum Richards (RKR) ratio, which states that the organism tends to take nitrogen and phosphorus which incorporates new organic carbon. Likewise, the organic material broken down by bacteria releases phosphorus and nitrogen.
Based on the publication of NASA, the World Meteorological Association, IPCC, and the International Council for Sea Exploration, as well as scientists from NOAA, Woods Hole Oceanographic Institution, Scripps Institution of Oceanography, CSIRO, and Oak Ridge National Laboratory, human impact on the carbon cycle of the ocean is significant. Before the Industrial Revolution, the oceans were the net source of CO 2 to the atmosphere whereas now most of the carbon entering the ocean comes from atmospheric carbon dioxide (CO 2 ). The burning of fossil fuels and cement production has changed the balance of carbon dioxide between the atmosphere and the oceans, causing ocean acidification. Climate change, the result of the excess of CO 2 in the atmosphere, has increased the temperature of the ocean's atmosphere (global warming). The slowing rate of global warming that occurred from 2000-2010 may be due to observed increases in the ocean's upper ocean temperatures.
Video Oceanic carbon cycle
Karbon laut
Carbon compounds can be distinguished as organic or inorganic, and dissolved or particulate, depending on their composition. Organic carbon forms the backbone of key components of organic compounds such as proteins, lipids, carbohydrates, and nucleic acids. Inorganic carbon is found mainly in simple compounds such as carbon dioxide, carbonic acid, bicarbonate, and carbonates (CO 2 , H 2 CO 3 , HCO < sub> 3 - , CO 3 2 - respectively).
Marine carbons are further separated into particulate and dissolved phases. These pools are operationally defined by physical separation - the dissolved carbon passes through a 0.2 m filter, and particulate carbon is not.
Inorganic Carbon
There are two main types of inorganic carbon found in the oceans. Dissolved inorganic carbon (DIC) is composed of bicarbonate (HCO 3 - ), carbonate (CO 3 2 - ) and carbon dioxide (including dissolved CO 2 and carbonic acid H 2 CO 3 ). DIC can be converted to inorganic carbon particles (PIC) by precipitation of CaCO 3 (biologically or abiotic). DIC can also be converted into organic carbon particles (POC) through photosynthesis and chemoautotrophy (ie primary production). DIC increases with depth when organic carbon particles are submerged and drifted. Free oxygen decreases because DIC increases because oxygen is consumed during aerobic respiration.
Particulate inorganic carbon (PIC) is another form of inorganic carbon found in the oceans. Most PICs are CaCO 3 which compose the shells of various marine organisms, but can also form in the desired event. Sea fish also emit calcium carbonate during osmoregulation.
Several inorganic carbon species in the ocean, such as bicarbonate and carbonate, are major contributors to alkalinity, a natural ocean buffer that prevents drastic changes in acidity (or pH). The sea carbon cycle also affects the reaction and dissolution rates of some chemical compounds, regulating the amount of carbon dioxide in the atmosphere and the Earth's temperature.
Organic carbon
Like inorganic carbon, there are two major forms of organic carbon found in the ocean (dissolved and particulates). Dissolved organic carbon (DOC) is defined operationally as any organic molecule that can pass 0.2 Âμm filter. DOC can be converted to particulate organic carbon through heterotrophy and can also be converted back into dissolved inorganic carbon (DIC) through respiration.
The organic carbon molecules captured in the filter are defined as organic carbon particles (POCs). POC consists of organisms (live or dead), their droppings, and detritus. POC can be converted to DOC by molecular disaggregation and by exudation by phytoplankton, for example. POC is generally converted to DIC through heterotrophy and respiration.
Maps Oceanic carbon cycle
Marine carbon pump
Solubility pump
Full article: Solubility pump
The oceans store the largest collection of reactive carbon on the planet as DIC, introduced as a result of dissolving atmospheric carbon dioxide into seawater - solubility pumps. CO water 2 , carbonic acid ions, bicarbonate, and carbonate ions consist of dissolved inorganic carbon (DIC). DIC circulates across the ocean with Thermohaline circulation, which facilitates the incredible DIC storage capacity of the oceans. The chemical equation below shows the reactions experienced by CO 2 after entering the ocean and turning into an aqueous form.
First, carbon dioxide reacts with water to form carbonic acid.
Carbonic acid quickly dissociates into free hydrogen ions (technically, hydronium) and bicarbonate.
Free hydrogen ions meet carbonates, already present in water from dissolving CaCO 3 , and react to form more bicarbonate ions.
The dissolved species in the above equation, most bicarbonate, form the carbonate alkalinity system, the dominant contributor of alkalinity in seawater.
Carbonate pump
The carbonate pump, sometimes called a carbonate counter pump, begins with marine oceanic organisms that produce inorganic carbon particles (PICs) in the form of calcium carbonate (calcite or aragonite, CaCO 3 ). CaCO 3 This is what forms a hard body part like a shell. The formation of this shell increases atmospheric CO 2 due to the production of CaCO 3 in the following reaction with simplified stoichiometry:
Coccolithophores, an almost ubiquitous phytoplankton group that produces calcium carbonate shells, is a dominant contributor to carbonate pumps. Due to its abundance, coccolithophores have significant implications on carbonate chemistry, on the surface of the waters they occupy and in the ocean below: they provide a large mechanism for transport under CaCO 3 . Air-ocean CO 2 The flux induced by the marine biological community can be determined by the ratio of rain - the proportion of carbon from calcium carbonate compared to organic carbon in submerged particulate matter to the ocean floor (PIC/POC). The carbonate pump acts as a negative feedback on CO 2 brought to the ocean by the solubility pump. This happens with less power than the solubility pump.
Biological pump
Complete article: Biological pump
Particulate organic carbon, made through biological production, can be exported from the upper ocean in flux, commonly called biological pumps, or breathing (equation 6) back into inorganic carbon. In the first, dissolved inorganic carbon is biologically converted to organic material by photosynthesis (equation 5) and other forms of autotrophy which are then submerged and partially or completely digested by heterotrophs. Particulate organic carbon can be classified, based on how easily the organism can break it down for food, such as labile, semilabile, or refractory. Photosynthesis by phytoplankton is a major source for labile and semilabile molecules, and is an indirect source for most refractory molecules. The labile molecule is present at low concentrations outside the cell (in the pikomolar range) and has a half-life of only a few minutes when free in the oceans. They are consumed by microbes within hours or days of production and are at the surface of the oceans, where they contribute most of the volatile carbon flux. The semilabile molecule, much more difficult to consume, is capable of reaching depths of hundreds of meters below surface before it is metabolized. Refractory DOM consists mainly of high conjugated molecules such as polycyclic aromatic hydrocarbons or lignin. Refractory DOM can reach depths of more than 1000 m and circulate through the oceans for thousands of years. For one year, approximately 20 gigatons of carbon-produced fabril and photosynthetic fixed semilabile have been taken by heterotrophs, while less than 0.2 gigatons of refractory carbon are consumed. Marine soluble (DOM) materials can store carbon as much as the current CO2 supply in the atmosphere, but industrial processes alter the balance of this cycle.
Input
Inputs for the marine carbon cycle are numerous, but the main contribution, net, comes from the atmosphere and rivers. Hydrothermal vents generally supply the same carbon as the amount they consume.
Atmosphere
Prior to the Industrial Revolution, the oceans were the source of CO 2 to an atmosphere that balances the impact of weathering and organic carbon on terrestrial particles; has now become a sink for excess atmospheric CO 2 . Carbon dioxide is absorbed from the atmosphere at sea level with exchange rates varying locally but on average, the oceans have a net absorption of CO 2 2.2 Pg C per year. Since the solubility of carbon dioxide increases as the temperature decreases, the cold regions may contain more CO 2 and remain in equilibrium with the atmosphere; In contrast, rising sea surface temperatures decrease the capacity of the oceans to extract carbon dioxide. The North Atlantic and Nordic seas have the highest carbon absorption per unit area in the world, and in convection within the North Atlantic transport about 197 Tg per year from non-refractory carbon to depth.
Carbon dioxide exchange rates between oceans and atmosphere
The ocean atmospheric exchange of CO 2 depends on the concentration of carbon dioxide already present in both the atmosphere and the oceans, temperature, salinity, and wind speed. This exchange rate can be approximated by Henry's law and can be calculated as S = kP, where the solubility (S) of carbon dioxide gas is proportional to the amount of gas in the atmosphere, or its partial pressure.
Revelle factor
Since carbon dioxide ocean intake is limited, the entry of CO 2 can also be explained by the Revelle factor. Revelle Factor is the ratio of changes in carbon dioxide to changes in dissolved inorganic carbon, which serves as an indicator of dissolution of carbon dioxide in the mixed layer considering the solubility pump. The Revelle Factor is an expression for characterizing the thermodynamic efficiency of a DIC pool to absorb CO 2 into bicarbonate. The lower the Revelle factor, the higher the capacity of sea water to take up carbon dioxide. While Revelle calculated a factor of about 10 in his time, the 2004 study data showed Revelle factors ranging from about 9 in the low to 15th low tropical region in the southern ocean near Antarctica.
River
The river can also transport organic carbon to the sea by weathering or erosion of aluminosilicates (equation 7) and carbonate rocks (equation 8) on land,
or by decomposition of life (equation 5, eg crops and soil material). The river accounts for approximately the same (~ 0.4 GtC/yr) of DIC and DOC to the oceans. It is estimated that about 0.8 GtC (DIC DOC) is transported annually from river to sea. The rivers flowing into the Chesapeake Bay (Susquehanna, Potomac, and James river) input about 0.004 Gt (6.5 x 10 10 mol) DIC per year. Total carbon transport of the river represents about 0.02% of the total carbon in the atmosphere. Although seemingly small, on a long time scale (1000 to 10,000 years) the carbon entering the river (and therefore not entering the atmosphere) serves as a stabilizing feedback for greenhouse warming.
Output
The main outputs of the marine carbon system are the preservation of particulate organic matter (POC) and calcium carbonate (PIC) and reverse weathering. While there are areas with local CO loss sub  «2 to the atmosphere and the hydrothermal process, a net loss in the cycle does not occur.
Preservation of organic matter
Sedimentation is a long-term carbon sink in the ocean, as well as the largest loss of carbon from marine systems. Deep sea sediments and geologic formations are important because they provide a comprehensive life record on Earth and an important source of fossil fuels. Carbon marine can come out of the system in the form of a drowning detritus and buried in the seabed without being completely decomposed or dissolved. Sea surface oceans contribute 1.75x10 15 kg of carbon in the global carbon cycle At most, 4% of the organic carbon particles are from the euphotic zone in the Pacific Ocean, where primary production using light power occurs. , buried in marine sediments. Then it is implied that because there is a higher input of organic matter to the ocean than is buried, it is mostly used or consumed inside.
The fate of sinking organic carbon
Historically, sediments with the highest organic carbon content are often found in areas with high surface water productivity or those with low underwater oxygen concentrations. 90% of organic carbon degradation occurs in delta deposits and continental shelf and upper slopes; This is partly due to short exposure times due to shorter distances to the seafloor and the composition of organic materials already stored in the environment. Organic carbon cemetery is also sensitive to climatic patterns: the organic carbon accumulation rate is 50% greater during the glacial maximum than the interglacial.
Degradation
POCs are decomposed by a series of microbial processes, such as methanogenesis and sulfate reduction, prior to burial on the seafloor. POC degradation also produces the production of microbial methane which is the primary gas hydrate at the continental margin. Lignin and pollen are essentially resistant to degradation, and several studies have shown that inorganic matrix can also protect organic matter. The degree of preservation of organic matter depends on other interdependent variables that vary non-linearly in space and time. Although the breakdown of organic matter occurs rapidly in the presence of oxygen, microbes that use various chemical species (via redox gradients) can degrade organic matter in anoxic sediments. The burial depths in which stopping degradation depend on the level of sedimentation, the relative abundance of organic matter in the sediments, the type of buried organic material, and innumerable other variables. While decomposition of organic matter may occur in anoxic sediments when bacteria use oxidants other than oxygen (nitrate, sulfate, Fe 3 ), decomposition tends to end the complete lack of mineralization. This occurs because of the special decomposition of the labile molecule over the refractory molecule.
Funeral
Organic carbon cemetery is the energy input for underground biological environments and can regulate oxygen in the atmosphere on long time scales (& gt; 10,000 years). Funerals can only occur if organic carbon arrives at the seafloor, creating a continental shelf and coastal margins of primary storage of organic carbon from the production of terrestrial primers and oceans. Fjords, or cliffs made by glacial erosion, have also been identified as significant carbon burial areas, at a rate a hundred times larger than the average ocean. Particulate organic carbon is buried in ocean sediments, creating a pathway between carbon pools that are readily available in the ocean to their storage for geological time spans. Once carbon is sequestered in the seafloor, it is considered blue carbon. The funeral rate can be calculated as the difference between the rate at which the organic matter sinks and the rate at which it decomposes.
preservation of calcium carbonate
Calcium carbonate deposition is important because it results in loss of alkalinity and release of CO 2 (Eq. 4), and therefore changes in calcium carbonate preservation rates can alter CO = sub> 2 partial pressure in Earth's atmosphere. CaCO 3 is saturated in most of the ocean surface waters and undersaturated at depth, which means the shells are more likely to dissolve as they sink into the depths of the ocean. CaCO 3 can also be dissolved through metabolic dissolution (ie can be used as food and excreted) and thus deep ocean sediments have very little calcium carbonate. The precipitation and burial of calcium carbonate in the sea removes the inorganic carbon particles from the sea and eventually forms limestone. Timely scales larger than 500,000 years of Earth's climate are moderated by the carbon flux in and out of the lithosphere. The rocks formed at the bottom of the ocean are recycled through tectonic plates back to the surface and undergo bad weather or subduction into the mantle, the carbon is defeated by volcanoes.
Human impact
The oceans take 15-40% of the anthropogenic CO 2 , and so far approximately 40% of the carbon from burning fossil fuels has been brought into the oceans. As the Revelle factor increases with increasing CO 2 , a smaller fraction of the anthropogenic flux will be taken by the sea in the future. The current annual increase in atmospheric CO 2 is about 4 gigatonnes of carbon. This induces climate change that drives the process of carbon concentration and carbon climate feedback that modifies the ocean's circulation and the physical and chemical properties of seawater, which alters the absorption of CO 2 .
Ocean acidity analysis
Full article: ocean acidification
The pH of the ocean decreases due to the absorption of atmospheric CO 2 . Increased carbon dioxide reduces the availability of carbonate ions, reducing the saturation status of CaCO 3 , thereby making it thermodynamically harder to make CaCO 3 shell. The carbonate ions preferentially bind to hydrogen ions to form bicarbonate, so the reduction of carbonate ion availability increases the amount of unbound hydrogen ions, and decreases the amount of bicarbonate formed (Eq. 1-3). pH is a measure of the concentration of hydrogen ions, where a low pH means there are more unbound hydrogen ions. Therefore pH is an indicator of carbonate speciation (format of the existing carbon) in the ocean and can be used to assess how healthy the ocean.
List of organisms that may be struggling due to ocean acidification include coccolithophores and foraminifera (the base of seafood chains in many areas), human food sources such as oysters and shellfish, and perhaps the most striking, structures built by coral-organisms. Most surface water will remain saturated with respect to CaCO 3 (both calcite and aragonite) for some time on the current emission path, but the organisms requiring carbonate are likely to be replaced in many areas. Coral reefs are under pressure from overfishing, nitrate pollution, and water heating; Ocean acidification will add pressure to this important structure.
Iron fertilization
Complete article: Iron Fertilizer
Iron fertilization is an aspect of geoengineering, which deliberately manipulates the Earth's climate system, usually in aspects of carbon cycle or radiation imposition. Current geoerineering interest is the possibility of speeding up biological pumps to increase carbon exports from sea level. This increase in exports could theoretically remove excess carbon dioxide from the atmosphere to be stored in the deep ocean. Ongoing investigations of artificial fertilization exist. Due to the scale of the ocean and the rapid response time of the heterotrophic community to the increase in primary production, it is difficult to determine whether nutrient constraints result in increased carbon exports. However, most people do not believe this is a reasonable or feasible approach.
Dams and reservoirs
There are more than 16 million dams in the world that convert carbon transport from river to ocean. Using data from the Global Reservoirs and Dams database, which contains about 7000 reservoirs that hold 77% of the total volume of water held by dams (8000 km 3 ), it is estimated that carbon shipments to the sea have decreased 13% in 1970 and is projected to reach 19% by 2030. Excess carbon contained in the reservoir may emit an additional ~ 0.184 Gt of carbon into the atmosphere per year and an additional ~ 0.2 GtC will be buried in the sediments. Prior to 2000, Mississippi, Niger, and the Ganges River were responsible for 25 - 31% of all reservoir carbon sinks. After 2000, ParanÃÆ'¡ (home to 70 dams) and Zambezi (home to the largest reservoir). River watershed exceeds the burial by Mississippi. Other major contributors to the carbon burial caused by the dams occurred in the Danube, the Amazon, the Yangtze, the Mekong, the Yenisei, and the Tocantins River.
References
Source of the article : Wikipedia
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