Calcium cycle

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The calcium cycle is a transfer of calcium between dissolved and solid phases. There is a continuous supply of calcium ions into waterways from rocks, organisms, and soils. [1] [2] Calcium ions are consumed and removed from aqueous environments as they react to form insoluble structures such as calcium carbonate and calcium silicate, [1] [3] which can deposit to form sediments or the exoskeletons of organisms. [4] Calcium ions can also be utilized biologically, as calcium is essential to biological functions such as the production of bones and teeth or cellular function. [5] [6] The calcium cycle is a common thread between terrestrial, marine, geological, and biological processes. [7] Calcium moves through these different media as it cycles throughout the Earth. The marine calcium cycle is affected by changing atmospheric carbon dioxide due to ocean acidification. [4]

Contents

Calcium weathering and inputs to seawater

Calcium is stored in geologic reservoirs, most commonly in the form of calcium carbonate or as calcium silicate. [1] Calcium-containing rocks include calcite, dolomite, phosphate, and gypsum. [8] Rocks slowly dissolve by physical and chemical processes, carrying calcium ions into rivers and oceans. Calcium ions (Ca2+) and magnesium ions (Mg2+) have the same charge (+2) and similar sizes, so they react similarly and are able to substitute for each other in some minerals, such as carbonates. [9] Ca2+-containing minerals are often more easily weathered than Mg2+ minerals, so Ca2+ is often more enriched in waterways than Mg2+. [8] Rivers containing more dissolved Ca2+ are generally considered more alkaline. [8] Calcium is one of the most common elements found in seawater. Inputs of dissolved calcium (Ca2+) to the ocean include the weathering of calcium sulfate, calcium silicate, and calcium carbonate, basalt-seawater reaction, and dolomitization. [2] [1]

Biogenic calcium carbonate and the biological pump

Biogenic calcium carbonate is formed when marine organisms, such as coccolithophores, corals, pteropods, and other mollusks transform calcium ions and bicarbonate into shells and exoskeletons of calcite or aragonite, both forms of calcium carbonate. [10] This is the dominant sink for dissolved calcium in the ocean. [7] Dead organisms sink to the bottom of the ocean, depositing layers of shell which over time cement to form limestone. This is the origin of both marine and terrestrial limestone. [10]

Calcium precipitates into calcium carbonate according to the following equation:

Ca2+ + 2HCO3− → CO2+ H2O + CaCO3 [2]

The relationship between dissolved calcium and calcium carbonate is affected greatly by the levels of carbon dioxide (CO2) in the atmosphere.

Increased carbon dioxide leads to more bicarbonate in the ocean according to the following equation:

CO2 + CO32− + H2O → 2HCO3− [10]

Equilibrium of carbonic acid in the oceans Equilibrium of carbonic acid in the oceans .png
Equilibrium of carbonic acid in the oceans
Deposition of calcifying organisms/shells on the ocean floor LimestoneWithFossilUSGOV.jpg
Deposition of calcifying organisms/shells on the ocean floor
The carbonate cycle in the water environment The carbonate cycle in the water environment.jpg
The carbonate cycle in the water environment 
Effects of an acidic ocean (with pH projected for the year 2100) on a pteropod shell made of calcite - the shell progressively dissolves in the lower pH as calcium is drawn out of the shell Pterapod shell dissolved in seawater adjusted to an ocean chemistry projected for the year 2100.jpg
Effects of an acidic ocean (with pH projected for the year 2100) on a pteropod shell made of calcite - the shell progressively dissolves in the lower pH as calcium is drawn out of the shell

With ocean acidification, inputs of carbon dioxide promote the dissolution of calcium carbonate and harm marine organisms dependent on their protective calcite or aragonite shells. [10] The solubility of calcium carbonate increases with pressure and carbon dioxide and decreases with temperature. Thus, calcium carbonate is more soluble in deep waters than surface waters due to higher pressure and lower temperature. As a result, precipitation of calcium carbonate is more common in shallower oceans. The depth at which the rate of calcite dissolution equals the rate of calcite precipitation is known as calcite compensation depth. [13] [14]

Changes in global climate and the calcium cycle

Ocean acidity due to carbon dioxide has already increased by 25% since the industrial revolution. As carbon dioxide emissions continually increase and accumulate, this will negatively affect the lives of many marine ecosystems. The calcium carbonate used to form many marine organisms' exoskeletons will begin to break down, leaving these animals vulnerable and unable to live in their habitats. This ultimately has a flow on effect to predators, further affecting the function of many food webs globally. [13]

Changes in calcium concentrations over geologic time

Calcium stable isotopes have been used to study inputs and outputs of dissolved calcium in marine environments. [15] For example, one study found that calcium levels have decreased between 25 and 50 percent over a 40 million year timespan, suggesting that dissolved Ca2+outputs have exceeded its inputs. [16] The isotope Calcium-44 can help to indicate variations in calcium carbonate over long timespans and help explain variants in global temperature. Declines in the isotope Calcium-44 usually correlate with periods of cooling, as dissolution of calcium carbonate typically signifies a decrease in temperature. [17] Thus, Calcium isotopes correlate with Earth's climate over long periods of time.

Human/animal use of calcium

bodily homeostasis of calcium Calcium balance 2.jpg
bodily homeostasis of calcium

Being an essential element, calcium is obtained through dietary sources, the majority of which comes from dairy products. The three most significant mechanisms controlling calcium use within the body are intestinal absorption, renal absorption and bone turnover, which is controlled predominantly by hormones and their corresponding receptors in the gut, kidneys and bones respectively. This allows for calcium use throughout the body, namely in bone growth, cellular signalling, blood clotting, muscle contraction and neuron function. [18] [19]

Calcium is one of the essential components of bone, contributing to its strength and structure in addition to being the main site at which it is stored within the body. Within the muscles, its primary use is to enable contractions. Muscle cells draw calcium from the blood, allowing it to bind with troponin, a component of the muscle fibre that signals for a contraction by moving actin and myosin. After a contraction, calcium dissipates and the filaments move back to a resting state before the release of more calcium for the next contraction. [20] Furthermore, calcium plays a significant role in allowing nerve impulses to be transmitted between neurons. [21] The release of calcium ions from voltage gated ion channels signals for the release of neurotransmitters into the synapse. This allows for the depolarisation of a neuron, thus transmitting the signal to the next neuron where this process is once again repeated. Without the presence of calcium ions, the release of neurotransmitters would not occur, preventing signals from being sent and hindering body processes.

Negative feedback mechanisms are implemented in order to control calcium levels. When low calcium levels are detected in the body, the parathyroid releases parathyroid hormone (PTH) which travels through the bloodstream to the bones and kidneys. In the bones, the presence of PTH stimulates osteoclasts. These cells break down bone to release calcium into the bloodstream where it can be used by the rest of the body [22] in the above processes. In the kidneys, PTH stimulates re-absorption of calcium so it in not lost from the body through urine and returned to the bloodstream instead. Lastly, PTH acts on the intestines by indirectly promoting enzymes that activate vitamin D, a signal for the intestines to absorb more calcium, further increasing blood calcium levels. [23] This will continue until the body releases too much calcium into the bloodstream. Excess calcium then promotes the release of calcitonin from the thyroid gland, effectively reversing the process of PTH. Osteoclast activity is stopped and osteoblasts take over, utilising the excess calcium in the bloodstream to form new bone. Calcium re-absorption in the kidney is prevented, allowing the excretion of excess calcium through the urine. [24] Through these hormonal mechanisms, calcium homeostasis is maintained within the body.

Calcium in plants and soil

movement of calcium from the soil into the roots, through the xylem to the leaves of a plant How the Xylem Plays a Role in Transpiration.svg
movement of calcium from the soil into the roots, through the xylem to the leaves of a plant

Calcium is an essential component of soil. When deposited in the form of lime, it cannot be used by plants. To combat this, carbon dioxide produced by plants reacts with water in the environment to produce carbonic acid. Carbonic acid is then able to dissolve limestone, enabling the release of calcium ions. This reaction is more readily available with smaller particles of limestone than it is with large pieces of rock due to the increased surface area. When lime is leached into soil, calcium levels inevitably increase, both stabilising pH and enabling calcium to mix with water to form Ca2+ ions, thus making it soluble and accessible to plants to be absorbed and utilised by the root system. The calcium ions travel up the xylem of the plant alongside water to reach the leaves. The plant can utilise this calcium in the form of calcium pectate to stabilise cell walls and provide rigidity. Calcium is also used by plant enzymes to signal growth and coordinate life-promoting processes. [25] Additionally, the release of calcium ions enables microorganisms to access phosphorus and other micro nutrients with greater ease, improving the soil ecosystem drastically thus indirectly promoting plant growth and nutrition. [26]

Inevitable plant and animal death results in the return of calcium contained within the organism back into the soil to be utilised by other plants. Decomposing organisms break them down, returning the calcium back into the soil and enabling the cycling of calcium to continue. [27] Additionally, these animals and plants are eaten by other animals, similarly continuing the cycle. It is however important to note the modern introduction of calcium into the soil by humans (through fertilisers and other horticultural products) has resulted in a higher concentration of calcium contained within soil.

Industrial uses of calcium and its impact on the calcium cycle

The naturally occurring calcium cycle has been altered by human intervention. Calcium is predominantly extracted from limestone deposits to be utilised by many industrial processes. Purification of iron ore and aluminium, replacing asbestos brake linings and some coatings for electric cables, are some of these major uses of calcium. Furthermore, calcium is used within the household to maintain alkaline pH of swimming pools, counteracting acidic disinfectants and in the food production industry to produce bicarbonate soda, some wines and dough. [28]

Aerial view of limestone mines at Cedar Creek Limestone Mines at Cedar Creek.jpg
Aerial view of limestone mines at Cedar Creek

With its widespread uses, a large volume of calcium must be obtained from mines and quarries to supply the high demand. As more limestone and water is removed from mines, underground stores of rock are often weakened making the ground more susceptible to sink holes. Sinkholes and mining both affect the presence of groundwater, potentially leading to a lower water table or altered pathways of flowing water. This may affect local ecosystems or farmland as the water supply is restricted. Additionally, the water that is released from mining areas will have higher concentrations of dissolved calcium. This can either be released into oceans or absorbed by the soil. Whilst not always detrimental, it alters the natural calcium cycle which may have flow-on effects for ecosystems. Furthermore, water being pumped from mines increases the danger of downstream flooding whilst simultaneously decreasing the volume on water in upstream reservoirs such as marshes, ponds of wetlands [29] It is however important to note than limestone mining is comparatively less damaging than other mining process, with potential to restore the environment after the mine is no longer in use [30]

The importance of the calcium cycle and future predictions

The calcium cycle links ionic and non ionic calcium together in both marine and terrestrial environments and is essential for the functioning of all living organisms. In animals, calcium enables neurons to transmit signals by opening voltage gated channels that allow neurotransmitters to reach the next cell, bone formation and development and kidney function, whilst being maintained by hormones that ensure calcium homeostasis is reached. In plants, calcium promotes enzyme activity and ensures cell wall function, providing stability to plants. It also enables crustaceans to form shells and corals to exist, as calcium provides structure, rigidity and strength to structures when complexed (combined) to other atoms. Without its presence in the environment, many life-preserving processes would not exist. In the modern context, calcium also enables many industrial processes to occur, promoting further technological developments.

With its close relation to the carbon cycle and the effects of greenhouse gasses, both calcium and carbon cycles are predicted to change in the coming years. [31] Tracking calcium isotopes enables the prediction of environmental changes, with many sources suggesting increasing temperatures in both the atmosphere and marine environment. As a result, this will drastically alter the breakdown of rock, the pH of oceans and waterways and thus calcium sedimentation, hosting an array of implications on the calcium cycle.

Due to the complex interactions of calcium with many facets of life, the effects of altered environmental conditions are unlikely to be known until they occur. Predictions can however be tentatively made, based upon evidence-based research. Increasing carbon dioxide levels and decreasing ocean pH will alter calcium solubility, preventing corals and shelled organisms from developing their calcium-based exoskeletons, thus making them vulnerable or unable to survive. [32] [33]

Related Research Articles

<span class="mw-page-title-main">Calcium</span> Chemical element, symbol Ca and atomic number 20

Calcium is a chemical element; it has symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar to its heavier homologues strontium and barium. It is the fifth most abundant element in Earth's crust, and the third most abundant metal, after iron and aluminium. The most common calcium compound on Earth is calcium carbonate, found in limestone and the fossilised remnants of early sea life; gypsum, anhydrite, fluorite, and apatite are also sources of calcium. The name derives from Latin calx "lime", which was obtained from heating limestone.

<span class="mw-page-title-main">Carbonate</span> Salt of carbonic acid

A carbonate is a salt of carbonic acid (H2CO3), characterized by the presence of the carbonate ion, a polyatomic ion with the formula CO2−3. The word carbonate may also refer to a carbonate ester, an organic compound containing the carbonate groupO=C(−O−)2.

<span class="mw-page-title-main">Calcite</span> Calcium carbonate mineral

Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratch hardness comparison. Large calcite crystals are used in optical equipment, and limestone composed mostly of calcite has numerous uses.

<span class="mw-page-title-main">Calcium carbonate</span> Chemical compound

Calcium carbonate is a chemical compound with the chemical formula CaCO3. It is a common substance found in rocks as the minerals calcite and aragonite, most notably in chalk and limestone, eggshells, gastropod shells, shellfish skeletons and pearls. Materials containing much calcium carbonate or resembling it are described as calcareous. Calcium carbonate is the active ingredient in agricultural lime and is produced when calcium ions in hard water react with carbonate ions to form limescale. It has medical use as a calcium supplement or as an antacid, but excessive consumption can be hazardous and cause hypercalcemia and digestive issues.

<span class="mw-page-title-main">Lysocline</span> Depth in the ocean below which the rate of dissolution of calcite increases dramatically

The lysocline is the depth in the ocean dependent upon the carbonate compensation depth (CCD), usually around 5 km, below which the rate of dissolution of calcite increases dramatically because of a pressure effect. While the lysocline is the upper bound of this transition zone of calcite saturation, the CCD is the lower bound of this zone.

<span class="mw-page-title-main">Alkalinity</span> Capacity of water to resist changes in pH that would make the water more acidic

Alkalinity (from Arabic: القلوية, romanized: al-qaly, lit. 'ashes of the saltwort') is the capacity of water to resist acidification. It should not be confused with basicity, which is an absolute measurement on the pH scale. Alkalinity is the strength of a buffer solution composed of weak acids and their conjugate bases. It is measured by titrating the solution with an acid such as HCl until its pH changes abruptly, or it reaches a known endpoint where that happens. Alkalinity is expressed in units of concentration, such as meq/L (milliequivalents per liter), μeq/kg (microequivalents per kilogram), or mg/L CaCO3 (milligrams per liter of calcium carbonate). Each of these measurements corresponds to an amount of acid added as a titrant.

<span class="mw-page-title-main">Dissolved inorganic carbon</span> Sum of inorganic carbon species in a solution

Dissolved inorganic carbon (DIC) is the sum of the aqueous species of inorganic carbon in a solution. Carbon compounds can be distinguished as either organic or inorganic, and as dissolved or particulate, depending on their composition. Organic carbon forms the backbone of key component of organic compounds such as – proteins, lipids, carbohydrates, and nucleic acids.

<span class="mw-page-title-main">Carbonate rock</span> Class of sedimentary rock

Carbonate rocks are a class of sedimentary rocks composed primarily of carbonate minerals. The two major types are limestone, which is composed of calcite or aragonite (different crystal forms of CaCO3), and dolomite rock (also known as dolostone), which is composed of mineral dolomite (CaMg(CO3)2). They are usually classified based on texture and grain size. Importantly, carbonate rocks can exist as metamorphic and igneous rocks, too. When recrystallized carbonate rocks are metamorphosed, marble is created. Rare igneous carbonate rocks even exist as intrusive carbonatites and, even rarer, there exists volcanic carbonate lava.

<span class="mw-page-title-main">Ocean acidification</span> Climate change-induced decline of pH levels in the ocean

Ocean acidification is the decrease in the pH of the Earth's ocean. Between 1950 and 2020, the average pH of the ocean surface fell from approximately 8.15 to 8.05. Carbon dioxide emissions from human activities are the primary cause of ocean acidification, with atmospheric carbon dioxide levels exceeding 410 ppm. CO2 from the atmosphere is absorbed by the oceans. This produces carbonic acid which dissociates into a bicarbonate ion and a hydrogen ion. The presence of free hydrogen ions lowers the pH of the ocean, increasing acidity. Marine calcifying organisms, such as mollusks and corals, are especially vulnerable because they rely on calcium carbonate to build shells and skeletons.

The carbonate compensation depth (CCD) is the depth, in the oceans, at which the rate of supply of calcium carbonates matches the rate of solvation. That is, solvation 'compensates' supply. Below the CCD solvation is faster, so that carbonate particles dissolve and the carbonate shells (tests) of animals are not preserved. Carbonate particles cannot accumulate in the sediments where the sea floor is below this depth.

<span class="mw-page-title-main">Carbonate–silicate cycle</span> Geochemical transformation of silicate rocks

The carbonate–silicate geochemical cycle, also known as the inorganic carbon cycle, describes the long-term transformation of silicate rocks to carbonate rocks by weathering and sedimentation, and the transformation of carbonate rocks back into silicate rocks by metamorphism and volcanism. Carbon dioxide is removed from the atmosphere during burial of weathered minerals and returned to the atmosphere through volcanism. On million-year time scales, the carbonate-silicate cycle is a key factor in controlling Earth's climate because it regulates carbon dioxide levels and therefore global temperature.

Marine chemistry, also known as ocean chemistry or chemical oceanography, is influenced by plate tectonics and seafloor spreading, turbidity currents, sediments, pH levels, atmospheric constituents, metamorphic activity, and ecology. The field of chemical oceanography studies the chemistry of marine environments including the influences of different variables. Marine life has adapted to the chemistries unique to Earth's oceans, and marine ecosystems are sensitive to changes in ocean chemistry.

Enhanced weathering, also termed ocean alkalinity enhancement when proposed for carbon credit systems, is a process that aims to accelerate the natural weathering by spreading finely ground silicate rock, such as basalt, onto surfaces which speeds up chemical reactions between rocks, water, and air. It also removes carbon dioxide from the atmosphere, permanently storing it in solid carbonate minerals or ocean alkalinity. The latter also slows ocean acidification.

<span class="mw-page-title-main">Oceanic carbon cycle</span> Ocean/atmosphere carbon exchange process

The oceanic carbon cycle is composed of processes that exchange carbon between various pools within the ocean as well as between the atmosphere, Earth interior, and the seafloor. The carbon cycle is a result of many interacting forces across multiple time and space scales that circulates carbon around the planet, ensuring that carbon is available globally. The Oceanic carbon cycle is a central process to the global carbon cycle and contains both inorganic carbon and organic carbon. Part of the marine carbon cycle transforms carbon between non-living and living matter.

<span class="mw-page-title-main">Shell growth in estuaries</span>

Shell growth in estuaries is an aspect of marine biology that has attracted a number of scientific research studies. Many groups of marine organisms produce calcified exoskeletons, commonly known as shells, hard calcium carbonate structures which the organisms rely on for various specialized structural and defensive purposes. The rate at which these shells form is greatly influenced by physical and chemical characteristics of the water in which these organisms live. Estuaries are dynamic habitats which expose their inhabitants to a wide array of rapidly changing physical conditions, exaggerating the differences in physical and chemical properties of the water.

<span class="mw-page-title-main">Ocean acidification in the Great Barrier Reef</span> Threat to the reef which reduces the viability and strength of reef-building corals

Ocean acidification threatens the Great Barrier Reef by reducing the viability and strength of coral reefs. The Great Barrier Reef, considered one of the seven natural wonders of the world and a biodiversity hotspot, is located in Australia. Similar to other coral reefs, it is experiencing degradation due to ocean acidification. Ocean acidification results from a rise in atmospheric carbon dioxide, which is taken up by the ocean. This process can increase sea surface temperature, decrease aragonite, and lower the pH of the ocean. The more humanity consumes fossil fuels, the more the ocean absorbs released CO₂, furthering ocean acidification.

<span class="mw-page-title-main">Marine biogeochemical cycles</span>

Marine biogeochemical cycles are biogeochemical cycles that occur within marine environments, that is, in the saltwater of seas or oceans or the brackish water of coastal estuaries. These biogeochemical cycles are the pathways chemical substances and elements move through within the marine environment. In addition, substances and elements can be imported into or exported from the marine environment. These imports and exports can occur as exchanges with the atmosphere above, the ocean floor below, or as runoff from the land.

<span class="mw-page-title-main">Marine biogenic calcification</span> Shell formation mechanism

Marine biogenic calcification is the process by which marine organisms such as oysters and clams form calcium carbonate. Seawater is full of dissolved compounds, ions and nutrients that organisms can use for energy and, in the case of calcification, to build shells and outer structures. Calcifying organisms in the ocean include molluscs, foraminifera, coccolithophores, crustaceans, echinoderms such as sea urchins, and corals. The shells and skeletons produced from calcification have important functions for the physiology and ecology of the organisms that create them.

<span class="mw-page-title-main">Ocean acidification in the Arctic Ocean</span>

The Arctic ocean covers an area of 14,056,000 square kilometers, and supports a diverse and important socioeconomic food web of organisms, despite its average water temperature being 32 degrees Fahrenheit. Over the last three decades, the Arctic Ocean has experienced drastic changes due to climate change. One of the changes is in the acidity levels of the ocean, which have been consistently increasing at twice the rate of the Pacific and Atlantic oceans. Arctic Ocean acidification is a result of feedback from climate system mechanisms, and is having negative impacts on Arctic Ocean ecosystems and the organisms that live within them.

<span class="mw-page-title-main">Particulate inorganic carbon</span>

Particulate inorganic carbon (PIC) can be contrasted with dissolved inorganic carbon (DIC), the other form of inorganic carbon found in the ocean. These distinctions are important in chemical oceanography. Particulate inorganic carbon is sometimes called suspended inorganic carbon. In operational terms, it is defined as the inorganic carbon in particulate form that is too large to pass through the filter used to separate dissolved inorganic carbon.

References

  1. 1 2 3 4 Walker, James C. G.; Hays, P. B.; Kasting, J. F. (1981). "A negative feedback mechanism for the long-term stabilization of Earth's surface temperature". Journal of Geophysical Research. 86 (C10): 9776. Bibcode:1981JGR....86.9776W. doi:10.1029/jc086ic10p09776. ISSN   0148-0227.
  2. 1 2 3 Berner, R. A. (2004-05-01). "A model for calcium, magnesium and sulfate in seawater over Phanerozoic time". American Journal of Science. 304 (5): 438–453. Bibcode:2004AmJS..304..438B. doi: 10.2475/ajs.304.5.438 . ISSN   0002-9599.
  3. ↑ Ridgwell, Andy; Zeebe, Richard E. (2005-06-15). "The role of the global carbonate cycle in the regulation and evolution of the Earth system". Earth and Planetary Science Letters. 234 (3–4): 299–315. doi:10.1016/j.epsl.2005.03.006. ISSN   0012-821X.
  4. 1 2 Raisman, Scott; Murphy, Daniel T. (2013). Ocean acidification: Elements and Considerations. Hauppauge, New York: Nova Science Publishers, Inc. ISBN   9781629482958.
  5. ↑ Nordin, B. E. C (1988). Calcium in Human Biology. ILSI Human Nutrition Reviews. London: Springer London. doi:10.1007/978-1-4471-1437-6. ISBN   9781447114376. OCLC   853268074. S2CID   9765195.
  6. ↑ Rubin, Ronald P.; Weiss, George B.; Putney, James W. Jr (2013-11-11). Calcium in Biological Systems. Springer Science & Business Media. ISBN   9781461323778.
  7. 1 2 Fantle, Matthew S.; Tipper, Edward T. (2014). "Calcium isotopes in the global biogeochemical Ca cycle: Implications for development of a Ca isotope proxy". Earth-Science Reviews. 131: 148–177. doi:10.1016/j.earscirev.2014.02.002. ISSN   0012-8252.
  8. 1 2 3 Stallard, Robert F. (1992). Butcher, Samuel S.; Charlson, Robert J.; Orians, Gordon H.; Wolfe, Gordon V. (eds.). 6 Tectonic Processes, Continental Freeboard, and the Rate-controlling Step for Continental Denudation. pp. 93–121. ISBN   0-12-147685-5.
  9. ↑ Reddy, M. M.; Nancollas, G.H. (1976). "The Crystallization of Calcium Carbonate IV. The effect of magnesium, strontium and sulfate ions". Journal of Crystal Growth. 35 (1): 33–38. Bibcode:1976JCrGr..35...33R. doi:10.1016/0022-0248(76)90240-2.
  10. 1 2 3 4 Raisman, Scott; Murphy, Daniel T. (2013). Ocean Acidification : Elements and Considerations. Hauppauge, New York: Nova Science Publishers, Inc. ISBN   9781629482958.
  11. ↑ Winck, Flavia Vischi; Páez Melo, David Orlando; González Barrios, Andrés Fernando (2013). "Carbon acquisition and accumulation in microalgae Chlamydomonas: Insights from "omics" approaches". Journal of Proteomics. 94: 207–218. doi:10.1016/j.jprot.2013.09.016. PMID   24120529.
  12. ↑ Zhang, Junzhi; Li, Luwei; Qiu, Lijia; Wang, Xiaoting; Meng, Xuanyi; You, Yu; Yu, Jianwei; Ma, Wenlin (2017). "Effects of Climate Change on 2-Methylisoborneol Production in Two Cyanobacterial Species". Water. 9 (11): 859. doi: 10.3390/w9110859 . CC-BY icon.svg Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License.
  13. 1 2 Milliman, John D. (1993). "Production and accumulation of calcium carbonate in the ocean: Budget of a nonsteady state". Global Biogeochemical Cycles. 7 (4): 927–957. Bibcode:1993GBioC...7..927M. doi:10.1029/93gb02524. ISSN   0886-6236.
  14. ↑ Ridgwell, A; Zeebe, R (2005-06-15). "The role of the global carbonate cycle in the regulation and evolution of the Earth system". Earth and Planetary Science Letters. 234 (3–4): 299–315. doi:10.1016/j.epsl.2005.03.006. ISSN   0012-821X.
  15. ↑ Fantle, Matthew S.; DePaolo, Donald J. (2005). "Variations in the marine Ca cycle over the past 20 million years". Earth and Planetary Science Letters. 237 (1–2): 102–117. Bibcode:2005E&PSL.237..102F. doi:10.1016/j.epsl.2005.06.024. ISSN   0012-821X.
  16. ↑ Horita, Juske (2002). "Chemical evolution of seawater during the Phanerozoic: Implications from the record of marine evaporites". Geochimica et Cosmochimica Acta. 66 (21): 3733–3756. Bibcode:2002GeCoA..66.3733H. doi:10.1016/S0016-7037(01)00884-5.
  17. ↑ DePaolo, Donald J.; Rocha, Christina L. De La (2000-08-18). "Isotopic Evidence for Variations in the Marine Calcium Cycle Over the Cenozoic". Science. 289 (5482): 1176–1178. Bibcode:2000Sci...289.1176D. doi:10.1126/science.289.5482.1176. ISSN   0036-8075. PMID   10947981.
  18. ↑ Espeso, Eduardo A. (2016). "The CRaZy Calcium Cycle" (PDF). Yeast Membrane Transport. Advances in Experimental Medicine and Biology. Vol. 892. Springer, Cham. pp. 169–186. doi:10.1007/978-3-319-25304-6_7. hdl:10261/151198. ISBN   978-3-319-25302-2. PMID   26721274.
  19. ↑ Peacock, Munro (2010-01-01). "Calcium Metabolism in Health and Disease". Clinical Journal of the American Society of Nephrology. 5 (Supplement 1): S23–S30. doi: 10.2215/CJN.05910809 . ISSN   1555-9041. PMID   20089499.
  20. ↑ Berchtold, Martin (2000). "Calcium Ion in Skeletal Muscle: Its Crucial Role for Muscle Function, Plasticity, and Disease". Physiological Reviews. 80 (3): 1215–1265. doi:10.1152/physrev.2000.80.3.1215. PMID   10893434.
  21. ↑ Katz, B.; Miledi, R. (May 1970). "Further study of the role of calcium in synaptic transmission". The Journal of Physiology. 207 (3): 789–801. doi:10.1113/jphysiol.1970.sp009095. ISSN   0022-3751. PMC   1348742 . PMID   5499746.
  22. ↑ Parfitt, A. M. (August 1976). "The actions of parathyroid hormone on bone: relation to bone remodeling and turnover, calcium homeostasis, and metabolic bone diseases. II. PTH and bone cells: bone turnover and plasma calcium regulation". Metabolism: Clinical and Experimental. 25 (8): 909–955. doi:10.1016/0026-0495(76)90124-4. ISSN   0026-0495. PMID   181659.
  23. ↑ Nemere, I.; Larsson, D. (2002). "Does PTH have a direct effect on intestine?". Journal of Cellular Biochemistry. 86 (1): 29–34. doi:10.1002/jcb.10199. ISSN   0730-2312. PMID   12112013. S2CID   39465204.
  24. ↑ "Calcitonin | You and Your Hormones from the Society for Endocrinology". www.yourhormones.info. Retrieved 2018-10-04.
  25. ↑ "What's the Function of Calcium (Ca) in Plants?". Greenway Biotech, Inc. Archived from the original on 2019-04-03. Retrieved 2018-10-04.
  26. ↑ "85.07.08: The Calcium Cycle". teachersinstitute.yale.edu. Retrieved 2018-10-04.
  27. ↑ "Decomposers | Encyclopedia.com". www.encyclopedia.com. Retrieved 2018-10-04.
  28. ↑ "Amazingly Versatile Uses of Calcium Carbonate". ScienceStruck. Retrieved 2018-10-29.
  29. ↑ "Environmental Hazards of Limestone Mining" . Retrieved 2018-10-29.
  30. ↑ Gatt, Peter (2001-04-01). Limestone quarries and their environmental impact. Hubert H Humphrey Seminar.
  31. ↑ Komar, N.; Zeebe, R. E. (January 2016). "Calcium and calcium isotope changes during carbon cycle perturbations at the end-Permian". Paleoceanography. 31 (1): 115–130. Bibcode:2016PalOc..31..115K. doi: 10.1002/2015pa002834 . ISSN   0883-8305. S2CID   15794552.
  32. ↑ "PMEL CO2 - Carbon Dioxide Program". www.pmel.noaa.gov. Retrieved 2018-10-29.
  33. ↑ "Ocean Acidification". Smithsonian Ocean. Retrieved 2018-10-29.
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