Calcium carbonate reefs

Aragonite. Calcium carbonate is a common deposit in shallow tropical waters as a constituent of muds, or in the upper part of coral reefs where it precipitates from carbon dioxide-rich waters supersaturated with carbonate from intense biological photosynthesis and solar heating. Deposits of ooHtic aragonite, CaCO, extending over 250,000 km in water less than 5 m deep ate mined for industrial purposes in the Bahamas for export to the United States (19). 

In addition to climate change, the increased atmospheric concentration of C02 is likely to have wide-spread ecological effects in various environments, since C02 is a physiologically active gas, in plants as well as animals. The acidic nature of C02 will also lead to changes in the chemistry of the ocean s surface, which is in equilibrium with the atmosphere. Once the shift in the oceanic chemical balance becomes significant, it will affect ecosystems. It has been shown, for example, that doubling C02 concentration in the atmosphere will reduce the rate of calcium carbonate deposition in coral reefs by 30-40% (Langdon et al., 2000). 

Langdon, C., Takahashi, T., Sweeney, C., Chipman, D., Goddard, J., Marubini, F., Aceves, H., Barnett, H., and Atkinson, M.J., Effect of calcium carbonate saturation state on the calcification rate of an experimental coral reef, Global Biogeochem. Cy., 14, 639-654,2000. 

Eggshells are mostly calcium carbonate. Seashells, pearls, limestone, and chalk are also made of calcium carbonate. So are some of the most beautiful and complex places on earth—coral reefs. 

Animals called corals build coral reefs. Corals take calcium and carbonate ions in seawater and make calcium carbonate skeletons.The ocean is naturally basic, with a pH a little above eight. When the pH is lowered, even if it s still somewhat basic, there aren t as many carbonate ions floating around and it s harder for corals to make their skeletons. When there aren t enough raw materials, the corals can t work efficiently. 

Goreau, T. F. Calcium carbonate deposition by coralline algae and corals in relation to their roles as reef-builders. Ann. N. Y. Acad. Sci. 109, 127—167 (1963). 

Paul, V. J., Secondary metabolites and calcium carbonate as defenses of calcareous algae on coral reefs, Proc. 8th Int. Coral Reef Symp., 1, 707, 1997. 

The most actively cycled reservoir of carbon is atmospheric C02 (it constitutes 0.034% of the atmosphere). Carbon dioxide dissolves readily in water and is in direct equilibrium with dissolved inorganic forms of carbon (H2C03, HCO, and CO7-, see Section 6.2.1.3). Once there, it may precipitate as solid calcium carbonate (limestone). Corals and algae encourage this reaction and build up limestone reefs in the process, but a much larger portion in the deep sea equilibrates only at the slow rate of... 

In the oceans, reef and planktonic organisms precipitate calcium carbonate (both calcite and aragonite), which comprises a major component of marine sediments. The precipitation of calcium carbonate is essentially the reverse of reaction (la) above ... 

The polyps secrete calcium carbonate to make their shells or skeletons. When the polyps die, the calcium carbonate structures remain and accumulate over time to form a reef This reef building is possible because calcium carbonate is only slightly soluble in water. 

The Ksp for calcium carbonate is 2.8 x 10 and the K value for calcium sulfate is 9.1 X 10. If coral polyps secreted calcium sulfate rather than calcium carbonate, how would this affect the formation of the coral reef ... 

Calcium Calcium is an essential element for humans, especially in maintaining healthy bones and teeth. Calcium is found widely in nature, mainly combined with carbon and oxygen in calcium carbonate. This compound is the main ingredient in rocks such as limestone, chalk, and marble. Coral reefs build up from calcium carbonate exoskeletons that are created by marine animals called corals. Calcium carbonate is used in antacid tablets and as an abrasive in toothpaste. An abrasive is a hard material used to polish, smooth, or grind a softer material. Emery boards and sandpaper are examples of abrasive materials. 

Smith, S.V. and Harrison, J.T., 1977. Calcium carbonate production of the Mare incogni-tum, the upper windward reef slope, at Enewetak Atoll. Science, 197 556—559. 

Smith, S.V. and Kinsey, D.W., 1976. Calcium carbonate production, coral reef growth, and sea level change. Science, 194 937—939. 

Two further points merit brief attention. If conditions in Table 2.5.12 approximate to the yearly norm, then a windward reef flat of about 400 m width would represent the equilibrium situation on which the production of calcium carbonate would exactly balance the amount lost. Most windward reef flats in fact vary in width between 100—400 m. 

In contrast to the carbon turnover, all reefs examined showed a net gain of calcium carbonate. 

Calcium carbonate deposited in windward perimeter zones at or near the surface is removed and transported in a leeward direction, where it forms prograding sand wedges infilling lagoons, and leeward extension of the reef. Windward reef zones eire likely to be net destructional and not constructional sites. 

There are three important minerals used by organisms to form hard tissues such as bones and shells. The most widespread of these is calcium carbonate, an important structural component in animals ranging from Protozoa to Mollusca and Echinoder-mata. It is also a minor component of vertebrate bones. Its widespread use is probably related to the generally uniform distribution of dissolved calcium bicarbonate. Animals employing calcium carbonate are most abundant in fresh waters containing large amounts of calcium and magnesium ("hard water") and in warm, shallow seas where the partial pressure of carbon dioxide is low (e.g., the formation of coral reefs by coelenterates). The successful precipitation of calcium carbonate depends upon the equilibrium ... 

Beachrock is a friable to well-cemented sedimentary rock that results from rapid lithification of sand and/or gravel by calcium carbonate cement precipitation in the intertidal zone. It occurs predominantly on tropical ocean coasts, but is also found in temperate realms that extend up to 60° latitude. In contrast to the implications of the name, beachrock precipitation phenomena are not restricted to beaches but also occur on reef ridges, tidal flats and in tidal channels. Intertidal beachrock may be confused with other sediments lithified in the intertidal and subtidal zones, such as hardened crusts or certain reef limestones. 

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