Calcium carbonate compensation

Biogenic Ma.teria.ls, Deep ocean calcareous or siUceous oo2es are sediments containing >30% of biogenic material. Foraminifera, the skeletal remains of calcareous plankton, are found extensively in deep equatorial waters above the calcium carbonate compensation depth of 4000 to 5000 m. 

Calcite compensation depth See Calcium carbonate compensation depth. 

Calcium carbonate compensation depth (CCD) The depth below which calcium carbonate is not found in marine sediments due to its dissolution. 

Carbonate compensation The ocean s response to perturbations through shifts in its carbonate chemistry. These shifts require changes in the carbonate ion concentration that change the depth of the calcium carbonate compensation depth and hence lead to changes in the burial rate of carbon as biogenic calcium carbonate. 

Figure 7. The depth distribution of the Ro and calcite saturation levels, the foraminiferal lysocline and the calcium carbonate compensation depth in the Western and Eastern Atlantic Ocean (after Ref. 40)...

There are several other topics that would be equally appropriate to consider in a review of this type. Some of these, such as the record of seawater and the history of the calcium carbonate compensation depth (CCD), are mentioned briefly as they relate to records that are discussed in greater detail. Other topics have been omitted. We hope readers will recognize that the topics covered here are determined not only by the scientific interests of the authors, but also by the practical limits of what can be covered in a single review. 

Atlantic Ocean Nodule abundance in the Atlantic Ocean appears to be more limited than in the Pacific or Indian Oceans, probably as a result of its relatively high sedimentation rates. Another feature which inhibits nodule abundance in the Atlantic is that much of the seafloor is above the calcium carbonate compensation depth (CCD). The areas of the Atlantic where nodules do occur in appreciable amounts are those where sedimentation is inhibited. The deep water basins on either side of the Mid-Atlantic Ridge which are below the CCD and which accumulate only limited sediment contain nodules in reasonable abundance, particularly in the western Atlantic. Similarly, there is a widespread occurrence of nodules and encrustations in the Drake Passage-Scotia Sea area probably due to the strong bottom currents under the Circum-Antarctic current inhibiting sediment deposition in this region. Abundant nodule deposits on the Blake Plateau can also be related to high bottom currents. 

Of course, this argument is perfectly true where it can be positively demonstrated that MU water requirements really are very low. Once again however, if this is not the case, then—most treatment programs are designed primarily for corrosion control and do not compensate for undue hardness entering the boiler—calcium carbonate scale can and does develop over time. This process takes place even where the MU water is relatively soft, and results in the formation of insulating boiler tube deposits or boiler vessel sludge. 

Further addition of lime converts soluble magnesium or sodium carbonate into the insoluble hydroxide and further insoluble calcium carbonate. In theory it is possible to limit the lime addition to maintain the magnesium salt as soluble carbonate, but in practice some magnesium hydroxide is always formed (say, 10%), so it necessary to compensate for this by the addition of more lime ... 

The solubility of calcite and aragonite increases with increasing pressure and decreasing temperature in such a way that deep waters are undersaturated with respect to calcium carbonate, while surface waters are supersaturated. The level at which the effects of dissolution are first seen on carbonate shells in the sediments is termed the lysocline and coincides fairly well with the depth of the carbonate saturation horizon. The lysocline commonly lies between 3 and 4 km depth in today s oceans. Below the lysocline is the level where no carbonate remains in the sediment this level is termed the carbonate compensation depth. 

Fillers. Inert inorganic substances such as calcium carbonate, clay, silicates, and asbestos are often utilized in vinyl compositions where clarity is not a requirement. While the carbonates and clay are used ostensibly to reduce cost, beneficial results are forthcoming. The carbonates produce a dry, matte surface and are claimed, because of their alkaline nature, to benefit heat and light stability. Clay improves electrical insulation. Silicates enhance surface dryness. Asbestos fibers provide the reinforcement necessary for dimensional stability in floor tile. Antimony oxide, per se or as a surface coating on an inert carrier, provides flame retard-ance. Their only major adverse effects are to reduce tensile strength and elongation and require an increase in plasticizer level to compensate... 

The carbonate compensation depth (CCD) occurs where the rate of calcium carbonate dissolution is balanced by the rate of infall, and the calcium carbonate content of surface sediments is close to Owt.% (e.g., Bramlette, 1961). The CCD has been confused with the calcium carbonate critical depth (sometimes used interchangeably with the lysocline discussed next), where the carbonate content of the surface sediment drops below 10 wt.%. A similar marker level in deep-sea sediments is the ACD, below... 

Carbonate compensation depth the level of an ocean at which the rate of calcium carbonate deposition equals the rate of its resolution. 

Kinetic data measured for the decomposition of calcium carbonate under isothermal and under programmed-temperature conditions [11] and varied reaction environments influencing the ease of removal of the CO2 product, show that the apparent values of the kinetic parameters k, A and may be influenced by sample heating rate, reactant self-cooling, sample mass, geometry and particle size, which determine the rate because of the reversible nature of the decomposition [12]. These effects can lead to compensation behaviour [13]. 

Water can be determined in solid samples by infrared spectroscopy. The water content of calcium sulfate hydrates is to be measured using calcium carbonate as an internal standard to compensate for some systematic errors in the procedure. A series of standard solutions containing calcium sulfate dihydrate and a constant known amount of the internal standard are prepared. The solution of unknown water content is also prepared with the same amount of internal standard. The absorbance of the dihydrate is measured at one wavelength ( sample) along with that of the internal standard at another wavelength (As,d). The following results were obtained. 

The atmospheric concentration of CO2 rose from 280 ppm in 1800 to 370 ppm in 2000, mainly due to the consumption of fossil fuels. This increase in CO2 concentration is expected to have various environmental and ecological effects. For example, doubling of the CO2 concentration in the atmosphere reduces the rate of calcium carbonate deposition in coral reefs by 30-40%.Most of this rise has occurred over the last few decades, and, unless action is taken, the projected growth over the 21st century could lead to a doubling or tripling of the preindustrial level of C02. Unlike for SO2 emission, the total accumulation of CO2 matters rather than the rate of CO2 emission. Oceanic uptake of CO2 can compensate for some emissions, but this uptake will collapse once CO2... 

This section primarily focuses on the description of the deposition and accumulation of carbonates in shallow waters and in the deep ocean. The main depocenters for calcium carbonates are the continental shelf areas, as well as island arcs or atolls, which are the typical shallow water environments for massive carbonate formation, and the pelagic deep-sea sediments above the calcite compensation depth catching the rain of small calcareous tests formed by marine plankton in the surface waters. 

Observations from studies of surface sediments have allowed definition of regionally varying levels in the ocean at which pronounced changes in the presence or preservation of calcium carbonate result from the depth-dependent increase of dissolution on the seafloor. The first such level to be identified was simply the depth boundary in the ocean separating carbonate-rich sediments above from carbonate-free sediments below. This level is termed the calcite (or carbonate) compensation depth (CCD) and represents the depth at which the rate of carbonate dissolution on the seafloor exactly balances the rate of carbonate supply from the overlying surface waters. Because the supply and dissolution rates of carbonate differ from place to place in the ocean, the depth of the CCD is variable. In the Pacific, the CCD is typically found at depths between about 3500 and 4500 m. In the North Atlantic and parts of the South Atlantic, it is found... 

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