Calcite carbonate compensation depth

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. 

Calcite compensation depth See Calcium carbonate compensation depth. 

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)...

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... 

Surface seawater is oversaturated with respect to CaCOa (calcite, aragonite) and biogenic CaCOa forms in surface seawater. Solubility of CaCOa increases with increasing pressure (depth). CaCOa dissolves below CCD (carbonate compensation depth). 

Takahashi, T. Carbonate chemistry of seawater and the calcite compensation depth in the oceans, p. 11-26, ... 

At about 4000 m water depth, carbonate tests are dissolved, because their solubility depends on pressure (this depth in the ocean is called calcite compensation depth, abbreviated CCD). With the dissolution of tests the metals collected before are again liberated and can contribute to the growth of manganese nodules. 

By mapping the depth at which carbonate sediments exist on the floors of the oceans, it is possible to identify the level where the rate of supply of biogenic CaC03 is balanced by the rate of solution. This depth, known as the calcite compensation depth (CCD), is variable in the world s oceans, depending on the... 

A third example is the increasing solubility of calcite with depth in the ocean. Surface seawater is generally supersaturated with respect to calcite, whereas at depths below about 500 m the oceans become undersaturated with calcite (cf. Drever 1988). For this reason there is a tendency for carbonate materials to dissolve and disappear with increasing depth as they settle into ocean bottom sediments. Reasons for the shift to undersaturation with increasing ocean depth include declining temperatures, increased pressure (see Chap. 1, Section 1.6.2), and increasing CO2 concentrations. The depth at which a pronounced reduction in the carbonate content of ocean sediments is observed is termed the calcite compensation depth (CCD). Because of the slow rate at which the calcite dissolves, the CCD is found well below the approximately 500 m depth at which calcite becomes undersaturated. The CCD is thus at about 3.5 km depth in the Pacific Ocean and 5 km depth in the Atlantic Ocean (Drever 1988). 

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. 

CaCOs production comprises the total amount produced in the surface waters. Accumulation is the - much smaller - portion which becomes buried in the deeper sediment. The difference between both comprises the dissolution in the water column and in the upper parts of the young sediment, from where dissolved inorganic carbon (DIC) still can be transferred to the bottom water. Thus the sediment below the calcite compensation depth (CCD) is characterized by no calcite accumulation. Below the CCD calcite particles may reach the seafloor and may even be found in the upper few decimeters of the young sediment, but they will be dissolved according to processes of early diagenesis. 

The association of marine barite with organic matter complicates the interpretation of occurrence of increased barite deposition found along midocean ridges because greater preservation of organic matter also occurs with increased carbonate sedimentation above the calcite compensation depth. Additionally, basin-scale dispersal of hydrothermal particles appears limited, especially for the relatively dense barite. Studies of marine barite saturation show that barite is below saturation in the water column but rapidly approaches saturation in the pore waters of deep-sea sediments. Discrete barite particles are nevertheless found in the microenvironments of suspended... 

---