Carbonate Compensation Depth

Definition

Calcifying organisms in the surface supply CaCO₃ to deep waters when they die, and their tests or shells fall through the water column. As a result of respiration, increasing pressure, and decreasing temperature, waters become increasingly undersaturated with respect to CaCO₃ with depth, allowing the tests to dissolve more readily. The depth in the water column at which the rate of calcium carbonate supplied from the surface equals the rate of dissolution is called the carbonate compensation depth (CCD). If the sea floor lies above the CCD, these CaCO₃ tests can accumulate in the sediments; if the sea floor lies below the CCD, CaCO₃will be absent from the sediments. In this way, the CCD can be thought of as a “snowline” marking the separation between carbonate-rich sediments and carbonate-deficient sediments. This gives rise to an alternative definition of CCD as the depth at which the carbonate content of the sediments is 0 % by weight. This is a more practical definition...