What is the Calcite Compensation Depth (CCD) and what is its significance for carbonate deposits?
The Calcite Compensation Depth is the depth below which all calcite minerals are dissolved. The solubility of calcite (and the amorphous variant aragonite) depends on both pressure and temperature. Under high pressure, low temperature conditions calcite is most soluble, and in deep parts of the ocean only siliceous deposits are found.
Typical values for the CCD are between 3000 and 4000 m, but since the CCD also depends on the amount of calcite in the water it can occur as shallow as 2500 m (in parts of the Pacific Ocean). These shallow zones are often caused by high biological activity of carbonate shell forming organisms.
Taking all this together it becomes clear carbonate deposits can form and/or be preserved only above the CCD.