<P> Calcite compensation depth (CCD) is the depth in the oceans below which the rate of supply of calcite (calcium carbonate) lags behind the rate of solvation, such that no calcite is preserved . Aragonite compensation depth (hence ACD) describes the same behaviour in reference to aragonitic carbonates . Aragonite is more soluble than calcite, so the aragonite compensation depth is generally shallower than the calcite compensation depth . </P> <P> Calcium carbonate is essentially insoluble in sea surface waters today . Shells of dead calcareous plankton sinking to deeper waters are practically unaltered until reaching the lysocline where the solubility increases dramatically . By the time the CCD is reached all calcium carbonate has dissolved according to this equation: </P> <Dl> <Dd> C a C O 3 + C O 2 + H 2 O ⇌ C a 2 + (a q) + 2 H C O 3 − (a q) (\ displaystyle \ mathrm (CaCO_ (3) + CO_ (2) + H_ (2) O \ \ rightleftharpoons \ Ca ^ (2 +) (aq) + 2 \ HCO_ (3) ^ (-) (aq))) </Dd> </Dl>

The ccd is much deeper in the pacific ocean compared to the atlantic