Final answer:
Calcareous material dissolves below the CCD because the acidic conditions in deeper ocean waters increase the solubility of calcium carbonate, especially as CO2 levels rise and ocean acidity increases.
Step-by-step explanation:
The reason why calcareous material dissolves below the Carbonate Compensation Depth (CCD) is largely due to the solubility of calcium carbonate (CaCO3) in acidic solutions. The solubility product (Ksp) for calcium carbonate is an equilibrium constant that represents its solubility in pure water. However, in an acidic solution, the solubility is significantly enhanced as the equilibrium constant for this net reaction is much greater than the Ksp. The introduction of carbon dioxide (CO2) from the atmosphere into the ocean increases the acidity of the water, forming carbonic acid (H2CO3), which reacts with calcium carbonate to form calcium ions (Ca2+) and bicarbonate ions (HCO3-). As a result, when ocean waters become more acidic, especially below the CCD, the calcium carbonate in the skeletal structures of coral reefs and other marine organisms becomes more prone to dissolution.