Carbonate Compensation Depth (CCD)

The carbonate compensation depth (CCD) is the depth below which calcium carbonate dissolves faster than it rains down from above, so seafloor sediments hold essentially no carbonate. It marks the transition from carbonate ooze to red clay. The CCD lies deeper than the lysocline, the depth where dissolution sharply intensifies as deep water becomes undersaturated in carbonate ion. The calcite CCD is shallower in the Pacific, near 4,000 to 4,500 m, because aged deep water there is CO2-rich and corrosive, and deeper in the Atlantic, near 5,000 to 5,500 m. Ocean acidification shoals the CCD.