the ACD (or CCD, calcium compensation depth) is the depth in the ocean at which pteropods disappear from the sediments; it varies greatly between and within ocean basins; average CCD depth is near 1.5 km for low latitudes, with the Atlantic having typical values between 2 and 3 km, and Pacific and Indian ocean values between 0.5 and 1.5 km. ACD values shoal towards high latitudes and on the continental slope; the maximum depth is 3.4 km in the N-Atlantic (Berger,1978).

Alternative forms for aragonite compensation depth : ACD, CCD.