Here Ω is the product of the concentrations (or activities) of the reacting ions that form the mineral ( and ), divided by the product of the concentrations of those ions when the mineral is at equilibrium (), that is, when the mineral is neither forming nor dissolving. In seawater, a natural horizontal boundary is formed as a result of temperature, pressure, and depth, and is known as the saturation horizon. Above this saturation horizon, Ω has a value greater than 1, and does not readily dissolve. Most calcifying organisms live in such waters. Below this depth, Ω has a value less than 1, and will dissolve. However, if its production rate is high enough to offset dissolution, can still occur where Ω is less than 1. The carbonate compensation depth occurs at the depth in the ocean where production is exceeded by dissolution.