The Lysocline and Calcium Carbonate Concentration Depth in the Sea

Abstract

An examination has been made of the dissolution behavior of 100 ppm magnesium calcite in natural and artificial seawaters at pressures between 20 and 680 atmospheres. The behavior of the various systems indicates that the lysocline is partially a function of pressure and seawater composition, with magnesium and calcium concentrations dominating the composition variable. The lysocline and the compensation depth, which must be defined relative to a specific calcite and a specific seawater, are essential consequences of the transition between the pressure domain in which various magnesian calcites can be in equilibrium or steady-state and the pressure domain in which no calcite can be in equilibrium or steady-state. The presence of magnesium is shown to be essential for the maintenance of the lysocline and the compensation depth. The seawater composition effects have been investigated and further support the proposal that the system may best be described by phase rule. The role of salinity in seawater aggressiveness is discussed in terms of magnesium and calcium concentrations and how these affect the system both by being components of solid magnesian calcite and by being common ions.