Question

Why the lysocline shallows as ph increases?

Answer 1

The main control on carbonate sediment accumulation is the Carbonate Compensation Depth (CCD). At the ocean’s surface, the water is super-saturated in CaCO3. Sediments from land and skeletons from microorganisms living in the ocean (such as plankton and foraminifera) provide a constant source of new CaCO3 to the surface ocean. CaCO3 has a finite solubility, and the supply in most of the surface ocean is much greater than that solubility. (A combination of CaCO3 and alkaline compounds actually buffer the acidity from dissolved CO2, moderating the effect of atmospheric CO2 concentrations on the ocean through a type of negative feedback loop. A chemical oceanographer could explain this better than me.)

Calcite is more soluble with increasing pressure and decreasing pH (increasing acidity). The Lysocline is the depth at which increasing pressure and decreasing pH have eliminated the super-saturation, and the existing (solid) CaCO3 begins to dissolve more rapidly.

Below the lysocline, the amount of CaCO3 decreases. At some point all of the CaCO3 raining down from above is dissolved. The depth at which the rate of supply of CaCO3 equals the dissolution rate is called the Carbonate compensation depth. Below that depth, all available CaCO3 is dissolved into the water, and therefore cannot deposit as sediments on the seafloor. An increase in ocean pH deepens the dissolution horizons (Lysocline and CCD), increasing the amount of the seafloor above these depths, and therefore increasing global deposition rates. A decrease in ocean pH (more acidity) does the opposite, decreasing the amount of the ocean floor where Ca