A few things more about the Chemistry in the depths of the oceans, Calcium, CO2, and volcanism.

"The carbonate compensation depth (CCD) is the depth, in the oceans, at which the rate of supply of calcium carbonates matches the rate of solvation. That is, solvation 'compensates' supply. Below the CCD solvation is faster, so that carbonate particles dissolve and the carbonate shells (tests) of animals are not preserved. Carbonate particles cannot accumulate in the sediments where the sea floor is below this depth.”

"Adding a reactant to the above chemical equation pushes the equilibrium towards the right producing more products: Ca2+ and HCO3−, and consuming more reactants CO2 and calcium carbonate according to Le Chatelier's principle.”

(Note: HCO3- is the bicarbonate ion which is the conjugate base of carbonic acid and a buffering agent which inhibits large swings in pH).

"At the present time the CCD in the Pacific Ocean is about 4200–4500 metres except beneath the equatorial upwelling zone, where the CCD is about 5000 m.” (Notes: The average depth of the ocean floor is 3700 m and there are vertebrate mussels and mollusks around the Challenger Deep at 11,000 m depth. That signifies that dissolved Ca 2+ is taken up by these vertebrates.)

"In the geological past the depth of the CCD has shown significant variation. In the Cretaceous through to the Eocene the CCD was much shallower globally than it is today; due to intense volcanic activity during this period atmospheric CO2 concentrations were much higher. Higher concentrations of CO2 resulted in a higher partial pressure of CO2 over the ocean. This greater pressure of atmospheric CO2 leads to increased dissolved CO2 in the ocean mixed surface layer. This effect was somewhat moderated by the deep oceans' elevated temperatures during this period.[6] In the late Eocene the transition from a greenhouse to an icehouse Earth coincided with a deepened CCD.”

That damned submarine volcanism heating the deep abyssal waters and screwing with the Chemistry of the atmosphere. Just like today.

The volcanism, by heating the ocean waters, caused more exolution (degassing) of CO2 ….. after a little lag time. Just as observed in ice cores.