Alkalinity and dissolution of calcium carbonate particles in the ocean

　The formation and dissolution of calcium carbonate particles is a major determinant of the alkalinity in the ocean. The conditions under which calcium carbonate particles dissolve in seawater are described below. Calcium carbonate particles in surface seawater do not dissolve permanently. This is because surface seawater is supersaturated with calcium carbonate. In deep seawater, under some conditions, it is undersaturated for calcium carbonate and the particles will dissolve.

　Why was this found to be the case? It is because it is clear that the compositional distribution of marine sediments differs greatly between the Atlantic and Pacific Oceans.

Compositional distribution of marine sediments

Introduction to Oceanography by Paul Webb,  figure 12.6.1 used under a CC-BY 4.0 international license.
Download this book for free at http://rwu.pressbooks.pub/webboceanography
The figure 12.6.1 was referred from Steven Earle, “Physical Geology” open access text book)
　
　The figure above shows the main composition of the mud deposited on the seafloor and shows that in the Atlantic Ocean, calcium carbonate mud (ooze) covers a wide area. In the North Pacific Ocean, there is no calcium carbonate covering the seafloor. This means that in the Atlantic Ocean, calcium carbonate remains undissolved on the seafloor, while in the North Pacific Ocean, it is all dissolved and gone.