The ocean is a buffer of carbonic acid and carbonates in the form of ocean sediments from dead sea creatures and the limestone that the sediment eventually turns into.
Buffered systems resist changes in pH. In fact it is very difficult to change the pH of a buffer.
The ocean pH will be slightly basic for the foreseeable future no matter what human beings do.
The only effect people can have on ocean water is on a small, local level.
Post 6 hits the nail on the head. If you look at total carbon - the atmosphere is 1, the oceans are around 50, and the carbonate rocks are about 250. When the oceans start to get too acidic limestone is deposited on the bottom of the ocean by a very complicated clay mineral process. The ocean botton is then subducted and the limestone appears on the Earth’s surface in about 250 million years where it starts to decompose and start the cycle again. The oceans are pretty good at taking core of themselves. Also note if you ever get too hungry you can pick up a piece of limestone and extract the carbon from it and assemble some proteins. If you are smart enough, you will never starve.