I understand that the wee bubbles that appear when you heat water are oxygen coming out of solution. Oxygen solubility in water is best at very cold temperature, close to freezing.
This source shows that CO2 has a similar trend....
Carbon Dioxide Solubility in Water
.... that CO2 solubility in water falls with elevated temnperature.
So, if you just heat the ocean, the CO2 count in the water will fall. This one shows that at 20 degC, the CO2 solubility is about 1/3 less than at 10 degC.
It would seem that a warming ocean may be more than a bit reluctant to absorb that CO2 they keep talking about. Perhaps it's different in salt water, but this summary shows a similar trend to fresh-water...
Science Links Japan | Study of Solubility of Carbon Dioxide in Seawater
Now this bit is good. For both freswater and salt water, elevate the temperature and your CO2 will leave the water to the atmosphere, dropping the acidity of the water.
For fresh water, unless in the same heating time period, the CO2 count goes up by 1/3, fresh water will become less acidic.
It looks very much like a heating ocean will yield CO2, and not absorb it.
I will try to find a similar graph for salt water, but I have not, as yet.
If the temperature does not rise though, the acidity will go up, yes, but the global warmists better hope the water temperature does not rise, and such hope does not come easy to them, does it?