May I make a guess that you are in some way involved in physical therapy with people?
Why Alkaline Minerals help retain more OXYGEN in the body?
The simplest reason is that they have an affinity for the OXYGEN molecule over the HYDROGEN molecule!!
But I do not know if I should go into any deeper info than this , as it may be confusing for many people.
For the same mineral may change it's action as far as being Acidic or Alkaline in nature by the ratios of Nitrogen to the Hydrogen which it becomes bound to!!
For many elements are isotopes, and this means that they may cause reactions of the opposite from each other depending upon the above mentioned!
This is one of the reasons for the mood swings which people face with the changing of the Moon cycles, for this causes a change in the ratios of positive ions to negative ions in the atmosphere, which causes a change in the ratio between the acidity and alkalinity of the body!!
This is why Hydro-therapy will work if understood properly and applied properly, by using Hot and Cold, for this will change the body's pH, by it's self!!
As to the carbonic acid and the oxygen: What you have to start with is carbon dioxide which is released first, which turns into carbonic acid!
OXYGEN is a very strong OXIDZER, which means that it will neutralize an Acid!!
So if the body becomes too acidic from carbonic acid release and there is not enough of the Alkaline Minerals to neutralize the carbonic acid, then the carbonic acid will react with all of the available OXYGEN and use it up and the person starves for Lack of OXYGEN, this is what brings on Death!!
Now concerning excersize and breathing in more OXYGEN vs the release of carbonic acid from the process of excersize!!
To gain the most free OXYGEN for Alkalizing the body by the process of excersize without producing too much release of carbonic acid, which will only make the body more acidic, one needs to understand proper excersize!!
The proper way to accomplish this is by excersizing rapidly to bring your self to deep breathing, and then rest for several minutes.
Example: Excersize hard for 1-3 minutes on a trampoline to bring about deep breathing, and then stop and rest for 5-15 minutes!! And then repeat this process all over again!!
By doing this one may oxidize the body much more than one will cause the muscles to release too much carbonic acid, which will make the body more acidic, and thus a person will not develop sore muscles from this excersize process and you will build Health instead of cause sickness!!
Your reference about (Bohr Law) and CO2 in the blood liberating oxygen to the tissues may not be correct!!