This is a setup of two bodies of water with a air passage connecting them. CO2 goes into solution and out of solution very easily, so there is a constant flow of CO2 from any body of water and the air in contact with it, going both ways. This means an equillibrium must be reached, where as many CO2 molecules enter the air (or water) as leave it. So, two such bodies of water will both reach equillibrium with the air passage connecting them and both must have the same ppm of CO2 for that to be so. If one body of water changes in CO2 concentration, that changes the amount of CO2 in the air passage contacting that water, and that change then changes the CO2 concentration in the other body of water until it is equal to the first one. All of this takes place pretty slowly, like over an hour for equillibrium to be reached. |