[SAJ]

Would you please discuss how dissolving carbon dioxide in salt water increases the level of hydrogen ionisation? This seems entirely counterintuitive.

TIA!

[AdmSmith]

You may take a look at this http://en.wikipedia.org/wiki/Carbonic_acid

[lepton]

Would you please discuss how dissolving carbon dioxide in salt water increases the level of hydrogen ionisation? This seems entirely counterintuitive.

The salt is largely irrelevant, though at extremes it may act as a buffering agent. Soda water is slightly acidic. As example, watch how you can shine pennies in soda water - it is the carbonic acid which causes that effect.

[Blueflag]

Simply put, the hydrogen ions come from water, H2O. Carbonic acid is the result as shown by a prior post. When the vapor pressure ( of dissolved CO2 ) changes, more CO2 enters or leaves the water, and the amount of carbonic acid correspondingly changes.

This is NOT an open system, it is a closed loop system. CO2 enters and leaves the oceans all the time. The oceans are not just a carbon sink.