Critically for many shell-forming marine organisms, carbonate (CO3-2) is simultaneously consumed by reaction of the excess of hydrogen ions produced from the reaction above:
H+ + CO3- => HCO3-
Combining the two reactions, the net affect is approximately that one unit of carbonate ion is consumed for each unit of carbon dioxide added to seawater.
CO2 + H2O + CO3-2 ↔ 2HCO3-
Because the reactions run simultaneously, both pH and the availability of carbonate are reduced as the atmospheric concentration of carbon dioxide rises.
sea levels rising due to glacial melt is good now