If the ice caps melt and freshwater is added to the ocean, won?t this simply dilute the acidity?
Fresh water from melting ice caps dilutes the concentrations of all the various components of the carbonate system in seawater (described above), as well as the total alkalinity and salinity (both of which affect pH). For example, a liter of “typical” Arctic seawater (temperature, 5°C; salinity, 35; total alkalinity, 2244 micromoles/kilogram) that is exposed to today’s atmospheric CO2 level of 390 ppm has a total carbon content of 2100 micromoles/kilogram and a pH of 8.04 (total scale, here and below). Adding a kilogram of freshwater to the kilogram of seawater would dilute the salinity, alkalinity, and carbon content to half of what they were, and the initial pH would increase to 8.21. However, that seawater is out of equilibrium with the atmosphere (it now has a pCO2 of 151 ppm, while the pCO2 level of the overlying atmosphere is 390 ppm) and so it will absorb CO2 until the seawater pCO2 also equals 390 ppm, at which point the pH will have dropped to 7.83.— Richard A.
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