This is an interesting problem.  Alkalinity is the measure of how resistant water is to pH change - it is not a measure of pH.  Water with a pH below 7.0 is said to be acid - above 7.0 it is called alkaline.  The use of the alkaline only applies to the pH.  One method for measuring alkalinity is by measuring the amount of acid added to a sample to bring about a decrease of the pH of that sample to some target value.  The more acid it takes, the higher the buffering capacity, or alkalinity of the water sample.

Surface water in much of middle America has been exposed to soils originating from limestone and dolomite rock.  Both rocks contain high levels of calcium and magnesium carbonates occurring as the minerals calcite and dolomite, primarily.  Both of the minerals are soluble by acid in rainwater; consequently, the acid is usually neutralized by the soil.  This phenomenon explains why acid rain is not nearly the problem in the southeast where coal is burned in order to generate electricity.  The soils in the northern states and in Canada originate from granitic rocks and have very little capacity to neutralize acid.  Even though the acid concentrations in the rainfall there are much lower than in the southeast, the impact in the lakes and streams is dramatic.

If the alkalinity of the water is known, then the amount of acid necessary to change the pH should be calculable.  If the estimates of petroleum deposits are accurate, the population growth rate remains unchanged and the rate of consumption of fossil fuels per capita are stable, then the day when the process of ocean acidification will reverse should be predictable.  When the growing population exhausts the supply of petroleum for heat and transportation, the waters should start healing.  If the doomsday prophets are correct, that could be any day now.

A graphic in the Scientific American article predicts increasing acidity to the year 3000.  I don't think the fossil fuels will last that long.  By that time, we should be relying on relatively non-polluting products like hydroelectricity, wind and solar power, hydrogen, etc.  If we rely on nuclear reactions to provide energy, we may drastically reduce the demand for energy from all sources.  THAT mass extinction will inconvenience our hobby.