How does rising atmospheric CO2 affect marine organisms?

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Possible Future Global Change Effects on Seawater Salinity and Acidity
Loaiciga, H.A. 2006. Modern-age buildup of CO2 and its effects on seawater acidity and salinity. Geophysical Research Letters 33: 10.1029/2006GL026305.

The author notes that "seawater acidity and salinity are of biological, physical, and chemical significance," and that "the U.S. Environmental Protection Agency (1976) recommended a range of pH in seawater between 6.5 and 8.5 for marine aquatic life, but not more than 0.2 pH units outside the normally occurring range."

What was done
In evaluating potential seawater impacts of (1) model-predicted global warming and (2) direct seawater chemical consequences of a doubling of the air's CO2 concentration, Loaiciga used a mass-balance approach "to estimate the change in average seawater salinity caused by the melting of terrestrial ice and permanent snow in a warming earth," and he applied "a chemical equilibrium model for the concentration of carbonate species in seawater open to the atmosphere" in order to "estimate the effect of changes in atmospheric CO2 on the acidity of seawater."

What was learned
In the words of Loaiciga, "assuming that the rise in the planetary mean surface temperature continues unabated, and that it eventually causes the melting of terrestrial ice and permanent snow, it is calculated that the average seawater salinity would be lowered not more than 0.61%o from its current 35%o." He also reports that across the range of seawater temperature considered (0 to 30C), "a doubling of CO2 from 380 ppm to 760 ppm increases the seawater acidity [or lowers its pH] approximately 0.19 pH units."

What it means
Loaiciga concludes that "on a global scale and over the time scales considered (hundreds of years), there would not be accentuated changes in either seawater salinity or acidity from the rising concentration of atmospheric CO2." Hence, any changes that might occur would have little to no negative biological ramifications, as we have reported repeatedly in Journal Reviews archived under Coral Reefs (Calcification) in our Subject Index.

U.S. Environmental Protection Agency. 1976. Quality Criteria for Water. Washington, DC, USA.

Reviewed 6 September 2006