ORNL/CDIAC-105

Program Developed for CO2 System Calculations
(February 1998)

E. Lewis and D. Wallace
Brookhaven National Laboratory

Investigators interested in studying the ocean carbonate system are not in complete agreement on how to calculate inorganic carbon speciation in seawater. Over the years there have been many determinations and reviews of the constants used to describe the dissociation of carbon dioxide (CO2) in the ocean, but no universally accepted set of constants exists. Several subtly different pH scales remain in common use, as do variations in the definition of total alkalinity and arguments over the relative merits of reporting the partial pressure vs the fugacity of CO2. As ocean CO2 measurements become steadily more accurate and investigators seek to evaluate very small changes in concentrations, these issues grow in importance.

It is hoped that the recently released a computer program will be of general use and perhaps help to clear up some of the confusion. Given any two of the four measurable carbonate system parameters, this program calculates the other two, together with the inorganic carbon speciation and the saturation of calcite and aragonite. The program also allows the user to select from four different pH scales and several sets of dissociation constants widely cited in the literature.


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