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Seawater pH and Carbonate Equilibria Program (Demonstration)

Use this program to calculate the pH and carbonate equilibria (K*) in seawater, and the changes in these quantities caused by varying the water composition relative to normal seawater stoichiometry. For complete explanations of the model output, see the notes pages for the examples of a simple case (for which only section 1 should be filled in below), and a natural water with an altered composition (for which there must also be entries in section 2).

Fill in the form below (blanks in section 2 will be treated as zero), and press the Submit button.

1. Enter the temperature (0 to 45 oC), and the salinity (1 to 40)

Temperature (oC):      Salinity:


2. Vary the composition of the seawater, if needed

Vary Na+ by (%):   as:              Vary Mg2+ by (%):   as:
Vary Ca2+ by (%):   as:              Vary Cl− by (%):   as:
Vary SO42− by (%):   as:                Vary HCO3− by (%):   as:
Vary CO32− by (%):   as:                Vary B(OH)3 by (%):

There are limits to the percentages that can be entered here. For example, if the moles of Cl− in the seawater are reduced by removing CaCl2, then the percentage reduction in Cl− is limited by the fact that for every mole of total Cl− in solution there are only about 0.0189 moles of Ca2+. Therefore the greatest reduction that can be achieved in this way is 1.89%. The mole ratios of the ions in the seawater, relative to Cl− = 1.0, are: Na+ = 0.784, Mg2+ = 0.0962, Ca2+ = 0.0189, K+ = 0.0186, SO42− = 0.0514, HCO3− = 0.00315, CO32− = 0.000438, B(OH)3 = 0.000576. (See note 1, below.)



Results will be displayed below. Click here:    (allow up to 20 secs for a result)

Notes

The model used for these calculations was produced for demonstration purposes, and is still a work in progress. Hence, the uncertainties in the ion-ion interactions are estimates (generally pessimistic ones) but, more important, some interactions are not yet included. If you would like to know more, please contact the author (s.clegg@uea.ac.uk).

1.  Values of the ion/Cl− ratios for individual for carbonate and borate species change with T, S, and pH. Those listed here, for guidance in the use of this demonstration program, are taken from Table 4 of Millero et al. (Deep Sea Res. I, 55, 50-72, 2008) and are for S = 35. The changes in solution composition applied by the model will be based upon the calculated speciation at your input T and S.