Examples for Calculation of the Calcite-Carbonate-Equilibrium in Ocean Waters

4 Examples for Calculation of the Calcite-Carbonate-Equilibrium in Ocean Waters 

exemplary results will be introduced which were obtained from model calculations of the cal- 

In the first example shown in Table 9.2, a warm (25°C) water from the ocean s surface (1 atm) has been modeled. In the zone near the equator, where this water sample had been taken, carbon dioxide partial pressures of 400 patm (equivalent to a pCO of 0.0004 atm or a log pCO of -3.40) have been measured which is somewhat higher than the corresponding atmospheric value. This sample of ocean water thus displays a CQ -gradient directed towards the atmosphere and therefore continually releases CQ into the atmosphere. This situation is accounted for in the model by pre-setting pCO to 0.0004 atm as an open boundary condition with regard to CQ. Accordingly, a state of supersaturation ensues equivalent to a SI, , value of 0.77 or an f2, , value of 5.9. Such a supersaturation state is, according to the 

In the model calculation presented in Table 9.3, the constant of the solubility product of calcite was adjusted to temperature (6°C) and pressure (100 atm) relative to a depth of about 1000 m. Therefore, the pressure-corrected constant derived from the model SOLMINEQ (Kharaka et al. 

1988) was entered into the database of the model PHREEQC, and the correction procedure for temperature integral to this model was used. Furthermore, an organic substance which also contained nitrogen and phosphorus in a C N P ratio of 106 16 1 (Redfield 1958), was decomposed down to a low residual concentration of dissolved oxygen. The calculation was then run under conditions 

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