Table 7. The effect of constants on the calculation of the fugacity of CO₂ (fCO₂) at 20�C^a



Source of constants	Input	Input	Input	Input	Output	Output	Output
Source of constants	DIC	Si(OH)₄	PO₄	fCO₂@4�C	TAlk	fCO₂@20�C	ΔfCO₂@20�C/ΔDIC

Roy et al. (1993)	2260	135	2.3	531.8	2371.3	1080	7.1
Goyet and Poisson (1989)	2260	135	2.3	531.8	2371.3	1076.4	7.1
Hansson (1973a,b) refit by Dickson and Millero (1987)	2260	135	2.3	531.8	2377.4	1018.8	6.7
Mehrbach et al. (1973) refit by Dickson and Millero (1987)	2260	135	2.3	531.8	2368.4	1033.0	7
Dickson and Millero (1987) refit of Hansson/Mehrbach	2260	135	2.3	531.8	2372.5	1042.7	6.9
GEOSECS (Takahashi et al. 1982)	2260	135	2.3	531.8	2367.2	1016.8	6.9
Peng et al. (1987)	2260	135	2.3	531.8	2378.1	1013.3	6.7

^aAll values were calculated using theQUICKBASIC computer program of Lewis and Wallace (1998) with the default values for the secondary constants;the correction from 4�C to 20�C can cause the resulting pCO₂ to differ by 65 µatm depending on the constants used. The ΔfCO₂@20�C/ΔDIC values in µatm/(µmol/kg) show that in Pacific deep water a precision of 1.5 µmol/kg in DIC corresponds to approximately 10 µatm in fCO₂.

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