CHAPTER 1 • The Carbonate System in Marine Environments
17
The percent of TA due to the various bases is shown in Table 1.2 for ocean waters
with pH = 8, [SiO(OH);] = 10- 5 . 25 and [HPO~-] = 10- 5 . 52 • For most waters, [HCO;], [CO~-]
and [B(OH)4"] are the most important bases. For anoxic waters, HS- and NH3 can also
contribute to the total alkalinity.
The carbonate alkalinity, CA, is defined by
CA = [HCO;] + 2 [CO~-]
(1.20)
and is calculated from
(1.21)
where l.:Bi = [B( OH)4"] + ... , the sum of all the bases other than HCO; and CO~-. The
[B(OH)4"] concentration, which is the largest source of [BJr, can be calculated from
(1.22)
where [BJr is the total concentration of boron. The contribution due to other bases
(phosphate, silicate, ammonium, and hydrogen sulfide) can be determined using the
dissociation constants for the appropriate acid (Appendix). The methods used to determine the TA are given elsewhere (Millero et al. 1993b).
Although it is possible to determine TC02 from a titration, more reliable values can
be obtained by direct measurements. This is done by stripping the inorganic CO 2 with
nitrogen after the addition of phosphoric acid. The CO2 can be collected in a liquid
air trap and analysed by gas chromatography, infrared spectroscopy or by conductivity. By collecting the CO2 in a DMSO solution with ethyleneamine, the CO2 can be coulometrically titrated with OH- produced on a Pt electrode. Routine measurements of
TC02 on 30 cm 3 sea water can be made to a precision of 1 flmol kg -I and an accuracy of
2 flmol kg- I (Johnson et al. 1993).
The partial pressure of CO2 in sea water is determined by equilibrating the sample
with air or nitrogen. The CO2 in the equilibrated gas is measured using gas chromatography or an IR analyser. By passing sea water through a shower head equilibrator,
one can make continuous measurements on surface sea water (Wanninkhof and
Thoning 1993). The system can be calibrated using standard CO2 gas mixtures and yield
values of Pe0 2 to a precision of 1 flatm.
Table 1.2. Contribution of
various components to the
Species
TA(%)
total alkalinity (TA) of sea
water
HCO;
89.8
C0 2 -
3
6.7
B(OH)4
2.9
SiO(OH);
0.2
MgOH+
0.1
OH
0.1
HPO;0.1
17
The percent of TA due to the various bases is shown in Table 1.2 for ocean waters
with pH = 8, [SiO(OH);] = 10- 5 . 25 and [HPO~-] = 10- 5 . 52 • For most waters, [HCO;], [CO~-]
and [B(OH)4"] are the most important bases. For anoxic waters, HS- and NH3 can also
contribute to the total alkalinity.
The carbonate alkalinity, CA, is defined by
CA = [HCO;] + 2 [CO~-]
(1.20)
and is calculated from
(1.21)
where l.:Bi = [B( OH)4"] + ... , the sum of all the bases other than HCO; and CO~-. The
[B(OH)4"] concentration, which is the largest source of [BJr, can be calculated from
(1.22)
where [BJr is the total concentration of boron. The contribution due to other bases
(phosphate, silicate, ammonium, and hydrogen sulfide) can be determined using the
dissociation constants for the appropriate acid (Appendix). The methods used to determine the TA are given elsewhere (Millero et al. 1993b).
Although it is possible to determine TC02 from a titration, more reliable values can
be obtained by direct measurements. This is done by stripping the inorganic CO 2 with
nitrogen after the addition of phosphoric acid. The CO2 can be collected in a liquid
air trap and analysed by gas chromatography, infrared spectroscopy or by conductivity. By collecting the CO2 in a DMSO solution with ethyleneamine, the CO2 can be coulometrically titrated with OH- produced on a Pt electrode. Routine measurements of
TC02 on 30 cm 3 sea water can be made to a precision of 1 flmol kg -I and an accuracy of
2 flmol kg- I (Johnson et al. 1993).
The partial pressure of CO2 in sea water is determined by equilibrating the sample
with air or nitrogen. The CO2 in the equilibrated gas is measured using gas chromatography or an IR analyser. By passing sea water through a shower head equilibrator,
one can make continuous measurements on surface sea water (Wanninkhof and
Thoning 1993). The system can be calibrated using standard CO2 gas mixtures and yield
values of Pe0 2 to a precision of 1 flatm.
Table 1.2. Contribution of
various components to the
Species
TA(%)
total alkalinity (TA) of sea
water
HCO;
89.8
C0 2 -
3
6.7
B(OH)4
2.9
SiO(OH);
0.2
MgOH+
0.1
OH
0.1
HPO;0.1