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Chemical Oceanography, 4th Edition
pK 0
1 = –126.34048 + 6320.813/T + 19.568224 ln(T)
pK 0 2 = –90.81333 + 5143.692/T + 14.613358 ln(T)
where the adjustable parameters A i , B i , and C i are demonstrated by
A i = a 0 S 0.5 + a 1 S + a 2 S 2
B i = a 3 S 0.5 + a 4 S
C i = a 5 S 0.5
The coefficients for all the fits of these equations are summarized in Table 7.5 for all of
the pH scales.
7.4 Parameters of the CO 2 System in Seawater
To characterize the various components of the carbonate system in seawater, one must
measure at least two of the four measurable parameters:
1. pH
2. Alkalinity, total alkalinity (TA)
3. Total CO 2 (TCO 2 )
4. Partial pressure of CO 2 , (pCO 2 )
The pH can be measured using electrodes or indicators. If the electrodes are calibrated
using seawater buffers, the accuracy is ±0.01, and the precision can be ±0.002 pH units.
If the measurements are made at 25°C and 1 atm, it is necessary to determine the in situ
values at a given depth in the ocean. The effect of temperature can be determined from
pH t = pH 25 + A + B t + C t 2
(7.82)
where
A = –2.6492 – 0.0011019 S + 4.9319 × 10 –6 S 2 + 5.1872 X – 2.1586 X 2
(7.83)
B = 0.10265 – 0.20322 X + 4431 X 2 + 3.1618 × 10 –5 S
(7.84)
C = 4.4528 × 10 –5
(7.85)
where X = TA/ TCO 2 . The effect of pressure can be estimated from
pH t
P = pH t
0 + A P
(7.86)
–10 3 A = 0.424 – 0.0048(S – 35) – 0.00282 t – 0.0816(pH t
0 )
(7.87)
where pH t
0 is the pH at temperature t°C and 1 atm.