16
1.0
0.8
0.6
0.4
0.2
0.0 L __ . . . . . ~---v~p!J~8
2
4
6
8
pH
10
12
Fig. 1.5. The fractions of carbonic acid in sea water as a function of pH (Millero 1996)
1.3
Parameters of the CO 2 System in Sea Water
F.J. Millero
14
To characterize the various components of the carbonate system one must measure at
least two of the four measurable parameters
1. pH
2. total alkalinity (TA)
3. total CO2 (Te02)
4. partial pressure of CO2 (Peo)
The pH can be measured using electrodes or indicators. If the electrodes are calibrated
using seawater buffers (Millero 1981; Millero et al. 1993a), the accuracy is ±O.Ol and the
precision can be ±O.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 pressure and temperature can be determined from equations given elsewhere (Millero 1995).
The total alkalinity of sea water is defined as the concentration of all the bases that
can accept H+ when a titration is made with HCI to the carbonic acid end point. The
value of TA is given by (Dickson 1981)
TA = [HCO;-] + 2 [CO~-] + [B(OH)4] + [OW]- [H+]
+ [SiO(OH);-] + [MgOH+] + [HPO~-] + [PO~-]