Calculation formula for seawater oxygen saturation concentration (vs atmospheric oxygen) and graph of calculation results
Calculation formula for oxygen saturation concentration in seawater (Garcia and Gordon, 1992)
[O2saturation(mmol/m3)] = (1000/Mv)・exp[A0 +A1・Ts + A2・Ts2 + A3・Ts3 + A4・Ts4 + A5・Ts5 + S(B0 + B1・Ts + B2・Ts2 + B3・Ts3) + C0・S2]
Ts = ln[(298.15 - T)/(273.15 + T)]、 T：water temperature（℃）、 S：salinity（‰）
Mv：molar volume of oxygen(22.3916 L/mol)
|
A0 |
A1 |
A2 |
A3 |
A4 |
A5 |
|
2.00907 |
3.22014 |
4.05010 |
4.94457 |
-0.256847 |
3.88767 |
|
B0 |
B1 |
B2 |
B3 |
C0 |
|
|
-6.24523×10-3 |
-7.37614×10-3 |
-1.03410×10-2 |
-8.17083×10-3 |
-4.88682×10-7 |
|
Although it is a fairly long formula, it is convenient to enter the formula into a spreadsheet on your PC. The water temperature and oxygen saturation concentration are shown (thick solid line in the figure below). When we actually measure the oxygen concentration in surface seawater, we often find that it is higher than the oxygen saturation concentration calculated using the above formula (↑ in the figure below).
The causes of supersaturation of oxygen in seawater are: 1) decrease in solubility due to rising water temperature, 2) bubble penetration during rough weather, and 3) oxygen generation through photosynthesis. To correct for these effects, it is necessary to compare the concentration of inert gases (chlorofluorocarbons, nitrogen, argon) or carbon dioxide with the concentration of oxygen. In many cases, the oxygen in seawater can be considered to be in equilibrium (saturated) with the atmosphere.
