Formula for Calculating Oxygen Saturation Concentration in Seawater (Excel file)
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Equation for calculating oxygen saturation concentration for 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
This is a rather long formula, but it is convenient to enter the formula in a spreadsheet sheet on your own PC. The water temperature and oxygen saturation concentration are shown below (thick solid line in the figure below). When the oxygen concentration in surface seawater is actually measured, there are many cases (↑ in the figure below) where the oxygen saturation concentration is higher than that calculated by the above equation.
Oxygen supersaturation in seawater can be caused by 1) a decrease in solubility due to increased water temperature, 2) bubble penetration during rough weather, and 3) oxygen generation through photosynthesis. To compensate for these effects, it is necessary to compare the concentration of inert gases (CFC, nitrogen, argon) and carbon dioxide. In most cases, oxygen in seawater can be considered to be in equilibrium (saturated) with the atmosphere.
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Here is a file with the above formula entered into Excel.
Download it and be ready to calculate at any time.
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