I am trying to understand the behavior of oxygen dissolved in seawater. I have always been under the impression that if a gas is in equilibrium between its gaseous and aqueous forms, that it will always have the same partial pressure in the air as in the water. For example, both air and air saturated seawater have a pO2 of 21.227 kPa (101.325 kPa x 20.95%). I recently, however, came across this tool from a company that creates dissolved O2 measuring devices which indicates that temperature has an effect on this relationship. It indicates that if atmospheric pressure is 101.3 kPa (pO2 in the atmosphere = 21.222 kPa) then the pO2 in seawater could be anything from 21.094 kPa at 0*C to 20.331 at 30*C.
If this is true, what causes this relationship? How can I calculate expected seawater pO2 given atmospheric pressure and temperature?
Bonus if you know of a function or package in R that could do this. Perhaps in the