The deep-sea temperature was $12º$C higher $50$ My ago.
I would like to know how much the atmospheric pressure at sea level had decreased and how much the water-vapour changed.
One can consider no ice-sheets and that the sea surface temperature varyed by the same amount and that by now there is $0$% of water vapor in the atmosphere (in fact it is between 0% and 4% function of latitude and altitude and assume the conservation of atmospheric masses of $O_2, N_2$).
This issue is very important because in this paper:
"Temperature-dependent hypoxia explains biogeography and severity of end-Permian marine mass extinction" is established a link between an increase of the global temperature by 10ºC and the Great Dying global extinction via a global hypoxia. The solubility of O2 in water is function of the temperature, atmospheric pressure and salinity and the paper only mentions the temperature.
This is a call to moderators to return this question to the PSE site where it was originally formulated.
This question is specifically formulated in the field of thermodynamics with matter subject to a gravitational field and the most appropriate site to get a correct answer is the PSE as the numbers clearly show: On the Physics website (PSE) there are 8,489 active issues marked with Thermodynamics and in this EarthScience site there are only 122 questions. I will offer a bounty of 500 points as a reward for the first correct answer after it is returned to the correct site.