How does the concentration of Oxygen affect the rate of corrosion of steel in seawater and on land?
Generally, it is required in stoichiometric ratios with water. Relative humidity affects corrosion more than oxygen, but both water and oxygen are usually plentiful.
Seawater is particularly corrosive because it also contains chlorides. Oxygen availability underwater may reduce the rate compared to a wet environment on land.
Some excellent sources with calculations and other considerations for this problem are here: