Is Oxygen SOLUBLE in water?
Oxygen is soluble in water, but the extent to which it dissolves is nowhere near the extent to which gases such as carbon dioxide, ammonia, and hydrogen chloride dissolve in water. The solubility decreases with increasing temperature. Hence, at the freezing point of water and 1 atm pressure (zero salinity), the solubility is approximately 10 mL/L; at 50 degrees Celsius, it is about 4.6 mL/L. The presence of salt depresses the solubility. As you noted, soluble gases should dissolve: however, once the water is saturated with oxygen, no more can dissolve; it remains in the gaseous state. As oxygen is used up by marine life, then more dissolves from the atmosphere.
