This increases their buoyancy which may result in the development of a warm and stable layer at the surface. This warm water rests on top of colder water and may extend only as deep as wave action can mix warm surface water into the ocean. This warm layer acts like a lid, preventing the mixing of surface waters with colder, deeper water. Excess oxygen gas from photosynthesis builds up in this mixed layer and is subsequently released into the atmosphere. The amount of dissolved gas that water can hold depends upon its temperature.
Seawater can hold fewer dissolved gas molecules when it heats up.
The three major dissolved gases in the surface waters of the ocean are oxygen, nitrogen, and argon. The ratio that they exist dissolved in the ocean is not the same as is the ratio existing in the atmosphere. Nitrogen gas is not as soluble as oxygen and argon, so when water releases its dissolved atmospheric gases, the air becomes relatively enriched in oxygen. When the surface waters heat up, a slight enrichment of atmospheric oxygen occurs in the overlying air. During winter periods, colder water absorbs more dissolved gases.