Gases are also dissolved in seawater which are mainly used in biochemical processes. The major gases dissolved in the marine environment include nitrogen, oxygen, and carbon dioxide. Helium, neon, argon, krypton and xenon also occur in lesser quantities.

The amount of gases in water is dependent on temperature, pressure, and salt content. The amount of oxygen availability with depth is a limiting factor for many organisms. There is an oxygen minimum level or oxygen poor zone a few hundred meters in depth.

Seawater has two sources of oxygen, the surface interface with gases in the atmosphere and plants. Through photosynthesis plants produce oxygen gas. With depth photosynthesis decreases because plants are dependant on light for these chemical processes to occur. Plants produce oxygen and other organisms consume it. The consumption of oxygen is high in the upper 200 meters, so it is easy to understand how oxygen can be removed from the system.

Oxygen minimum zone