It is usually divided into four sub-disciplines:

• Physical Oceanography ? the study of waves, currents, tides, and ocean energy.
• Geological Oceanography ? the study of the sediments, rocks, and structure of the seafloor and coastal margins.
• Chemical Oceanography ? the study of the composition and properties of seawater and how it is affected by physical mixing processes and interactions with the seafloor, the atmosphere, and ocean life.
• Biological Oceanography ? the study of marine organisms and their interactions with the ocean environment.

All of these sub-disciplines are highly interrelated, as well as being closely aligned to other fields such as meteorology/atmospheric science, geophysics, and ocean engineering.