The four branches of oceanography are chemical oceanography, marine geology, physical oceanography and marine ecology. The first three fields deal primarily with the physical aspects of oceans and seas, while marine ecology pertains to animals and plants in the sea.
Chemical oceanography concerns composition of seawater and biogeological cycles acting on it. Marine geology involves study of the features and structures of ocean basins and how they evolved.
Physical oceanography is about properties and movement of seawater and how the ocean interacts with the atmosphere. Marine ecology, or biological oceanography, studies life cycles and food production of animals and plants.