Oceanography can be divided into four branches: Biological Oceanography, Chemical Oceanography, Geological Oceanography, and Physical Oceanography.
Biological oceanography is concerned with studying the living aspects of the ocean. Organisms that live in the ocean include the tiniest organisms, or plankton, and the largest organisms, or whales. Examples of topics studied by biological oceanographers include the distribution of organisms in the ocean, the types of organisms found in specific locations, the interactions between living organisms, and the abundance of specific types of organisms.
Chemical oceanography focuses on the chemicals found in water. As you will learn later, there is a wide variety of chemicals dissolved in seawater, from common salt, or sodium chloride, to even gold. Chemical oceanographers may study the concentration of various chemicals and how they are distributed both horizontally and vertically. These chemicals could be naturally occurring or may enter the water through man-made processes.
Geological oceanography focuses on the geological materials and processes that occur in our oceans. Geological oceanographers can study the constituents that make up the seafloor, the shape of the seafloor, and the processes that create the oceans. As you'll learn, geological oceanography encompasses a wide variety of research, which can span millions of years of natural processes.
Physical oceanography focuses on the physical movement of the oceans. This includes the study of waves, tides, and water currents. Physical oceanographers could study deep water currents, physical processes occurring along the shore, and even interactions between the ocean and the atmosphere.
As you can probably tell, these fields of study are closely related to one another. Oceanographic research may span multiple branches of oceanography, and some of the most interesting investigations include scientists from all four branches.
Check out this article to see what oceanographers have learned in the last decade: https://www.smithsonianmag.com/science-nature/biggest-stories-ocean-science-last-decade-180973793/
Go to this website to learn about the tools oceanographers use to study the ocean: https://www.nsf.gov/geo/oce/whatis/tools.jsp