The abyssal plain bottom of the ocean. It is covered with mud, sand, and sea animals. A chain of mountains runs down the center of every major ocean called mid-ocean ridges . The deepest part of the ocean are the trenches . Rift valleys also form on the floor of the ocean.
Ocean water is very salty.
The amount of salinity in the ocean affects the buoyancy of an object. Scientists group types of ocean life by their marine environments. The three environments are plankton , nekton , and benthos . The food cycle in the sea begins with the plankton . Plankton consists of two categories of organisms, phytoplankton and zooplankton .