Sound waves travels by pushing matter in a repeating wave.
The SOFAR channel is an area in the ocean that allows sound waves to travel large distances by keeping them from going out of the waters surface and from hitting the sea floor.
Marine organisms could use sound to communicate, find each other, or find prey in the ocean.
People use sonar in the ocean by sending a sound wave out into the water and processing the information to find fish, enemy ships, or maping the envorment.