The unreflected light rays penetrate into the depth of the ocean, and thus we divide the ocean into two main layers, the surface and the deep part. The surface of the ocean is characterized by the light and warmth, whereas the deep is characterized by darkness. These two parts of the ocean differ with respect to their properties and characteristics, and the surface is further separated from the deep part by waves. These internal waves were only discovered in the year 1900. The internal waves cover the deep waters of seas and oceans because the deep waters have a higher density than the waters above them.
Internal waves act like surface waves.
They can also break just like surface waves. Internal waves cannot be seen by the human eye, but they can be detected by studying temperature or salinity changes at a given location. Underneath these waves which separate the two parts of the ocean, the darkness begins. Fish at these depths cannot see. Their only source of light is from their bodies.