Temperature differences in the water cause layers.

Both temperature and salinity play a roll in creating laying in the oceans. Colder water is denser than warm water so, it sinks. Additionally higher salt contents also increase density. Of these two factors, temperature is the more important, but both play a roll.

Layers of the Ocean Scientists have divided the ocean into 5 main layers. These layers, known as "zones", extend from the surface to the most extreme depths where light can no longer penetrate. These deep zones are where some of the most bizarre and fascinating creatures can be found. As we dive deeper into these largely unexplored places, the temperature drops and the pressure increases at an astounding rate. The following chart lists each of these zones in order of depth. http://www.seasky.org/monsters/sea7a4.html Sunlit Zone (0-600 feet): In the sunlit zone the water is very warm because that is where the sun hits. Most of the plants and animals live in the sunlit zone. This is were you will find most sharks although there is some sharks that live near the ocean floor. Twilight Zone (600-3,300 feet): The twilight zone temperature can be as low as 41 degrees F. Because there is less light there than in the sunlit zone. Dark Zone (3,300-13,200 feet): In the dark zone the temperature is about 35 degrees F. There is not so much food in this zone. Abyss (13,200-19,800 feet): In this layer the mud is made from the skeletons of other small sea animals. The mud can be more than a mile thick. Trenches (over 19,800 feet): Only animals that are adapted to the freezing water can survive in this layer. http://library.thinkquest.org/J0112423/ocean_layers.htm http://www.bbc.co.uk/nature/blueplanet/infobursts/ocean_layers_bg.shtml In the study of any natural phenomena, we have to accept the facts first. Ocean appears to be divided into some layers of zones. A scientific classification of these will provide better communication between researchers of the same field. Ocen by itself is not layered. It is a natural variation from top to bottom.