The ocean can be divided into three density zones: the surface zone, the pycnocline, and the deep zone. The surface zone, also called the mixed layer, refers to the uppermost density zone of the ocean. Temperature and salinity are relatively constant with depth in this zone due to currents and wave action. The surface zone contains ocean water that is in contact with the atmosphere and within the photic zone.
It is also known as the intertidal zone because it is the area where tide level affects the conditions of the region.
In contrast, the littoral zone covers the region between low and high tide and represents the transitional area between marine and terrestrial conditions.