The correct answer is C. Pycnocline
Explanation
The ocean layers can be classified into three groups according to their features, the first is the mixed area of the surface where the temperature of the water and salinity varies by its direct contact with the outside air; the second is the pycnocline is the name by which the intermediate layer of water is known according to its density, characterized by the sudden change in its density related to the depth. This change in density has different explanations, while in bodies of water such as lakes this change in density is due to the depth, in salt waters such as seas and oceans this change occurs due to the depth and in some cases to salinity. Finally, there is the deep water zone where the water is denser and colder than in the other areas due to its depth. So, the correct answer is C. Pycnocline
