Ocean Stratification

Stratification refers to the layered nature of the ocean and the atmosphere. Ocean is consisting of several layers. This is a picture of the several layers lies in the ocean.

The mixed layer between the atmosphere and the ocean is called Marine boundary (mixed) layer. The layer from the surface until 100m deep is called the Mixed layer. Most action takes place in the mixed region since this is the layer that gets heated up by the sun.
from 100m 1000m is the isothermal layer. The layer below the isothermal layer is called Thermocline. The temperature decreases in this region with depth. There's very little vertical motion in this region

Ref
http://stream2.cma.gov.cn/pub/comet/MarineMeteorologyOceans/ocean_models/comet/oceans/ocean_models/navmenu.htm