vertical mixing, in the atmosphere or oceans, an upward and downward movement of air or water that occurs as a result of the temperature gradients (temperature differences between layers of the fluid). In the atmosphere vertical mixing is sometimes discernible as a form of atmospheric turbulence.

Does mixing occur in the ocean?

This is a natural phenomenon of our oceans, and can even occur in lakes. Winds and storms, such as hurricanes and typhoons, are the mechanisms by which the surface ocean is mixed with the deep ocean. On average, it takes the waters in the ocean's mixed layer and deep ocean about 1,000 years (or more) to completely mix.

Where is the mixed layer?

The mixed layer extends from the surface of the ocean to the top of the pycnocline (see illustration). The pycnocline is the region where seawater density changes rapidly with depth.