Where is the pycnocline also a thermocline

Where a decline in temperature with depth is responsible for the increase in density with depth, the pycnocline is also a thermocline. On the other hand, if an increase in salinity is responsible for the increase in density with depth, the pycnocline is also a halocline.

Because temperature tends to be the dominant factor influencing seawater density, the depth range and base of both the pycnocline and thermocline often tend to be similar. Therefore, below the pycnocline or thermocline, temperature and salinity are relatively constant. Skip to content. Like this: Like Loading Previous Previous post: Discuss about the four possible pathways which are suggested by IPCC to restrict the rise in global average temperatures within 1.

This is because the thickness of the surface mixed layer is typically m or less. The pycnocline acts as a porous boundary that allows some kinetic energy to penetrate into deep water. The strongest currents generally occur in the ocean's surface layer although some surface currents such as boundary currents like the Gulf Stream discussed later can be relatively strong to depths of several hundred meters.

Surface currents are changeable, continually responding to variations in the wind, precipitation, and heating or cooling. Stirring of surface waters by the wind produces a well-mixed layer of uniform or nearly uniform density. For this reason, the ocean surface is called the mixed layer. We know most about the mixed layer because ships, aircraft, and Earth-orbiting satellites can readily monitor it.

Recall that cold water is denser than warm water and salty water is denser than fresh water. Where a decline in temperature with depth is responsible for the increase in density with depth, the pycnocline is also a thermocline. On the other hand, if an increase in salinity is responsible for the increase in density with depth, the pycnocline is also a halocline.

Typically, the pycnocline extends to a depth of to m to ft. However, in middle latitudes seasonal pycnoclines may develop within the mixed layer.

The dark, cold deep layer below the pycnocline accounts for most of the ocean's mass. Within the deep layer, density increases gradually with depth and water moves slowly; in only a few locations usually near the bottom are water movements fast enough to be considered currents. The ocean's three-layer structure is an example of how gravity separates a fluid into layers such that the density of each layer is less than the density of the layer below it. More dense fluids sink and less dense fluids rise.

The ocean's pycnocline is very stable thus suppressing mixing between the mixed layer and deep layer; that is, the pycnocline acts as a barrier to vertical motion within the ocean. The concept of stability is useful in understanding this property of the pycnocline.