The barrier layer In physical oceanography is the layer between the thermocline and the halocline.
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It is called this because of its effect on the mixed layer heat budget due to the temperature at the bottom of the barrier layer being zero, which excludes heat loss to the underlying water via mixing. It is defined as the difference between the thickness of the isothermal layer and the mixed layer (determined by a defined change in density), with the isothermal layer generally being greater than or equal to the mixed layer depth. In the Western Pacific, an area with a barrier layer, horizontal temperature gradients are also very small, leading to the conclusion that the net heat flux at the ocean surface must be close to zero.