Mixed Layer Depth

The upper ocean surface presents a typical structure formed by a mixed layer, a seasonal pycnocline and a permanent pycnocline. The mixed layer is the region in which turbulent air-sea exchanges are taking place and all tracers, and specially density, are almost homogeneous. The mixed layer depth (MLD) is a key parameter for a variety of oceanographic processes but due to its vague definition subjective and several objective methods to its determination from profiles have been proposed. Below the mixed layer, the ocean interior is characterized by a smooth, almost linear, decaying density. In mid-latitudes the mixed layer and the permanent pycnocline are directly connected by the end of winter and are linked by a sharp gradient (the seasonal thermocline) the rest of the year.