a layer of water in which the vertical gradients of oceanographic parameters, including temperature, salinity, and density, increase sharply compared to the vertical gradients in the layers above and below. Transition layers are formed where there is intensive mixing of the surface layer caused by wind or convection or where two masses of water of different origin are superimposed on one another. Sharp temperature transitions (thermoclines) usually occur where the surface layer is strongly heated and mixed by the wind. Transition layers of salinity and density form where fresh waters from continental runoff or melting ice spread over the surface of the ocean. Submarines may use such layers as a “liquid floor.” The thicknesses of transition layers range from several meters to several tens of meters; the magnitude of the vertical gradient in such layers may exceed 8°-10°C per m for temperature, 5 parts per thousand per m for salinity, and 0.05–0.07 kg per m³ per m for density. Transition layers are typical of the upper layers of the sea. In some cases, several transition layers may be arranged vertically.