Basic characteristics and forming mechanism of the sharp thermocline in the Bohai Sea, Huanghai Sea and northern East China Sea

On the basis of the fact that the sharp thermocHne in the Bohai Sea and the northern Huanghai Sea is often distributed in the deep valley areas, it has been long thought that the reason of the formation of the sharp thermocHne is that the cold water can be easily kept in valleys.But recent investigations carried out in the southern Huanghai Sea in summer show that all of the sharp thermocHne areas were distributed in the shallow sloping-bottom areas but not in the deep valley areas.Only in autumn would the sharp thermoclines translate to the deep valley areas.In summer, they are characterized by shallow upper mixing layer and thin thickness in the southern Huanghai Sea.In addition to entrainment coming from lower boundary of upper mixing layer the entrainment from upper border of bottom homogeneous layer induced by tidal mixing also plays an important role in the growth and decay of thermoclines in these seas.