In regions of the sea where the vertical winter circulation encompasses the tops of svibmarlne 

 elevations and banks, the pnenomenon of the cold intermediate layer has certain peculiarities. 



Let us assume that at the time the lower boundary of the vertical winter circulation occupied 

 a certain position below the top of a submarine elevation, winter cooling ceased, and in conjunction 

 with the start of summer heating, formed the cold intermediate layer. Gradually, due to the ab- 

 sorption of solar radiation and due to frictional mixing, this layer will be eliminated from above. 

 At deep places it will be eliminated by frictional mixing from below, as well. If the submarine ele- 

 vation in question lies in the path of a warm current, as happens, e. g. , in the southern part of the 

 Barents Sea, the effect of the washing away of the remains of the winter regime by warm waters, 

 both from above and below, will be added to the effect of radiation and frictional mixing. Since the 

 velocity of the current above submarine elevations is less than above deep water troughs, it is nat- 

 ural that this washing effect is greater in the troughs. 



LITERATURE: 47, 62. 



Section 34. The Discontinuity Loyer 



We use the term discontinuity layer to designate that layer where the corresponding vertical 

 gradients are large — temperature, salinity, oxygen content, density, etc. , depending on which of 

 the oceanographic characteristics actually change most rapidly in the given layer. 



The discontinuity layer of density is naturally of particular significance in the ocean regime; 

 this Indicates the high stability of the surface which separates the given layers. 



As we have seen in Section 27, the overall stability of layers is comprised of the stability 

 which is determined by the vertical temperature distribution and the vertical salinity distribution. 

 It follows from this that there is great stability when the temperature and salinity stabilities are 

 combined e.g. , with simultaneously heating and salinity increase of the surface waters, or when 

 fresher, warmer shore waters are superimposed on more saline and colder ocean waters. 



Generally, in the surface layers of the low latitudes a temperature discontinuity layer pre- 

 vails which becomes weakened, and sometimes even eliminated, by convection due to an increase 

 in salinity during evaporation. In the temperate latitudes the temperature discontinuity layer is 

 characteristic of summer, and is usually eliminated by winter cooling. In the high latitudes in 

 summer, the salinity discontinuity layer is characteristic, forming as a result of a temperature 

 increase and the melting of ice, and disappearing in winter during ice formation. Thus, depending 

 on local conditions, the density discontinuity layer may be either temporary, seasonal, or contin- 

 uous. The depths of the disposition of the discontinuity layer also vary within wide limits, de- 

 pending on local conditions. We have seen that if the layer stability is high, frictional mixing is 

 very much hindered, or almost ceases. In this case the layers slide one along the other, as it 

 were, and the circulation in each of them has its own particular nature, reminiscent of the circula- 

 tion in shallows, where the current at the upper levels may be directed in one direction, while in 

 the lower levels, in the opposite direction, for compensation. 



The density discontinuity layer which is clearly expressed in certain ocean regions creates 

 another extremely interesting phenomenon, as for example the phenomena of "dead water," 

 "mire, " etc. 



If the discontinuity layer is located not far below the surface of the sea (within the reach of a 

 ship's draft), when a ship passes through the discontinuity layer waves are set up which increase 



83 



