a' bed . Thus, as a result of winter cooling and the subsequent summer heating, a cold inter- 

 mediate layer is formed between levels p and p ' . 



^l_f^ 



Figure 21. Formation of the cold inter- 

 mediate layer. 



We see that in time the cold intermediate layer, no longer maintained by cooling from above, 

 will be gradually eliminated from below by frictional mixing with lower lying layers, and from 

 above by continual heating and by frictional mixing with the upper, warmer layers, which is shown 

 on the temperature curve by a gradual elimination of points on the curve, as is shown in figure 21 

 by the dashed lines. 



If winter cooling, as compared with summer heating, were not sufficiently intense, in time all 

 traces of a cold intermediate layer would disappear. On the other hand, if winter cooling is suffi- 

 ciently intense traces of the cold intermediate layer will remain even toward the start of new cool- 

 ing. The cold intermediate layers formed as a result of vertical winter circulation and summer 

 heating are characteristic during spring and summer for all seas of the temperate and polar lati- 

 tudes with noticeable vertical salinity gradients. Depending on local conditions, the cold interme- 

 diate layer may be temporary, disappearing after a year, or continual, i.e. , maintained over many 

 years. Depending also on local conditions, the temperature of the cold intermediate layer may be 

 comparatively very high and very low — close to the freezing point. 



The less the summer heating and the stronger the winter cooling, the deeper the lower bound- 

 ary of the cold intermediate layer will drop, and the lower will be its temperature. When the verti- 

 cal winter circulation is accompanied by ice formation, the temperature of the cold intermediate 

 layer drops to the freezing point . 



Tables 24 and 25 give examples of spring and summer distribution of temperature and salinity 

 in regions of ice formation. 



81 



