only certain regions of the ocean. Finally, tidal phenomena act in both vertical and horizontal di- 

 rections periodically, and at different times in adjacent regions, which aids in creating high veloc- 

 ity gradients. 



For an elementary explanation of the occurrence of frictional mixing, let us assume that a 

 wind of continually increasing intensity comes up over an initially calm sea. When this happens, 

 capillary waves first appear on the surface of the sea, these gradually change into wind waves. 

 After the wind reaches a considerable force, whitecaps form, wave destruction begins, and eddies 

 form penetrating to ever increasing depths and mixing the surface layers. Simultaneously, thanks 

 to the friction of the wind against the water and the pressure of the wind on the rear surface of the 

 waves, a wind current arises. An analogous pnenomena occurs on the surfaces of separation of 

 water masses, where the role of the wind is played by the mass which moves with the greater ve- 

 locity. This requires a smaller velocity gradient than between the air and water to effect a frac- 

 ture of the surfaces of separation and the formation of eddies. 



The lower the stability of the layers and the larger the velocity gradients the more intensely 

 the waves and eddies develop and the stronger the mixing. From this, it follows that the magnitude 

 of the velocity gradient determines the intensity of mixing and the possibility of overcoming a given 

 stability. 



Large velocity gradients are created at the bottom, off-shore, in narrows, and in the shal- 

 lows, etc. For example, the waters contiguous with the Gorlo Belogo Morya (Neck of White Sea) 

 both on the Barents Sea side and the White Sea side, are quite sharply stratified (inter- 

 stratified). Despite this, the high speeds of the tidal currents and, as a result, the large 

 velocity gradients in certain regions of the Gorlo, completely mix the water from the surface 

 down to the very bottom, which imparts the nature of a river current to the waters of this 

 strait. However, in this same Gorlo Belogo Morya there are regions where such velocity gradi- 

 ents appear to be insufficient for overcoming the sharp stratification and consequently, the high 

 stability which exists here. 



Figure 13 according to V. A. Berezkin, shows the distribution of isotherms on 13 to 17 August 

 1926 in Gorlo Belogo Morya through the Pulong-intsy section at high tide. It is evident from the 

 figure that the isotherms in certain parts of the section run practically vertical, although usually 

 during the summer, the isotherms in the siirface layers of the sea are arranged practically hori- 

 zontally. This is explained by strong mixing, arising here as a result of strong tidal currents. 



Figure 13. The arrangement of isotherms 

 in the Gorlo Beloga Morya in 

 August. 



68 



