that high tide and low tide do not occur simultaneously along a transverse section of the strait and 

 this causes the difference in time of change of current. For example, while the flood tide is still 

 continuing along the shore, the ebb tide may already have begun in the central part of the channel, 

 etc. These facts, as well as the influence of the deflecting force of the earth's rotation, have a 

 substantial effect on the direction of the tidal currents. 



The different times of start of flood tide and change of tidal current, the channel currents and 

 compensating currents caused by this, and likewise the currents caused by the deflecting force of 

 the earth's rotation — all these bring about the meeting of currents of different directions, as a 

 result of which eddies and whirlpools are formed. 



The complexity of these phenomena in nature hardly permits the making of appropriate theo- 

 retical calculations. Obviously, direct observations in such a case can be of inestimable value. 



The broad observations made during the drift of the icebreaker Lenin verified the correct- 

 ness of the considerations which I have discussed. 



It is clear that the winds, which also bring about compression and thinning of ice, strongly 

 distort these phenomena. This is especially true in the case of strong winds and also for changing 

 winds. Storozhev has noted (and this is new and important in the study of drift of ice in the Laptev 

 Sea), as a result of observations of the drift of the icebreaker Lenin , that there is a relationship 

 between direction of wind and the hastening and retarding of tidal pressures relative to the theoret- 

 ical times. 



For example, it was determined that winds of a northerly direction hasten the start of tidal 

 compression of ice and, conversely, retard the start of thinning of ice. Winds of a southerly direc- 

 tion have the opposite effect. Winds of a westerly direction hasten the start of compression and also 

 lengthen its duration. These winds also retard the start of thinning. Winds of over 7 to 8 m/sec can 

 independently cause compressions destroying the orderly system of tidal compressions. 



Storozhev notes at the same time that the maximum height of hummocks which formed as a 

 result of tidal pressures lasting not over 2 to 3 hours did not exceed 2. 5 to 3 m while the greatest 

 observed height of hummocks was up to 8 m. 



It was also noted that the pressure ridges in the Laptev Sea are extended from west to east in 

 the central part of the sea and from west northwest to east southeast in the southwestern part of the 

 sea. This agrees with the position of cotidal lines of the sea. 



During a flight over the Laptev Sea from the icebreaker to Tiksi Bay in early April 1938 

 Storozhev testifies that clearly-defined open water spaces were seen in strips and also pressure 

 ridges with predominant direction along the cotidal lines. 



LITERATURE: 54, 55, 62, 77, 107, 126. 



Section 126. The Concept of Ice Time 



The changes of tidal compression and thinning have long been used in navigation in ice fields. 

 For example, we had to use the tidal thinning effect for movement forward during navigation in ice 

 on the fragile motor-sail ship Knipouich while rounding Franz Joseph Land in 1932. During the 

 approach from the east towards Franz Joseph Land through solid ice on the icebreaker Sadou in 

 1935 we also made broad use of this phenomenon. 



340 



