3. With the same wind force, the fluctuations increase with the stoppage of drift and, in 

 particular, with the break-up. 



4. Appearance of ice fluctuation anticipates the wind. 



Vertical ice fluctuations, which are caused by the wind even with a smooth ice surface, in- 

 volves break-up of a field into parts, superimposition of one block on another, and ice heaping. 



In such seas as the Barents and Greenland Seas, where the ice edge is clearly defined, the 

 wave is also important in the break-up of ice fields in addition to the action of the wind. This is 

 corroborated by the observations of the station "North Pole" and the Sedou. 



The drift of the icefields of the station "North Pole" first occurred quietly. The winterers oc- 

 casionally discovered fissures, which were formed in connection with the temperature changes. They 

 did not observe ice hummocks and powerful shocks till the end of January, 1938. Even rotation of the 

 icefields around the vertical axis were comparatively small, especially at the beginning of the drift. 



The first powerful shock was observed on 20 January 1938, and the first fluctuations of the the- 

 odolite level were discovered on the following day (the ice field was located in the Greenland Sea about 

 77° latitude). Without a doubt, this was related to the fact that the entire month of January was 

 stormy in the Greenland Sea. The wind velocity often reached 30 m/sec. Since the eastern part of the 

 Greenland Sea is always ice-free, the ice fields began to move somewhat as a result of this wind force. 



On 26 January, a storm set in which lasted six days. The ice field began to undergo more 

 powerful oscillations. The period of these oscillations was 10 to 12 seconds and was the sum of the 

 waves period and the period of its own fluctuations. The inclination of the ice field reached 60 

 angular seconds or more. As a result of these oscillations, tensions were generated in the ice 

 field, which finally caused it to break up on 1 February along lines approximately perpendicular to 

 the wind direction. A large surge undoubtedly caused these fluctuations and thus the break-up of 

 the ice field. The surge was caused by stormy winds in the neighboring ice-free areas of the 

 Greenland Sea and spread in all directions according to a general law. 



On 2 January 1940 , the first oscillations of the Sedov were observed by fluctuations of the the- 

 odolite tube at81°01.9' latitude and 3° 18' longitude. The fluctuations occurredinthe plane of the 

 meridian with a periodicity characteristic for a surge. At this time, the ice edge was not located 

 north of 80° latitude. 



On 12 January 1940, it was noted in the log of the Sedov: 



"2100, significant surge 30 m — when the ridge passed, ice was raised a little and broke open. 

 When the base of the wave had passed, the ice rejoined with a creak, characteristic of jamming. 

 The phenomenon occurred with a periodicity, characteristic for a heavy sea of 9-10 sec." 



LITERATURE: 11, 41, 42, 62, 77, 131. 



Section 95. Rotation of Ice and Its Break-up 



The break-up of ice fields occurs quite often during the rotation of ice, which is caused by 

 various factors. The first systematic research of the causes of ice rotation was carried out by 

 Gakkel and Khmyznikov during the expedition on the Chel iuskin in 1933-34. 



Let us assume that ice belts, consisting of several blocks, move along a rectilinear shore 

 (figure 88). If the ice is very firm, the littoral belt remains immobile as the seaward belt glides 



249 



