It is clear that such phenomena assume special significance when there is comparatively 

 little ice, which occurs at the beginning of winter. It is at this time that the greatest hummocking 

 and the greatest breaking up of ice formations, comprising a given field, occur. 



During the winter, the hummocked floes freeze together and form large fields. During the 

 summer, the ice fields form the so-called broken ice during hummocking. 



It is natural that, due to these processes, the surface of the floating ice is extremely uneven. 

 Only in unusual circumstances does level ice form by natural means. This occurs when old, hum- 

 mocky fields impinge against each other in such a way that "bays, " protected on all sides, are 

 created between them. * 



The southern limit of pack-ice distribution is the shore during the summer and the sea edge 

 of fast ice during the winter. 



The position of the northern limits of pack ice in the Arctic Basin is extremely mdetermiaate 

 and, in any case, extremely conditional. It can be considered as corresponding to the northern 

 limits of free navigation by steamships during the summer. It can also be considered that the 

 northern limit of pack ice follows approximately the 1, 000 m isobath. 



Plotting such a limit is possible first because it approximately corresponds to the northern 

 limit of free navigation by vessels in the Arctic Basin, and second, because in crossing from great 

 depths to the offshore shallows, the Atlantic waters, which fill the Arctic Basin in the form of 

 warm, intermediate layer, rise to the surface here and have a weakening effect on the ice. 



However, a comparison of the observations made of the "North Pole" stations and on the 

 Sedou , and also observations from airplanes during flights made in organizing the "North Pole" 

 station, has shown that there is no special difference between the ice which, let us say, fills m all 

 and part of the Laptev Sea and the ice in which the ship Sedov drifted, but on the other hand, the 

 ice on which the "North Pole" station was set up differed extremely from this ice. 



The observations made by Alekseev are given below, and also those by Zhukov during the 

 flight in May-June, 1937, from Rudolf Land (81° 45' north, 50° east) to the North Pole and back. 



Strongly hummocked (hummocks up to 3 m) young ice, with razvodyas and fissures, were 

 seen from Rudolf Land to 82° 30' north. Fragments of icebergs were found. Level areas measur- 

 ing 100 of 200 square m were rarely found. From 82° 30' to 85° 30', the size of the fields In- 

 creased to 20 km across. Level areas measuring 250 or 350 square m were found quite often. On 

 6 June 1937, when the airplane landed at 84° north, the thickness of the ice proved to be 100 to 200 

 cm. The ice was level with a great amount of ropaki, covered on top by a layer of snow up to 40 cm 

 thick. The snow was slightly salty on top. 



North of 85° 30', old ice began, wherein the ice fields were small, highly hummocked, the 

 rasvodya were jammed with small ice, brash ice, and young ice. A landing by an airplane on such 

 airfields was impossible without crashing. 



* Exceptions to this rule are the regions of strong tidal phenomena. Thus, in the White Sea 

 estuary, even after lengthy and strong frosts, the main mass of the ice is composed of large and 

 small, extremely hummocked floes. This is particularly noticeable in the region of Menzenskii 

 Gulf. 



116 



