CHAPTER XIII 



SEASONAL AND LONG-TERM FLUCTUATIONS 

 OF ICE ABUNDANCE 



Section 154. Ice Abundance 



The quantity of ice cover in the sea is a function of the area occupied by ice, ice thickness 

 and solidity. Most indicative and easiest to observe is the area occupied by the ice. It is deter- 

 mined either in percentages with respect to the sea area, or in tenths. 



Seas may be classified, firstly, by the origin of the ice encountered in them, and secondly, by 

 the length of time in which ice is found in the given region. 



In respect to origin of ice, I divide the individual ice regions of the World Ocean into the 

 following basic groups: 



1. Regions where the ice is entirely or predominantly of local origin. Such, for example, 

 are the Barents, Kara and White Seas. 



2. Regions where the ice is entirely or predominantly not of local origin, but is carried in by 

 winds and currents from other regions. Thus, for example, is the region south of Newfoundland 

 where icebergs are constantly being carried which originated along the shores of Baffin Bay and 

 which have consequently completed a journey of 2000 to 3000 km. 



In respect to time during which ice is found, I divide the ocean ice regions into "ice regions, " 

 "freezing regions, " and "ice-free regions. " Ice regions are in turn subdivided into polar and sub- 

 polar regions. In both of these the ice usually remains throughout the entire year, representing an 

 essential feature of the sea picture. In the polar regions, open water never exceeds in area the 

 sea area covered by ice. In other words, the ice abundance of these regions is never less than 

 one-half. In the subpolar regions the quantity of ice decreases considerably in the summer season 

 and in the most favorable years it disappears completely . 



Freezing regions are completely cleared of ice in the summer season. In respect to the ex- 

 tent of time in which they are covered with ice they are subdivided into freezing seas of greater and 

 lesser ice abundance. To the first group belongs, for example, the White Sea, where ice is found 

 during more than half the year. To the second group belongs, for example, the Gulf of Finland, Sea 

 of Azov, and the northern part of the Caspian Sea. 



In ice-free regions ice is found only under exceptional conditions. 



The greatest anomalies in ice distribution are caused by ocean currents. Figure 176 shows 

 the average monthly positions of the ice edge in the summer in the Greenland and Barents Seas. 

 From the chart we can see how far north the influence of the Spitzbergen and Norwegian currents 

 extend. 



445 



