found in western Baffin Bay and Davis Strait, eastern Foxe Basin 

 and the southern part of the Gulf of Boothia. By November the 

 estuaries and gulfs are again unnavigable. 



The White Sea begins to freeze in mid-October. In some win- 

 ters fixed ice may cover the whole Sea. There is little floe ice, and 

 polar ice only penetrates the northern section where from Novem- 

 ber to May much floating ice makes navigation dangerous. The 

 ice breaks up and the sea is usually navigable by June, although 

 there have been years when ice remained during the summer. 



The Gulf of Ob (Obskaya Guba) is unnavigable after the first 

 week in October. Both the Ob River and the Gulf are frozen over 

 from November to the break-up, which begins on the river about 

 the first of June and in the Gulf about the middle of June. Navi- 

 gation is possible on the river in the first week of June; however, 

 it is a month later before the Gulf is safe for ships. 



In the beginning of October the Gulf of Yenisei freezes and the 

 river freezes by mid-October. The break-up usually occurs on the 

 river in the middle of June. The ice on the Gulf does not break 

 up until mid-July. 



The Lena River has a very short period during which navigation 

 is possible. Ice covers the river from the first of October until 

 the end of May, but the delta remains frozen until late June or 

 July. Sometimes the river is ice-blocked throughout the year. 



The break-up on the rivers is a rapid and violent event. The 

 force of the waters flooding down the channels tears up the ice and 

 drives it seaward at a rate of about 4 knots. Bends or constric- 

 tions in the channel cause temporary piling up of the ice. The 

 water and bergs flood the valleys until the pressure breaks the ice 

 barrier. In a week or less an entire river will rid itself of ice. 

 River levels rise tremendously during the break-up, reaching 

 heights of 70 feet or more over the winter levels. 



WATER TEMPERATURE AND SALINITY 



Much of the knowledge of temperatures and salinity come from 

 the explorers and the men who made the famous drifts across the 

 polar basin. From the Fram expedition of 1893-1896 it was 

 learned that three layers of water exist. To a depth of 500 to 600 

 feet the water is cold with temperatures between 28.6° F. and 

 32° F. This upper layer has comparatively low salinity. Below 

 this layer, to depths of 2,500 feet the water is more saline and 

 warmer. This is probably the current from the Gulf Stream which 



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