2, Mean Ice Potential 



Figure 1, which shoirs the potential ice thickness ai'eally for 

 STjmmer of a single year, is compsrable to a chart of mean >?eathsr 

 conditions over a period of perhaps two or three months. The next 

 logical step is the construction of mean charts of the ice potential 

 by averaging the data covering a number of years. Such a chart is pre- 

 sented as figure 2« By dratving mean charts of the ice potential, the 

 average stability for every location can be exajnined to find areas of 

 persistent high or lovr potential ice thiclmess. It is natural that 

 the high and low values of ice potential should be found in nearly the 

 same locations year after year, because the data reflect the quasi- 

 permanent water cijrrents and the regular; annual nearshore cycle of 

 freezing and melting and sxirface runoff . \ 



As can be seen from figure 2, the main features of the chart for 

 1951 J figure 1, are characteristic for the five-year period, 1950~195U« 

 The area of greatest potential ice thickness is the center of the 

 Beaufort Sea, with an extension southward to the Alaskan coast between 

 Barter and Herschel Islands. In the coastal area east of Point Barrow 

 the ice potential is small and increases eastward, A second area of 

 low ice potential is located outside the entrance to Amundsen Gulf, 

 between 123'^ ana 130"^ and 70*^ to 73°N. This area is evidently of 

 dynamic origin, which' is quite unlike that around Point Barrow « 



In view of the incomplete knoifledge of currents and water masses 

 in the Beaufort Sea area at this time, only tentative postulates may 

 be made as to the origin of the areas of high and low ice potential 

 sho^m in figure 2,' The great potential ice thicknesses indicated in 

 the center of the polar basin are characteristic of the extremely cold 

 surface waters of that area. The extension of the great potential 

 ice thicknesses to the shore near the Alaskan^Tukon border may be 

 caused by an onshore eddy which may curve counterclockwise along tlie; 

 coast and across Mackenzie Bay. This surface eddy was apparent in 

 examining ice movements d-oring the summer of 19$k« The sxea of low 

 ice potential around Point Barrow is fjrobably the result of advection 

 of warm water from Bering Strait. Somd portion of this current of 

 warm water apparently proceeds eastward along the Alaskan coast, lo^t'ttg 

 heat as it moves eastward and accounting for the increase in ice 

 potential from Point Barrow eastward. 



The most interesting featui'e of figure 2 is the area of low ic& 

 potential southwest of Banks Island. A priori, this area should not 

 be much different from the area around Barter and Herschel Islands, 

 for there is no knoim so\rrce of warm currents in this part of the Arctic. 

 However, the area of Io^t ice potential is evident for each of the five 

 years from 1950 to 195ii and, therefore, must be regarded as .a normal 

 feature. It is believed that this feature is of dynainic origin rather 

 than advective in nature like the ai'ea around Point Barro-f. It is 

 possible that the bottom topography of the eastern Beaufort Sea and 

 Amundsen Gulf causes tidal phenomena which could change the ice poten- 

 tial of the surface waters in that area. Tidal raii-ge throughout the 

 area is small, amounting to less than 2 feet reerly everyivhsre. Ces- 



„5« 



