I computed table 69 on the basis of formula (10). 



It can be seen from this table that daily ice accretion beneath quite thick ice is very slight 

 even with very low air temperatures, but it is comparatively great on an ice-free sea surface. As 

 a result, young ice forms and accretes very rapidly in-polynyas and cracks when the air tempera- 

 tures are very low and in individual cases, the values can be considerably higher than those in the 

 table. Nansen noted that once he observed ice that became 8 cm thick overnight, 15 cm thick in 

 the first three days, and 40 cm in 15 days. This should be explained by the fact that ice formation 

 in narrow cracks is promoted not only by low air temperature, but also by the low temperature of 

 the adjacent parts of the ice. 



The fact that the accretion of thin ice occurs considerably faster than that of thick ice Is ex- 

 ploited along the arctic coast in repairing the underwater parts of vessels by freezing the vessel 

 out, i.e. , by constructing "ice docks. " To do this, the snow surrounding the vessel to be re- 

 paired is first removed, which increases ice growth considerably, as we shall see below. Then, 

 when the ice becom.es 50 to 60 cm thick, it is chopped away such that a strip of ice not more than 

 30 cm thick always remains around the ship. Understandably, the underwater part of the vessel 

 becomes more and more exposed with time. This continues until repairs are possible. Wooden 

 braces are placed around the ship to give it stability. By the end of January 1943, the ice dock in 

 Tiksi Bay, for example, was already 3 m deep (while the thickness of the natural ice was about 

 180 cm). 



SOO 



BOO 



10 



10 



30 



40 



a: 



lU 



400 



u 



ZOO 



2000 itiOO 6000 



FREEZING DEGREE. DAYS 



8000 



50 



60 



70 



80 



30 

 WO 

 110 

 120 

 130 

 140 

 150 



10000 



Figure 72 . Graph for computing the ice increment vs . number 

 of freezing degree-days . 



I constructed the graph (figure 72) from formulas (6) and (10). The initial ice thickness in 

 centimeters is plotted on the Y-axis and the number of freezing degree-days on the X-axis . The 

 slanted lines represent the isolines of ice increment in centimeters . The graph is easy to use . 



209 



