Physics 61 



After the ponds become ice-free, the sediments thaw rapidly and half 

 of the total thaw occurs in the first 10 to 20 days (Figure 3-6). There is 

 little between-pond difference in a given year but there are climatic 

 differences from year to year. Thus, the sediments of Pond C thawed more 

 rapidly in 1970 than did Pond A in 1973 (Figure 3-6) but at the same time 

 there was 43% more solar radiation in July of 1970 than in July of 1973. 

 Kalff (1965) found much the same thing in a pond where the thaw depth 

 was 41% greater and the solar radiation was 32% higher in 1964 than in 

 1963. 



The pond sediments reach their maximum thaw depth, 25 to 36 cm, in 

 late August (Table 3-5). After 1 September, the sediments begin to slowly 

 refreeze from the bottom but a permanent ice cover does not form on the 

 water until 7 to 16 September (Table 3-4). Because of the permafrost, the 

 sediments begin to refreeze from the bottom, but this is a slow process and 

 most of the freezing of the sediments occurs from the top down after the 

 water is completely frozen. In 1970, it took an additional two weeks more 

 for the sediments to become completely frozen; the two freezing fronts met 

 at a depth of 20 to 30 cm in the sediments. 



The shallow lakes in the vicinity of Barrow get their first ice cover at 

 about the same time as the ponds but thaw about one month later. Brewer 

 (1958) states that lakes less than 1 m deep become ice-free in late June but 

 slightly deeper lakes, e.g., Imikpuk Lake (2.8 m), become ice-free between 

 17 and 28 July. Ikroavik Lake did not lose its ice until 4 August in 1970 

 but was ice-free on 14 July 1971. Still deeper lakes, such as the 40-m-deep 

 Lake Peters in the Brooks Range, do not freeze until October (Hobbie 

 1973). Much of the difference in thaw dates is a result of the time required 

 to melt the thick ice sheets of deep lakes. Aerial photos and ERTS 



TA BLE 3-5 The Maximum Depth of Thaw A cross the Same 

 Transects in Ponds C and E, 1970 to 1972 



Year and date Pond Depth of thaw ± SD (cm) 



