74 M.C. Miller etal. 



The summer climate at Barrow during the 4 years of our study was 

 slightly warmer than the 30-year mean. Precipitation was near normal but 

 the average includes both a very dry and a very wet summer. Solar 

 radiation decreased each summer from 1971 to 1973 as a result of 

 increasing cloud cover. This affected water temperature and 

 photosynthesis. 



The ponds are well mixed by wind and by convection. Ponds with 

 similar depths have similar temperatures. In general, mean daily water 

 temperatures rose rapidly in June from 2° to 12°C. After early July, 

 temperature slowly declined; the range in July was 7° to 12°C and in 

 August was 3° to 9°C. Within this general pattern there was a great deal of 

 variability because the water temperature often dropped 9° to 10°C in one 

 day as the air temperature changed. In fact, the water temperature was 

 higher than the air temperature; over 4 weeks the average was 7.1° and 

 3.7°C, respectively. The highest temperature recorded was 20°C; the 

 lowest was 0°C after a mid-August snowstorm filled the pond with snow. 

 The average water temperature was about 6 to 8°C. 



Sediment temperatures were the same as the water temperatures at 

 their interface. However, at 10 cm below the sediment surface the average 

 temperature was 2.3°C less than the water. In addition, the daily 

 temperature range was also reduced (to 1 .5°C). 



The pond ice melted between 10 and 17 June. Pond sediments thawed 

 rapidly thereafter and half of the total thaw occurred in the first 10 to 20 

 days. The thawing rate then slowed; the maximum depth of thaw, 25 to 36 

 cm into the sediment, was reached in late August. After 1 September, the 

 sediments began to refreeze from the bottom. Between 7 and 16 

 September a permanent ice cover formed on the ponds but the ponds were 

 not completely frozen for several weeks or more. When this occurred, the 

 sediments froze from two directions; the two freezing fronts met at a depth 

 of 20 to 30 cm in the sediment. 



The total snowfall at Barrow is 45 to 1 04 cm year ~ ^ but most of this is 

 compacted, blown away, or sublimated. At the pond site, the maximum 

 snowpack was 18 to 31 cm; the snow is 40% water. Summer precipitation, 

 which is about half of the total, ranged from 1.7 to 13.2 cm of water from 

 1970 to 1973 but the long-term average is 6.7 cm. 



The runoff from the pond site was difficult to measure accurately; 

 there were no well-developed channels so the flow had to be measured at a 

 number of sites. The watershed includes more than 100 ponds but the exact 

 boundary is unknown. Most of the runoff takes place within 2 weeks in 

 late June. Some of the meltwater does not run off but instead goes to fill 

 up the ponds. As described earlier, the ponds decrease in size and depth 

 during late summer so the ponds are far from full when they are frozen. 

 The measured runoff of 5.7 cm in 1972 and 5.9 cm in 1973 was 83% and 

 51% of the expected runoff calculated from the snowpack data. This 

 matches the water level data which showed a higher pond level in late 

 summer of 1971 than in late summer of 1972. Usually, the pond water 



