SEA ICE ON MCMURDO SOUND, ANTARCTICA - DEEP FREEZE-67 THICKNESS AND TEMPERATURE STUDIES.

The annual sea ice on McMurdo Sound, Antarctica, is extensively used as a runway by heavy cargo aircraft. Safe utilization requires a better understanding of thickness, temperature, and strength - basic properties affecting the load-carrying capacity of ice sheets. Thickness and temperature are the two parameters required to use load-carrying curves being developed by the Naval Civil Engineering Laboratory (NCEL). Annual sea-ice thickness varies seasonally between 8 and 11 feet by the end of the growth period. Thinning by bottom melting starts about mid-December and continues until breakout in late January or early February. The average ice-sheet temperature has increased each season since Deep Freeze 65 (DF-65), and becomes essentially isothermal about the same time bottom melting begins. For operational safety, the ice sheet should be monitored for thickness and temperature as described in this report. The surface temperature, T sub s, measured at a depth below the influence of diurnal air temperature fluctuations, is needed to select the correct NCEL load-carrying curve. A depth of 24 inches is beyond the influence of this fluctuation and is suitable for determining T sub s on a daily or weekly basis. The average ice-sheet temperature, based on the freezing point of seawater, is (T sub s + 1.8)/2. Both the surface temperature and the average ice-sheet temperature gradually change with time. (Author)