The erosive capability of water ciirrents is manifested by recent 

 experiments in the Antarctic, Specially shaped propellers driven by 

 small motors were suspended through holes in the ice of McMurdo Sound. 

 The propellers created vigorous currents which eroded the ice from 

 below, A 10-horsepower device reportedly required I83 hours to open 

 an area 30 by 85 feet in 8-foot-thick ice. An additional swath of ice 

 200 feet long was eroded to a thickness of I8 inches; soon afterward, 

 it fell through. 



Analysis of data obtained with the Roberts current meters revealed 

 no permanent current. Mass transport of water in the area was attri- 

 buted to tidal action. Peak tidal current speed was approximately 0,2 

 knots (based on threshold value of the instrument). 



COKCLUSIONS 



The bubbling system operates as a huge pump capable of performing 

 work on contiguous subsurface water. The rising streams of bubbles 

 initiate a system of circulatory cells which extend from the bubbled 

 region into adjacent water. Water from depths exceeding 15 meters is 

 clrc;jlated into the agitated columns adjacent to the pier and brought 

 to the siorface. 



At the time of initial ice formation in 1959^ convective mixing 

 had occurred throughout the upper 15 meters of Worth Star Bxigt, The 

 density gradient below the 15-meter level gradually weakened with ice 

 growth, and the entire water column cooled to the freezing point. 

 After elimination of the warm water supply, maintenance of an open 

 water area adjacent to the pier was attributed to the ice-dispersive 

 and erosive activity of the induced currents coupled with the possi- 

 bility that the turbulent energy also sufficed to prevent crystalline 

 growth about ice nuclei. Efficiency of the system varied directly 

 with turbulence. 



Considerable narrowing of the polynya by mid-winter was attrib- 

 uted to marked increase of tensile strength with consequent increased 

 resistance to erosive action of the induced currents as the tempera- 

 ture of the ice dropped below -9.2° F. Vertical growth of the newly 

 formed ice cover within the bubbled area was inhibited by this ero- 

 sive action because the undersurface of the ice is weakest when its 

 temperature equals that of the water„ Increase in the dimensions of 

 the ice-free area was observed to concur with an increase of air 

 temperature to approximately 0° F in early spring. This increase was 

 attributed to marked decrease of tensile strength with consequent 

 decreased resistance to erosion as the temperature of the ice rose 

 above -9,20 f. 



