CRYSTALLOGRAPHIC STUDIES OF SEA ICE IN MCMURDO SOUND, ANTARCTICA 



Technical Report R-494 



Y-F015-n-01-026 



by 



R. A. Paige 



ABSTRACT 



The sea ice in McMurdo Sound is used extensively for aircraft operations, 

 travel, and docking areas. The safety and efficiency of utilizing the sea ice depends 

 upon many factors affecting its physical properties throughout the season. 



Sea ice is a crystalline solid with physical properties that are highly temperature 

 dependent between -1.8°C and -10 C. This dependence becomes less with decreasing 

 temperatures. A study of various crystal parameters and structure is essential for a 

 better understanding of their relationship with strength properties. Horizontal 

 banding in the ice sheet was studied to determine the effect of temperature fluctu- 

 ations on band frequency. Various crystal parameters such as subcrystal platelet 

 width, crystal length-to-width ratios, and crystal size were measured from photographs 

 of thin sections. 



Subcrystal platelet width increased with depth from about 0.5 mm at the surface 

 to about 1 mm at 2.8 meters. The length -width ratio of single crystals increased 

 from 2 to 1 near the surface to more than 5 to 1 at depths greater than 2 meters. 

 The number of crystals per unit area decreased with depth. Strained ice from a 

 pressure ridge showed preferred c-axis orientation and wavy extinction similar to 

 that observed in strained quartz. There is apparently no correlation between strength 

 and crystal structure in a mature isothermal ice sheet. 



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The Laboratory invites comment on this report, particularly on the 



results obtained by those who have applied the information. 



