CONCLUSIONS 



1. The vertical variation of ring-tensile strength in a thick isothermal ice sheet does 

 not correlate well with subcrystal platelet width or other crystal parameters. The 

 strength variations observed in McMurdo Sound sea ice were caused by temperature 

 differences and varying stages of internal deterioration. 



2. The growth history of the annual sea ice in McMurdo Sound varies with time 

 and location, and is affected by climatic differences, water circulation and depths, 

 exposure to wind, and snow cover. A detailed study of large- and small-scale 

 features such as banding, brine drainage, and crystal structure provides much informa- 

 tion concerning growth conditions of ice at particular locations. 



3. Stressed sea ice in pressure ridges has distinct optical properties, such as wavy 

 extinction under crossed polarized light and preferred c-axis orientation. This 

 indicates that stress conditions in an ice sheet may be determined by studying the 

 crystal structure and optical properties. However, more data are needed under a 

 wider variety of stress conditions to establish better interpretive criteria. 



4. Measurements of various crystal parameters, both horizontally and vertically, 

 are restricted in 7.62-cm-diameter core specimens. Measurements are needed from 

 large blocks of sea ice to further study the relationship between crystal structure and 

 sea ice strength. 



ACKNOWLEDGMENTS 



Dr. A. J. Gow and Mr. Steven Roth rendered invaluable help in photographing 

 many of the thin sections. Dr. W. F. Weeks and Mr. Justin Dykins have contributed 

 much helpful discussion and many useful suggestions, Mr, C. W. Henderson furnished 

 excellent assistance in the field and laboratory. 



REFERENCES 



Anderson, D. L. "A model for determining sea ice properties," in Arctic sea ice, 

 Washington, D. C, National Research Council Publication 598, Dec, 1958, pp. 148- 

 156. 



Anderson, D. L., and Weeks, W, K, "A theoretical analysis of sea-ice strength," 

 American Geophysical Union, Transactions, vol. 39, no. 4, Aug. 1958, pp. 632-640. 



Assur, A. "Composition of sea ice and its tensile strength," in Arctic sea ice. 

 Washington, D. C, National Research Council Publication 598, Dec. 1958, pp. 106-138, 



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