832 POUNDER [sect. 7 



values of brine content, using this term to express the fraction of the ice 

 volume occupied by liquid brine or air. Brine content is mainly a function of 

 temperature, rising very sharply as the freezing point is approached. He shows 

 that Young's modulus decreases rapidly with increases in the brine content. 

 Pounder and Stalinski measured Young's modulus, E, and salinity for 

 cylindrical bars cut from cold Arctic ice and obtained the empirical relation 



E = (9.75 - 0.242>S') x IQio dynes cm-2. (1) 



The measurements were all made on ice at — 20°C. 



Very little data are available about the other elastic parameters of sea-ice. 

 Poisson's ratio has been measured for fresh ice using torsional oscillations of a 

 bar, seismic methods and sonic methods. The results are in good agreement. 

 Northwood (1947) obtained 0.33 and his value is considered the best. Peschansky 

 (1957) quotes 0.29 for sea-ice. 



C. Visco-elastic Properties 



Pure ice ranges from being almost perfectly elastic for rapidly varying 

 stresses (small enough in amplitude not to produce fractures) to being ex- 

 tremely plastic for static loads. Numerous investigations of the visco-elastic 

 nature of pure ice and snow have been carried out in recent years. Most of these 

 have consisted of measurements of creep curves using static loading (see Glen, 

 1952; Glen and Perutz, 1954; Jellinek and Brill, 1956; and Griggs and Coles, 

 1954, for example), but Nakaya (1959) has also applied sonic methods to 

 obtain both elastic and visco-elastic parameters. 



Comparable studies on sea-ice are rare, the main investigator being Tabata 

 (1955, 1958) who measured creep curves for in situ ice beams and for statically 

 loaded, small cylinders. He found that the visco-elastic behaviour could be 

 described adequately by a rheological model consisting of a Maxwell unit and 

 a Voigt unit in series. The temperature range ( — 1° to — 7°C) was too limited to 

 obtain any information about the dependence of the parameters on tempera- 

 ture, which one would expect to be large. The range in salinity was also small. 



3. Thermal Properties 



Owing to the brine cells in sea-ice, any change of temperature will involve a 

 phase change of some of the ice. The concepts of specific heat and latent heat 

 are thus thoroughly interrelated. The specific heat of sea-ice of any appreciable 

 salinity is much higher than that of pure ice, particularly near the freezing 

 point, because of this melting or freezing of additional ice. The ordinary 

 definition of latent heat of fusion is not applicable to sea-ice, both because 

 there is no fixed melting point and because the phase change is not reversible. 

 If sea-ice is melted and then cooled to its initial temperature, the resulting 

 material may be in quite a different state since the formation of sea-ice is so 

 dependent on the freezing rate. 



