93 



distances. Because of its limited range, it is of little value in the defining of 

 pack ice limits. 



The electronic-position-indicator, recently developed by the Coast Survey 

 for offshore survey at distances of 12 to 500 miles, is useful in surveying sea 

 ice areas. Its great accuracy (average error 0.2 microseconds for a series of 

 tests at ranges of 45 to 90 miles) permits the drift of a vessel on station to be 

 determined in a relatively short period. By measuring the movement of ice 

 relative to the water mass, it offers a means of obtaining ice drift and the verti- 

 cal current structure by direct observation. It is especially valuable for bad 

 visibility areas in which the conventional methods of navigating fail or are lack- 

 ing. Using it, detailed offshore soundings can be expected to increase greatly 

 in value. 



PHYSICAL AND CHEMICAL PROPERTIES OF SEA ICE 



The study of the physical and chemical properties of sea ice is compli- 

 cated by the fact that it is not a pure compound, but a non-homogeneous, ever- 

 changing mixture of ice and the sea salts containing occluded brine. The rela- 

 tive amounts of brine, salt crystals and ice present is dependent upon the salt 

 content of the original sea water, the rate of freezing, age, temperature and the 

 thermal history of the ice since it was first formed. Freezing and thawing 

 freshens sea ice as a whole and causes a change in the distribution of brine and 

 salt within the ice. Ice fields move under wind and current. Pressure built 

 up by the relative movement within the field or at the- edges results in large 

 scale rearrangements of the ice from cakes turning over, over-riding one an- 

 other and interleafing, and ice cakes originating hundreds of miles apart oc- 

 casionally intermingling with each other. Snow cover and new-formed ice con- 

 tribute to the physical discontinuity of the new configurations. The structure of 

 newly formed winter ice of simple thermal history from a given locality that has 

 not been subject to breaking and rearrangement, is less complex. Further- 

 more, ices differing in origin and history, when sufficiently aged, may be 

 freshened to the extent that a close similarity of properties exists, determined 

 largely by the existing thermal structure within the ice. Dichtel and Lund- 

 quist's (1950, 1951) investigation of the physical and electrical characteristics 

 of comparatively simple sea ice are among many which show even its great var- 

 iablity. In making and interpreting physical and chemical measurements, al- 

 lowance must be made for the more or less confused arrangement of the ice, its 

 variable composition and continuously changing properties. It is necessary to 

 measure many of the physical and chemical properties of the ice in situ to avoid 

 changes that would accompany removing and storing the samples. 



Physical properties of ice now being studied or contemplated, include the 

 mechanical, thermal, acoustic, optical and electrical. Chemical investigations 

 include those of salt and gas content, ion ratios, freezing, thawing and related 

 processes, as they affect the salt-water-ice system; foreign substances in ice, ice 

 aging processes, history and dating of ice. The necessary measurements can 

 largely be made by existing instrunnents or simple modifications thereof. 

 Progress made in solving many of the problems recognized as early as the 

 FRAM expedition has not been in keeping with the instruments directly available 

 or adaptable. A continuing and intimate contact with ice problems of an ade- 

 quate number of well trained scientists has been lacking. Not more than one or 

 two full time oceanographers in the United States have devoted their efforts pri- 

 marily to the study of sea ice, and no schools give specific training and instruc- 

 tion in the field. The present deficiency in knowledge of sea ice stems primari- 

 ly from shortage of scientific personnel and inadequate facilities and not as yet 

 any fundamental deficiency in instrumentation. 



