720 ANNUAL EEPORT SMITHSONIAN INSTITUTION, 1912. 



LIMITS OF REGION OF ICEBERGS. 



It has been found that in April, May, and June are the greatest 

 number of icebergs. They have been seen as far south as the thirty- 

 ninth degree of latitude and as far east as longitude 38° 30'. In 

 general, it may be stated that floating ice may be met with anywhere 

 in the north Atlantic Ocean northward of the fortieth degree of 

 latitude at any season of the year. 



SURFACE TEMPERATURE OF THE LABRADOR CURRENT IN WINTER AND 



SUMMER. 



During the winter months the surface temperature of the Labrador 

 current often falls to the freezing point of salt water, about 28° F., 

 but it is more often at 29° or 30° F. As the spring advances the line 

 of low temperature advances farther north, until in July or August 

 the temperature on the Grand Banks toward the Strait of Belle Isle 

 reaches 40° or 45° F., and gradually falls northward to 29° F. in 

 Hudson Straits. The surface temperature varies considerably, 

 depending on the proximity of ice or land, as will be explained 

 shortly. No measurements have been made north of the Banks in 

 winter or spring, when the Strait of Belle Isle is icebound. Reports 

 of the temperature of the ice track are frequently given by sea cap- 

 tains. Results as low as 22° F. have been shown to me, but I believe 

 these to be impossible, and due to some error of measurement arising 

 from the crude method now in vogue on our Atlantic liners. 



INFLUENCE OF ICEBERGS ON THE TEMPERATURE OF THE SEA. 



There can be no question but that icebergs have an important 

 influence on the temperature of the sea. Composed of frozen fresh 

 water from the north, they melt rapidly when they drift down to the 

 warmer waters of the Banks and when they reach the Gulf Stream. 

 On account of the small conductivity of the water, no appreciable 

 coolmg can result from this cause. If it were not for the currents in 

 the sea and the circulation set up by the melting berg, no cooling effect 

 would be appreciable. That there is a small cooling effect has been 

 shown by captains and others, but this has not been made use of for 

 telling the proximity of ice with any success. What is called salt- 

 water ice — that is, ice formed by the freezing of salt water — contains 

 a small trace of salt in its composition and frequently holds salt 

 mechanically, but there is very little difference in the purity of the 

 ice. It is well known that water in freezing expels all the impurities, 

 hence it is erroneous to say that salt-water ice floats under the sur- 

 face. What is called salt-water ice is really the same as field ice, and 

 is exceedingly hard to break. Its structure is not uniform, and, 

 composed often of irregular broken pieces, it has no line of cleavage. 



