109 



meter, and lower levels, and tell nothing directly about the tempera- 

 ture of the 50-foot level. Nevertheless, a study of temperature curves 

 made from the station figures shows that 10° F. is a conservative 

 estimate to make for the average increase in temperature at the 50- 

 foot level between March 25 and Juh^ 3. 



Let us neglect the tremendous sum total warming that takes place 

 in decreasing increments in the 50-foot la^'ers of water below the 50- 

 foot layer that has its upper boundary at the surface of the sea. We 

 can for the purpose of this discussion simply assume that the total 

 effect of solar warming from March 25 to July 4 is not less than enough 

 to warm all the water from the surface down to the 50-foot level in the 

 "melting area" an average amount of 12° F. 



Now a rise of 12° F. in 100 days means that the average rise is 0.12° 

 F. per day. It has been shown that 0.01° F. is a very generous 

 amount to allow for the chilling effect of a full season's bergs south of 

 the forty-eighth parallel on a 50-foot layer of the "melting area." 

 One one-hundredths degree Fahrenheit is only one-twelfth as much as 

 the average daily rise of 0.12° F. In other words the total chilling 

 effect of bergs in the "melting area" is not sufficient to nullify more 

 than two hours of the average vernal warming effect that is active 

 throughout the ice-patrol season. 



This seems hard to believe at first when one looks at the ice charts 

 of the ice patrol. It must be kept in mind that the bergs marked on 

 these charts must be large enough to be plainh' seen. As drawn they 

 are far too big in proportion to their proper scale size. The real 

 amount of glacial ice south of the forty-eighth parallel each year is 

 comparativel}' small when considered in relation to water volumes of 

 50-foot layers of the "melting area." 



One way to get a conception of the relative smallness of the 26 

 billion cubic feet of glacial ice that came south of 48° N. during the 

 hea^*A' 1929 ice season is to assume it to be spread out evenly over the 

 surface of the "melting area," of 74,000 square miles, or 2,664 billion 

 square feet. The whole season's bergs spread out at once would 

 make a uniform layer of glacial ice only about 0.01 foot, or one-eighth 

 inch thick. 



A skim of ice only one-eighth inch thick would not be expected to 

 last long or to interfere much with vernal warming of a fresh-water 

 lake. It should be expected to last far less time and to interfere with 

 warming no more over the "melting area." On second thought the 

 comparatively negligible effect of the bergs south of the forty-eighth 

 parallel on the water masses there is seen to be quite plausible. 



It is recognized that none of the variables that have been considered 

 in arriving at the conclusions reached in this section are accurately 

 known. Therefore, the results can be only approximate and can only 

 serve to give an idea of the orders of magnitude involved. In cases 



