107 



to well over 5 per cent of the effect of the melting bergs. The larger 

 this percentage loss is, the less will be the chilling effect on the local 

 waters of the bergs that melt in the "melting area." 



The 0.01° F. figure is a maximum for still another reason not pre- 

 viously brought out. During a 100-day ice-patrol season, the cold 

 current is entirely renewed at least once throughout the "melting 

 area" if the average southerly drift of the current is only 4 sea miles 

 per day. But the southerly drift of the ice bearing waters averages 

 much more rapid than this. Therefore, the chilling effect of the sea- 

 son's bergs should not be figured upon the simple extent of the 74,000 

 sc^uare sea miles. It should be spread out over a water volume cover- 

 ing a surface more than twice as large, over the total area of cold 

 water that passes through the "melting area" during the ice season. 



These conditions need not be emphasized because the approximate 

 figure of 0.01° F. which was arrived at is already sufficiently small to 

 indicate the relative unimportance of the bergs as chilling agents in 

 the southern reaches of the Labrador Current. Even if ver}^ large 

 miscalculations have crept in, and the total amount of berg ice to get 

 south of the forty-eighth parallel should by any chance be twice as 

 large as has been estimated, still its effects will be so small as to make 

 them extremely unimportant. 



An oceanic effect diametrically opposite to the chilling influence of 

 melting bergs is to be found in the vernal w^arming at and near the 

 surface about the Grand Banks. The next paragraphs will discuss 

 that part of the tremendous seasonal warming which the ice patrol 

 is able to observe, and will compare its magnitude with the 0.01° F. 

 chilling value just deduced. 



The normal ice-patrol season can be taken as 100 da3^s long, from 

 March 25 to July 3. A slight amount of exterpolation is necessary 

 to arrive at the March 25 and Juh^ 3 surface temperature values in 

 3'ears when the active patrol season begins late or ends unusually 

 early. On the whole such allowances are easy to make and the ice- 

 patrol period can be used as a convenient measuring stick. 



Since the normal ice-patrol season extends from just past the vernal 

 ec^uinox to well past the time of the sun's most northerly declination, 

 the sun has a high position in the heavens at noon, and the surface 

 waters warm up rapidly over the whole Grand Banks regions through- 

 out the time. Although there are large local variations, and also 

 annual variations of less amount but larger significance, comparison 

 of the patrol's surface isotherm charts show that the rates and 

 amounts of warming in the same areas in different years agree closely. 



At the beginning of the season, just before April 1, the temperature 

 of the Grand Banks surface water is about 33° F. At the close of the 

 season, a little after July 1, it is about 55° F., a rise of 22° F. Over 

 the varying extent of cold Arctic stream water south of the Tail, the 



