Ice in the Sea 



279 



The iceberg season usually lasts from 15 March to 15 July, but the number of ice- 

 bergs decreases rapidly after the middle of June (see Fig. 117). From the middle of 

 July to the following spring the area south of the Grand Banks is almost free of ice- 

 bergs. The variations in iceberg frequency from year to year are very large. South 

 of 48° N. there were in 1929 a total of 1351 icebergs, in 1924 only eleven. An accurate 

 monthly record of these values is available starting from 1900. Together with the 

 previous data compiled by Mecking there is now a complete series of records available, 

 covering a period of 50 years for the iceberg frequency off Newfoundland. This is 

 shown graphically in Fig. 129. With these more or less homogeneous data it is possible 



1880 



1890 



1900 1910 



Years 



1920 



1930 



Fig. 129. Character of the iceberg-years from 1880 to 1930 off Newfoundland (ten step- 

 scale, according to Smith). 



to investigate with some hope for success the causes of the aperiodic variations in 

 numbers of icebergs. In the first place there appears to be a correlation between the 

 atmospheric pressure gradient from Iceland to Greenland-North America a few 

 months previously and the iceberg maximum off Newfoundland. Determination of 

 the air pressure anomaly for the North Atlantic for the months December to March 

 during 6 years of low iceberg frequency, in this case with a total of 275 icebergs, and 

 for the same months in 5 years with a high iceberg frequency with a total of 774 

 showed completely opposite conditions (Fig. 130). A weak Icelandic low pressure area 

 during the spring and the autumn with a weak pressure gradient over Baffin Bay and 

 Davis Strait seems to be followed by the low-frequency iceberg years. During ice- 

 berg-rich years, on the other hand, the Icelandic low-pressure area is intensified and 

 the strong pressure gradient to the west is accompanied by strong air movements and 

 stronger wind drift in the iceberg area along the North American coast. Smith has 

 also tried a quantitative determination of this relationship using the correlation 

 method, and has obtained a prognostically valuable formula. An increase in the ice- 

 berg frequency in the north-western Atlantic is thus accompanied by an intensification 

 of the atmospheric circulation in the polar areas which corresponds to an increase in 

 the outflow of polar air and of the arctic water towards the south. These relation- 

 ships of course take into account only the meteorological effects and not the possible 

 fluctuations in the production of icebergs by the western Greenland glaciers. At the 

 present time it is not possible to make an estimate of these. 



5. EflFect of Polar-Ice Conditions on the Atmospheric and Oceanic Circulation 



The total annual ice outflow along the whole of the west coast of Greenland has 

 been estimated by Smith as between 42 and 63 km^ (see p. 272) ; the American coast 



