268 



Ice in the Sea 



(c) Aperiodic Variations in the Polar Ice Conditions 



It is not surprising that a natural phenomenon such as the polar ice coverage de- 

 pending on such a large number of different factors should show large aperiodic 

 variations. In addition to their scientific interest these variations are of considerable 

 practical importance for life and commerce in the polar regions. Statistics of the 

 changes in ice coverage in the polar seas do not go very far back. 



Following a resolution of the seventh international meeting of geographers, Berlin, 

 1899, the Royal Danish Meteorological Institute has published since 1894 an annual 

 ice-record for the Arctic, and these annual reports are now the most important source 

 of data of this type. However, knowledge of the extent and movement of the ice is 

 confined mostly to shipping routes and fishing areas. The available data are thus in- 

 homogeneous and incomplete. However, more accurate observations of the polar 

 zones from the air will probably lead in the future to further progress, especially also 

 because of the increasing military interest. 



Variations in the ice conditions of polar and subpolar regions do not proceed every- 

 where in the same way; because they appear to be due, in the first place, to variations 

 in the atmospheric and oceanic circulation, both of which regionally cause quite 

 different effects. Somewhat more detailed investigations of these aperiodic variations 

 have been made for the oceanic regions around Iceland, Davis Strait and Newfound- 

 land and also, in part, for the Barents Sea. 



Meinardus (1906) has examined the duration and the intensity of ice in the area 

 around Iceland for the years 1800 to 1904. Figure 123 shows that Iceland is situated on 



40 



1800 



1820 



1840 



I860 

 Years 



1880 



1900 



1920 



Fig. 123. {a) Character of the ice-years around Iceland for the period 1800-1904 (according 



to Meinardus). {b) Numbers of ice-character for the Davis Strait region for the period 



1820-1930 (according to Speerschneider). 



the edge of the East Greenland Current and the North Iceland Current; these ice- 

 bearing currents often cause the occurrence of severe "ice-years". Ice-rich years recur 

 rather regularly and there has been a very noticeable ice minimum during the 'forties 

 and the beginning of the following decade in the nineteenth century. There appears to 

 be a 4-to 5-year cycle governing the recurrence of ice-rich years ; this is shown quite 

 clearly in Table 102, which gives mean values based on a 4|-year cycle, beginning 

 always with a maximum for the period 1880-1904. An accurate determination by 

 periodograms gave the period of the cycle as 4-76 years. However, the great variability 

 of the phenomenon does not allow reliable ice-prognoses since the correlation coeffi- 

 cient of a value with the following fourth and fifth values is only —004 and 0-06 

 respectively. 



