reverse current of deep water out into the open ocean is intensified. When the surface water 

 recedes, the phenomenon occurs in reverse. The similarity of tidal phenomena and wind-caused 

 phenomena lies also in the fact that comparatively small changes in surface level are accompanied 

 by very great amplitudes of rise and fall of deep water. 



Petterson first called attention to the internal waves of large period in his study of the 

 seasonal vertical fluctuations in salinity in the Danish Strait and at the same time he connected the 

 period of these fluctuations with periods of astronomical phenomena. 



Danus called the tidal on-shore driving "transgressions." Comparing the conclusions of 

 Petterson, L'AUemand, Prevaux and others, he found that the basic periods which determine the 

 nature of transgressions of surface water (on-shore driving) and deep water (off-shore driving) are 

 as follows: 1 — 4.65 — 9.3 — 18.6 — 111 years, etc. Actually, when Petterson studied the long- 

 term fluctuations in catch of fish in the Danish Strait he found a period of 111 years. Dorsey 

 Thomas found that the maximum catches of fish at Edinburgh occurred every 18.6 years, etc. 



The largest astronomical period to have an effect on the ice abundance in the Atlantic sector 

 of the arctic, as analyzed by Petterson, is equal to 1, 800 years. Every 1, 800 years the sun, moon 

 and earth are in one plane and on one straight line under conditions of shortest distance from the 

 earth to sun. At such moments the tide-forming force reaches its maximum intensity and on 

 account of this the maximum disturbances of equilibrium are provoked both in the atmosphere and 

 in the hydrosphere . 



Such mutual positions of the heavenly bodies occurred in the years 2100 and 360 before our 

 era and in the year 1433 of our era. * The historical research of Petterson indicates that great 

 climatic and oceanogr^hlc variations occurred around these years in the North Atlantic. 



The Norwegian Vikings in the 10th and 11th centuries evidently experienced no difficulties 

 due to ice when sailing to Greenland. Eric the Red, in the course of his voyage of 984 to 987, 

 passed along the east coast of Greenland from Angmagsalik to the southern extremity of Greenland. 

 In these times, according to Petterson's opinion, the East Greenland current was as free of ice as 

 is the East Iceland current at the present time, and the Greenland ice did not go past Cape Farewell 

 into Baffin Bay. The climate of Greenland in those times was similar to the present climate of 

 Norway in the same latitudes. Starting with the year 1261 the first written indications appear of an 

 ice blockade of Iceland. 



At the same time there began some very severe winters in Norway and catastrophic floods on 

 the east coasts of the North Sea. 



LITERATURE: 62, 77, 101, 148, 149, 159, 163. 



Section 159. Geological Factors 



Nansen paid great attention to the discussion of the effect of geological factors on the ice 

 abundance of the Arctic Ocean. He considered that the oceanographic conditions in the Arctic 

 Basin very obviously exert a great influence on climate. 



The arctic water, of low salinity and below temperature, protects the lower-lying Atlantic 

 water from cooling and thus makes the arctic climate more severe. If this layer did not exist, the 



"The Soviet author does not employ "B.C." and "A.D." - Translator. 



461 



