190 



BIOLOGY OF THE SEAS OF THE U.S.S.R. 



the Polar regions may cause considerable fluctuations of the ocean's level 

 either by their melting or by their massing. During the last Glaciation Period 

 ( Wechseleiszeit), the ice masses of the northern hemisphere exceeded those of 

 the present day by 32,800,000 km 3 ; for the southern hemisphere the difference 

 is 4,100,000 km 3 . The level of the ocean must have been 93 m lower than it is 



ANCYL TAPES-LITTORINA 



PERIOD PERIOD 



-7 -6 -5 -4 -3 -2 -1000 



m00 +1900 



YOLDIAN 



PERIOD 

 -13000 -12 -11 -10 -9 -8 

 +10 

 ±0 



-20 

 -40 

 -BO 

 -80 

 -WO 

 -120 

 -140 

 -WO 

 -180 



Fig. 135. Eustatic and isostatic fluctuations of level of Baltic Sea in post-glacial 



period at Lysekil (Antew). 



now on account of the increase of the Polar ice (corresponding approxi- 

 mately to 34,000,000 km 3 of water). Northern glaciation alone must have 

 resulted in a lowering of the sea-level by 88 m (Antew, 1928). It has been 

 established that some thousands of years ago the ocean level was 5 to 6 m 

 higher than it is at present ; this might be related to intensive melting of the 

 Polar ice during the warm phases of the post-glacial period (Boreal, Atlantic 

 and sub-Boreal periods 3,000 to 9,000 years ago) and to the isostatic* varia- 

 tions of the level of the mainland at some point of the Swedish coast of the 

 Skagerrak. 



The Ice Lake Sea 



As a result of the violent melting of ice, which took place fifteen or twenty 

 thousand years ago, the Baltic depression was filled with huge masses of 

 melted ice water. The level of the Ice Lake Sea which had formed in this way 

 and spread widely was considerably higher than that of the ocean. This body 

 of water had an outflow to the ocean in the west ; on the east it was connected 

 with Lake Ladoga; it existed 13,000 years ago. 



The Yoldian Sea 



As the masses of continental ice which had supported the level of the Baltic 

 Ice Lake receded, the level fell, until at last masses of cold saline ocean waters 

 rushed into the Baltic Sea through the broad passage which was formed 

 * Caused by the lowering or rising of land. 



