22 POLAR PROBLEMS 



his cotidal map in conformity with that formula. But it must be 

 noted that, to bring the different observations into agreement, he 

 found it necessary to assume depths across the Arctic Sea less than 

 those given by Nansen. 



While Fjeldstad's cotidal map coordinated the times of the 

 observed tides, the wide difference in the range at Bennett Island 

 and on the coast of Alaska remained inexplicable. The obstruction 

 postulated by Harris explained that difference nicely. Likewise 

 the fact that flood at Point Barrow comes from the west and the 

 relatively small diurnal tides remain unexplained on the assumption 

 of a simple tide wave progressing directly toward Alaska across an 

 unobstructed Arctic Sea. 



H. U. SvERDRUP's Investigations 



Recently, H. U. Sverdrup, scientific leader of the Maud expedition 

 of 1922-1925, studied these questions anew. During this expedition 

 Sverdrup made a number of tide observations on the North Siberian 

 shelf and also systematic observations on the tidal currents. ^^ He 

 found these currents rotary in character— almost circular at con- 

 siderable distances from the coast. But at all these stations the 

 direction of rotation was clockwise, indicating clearly that this was 

 due to the deflecting force of the earth's rotation. ^^ 



In the "Dynamic of Tides on the North Siberian Shelf" Sverdrup 

 contributes an important hydrodynamic study of the behavior of 

 the tide wave on continental shelves, taking into consideration the 

 effect of the resistance along the bottom and the effect of the deflecting 

 force of the earth's rotation. The latter varies with the latitude, in- 

 creasing from the equator to the poles, where it attains its maximum 

 value. Harris had assumed that, notwithstanding the fact that 

 the deflecting force of the earth's rotation reaches a maximum at 

 the pole, its effect on the diurnal tides in a deep polar basin would be 

 small in comparison with the direct effect of the tide-producing forces, 

 since the free period of oscillation of such a deep basin is but a frac- 

 tion of the period of the diurnal tide.^* 



From Sverdrup's mathematical discussion it appears that in 

 the progress of a tide wave across a continental shelf the effects of 

 friction and of the deflecting force of the earth's rotation are of 

 primary importance and modify profoundly the simple character of 

 the progressive tide wave traveling across deep oceanic basins. The 



12 H. U. Sverdrup: Dynamic of Tides on the North Siberian Shelf: Results from the Maud 

 Expedition, Geofys. Publikasjoner, Vol. 4, No. S, Oslo, 1926. 



"In 1912, northwest of Spitsbergen, Nansen had already determined that the tidal currents 

 rotate clockwise (Spitsbergen Waters: Oceanographic Observations During the Cruise of the "Vesle- 

 moy" to Spitsbergen in 1912, Videnskapsselkapels Skrifler: I, Mal.-naturv. Klasse, 1915, No. 2, 

 Christiania). 



i< Harris, Undiscovered Land in the Arctic Ocean, p. 57. 



