THE ATLANTIC FLOOR 25 



FORMER LAND CONNECTIONS ACROSS SHALLOW SEAS 



As shallow seas we will consider those areas considerably less than 4000 m 

 in depth. For the Atlantic this actually consists of one connection across the 

 Faeroe-Iceland-Greenland-Canada Ridge. Although it may well be that a 

 connection existed between Spitzbergen and Greenland,* if a connection did 

 exist across the Nansen Straits its disruption was probably due to the opposed 

 continental displacements of Europe and North America. 



At the present time, the 500 m contour connects almost completely across 

 the Faeroe-Iceland-Greenland Ridge from Europe to Greenland (Fig. 1). In 

 two small gaps, one near the Faeroes and another in Denmark Strait, depths 

 are slightly greater. Little can be said concerning the geological history and 

 origin of this ridge for at present no cores nor dredge hauls of ancient rock 

 have been reported from anywhere along the ridge. Since the top of this 

 ridge lies close to sea level, minor vertical movements of the Earth's crust could 

 either cause an emerged land link or a submerged sill. At the present time it 

 would seem that the Tertiary history of a possible land bridge across the 

 Faeroe-Iceland-Greenland Ridge could be best estimated from data obtained 

 from the fossil and contemporary biota (Love and Love, 1956). 



On the other hand, we can perhaps be somewhat more definite about 

 possible land connections in the Middle and Late Pleistocene. Due to the 

 relatively short interval of time involved we can perhaps exclude really large 

 tectonic changes in the absolute elevation of the ridge and restrict ourselves to 

 considerations of the effects of glacial eustatic changes of sea level. In recent 

 years studies of eustatic changes in sea level have been made in widely separ- 

 ated parts of the world (Fairbridge, 1961). A prominent submerged shoreline 

 found in depths of 160 m off of North America, South America and Africa 

 is generally ascribed to the sea level associated with the penultimate glaciation. 

 Studies of the probable ice volume based on the distribution of ice and 

 studies of its probable thickness based on Post-glacial rebound of the land 

 have allowed the calculation of the probable volume of water tied up in the 

 glaciers of the penultimate glaciation (Donn et al, 1962). This volume as 

 given by Donn, Farrand and Ewing is approximately 85-100 X 10** km^. 

 This would account for lowering of sea level of approximately 140-160 m. 

 Their estimates for the two uhimate glaciations are 70-84 and 75-88, with 

 resulting sea level lowerings of 105-123 m and 114-134 m (Table 1). It is 

 generally considered that the earlier glaciations were less extensive, that the 

 maximum lowering of sea level should have occurred during the penultimate 

 glaciation (Farrand, 1962). If the Iceland-Greenland Ridge has neither been 

 elevated nor depressed nor seriously eroded during the past 200,000 years, 

 then no land bridge could have existed across the Faeroe-Iceland-Greenland 



* Depths in this area exceed 3000 m, recent Soviet expeditions having disproved the 

 existence of the so-called Nansen Sill (Hope, 1959). 



