194 DEPTHS OF THE OCEAN 



4. Depth and Deposits of the North Atlantic Ocean 



The North Atlantic may be called a circumscribed ocean, 

 being practically land-locked except towards the south. Its super- 

 ficial area is small compared with the other ocean basins, but 

 the area draining into it is enormous, since the Arctic Ocean, 

 the Mediterranean Sea, the Baltic Sea, the Gulf of Mexico, and 

 the Caribbean Sea all communicate with it. Indeed, it has 

 been estimated that nearly one-half of the entire world drains 

 directly or indirectly into the Atlantic Ocean ^ as a whole, or 

 about four times the area draining into the great Pacific Ocean, 

 and of this by far the larger portion drains into the North 

 Atlantic as distinct from the South Atlantic ; the largest river 

 of South America, the Amazon, enters the Atlantic just on 

 the equator, and its outflowing waters, with their burden of 

 sediment, are carried mostly into the North Atlantic. It has 

 further been estimated that more than one-half of the total 

 rainfall of the globe falls on the Atlantic drainage area, equal 

 to more than three times the amount- falling on either the 

 Pacific or Indian Ocean drainage area.^ Remembering these 

 facts, and the relatively large area occupied by the continental 

 shelf and continental slope, it is easy to understand why the 

 deposits covering the floor of the North Atlantic partake more 

 of a terrigenous character than those of the other ocean basins, 

 and this character is further emphasised by the floating icebergs 

 met with in the northern part of the ocean, and by the 

 proximity to the southern part of the ocean of the great desert 

 of the Sahara, the sand grains from which are sometimes 

 carried far out to sea by the wind. The North Atlantic is also 

 remarkable for the relatively high temperature of its waters at 

 all depths from surface to bottom, as compared with the other 

 oceans, and this is due partly to the influence of the dense 

 warm water flowing out from the Mediterranean at the Straits 

 of Gibraltar, and partly to the downward movement of the 

 dense surface water of the Sargasso Sea. Another characteristic 

 of the North Atlantic is the permanent anticyclonic area in the 

 Sargasso Sea region, which largely determines the direction of 

 the prevailing winds over a large part of that ocean, and hence 

 of the great surface currents like the Gulf Stream. 



The bathymetry of the North Atlantic, according to the 



1 Scott. Geogr. Mag., vol. ii. p. 554, 1S86. - Ibid. vol. iii. p. 67, 1887. 



