The Ocean 31 



(1938) taking into account numerous recent soundings. The Caribbean Basin is itself 

 further subdivided by two north-south ridges the Beata and the Aves Ridges into 

 three parts : the Magdalena Basin in the west, the Venezuela Basin in the middle and 

 the Aves Basin in the east. 



The general form of the bottom topography of the whole of the American medi- 

 terranean basins shows considerable regional differences that can be explained by 

 their different origins (see Dietrich, 1937, 1939). All three basins are to a large extent 

 cut off from the Atlantic Ocean; this is of decisive importance for the question of 

 renewal of the deep water of the individual basins. The Gulf of Mexico is connected 

 with the free ocean only through the Florida Straits (sill depth 800 m) and with the 

 Yucatan Basin through the Yucatan Channel (sill depth 1600 m). The Yucatan Basin 

 and the Caribbean Sea are connected over the Jamaica Ridge with a sill depth of not 

 more than 1400 m. The Yucatan Basin has a single connection with the Atlantic 

 Ocean, the Windward Passage between Haiti and Cuba with a sill depth of about 

 1600 m. The Caribbean Sea is connected with the open ocean by several gaps between 

 the West Indian Islands, the deepest of these are the Mona, the Jungfern and the 

 Anegada Passages, which are the only ones concerned in the renewal of the deep 

 water of this mediterranean sea. Their sill depths are 1600-1620 m and 1780-1800 m, 

 respectively. 



The European Mediterranean Sea. This falls into two clearly separated main divi- 

 sions, the Western Mediterranean from the Straits of Gibraltar (sill depth 320 m) 

 to the Sicilian Ridge (sill depth 324 m), and the Eastern Mediterranean. To the 

 latter are connected the Adriatic Sea and the Aegean Sea which in turn is connected 

 through the Dardanelles (sill depth 57 m) with the Sea of Marmora and further, 

 through the Bosphorus (sill depth 37 m) with the Black Sea, A modern bathymetric 

 chart for the European Mediterranean has been given by Stocks (1938). The Western 

 Mediterranean is separated by a ridge running from Tunis through Sardinia, Corsica 

 and Elba to the Italian mainland into two basins: the Balearic Basin in the west and 

 the Tyrrhenian Basin to the east (greatest depth 3731 m). The Eastern Mediterranean 

 goes down to considerable depths (more than 4000 m) especially in the Ionian Basin ; 

 the greatest depth is 4715 m south-west of Cape Matapan. 



Of the smaller mediterranean seas around the Atlantic, the Baltic and the Hudson 

 Bay may be mentioned, but will not be described further since they have largely the 

 character of shelf seas. The mediterranean seas of the other oceans are also of the 

 same type except for the Red Sea which is an elongated canyon-like trough with depths 

 of more than 2000 m and forming a real trench between the coastal strips of the 

 Arabian and Egyptian plateaus. Its outlet in the south is the Strait of Bab el Mandeb 

 with a sill depth of about 150 m. The Persian Gulf is a shelf sea with depth less 

 than 100 m (Stocks. 1944). 



