30 The Ocean 



Ridges and rises 



a Bonin Ridge 



b Eastern Pacific longitudinal Ridge 



c South Pacific transverse Ridge 



d Macquarie Ridge 



e Fanning Ridge 



f Hawaii Ridge 



g Fiji Ridge 



h New Hebrides Ridge 



As has already been mentioned above (see p. 24), the deep-sea trenches that are a 

 major characteristic of the Pacific Ocean are marginal, that is, they occur around 

 the rim of the ocean, either near the coast or beside outlying island chains. The main 

 part of the ocean forms a vast deep-sea basin that, judged by the rather sparse sound- 

 ings available, is not as strongly subdivided as the Atlantic and the Indian Oceans. 

 The western, and especially the north-western open Pacific Ocean, contains the greatest 

 continuous extension of the sea bottom below 5000 m and wide areas have a depth 

 even greater than 6000 m. The eastern and south-eastern parts are less deep. Sound- 

 ings have confirmed the deep-sea division, apparent from the individual chains of 

 islands, along a direction from north-west to south-east. In the central part of the 

 ocean, especially to the south, there are groups of islands that are not associated 

 with deep-sea trenches and that occur in clusters. It was earlier supposed that these 

 were on top of plateaus or ridges at no great depths. More recent soundings have 

 shown, however, that this is not the case; only islands that are very close have any 

 submarine connection, and the others usually rise separately as volcanic cones from 

 very great depths and form a very characteristic topographical feature of the South 

 Pacific. 



{d) Mediterranean and Adjacent Seas 



The Atlantic Ocean is connected with the greatest number of mediterranean seas, 

 which have also greatest extent. These are the Arctic Sea, which can also be regarded as 

 a continuation of the open ocean across the Greenland-Iceland-Faroes Ridge, and 

 the American and European mediterranean seas. 



The North Polar Sea, also known as the Arctic Mediterranean, includes: (1) the 

 North Polar Basin surrounded by the seas of the flat shelf of Northern Europe and 

 Northern Asia (Barents Sea, Karelian Sea, West Siberian Sea, Nordenskjold Sea, the 

 East Siberian Sea and the Tjuktjen Sea) and of North America (Beaufort Sea and the 

 large number of sea straits in the North American archipelago); (2) the European 

 North Sea south of the Spitzbergen Ridge (depth 1750 m); and (3) the Baffin Sea. 

 The total area amounts to 14-06 million km^. 



The European North Sea is divided by a ridge at a depth of about 2400 m, running 

 from Iceland through Jan Mayen to the Bear island into two basins; the southern 

 Norwegian deep and the northern Greenland deep, both with a depth of over 3000 m. 

 For the bottom topography of the North Polar Basin see WiJST (1941). 



The American Mediterranean is divided by the coastal orography and by the bottom 

 topography into three areas: the Mexico Basin (1-602 million km^), the Yucatan 

 Basin (0-760 million km^), and the Caribbean Basin (1-948 million km^) with a total 

 area of 4-310 million km^, A new bathymetric chart has been prepared by Stocks 



