32 Laege-Scale Features 



1175, which appears to represent South Atlantic conditions (low average 

 salinity). 



The North Atlantic Deep Water is characterized by temperatures be- 

 tween 3-5 and 2?2 C. and saUnities between 34-97 and 34-90 %o. This body 

 of water composes most of the North Atlantic by volume. It is extremely 

 homogeneous over the entire North Atlantic. It does not take part in the 

 wind-driven surface circulation, but does exhibit large transports in a 

 narrow stream near the western coasts of both the North and the South 

 Atlantic — presumably as a result of the thermodynamically driven part 

 of the circulation (see Chapter XI). It apparently originates in the most 

 northerly parts of the wintertime North Atlantic, but the exact way in 

 which it is formed is something of a mystery (see Worthington, 1954 a). 

 Near the very bottom it is probably mixed somewhat "v\-ith bottom water 

 of Antarctic origin. 



Between these two water masses, which may be regarded as the principal 

 masses of the North Atlantic, there are other, smaller, amounts of water 

 which are produced by mixing at intermediate depths along surfaces of 

 equal potential density (cr^ range: 27-2-27-8) with w^ater from the South 

 Atlantic and with an outflow from the Mediterranean Sea. The highly 

 sahne water from the Mediterranean is shoAMi by the point M.W. in fig. 8. 

 As the Mediterranean Water leaves the Straits of Gibraltar, it sinks along 

 the 27-6 (Tf surface and mixes with water over most of the eastern North 

 Atlantic. Its presence is obvious in both the two southern Armauer Hansen 

 stations. Similarly, there is a mixture at mid-depths ^vith water from the 

 South Atlantic Ocean, called Antarctic Intermediate Water. This water 

 mass, of low salinity, forms at the surface of the South Atlantic in a broad 

 band extending from the Cape of Good Hope to Cape Horn. It then sinks 

 beneath the surface and flows northward; and eventually it crosses the 

 equator and mixes with waters in the North Atlantic. The particular 

 stations chosen for fig. 8 do not show this minimum-salinity water very 

 well except at Atlantis station 1175, which is really characteristic of South 

 Atlantic conditions. A very small amount of low-sahnity Arctic Inter- 

 mediate Water is formed in the northern regions of the Atlantic Ocean ; 

 the effect of this mass shows up in General Greene station 1990. 



So far as the study of the Gulf Stream System is concerned, the most 

 important water mass is the North Atlantic Central Water, since it 

 occupies the upper 1000 m. of the central regions of the North Atlantic and 

 takes part in the wind-driven surface circulation which gives rise to the 

 Gulf Stream. In particular, there is a very large mass of nearly homo- 

 geneous water at temperatures between 17 and 18° C, as showTi in fig. 5, a. 

 It is not possible to explain the origin of this water satisfactorily on a 

 quantitative basis. Iselin (1939) calls attention to the fact that most of 



