Laege-Scale Features 33 



the (Ti surfaces in the North Atlantic Central Water intersect the ocean 

 surface at points where the surface T-S relation is similar to that at greater 

 depths. He suggests that the surface waters sink along (X^ surfaces, -without 

 mixing, preserving the T-S characteristics acquired at the surface. Sverdrup 

 (Sverdrup et al., 1942, p. 145) has suggested that vertical mixing is hkely 

 to be of considerable importance in the area. It is possible (see Worthing- 

 ton, 1954 a) that the entire treatment of the origin of the North Atlantic 

 Central Water to date has suffered from attempts to imagine it as a 

 stationary phenomenon, in which every water-producing process acts all 

 of the time. Upon closer scrutiny every scheme of circulation that has 

 been suggested exhibits some shortcoming. In addition to the subtleties 

 involved in the thermodynamical processes of a continuously stratified 

 fluid, slow density flows, and imperfectly understood vertical and horizontal 

 turbulent processes, there are a number of constraints of a dynamical 

 sort (p. 122), associated with the wind-driven horizontal circulation of the 

 North Atlantic, which probably play very significant roles in the forma- 

 tion of the North Atlantic Central Water. 



A fair idea of the exchange of heat and water across the surface can be 

 computed by semiempirical laws from a knowledge of average air and water 

 temperatures (Jacobs, 1942), but even with this detailed information of 

 net heat energy and water flux at the surface, the problem of the formation 

 of the North Atlantic Central Water defies quantitative explanation. 



Water masses of the Gulf Stream. — As is shown in the current chart 

 (fig. 2), most of the water which enters the Gulf Stream System is water 

 previously driven westward by the trade winds. The westward flow is a 

 broad band of moving water, called the North Equatorial Current, which 

 moves slowly, and, especially on its southern side, is very shallow (200 m.). 

 In reaching longitude 60° W. it divides its flow into two parts : one part 

 flows through the Caribbean, in a series of gradually narrowing channels 

 and straits, and eventually finds its way out into the North Atlantic 

 through the Florida Straits ; the other, northern, part flows north of the 

 West Indies, then joins the Florida Current over about 8° of latitude. The 

 combined flow, the mature Gulf Stream, leaves the coast at Cape Hatteras, 

 The total transport of the Gulf Stream off Chesapeake Bay (e.g., in April, 

 1932, 82 X 10^ m.^/sec, assuming a 2000 m. reference level) also includes 

 some water which recirculates in a long quasi-eUiptical orbit to the south- 

 east of the Stream, but which can hardly be properly called North 

 Equatorial Current water. The transports of these various currents and 

 parts of currents are shown in fig. 6. It is clear that since the various 

 portions of water which make up the Gulf Stream proper come from a 

 wide range of different locaUties in the North Atlantic, they bring to the 

 Stream rather distinctive T-S relations, and that these may be used, to 



