1 66 WATER MASSES AND CURRENTS OF THE OCEANS 



moderate depth to the bottom, the current remains relatively shallow, not 

 more than about 800 m deep, and carries no water colder than 6.5° until 

 it leaves the Blake Plateau in about latitude 33°N. According to Iselin 

 the current increases steadily in volume by absorption of Sargasso Sea 

 water, and as it leaves the Blake Plateau the depth and the volume of the 

 current suddenly increase by the joining in of water of a temperature con- 

 siderably below 8° that comes from the southwestern Sargasso Sea. 



The Gulf Stream. The middle portion of the Gulf Stream system, 

 for which the name ''Gulf Stream" is retained, continues as a well-defined 

 and relatively narrow current which, in contrast to the Florida Current, 

 flows at some distance beyond the continental shelf. To the right of the 

 current is the Sargasso Sea water, as previously, but to the left are now 

 found two water types : the coastal water, which covers the shallow shelf 

 areas, and the slope water, which, at temperatures between 4° and 10°, is 

 very similar to the Gulf Stream water, but which at higher temperatures 

 is of lower salinity. Within the upper layers of the slope water, great 

 seasonal variations in temperature and salinity occur, and, in addition, 

 eddies of Gulf Stream water occasionally intrude. The surface velocities 

 are very high, the computed values reaching, in lat. 36°N, long. 73°W, 

 more than 120 cm/sec, and in lat. 38°N, long. 69°W, reaching 140 cm/sec. 

 On the assumption of no motion at a depth of 2000 m, where the isosteres 

 are nearly horizontal, the volume transport of the Gulf Stream off 

 Chesapeake Bay is between 74 and 93 milHon mVsec. If these figures 

 are correct, they indicate that between 38 and 57 milhon mVsec of 

 Sargasso Sea water and deep water have been added to the Florida-Gulf 

 Stream after the Antilles Current, carrying 12 million mVsec, joined the 

 flow of 26 milhon mVsec through the Straits of Florida. Similarly, 

 between 34 and 53 million mVsec would have to be discharged toward the 

 south from the Gulf Stream between Chesapeake Bay and longitude 

 45° W, off the ''tail" of the Grand Banks, where, according to Soule, the 

 transport of the Gulf Stream is somewhat less than 40 million mVsec. 

 These conclusions are not supported by observations between the line 

 Chesapeake Bay-Bermuda and the Bahamas or between Bermuda and 

 longitude 45°W. The available data indicate that the inflow north of the 

 Antilles Current does not exceed 15 to 20 million m^/sec, and between 

 Bermuda and longitude 45° W the southward flow of Gulf Stream water 

 does not exceed 15 million m/sec. The computed transport can, however, 

 be interpreted differently. 



The dynamics of the Florida Current and the Gulf Stream, particu- 

 larly the downstream increase in volume as far as Cape Hatteras, is not 

 clearly understood. Rossby has compared the Florida Current and its 

 continuation, the Gulf Stream, to a wake stream which emerges from the 

 Straits of Florida, and has examined the effect on such a stream of 

 stresses due to lateral mixing. In a wake stream in homogeneous water 



