340 



THE DEEP SEA 



is perhaps the least compHcated of those I shall mention. The 

 depth D of this tAvo-layer ocean is an idealization of the two-layering 

 process. We shall discover that D is related to the balance struck 

 by cold water ascending from the depths and the turbulent transport 

 of heat down from the surface. The arrowhead part of our boundary 

 current indicates the region in which the Gulf Stream first breaks 

 into turbulent fragments and mixes with the surrounding colder 

 water. These fragments will play the dominant role in the dynamics 

 along the entire northern boundary of the upper layer. 



Continuity Requirements 



To give this statistically steady idealization pedagogic value 

 the quantitative consequences of the conservation of mass, momen- 

 tum, and heat must be discovered. In Fig. 2 appears a west to east 

 section of a two-layer Gulf Stream at latitudes south of the region 

 of fragmentation. Perhaps one of the more satisfying products of 

 the last decade of study of western boundary currents is the con- 

 firmation of their almost frictionless and geostrophic character. 

 In his book. The Gulf Stream, Stommel (1958) of the Woods Hole 

 Oceanographic Institution gives a lucid description of the d>Tiamics 

 of this flow. It is strange that although the southern part of the Gulf 

 Stream is the most steady and organized flow in the ocean the 

 northern part generates the most dramatic oceanic turbulence. 



WEST 



EAST 



T3=i/M = T,= ^^^^^D^ 



J 



Fig. 2. .An idealized two-lajer boundary current. 



