90 



DISTRIBUTION OF SALINITY, TEMPERATURE, DENSITY 



other. In these circumstances one obtains at subsurface depths a T-S 

 relation that is similar to the one which was found in the previous exam- 

 ple, but along the sea surface an entirely different T-S relation may 

 exist. The processes of mixing must in this case take place across at 

 surfaces in order to establish the T-S relation, but at subsurface depths 

 mixing along at surfaces is not excluded. At present it is impossible to 

 decide which process is of the greater importance. 



RrciONl or CONVERGENCE 



Fig. 21. A, Schematic representation of the formation of a water mass by sink- 

 ing along at surfaces (which coincide with the parallel temperature and salinity sur- 

 faces) in a region of convergence. The diagram to the right demonstrates that the 

 vertical T-S relation of the water mass agrees with the horizontal T-S> relation at the 

 surface in the region of convergence. B. Schematic representation of the formation 

 of a water mass by sinking of water types at two convergences and by subsequent 

 sinking. The diagram to the right illustrates that in this case the vertical T-S 

 relation of the water mass need not agree with the horizontal T-S relation at the 

 surface between the convergences. 



The point to bear in mind is that the waters of the ocean all attained 

 their original characteristics when the water was in contact with the 

 atmosphere or subject to heating by absorption of radiation in the surface 

 layers, and that in course of time these characteristics may become 

 greatly changed by mixing. This mixing can be either lateral — that is, 

 take place along at surfaces — or it can be vertical, crossing at surfaces. 



An example of lateral mixing between water masses is found off the 

 coast of California, where the water that flows north close to the coast 

 has a T-aS relation which differs greatly from that of the water flowing 

 south at some distance from the coast. Between these two water masses 

 are found waters of an intermediate character that could not possibly 



