VERTICAL AND HORIZONTAL MOVEMENTS IN THE OCEAN 619 



lateral spread of the thin plates within the zone of conflict is likely 

 to be slower but even so may be a matter of only a few years. In 

 this sense these plates could be said to be very, very young with an 

 age measurable in years on our fingers. Let us consider what C''' 

 determinations might show. 



The energy for the whole process is provided by a thermody- 

 namic cycle between equator and pole. One step in this cycle is the 

 creation of very heavy water by cooling of saline surface water in 

 the North Polar Basin. It is not established that even here COo is 

 in complete equilibrium between air and water (cf. Broecker 

 etal., p. 301). It is probably more nearly so than anywhere else in the 

 oceanic waters of the Northern Hemisphere. This water then sinks 

 into the deep basin of the Norwegian Sea where it resides for an 

 unknown time. Not again does it attain contact with the atmos- 

 phere. 



Then as a series of boluses, possibly connected by narrow necks, 

 it escapes into the Atlantic and descends to its appropriate density 

 platform. All the while, the boluses are mixing with enveloping 

 Atlantic water of considerable C''' age. By the time the boluses are 

 in a position to spread, their parentage has become very mixed. 

 Our search for an understanding of ocean circulation may be im- 

 peded, not helped, by attributing a C^^ age to water masses such as 

 these. We should be much helped if we could show that the C^^ 

 content of water of potential density 27.845 was higher than either 

 of the waters of density 27.831 and 27.862. This would mean that 

 the middle water in the sandwich included a proportion of water 

 which had quite recently been at the surface in the Norwegian 

 Sea. We have to remember that the waters of the ocean are mixing, 

 mixing, mixing all the time and that we have to train our resources 

 upon situations where these mixing processes can be unraveled. 

 To consider, as an end in itself, the integrated age ot a water mass 

 which has been cieated by a succession of mixing processes is to 

 miss the point. 



Fisheries Hydrography 



Now let us consider an application to fisheries hydrography. 

 A hypothesis that the success of the fisheries of the continental 

 shelves of northwestern Europe depends on the succession of cold 



