218 L. H. N. Cooper 



efficient use of the capital resources of the North Pacific by a process of homogeniza- 

 tion. 



The North Atlantic seems on the whole to be subject to impoverishment by exchange 

 across the equator. Loss of relatively rich deep water, tends to be compensated by 

 inflow from the south of relatively poor surface water. This is a process similar in 

 nature to the impoverishment of the Mediterranean by exchange of waters in the 

 Straits of Gibraltar. Consequently the deep phosphate resources of the North Atlantic 

 are only about one-third of those of the North Pacific. In spite of this, the North 

 Atlantic contains many of the world's richest fisheries. It is true that the North 

 Atlantic contains an undue proportion of the shallow shelves well suited to the growth 

 of fish, and that it is bordered by enterprising communities who make the most of 

 what nature offers. But when all allowance is made for these important considera- 

 tions, it still seems that the biological productivity of North Atlantic waters is greater 

 than it ought to be. The nutrient capital of the North Atlantic seems to be more 

 efficiently used than that of the North Pacific, except around Japan. The interlocking 

 hypotheses offered here provide a possible explanation of this. 



Again, judged by its phosphate resources the Mediterranean should be a near- 

 desert sea. Though not rich, it is certainly not a biological desert. Here again one is 

 forced to the conclusion that the slender phosphate capital of the Mediterranean is 

 put to maximum use. It might be worth enquiring whether the present hypotheses 

 could be usefully applied there. 



Attention has been focussed on the events possibly initiated by calving of boluses 

 of heavy cold water over ridges in high latitudes. There is another and different 

 mechanism which may produce similar results on a smaller and shallower but not 

 negligible scale. It may be illustrated from the Straits of Gibraltar. Here, light 

 Atlantic surface water flows into the Mediterranean, and heavy, relatively cold and 

 very saline deeper Mediterranean water flows out. In nature it is becoming ever 

 more evident that fluid motions such as this tend to be irregular or gusty. It is reason- 

 able to suppose that the outflow of Mediterranean water may not be as a steady 

 stream, but as a series of boluses separately calved. This would initiate a chain of 

 events similar to those already described for Faeroe-Iceland water, and augment the 

 efficient use of the nutrient capital of the Atlantic. It is less easy to see how this calving 

 process into the Atlantic might influence the Mediterranean regime, but some effect 

 there is possible. 



Two distinct speculative mechanisms have been described to transfer energy through 

 deep water from one part of an ocean to another and, by so doing, to facilitate enrich- 

 ment of surface waters with nutrients. These are (1) the hypothesis of upward dis- 

 placement due to the intrusion of colder and heavier waters at a greater depth, and 

 (2) the hypothesis of transfer of energy by internal waves, initiated by the sinking of 

 boluses of cold, heavy water calved from ridges in high latitudes. These two hypotheses 

 need not be mutually exclusive, but may merely express facets of a complex system 

 of energy transfer at depth. This, in the words of Otto Pettersson, might be 

 described as the systole and diastole of the ocean. Only many observations well 

 placed in space and time may show what weight should be given to each or any of the 

 component hypotheses. 



Finally, the whole argument suffers from a grave thermodynamic weakness. Ther- 

 modynamically, energy can be obtained only from a source and never from a sink. 



