Fluctuations in Arctic climate with biological productivity of the English Channel 2 I 7 



bottom layer containing phosphate equal to that at the point of inflexion. The defect 

 in phosphate content which would seem to have appeared near the bottom has 

 actually been moved upwards, and equivalent enrichment has appeared near the sur- 

 face. It should be clear that the molecules of phosphate which appear in the surface 

 waters are not those which have left the bottom. The process is akin to water moving 

 up a pipe. If the process went on long enough and unhindered, the whole ocean would 

 become homogenized from top to bottom. At an intermediate stage, it might seem 

 that phosphate was being transported from the bottom to the surface waters, without 

 the middle layers being affected in any way that could be recognized by chemical 

 analysis. 



Homogenization is a two-way process. In an ocean in which a nutrient salt increases 

 downwards, the shallower and poorer waters are enriched at the expense of the 

 deeper. Temperature or heat content, on the contrary, decreases downwards so that 

 the same process causes the deeper layers to warm up at the expense of the shallower. 

 Now let us consider an area of the sea near a continental slope: (a) where the broad 

 pattern of currents and winds as well as the amount of radiant energy received from 

 the sun remain unchanged but (b) where the intensity of deeper internal waves derived 

 from distant sources increases. Homogenization should increase so that the surface 

 layers would become colder but richer in nutrients. If then for some years the process 

 is reversed, internal waves from a distance would become weaker so that homogeniza- 

 tion against slopes would decrease. Loss of nutrients and accessory growth factors 

 from surface waters by sinking of faeces and detritus would not be fully made good. 

 In consequence the surface waters become poorer. At the same time, radiation received 

 from the sun would be retained in the upper waters, instead of being homogenized by 

 mixing with deeper colder water. The sea surface would warm up. Something very 

 like this seems to have happened in Western European waters in the last thirty years. 

 The changes in heat balance would be expected to produce some local changes in 

 winds, weather and currents, so that in places this generalization may not apply. 

 Averaged over a large ocean, however, and granted the premises, it seems inevitable. 

 Again, when very cold winters prevail in the Arctic, more cold heavy water will be 

 produced, and will spill over the ridges between Greenland and the Faeroes into the 

 Atlantic. The scale of everything will be increased, so that the amplitude of the system 

 of deep internal waves in the ocean should also increase. 



Let us now consider two oceans. In one, writhing boluses of newly arrived water 

 may initiate internal waves and subsequent homogenization right to the bottom in 

 4,000-5,000 m. In such an ocean, combination of the two separate processes of 

 upward displacement and homogenization will cause deep capital reserves of nutrients 

 to be made relatively quickly available for biological production in illuminated waters. 

 In the second ocean, sinking of cold water does not go deeper than, say, 1 ,500 m depth. 

 Below this depth there can be no writhing surfaces, no appreciable internal waves and 

 no homogenization against continental slopes. There is then no way by means ot 

 which nutrients below this depth can be got into circulation. Vast resources of nutrient 

 capital remain unused for long periods. In such an ocean only the resources above, 

 say, 1,500 m would be in effective circulation. 



In this parable the oceans in mind are the North Atlantic and the North Pacific. 

 The North Pacific is much the larger, so that for it the ratio of length of slope to volume 

 of water is much less than for the North Atlantic. This also militates against the 



