Fluctuations in Arctic climate with biological productivity of the tngiish Channel 2 1 3 



for this. Even when winds have been favourable for upwclling of nutrients by the 

 classical process, as in February, 1947, this has not occurred. 



The phenomenon of cascading was first examined (Cooper and Vaux, 1949) and 

 is now well authenticated (Lee, 1952; Boden and Kampa, 1953). It is primarily a 

 process of impoverishment, stripping from the shelf whatever nutrients happen to be 

 there. Work now in progress (1955) shows that this concept is too simple, and that 

 there may be an associated mechanism which leads to enrichment of water overlying 

 a cascade, though not of the area from which the cascade has come. 



Other hypothetical processes of enrichment, such as capsizing and submarine 

 eagres (Cooper, 1952 a, d) have also been proposed, but still lack observational 

 basis. 



At this point in the investigation, a satisfactory explanation of the fluctuations in 

 phosphate and biological productivity was still not in sight. There was no escaping 

 the conclusion that an answer would never be found whilst study was confined to the 

 shallow shelf. 



Then an investigation was undertaken which seemed at the time to be a false scent, 

 viz. the search for an explanation of the sudden appearance off Plymouth in the 

 autumn of 1950 of large numbers of boar fish, Capros aper. The hypothesis was 

 erected that these had been ejected about six weeks earlier from their normal habitat 

 in a coral-encrusted submarine canyon by a submarine eagre. A rider necessarily 

 followed, that the conditions in the Atlantic abreast of the slope between depths of 

 200 and 500 m must have been very different in the nineteen-thirties and forties from 

 what it had been in the nineteen-twenties. The Capros argument (Cooper, 1952 c) 

 was a logical one, but the threads were as thin as gossamer. It may well prove utterly 

 wrong. None the less it was this study which led to the decision that it was useless 

 further to pursue studies in shallow water, but that the deeper Atlantic ocean must 

 hold the key. 



There is no need to invoke hypothesis to establish that — whatever the mechanisms 

 may be — vertical mixing down to about 400 m occurs in winter south-west and west 

 of the English Channel. The conclusion is evident from every station that has ever 

 been worked there. There seems no good reason for believing that there has been 

 any major change in the nature of the physical processes occurring in the upper 400 m 

 during the last 40 years. However, the chemistry of these waters has changed, and we 

 are forced to seek an explanation in terms of physical processes occurring at a greater 

 depth. The enrichment with nutrients of the upper 400 metres can have come about 

 only by some form of overall upward displacement of the deeper water. The idea is 

 that, first, during the rich period, the layer of water containing, say, 0-8 to 0-9 ug- 

 atom/1 phosphate-P had been displaced upwards by some hundreds of metres, so 

 that the processes of vertical mixing always operative in the upper 400 metres can bring 

 them right to the surface, and that, secondly, during the poor years from 1931 to 

 about 1950, this layer had subsided so that the mixing processes could no longer bite 

 into it. Nutrient evidence to establish this argument beyond doubt does not exist. 

 Due to internal waves, the observed depth of a nutrient sample obtained by snap 

 sampling may diff"er by scores of metres from the mean depth. Consequently the 

 sparse data available from earlier years are hard to interpret. Argument can proceed 



only ex hypothesi. 



To achieve such a large-scale upward displacement of water, an equivalent volume 



