Fluctuations in Arctic climate with biological productivity of the English Channel 



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On this line of argument, the maximum enrichment of ihc surface waters of the 

 temperate Eastern North Atlantic with nutrients occurred in or shortly after the year 

 1921. 



If unusually large amounts of water sank in the North in these winters, they had to 

 be compensated by an equivalent amount of surface water, which could have been 

 supplied only by increased intensity of the North Atlantic Drift system. One event 

 associated with this increase in the North Atlantic Drift may be the incursion into the 

 English Channel of much unseasonably warm water in the autumn of 1921 (Harvhy, 

 1925). 



We have long had the suspicion that this incursion of warm water was in some way 

 associated with the rich phosphate observed by Atkins in his first analyses in the Eng- 

 lish Channel on 7 March, 1923. I, for one, have always had great difficulty in accepting 

 this explanation, since warm surface water is nearly always poor in nutrients. Today 

 there is no such warm water anywhere in the Bay of Biscay or Eastern North Atlantic 

 carrying an equivalent supply of nutrients. This objection now vanishes. 



This water in some area well to the south of the British Isles had been enriched 

 with nutrients by upward displacement following a period of cold Arctic winters and 

 the three winters of excessive polar sinking. During the warm summer of 1921 there 

 was time for the water to warm up by solar heating, but no considerable redistribution 

 of nutrients with the deeper water had taken place. The nutrient properties of this 

 particular warm water may well have been very far from the equilibrium state that 

 we commonly observe. 



DISCUSSION 



During the last thirty-five years there have been large changes in the distribution 

 of phosphate in the Western English Channel whilst the zooplankton has changed in 

 species and abundance. No explanation has been found locally, so that attention has 

 been extended to events in the Atlantic Ocean. 



A number of associated hypotheses have been erected to explain these changes in 

 the English Channel: 



(1) That in cold Arctic winters saline surface water is cooled further and made heavier 

 than in relatively mild ones. 



(2) That this leads to a greater recruitment of fresh deep water in the North Atlantic 

 after cold Arctic winters. 



(3) That to make room for this fresh deep water, an equal volume of water has to be 

 displaced upwards, i.e. a supply of nutrient-rich deep water is displaced towards the 

 illuminated surface layers. This process may be a diffuse one over the whole ocean 

 basin. 



(4) That the origin of the North Atlantic deep water should be considered not in terms 

 of a localized area, but in terms of physical processes which are occurring all the way 

 from Jan Mayen (72° N) to the southern tip of Greenland (58^^ N), and even further 

 south. 



(5) That in so far as special areas stand out, these lie over the ridges between Iceland 

 and Greenland on the west, and the Faeroe Islands on the East. Over the two ridges 

 the physical processes which yield heavy water seem to differ in detail, but m both are 



