258 PHYSICAL AND BIOLOGICAL CONDITIONS IN THE NORTH SEA. 



surface water of the Atlantic to the south-west coast of Norway, the 

 northern species moving at the bottom down the western side of the 

 North Sea. 



The observations of the Pomerania expedition previously mentioned, 

 show that in summer, in the deep depression, the temperature at the 

 bottom was not higher than 8° C, while at the surface it was 12° to 

 14° C. At the western side of the southern area the temperature at the 

 bottom was somewhat lower than at the surface, but not on the eastern 

 side. This is attributed to an inflow of cold water from the north. It 

 seems to me that it is with regard to this question of the flow of 

 the cold bottom water at different times of the year, that further infor- 

 mation from the physicists is most required. We know that northern 

 forms, such as haddock and lemon dabs, extend down the east coast of 

 England as far as the Thames, in greater numbers than on the conti- 

 nental side, and we know that there are isolated depressions over 20 

 fathoms in depth along this side, which are wanting on the continental 

 side. But it would be interesting to know further to what extent the 

 cold water makes its way southward beyond the latitude of the Wash, 

 and what is the cause of its movement ? 



Reference has already been made to Dickson's account of the entrance 

 of oceanic water down the east coast of Britain from the north, and his 

 opinion that the important property of this water is, that it contains 

 more oxygen than the bottom water of the deeper part of the North Sea, 

 which it replaces. In his interpretation of the observations, Dickson 

 has laid chief stress on the introduction of Atlantic water into the west 

 side of the North Sea at the bottom, and says little of the temperature 

 of the introduced water. Apparently the reason of this is, that the 

 Atlantic water was originally surface water, and was presumably 

 saturated with oxygen. Now, the question of the oxygen in the bottom 

 water introduced, or in that which it displaces, has not been directly 

 investigated. It seems to me that it is very desirable that Mr. Dickson 

 and the other physicists who are studying the phenomena in question, 

 should consider the movements of the water in relation to the contrasted 

 distribution of northern and southern fish, of which I have in this paper 

 attempted to trace the main features. The herring is a northern species, 

 abundant in the Norwegian Sea, and its incursions into the North Sea 

 must, I think, depend, like the presence of the other northern species 

 characteristic of the north-western part of that sea, on the introduction 

 not of Atlantic water, but of cold water from the Norwegian Sea. It 

 seems to me the question is one rather of temperature than of oxygen. 

 In Dickson's conclusions it is noteworthy that the introduced water is 

 a mixture of Atlantic water and water from the Norwegian Sea, and to 

 me the latter constituent and its low temperature appear to be the more 



