SOME RESULTS OF THE INTEHNATIONAL FISHERY INVESTIGATIONS. 449 



and temperature, it lies beneath surface water which is now much 

 colder than that at the bottom. The effect of this flooding of the 

 deeper regions of the Skagerak with warm dense water is that an 

 undercurrent of relatively warm Bank water is set up, and this passes 

 through the Cattegat and the Belt seas into the Baltic proper, where it 

 displaces the colder water which had accumulated during the previous 

 winter. In most years this undercurrent of warm Bank water may 

 pass as far into the Baltic as east of Bornholm. 



Finally, the hydrographic observations made in the English Channel 

 by the Marine Biological Association* show that the same periodic 

 flooding by warm and dense Atlantic water takes place in this area. 

 In the Channel, on account of the rapid and complicated tidal streams 

 and the contracted sea area, the conditions are more complex and 

 difticult of investigation. We have here to deal with two contributory 

 sources of water: (1) a current of relatively low salinity which flows 

 southwards from the Irish Sea ; and (2) Atlantic water which flows 

 northwards from the Bay of Biscay. The conditions are still further 

 complicated by the presence of coastal water. A general drift of water 

 up Channel has been observed, and successive areas of low and high 

 salinity water may pass to the east. During tlie summer and early 

 winter of 1903 the low salinity water of the Irish Sea predominated, 

 but in the winter the Channel was largely filled with Atlantic water 

 flowing past Ushant in a north-easterly direction. 



The main results which already appear from a study of the hydro- 

 graphic work of the International Fisheries research organization are 

 these : (1) the flooding of the seas of Northern Europe by a stream of 

 comparative!}^ warm and heavy Atlantic water which takes origin in 

 the Gulf Stream circulation ; and (2) the periodicity of this Atlantic 

 drift. Once a year the area covered by the gigantic Gulf Stream swirl 

 expands and contracts, and once a year, but a little later, the continual 

 northerly flow from the Atlantic to Britain and Northern Europe also 

 is augmented and diminished. It is in the remoter parts of the area 

 invaded by the European stream that the pulsations of the latter can 

 most easily be felt. In tlie English Channel, the North Sea, the 

 Cattegat and Baltic, the shores of Iceland, and tbe Barentz Sea, the 

 annual heat wave set up by the replacement of tlie colder and fresher 

 waters of those seas by the warmer and Salter waters of the Atlantic 

 has now been observed and studied. 



The efforts of the International organization are now being con- 

 centrated, so far as hydrographic research goes, on the study of the 



* Mattliews, Report {No. 2, Southern Area) Fishery and Hydrographic Investigations in 

 tlie North Sea and cu/juceut rcyiu/is, I'JOo, [>. '.iS'J (cd. ".^670). 



