The Hydrography of the Faeroe-Shetland Channel 79 



the central and western parts of the Norwegian sea, most of which has 

 probably originated in the area east and north-east of Newfoundland 

 and been carried across as a drift, mixing with the ' Irminger ' and 

 ' Greenland ' branches of the European stream. If the European 

 stream is below its normal strength, it seems likely that tins body of 

 water will attain unusual volume, and part of it will try to make its 

 way southward. Tbe comparatively cold salt water observed by the 

 Jackal in 1893 (Station VIII.), and again by Helland-Hansen in the 

 Jackal in 1902 [Nature, loc. cit.), in the north-western part of the North 

 Sea, is probably to be identified with it, as Helland-Hansen suggests, 

 and it seems likely that the importance of this factor has been under- 

 estimated by the earlier investigators, especially, perhaps, in my report 

 on the work of the Jackal in 1893. The second body of southward- 

 moving water (d) is that derived from the melting of ice in the Arctic 

 regions. This water is probably spread over the surface in summer 

 and autumn, and makes its way southward to the east of Iceland and 

 the Faeroe Islands. So far as the region under discussion is concerned, 

 it may probably be assumed that the water from the centre of the 

 Norwegian sea (c) has a salinity of 35 per mille to 35 - 3 per mille, and 

 that a salinity of less than 35 per mille indicates a large admixture of 

 water of Arctic origin (rf). 



The difficulty of interpreting the sections across the Faeroe-Shetland 

 Channel in the light of the above is immensely increased by the fact 

 that the line of section lies just in the region where the waters from 

 the sources mentioned meet and mix, and that we have no simultaneous 

 observations in the regions of origin. The difficulty is specially 

 apparent in studying the distribution of temperature, for, unlike 

 salinity, temperature may change without movement or mixture of 

 the waters. The most important point is evidently to note that when 

 the circulation is active, isothermals and isohalines are crowded 

 together, showing strong gradients of temperature and saltness, while 

 weak gradients are an indication of weak circulation, the waters moving 

 slowly and being very completely mixed. 



The °;eneral conditions controlling the movement and mixture of 



