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For the rest the salinity naturally depends a great deal on the rainfall, a point to which 

 we shall return later. 



In the true oceanic water, especially in the Gulf Stream, the periodic variations in 

 salinity in the course of the year are very small, so small indeed, that only a very large 

 material worked out statistically could show the changes. Thus it was found, for example, 

 on the Danish investigations in the regions between the Faroes and Iceland, that the 

 average salinity in March was ijioo°lo higher than normal, in October Vioo%o lower. In 

 the periodic variations in salinity of the Gulf Stream water we have thus to deal with 

 these very small amounts. Nevertheless the variations within the average Gulf Stream 

 region may be considerable at one and the same point, as there is a periodic, lateral 

 movement of the coastal water in relation to the Atlantic water. In the summer time the 

 coastal water extends far out into the sea and moves the boundary between the coastal 

 water and the Atlantic water on the Norwegian coast far to the west. In winter it again 

 contracts and the boundary once more retreats towards the land. This oscillation may 

 make itself strongly felt at any fixed point of the surface without in itself disturbing the 

 character of the Gulf Stream but only the position of this on the surface. 



2. Temperature at the Surface 



The large number of observations on the surface temperature have not yet been so 

 far worked up, that we can give reliable charts on the mean temperature at the surface. 

 The ten-day charts in the Bulletin enable us however to obtain a good view over the 

 temperature variations of the surface of the North Sea in the course of the year. 



It appears clearly from these charts that, as might have been expected, the fluctua- 

 tion in the surface temperature is extremely great close to the coast and in the coastal 

 waters, e. g. in the Kattegat, about 15 degrees, often more. The southern part of the 

 North Sea, which is a typical coastal water, shows for example in March 1906 a temp- 

 erature of 4 — 5° and in August for the same year 16 — 17°, — a range of 12°. In the 

 Northern North Sea, between the Shetlands and the Orkneys, the temperature in March is 

 6—7° and in August 11 — 12°, a range of only 5°. In the Northern North Sea the sur- 

 face temperature approximates to the true oceanic conditions. In the Gulf Stream the 

 yearly temperature variations amount to 3 — 5°. In the coastal water which washes the 

 outer reefs the yearly fluctuation is 10 — 15°. This increases in the fjords and decreases 

 towards the sea. 



3. Salinity and Temperature in the intermediate layers and at the bottom 



It is a very interesting fact that the distribution of the Atlantic water below the sur- 

 face is much greater than on the surface itself. It is found everywhere in the North Sea 

 at a depth of approximately 150 M. , and all the coastal water on the Norwegian coast 

 rests at this depth on a layer of Atlantic water. In the case of the fjords the depth on 

 the submarine threshold is determinative ; if this is more than 100 M. all the bottom 

 water is of Atlantic origin. Between the typical coastal water and the Atlantic under-layer 

 there is a boundary layer of 34 — 35 °/oo, which in the Norwegian coastal waters and partly 

 also in the North Sea may attain a fairly great, vertical extension. 



