58 hjort's hydrographic-biological studies 



In spring and summer the Baltic water flows out over the surface 

 of the Cattegat and Skagerack and along the west coast of Norway 

 like a broad, deep river, at a rate of twenty miles daily. It is then 

 of a high temperature, being warmed by the sun. 



In autumn and winter the volume of outflowing Baltic water is 

 greatly reduced, and from obvious causes it becomes ice-cold. 



The difference in density between the Baltic water and the water 

 in the North Sea basin inevitably results in perpetual efforts of the 

 denser water to fill the Baltic basin ; but after it has gained admittance 

 as a bottom current its density becomes reduced by mixture with the 

 fresh water of the Baltic, it rises towards the surface, and is swept out 

 again with the Baltic stream. The varying force of the Baltic current 

 necessarily induces variations in the amount and strength of the 

 inflowing bottom current. The character of the inflowing water also 

 depends on the season and the weather : in summer it is normal North 

 Sea water which enters the Skagerack ; in autumn and winter " bank 

 water " of less salinity from the western shores of Jutland and Norway 

 takes its place. 



It only remains to add that the outflowing Baltic current, after 

 rounding the Naze, flows northwards along the Norwegian coast. Here 

 it is well known to mariners, and may attain the high velocity of twenty 

 miles a day. (Mohn, 1887, p. 169.) 



It might well be imagined that variations in a current of such 

 magnitude would exercise a considerable influence upon the state of 

 the sea water off the west coast of Norway, and Hjort's enquiries 

 have furnished a striking confirmation of this expectation. This will 

 be clear from the statements made in the following sections: — 



'O 



1. Seasonal Contrasts. 



The seasonal contrasts in regard to hydrographic conditions off the 

 west coast of Norway are seen from Hjort's account to be essentially 

 similar to those recognized by Pettersson in the Skagerack. The great 

 arbiter of cold and heat, and the principal agent in the reduction of the 

 salinity of the water, is the same in both cases, viz., the Baltic current, 

 although the salinity of this current is not so low off the Norwegian 

 coast as in the east part of the Skagerack. This current, wide, thick, 

 and hot in summer, is, as a rule, narrow, thin, and cold in winter. 



In certain winters, generally accompanied by south-west gales {c.g.^ 

 that of 1893-4), the Baltic current is dammed up in the Cattegat, and 

 the shore along the whole west coast is then washed with a thick layer 

 of bank water of high salinity (33 per thousand and over) from the surface 

 down to a depth of fifty or sixty metres, beneath which is a thick layer 



