KONGL. SV. VET. AKADEMIENS HANDLINGAK. BAND. 24. N:0 II. 161 



3 (plate IX), in which (after the observations of the Drache-expedition) we have marked 

 the Atlantic water deep blue. 



From the deep basin of the Skagerack it flows (occasionally) into the Koster-channel 

 and the Christianiafjord but cannot surmount the ridge of the GuUmarefjord. Whether it 

 enters the deep channel of the Kattegat or not, is an open question. Hitherto there are 

 no certain observations indicating the existence of water of so high salinity as 35 "/^^ in 

 the Kattegat. If we may judge from a comparison between F. L. Ekman's observations 

 in 1869 and 1877 and our own in 1890 an alteration seems to have occurred with regard 

 to the quality and quantity of the Atlantic water in the basin of the Skagerack. Fifteen 

 or tAventy years ago the ocean-water in the Skagerack seems to have been a trifle salter 

 and (possibly) warmer, and to have attained a higher level than it does at present. The 

 niost prominent feature in the hydrography of the Skagerack, viz. the alternate infiux of 

 32 — 33-water in Avinter and 34 — 35-water in summer we believe to be an effect of the 

 alterations in the Baltic stream with the seasons. In winter when it is reduced merely 

 to a coaststream it exercises its reactive force principally upon the nearest layer of water, 

 which is the 'bank-water' of 32 and 33 Voo- ^^ summer the increasing mäss of the Baltic 

 stream spreads farther to the West and draws water of higher saltness from the North Sea 

 into the Skagerack and Kattegat. 



To these periodic changes in the nature of the inflowing Avater are due important 

 consequences with regard to the fish-fauna not only of the Skagerack and Kattegat, but 

 also, as we have tried to show on pages 147 — 150, of the western pai-t of the Baltic. Some 

 migratory iishes, as, for instance, the mackerel and the garfish, foUow the Atlantic and 

 the North Sea water, others, as the Avinter-herring, appear in the fjords of Bohuslän at the 

 same season as the 'bank-Avater' sets in, and — as far as our observations go — seem 

 to disappear Avith it. 



Sv. Vet. Akad. Handl. Band 24. N:.) 11. 21 



