1895 ^^^O. 9. HYDR.-BIOL. STUDIES OF THE XORAV. FISHERIES. 



Xorth Sea. have now obtained the name of the ^^ Baltic Current ^^^ and 

 this, each year, conveys vast bodies of fresh water into the Xorth Sea. 

 The water is very fresh in the Baltic. From the confines of Rügen and 

 Falster to Gothland, the saline contents of the surface water are but 8 

 per 1000, and this is due to the vast quantities of river water which pours 

 into the Baltic from the Swedish, Russian and German rivers. 



From Rügen upwards to the Scaw, the saline contents increase greatly, 

 the water becoming mixed with the salter element from the westward. The 

 North Western corner of the Baltic therefore forms a sort of mixing basin, 

 and off the shores of the Bohuslän in the latitude of The Scaw, the cur- 

 rent posesses an average salineness of 2"] per 1000. 



Pettersson and Ekman, supported by the obsen'ations of many \-ears, 

 found that all water which, North of the Scaw, containd less than 30 per 

 1000 of salt was of an outgoing current, whilst all above 32 per icxx) 

 belonged to an ingoing stream. 



Pettersson 1 has now shown that the outward Baltic Current must 

 follow the following laws: — 



1. The Baltic Current must be a surface one, and its water is fresher, 

 and therefore lighter than the in-going layers. 



2. It must keep to the Scandinavian Peninsula (on account of the rota- 

 tion of the World). 



3. The strength must be periodic, because tiie afflux of fresh water in the 

 Baltic varies at different times of the year. 



4. It is dependent on the direction of the wind and the strength of the 

 wind (Meteorological Conditions). 



During the Spring, when the ice melts, the rivers swell, and thereby- 

 the Baltic Current. It then flows at great speed as a surface current 

 above the salter layers in the deeps of the Skagerak, up towards the 

 Christiania Fjord, where it is increased b}' the water of the Norwegian 

 rivers and then turns Westwards, down the Norwegian Coast as the West- 

 ward Current, so well known to all seafaring folk. »This Current,« says 

 Mohn^, »which, according to our charts, runs towards the South West, 

 West, and North West, from the mouth of the Christania Fjord to Lister, 

 and on bevond that, at a rate of 10 knots a day, is well known to our 



1 Otto Pettersson : Nagera allmänna drag af Xordsjöns och Östersjöns hydrografi. (Some 

 General Outlines of the Hydrography of the North Sea and Baltic). Forhandlinger ved 

 de skand. naturf. mode. (Proceedings of the Meeting of Scandinavian Naturalists). Co- 

 penhagen 1S92. 



2 Loc. cit. page 16S. 



