370 Alf Trolle. 



layers in the sea to the upper layers in the mouth of Øresund, which 

 spread further from there in a horizontal direction by means of the 

 tidal currents. 



The area over which this mixing took place was certainly very 

 small in comparison with the surrounding water-masses, and the in- 

 crease in temperature and salinity after a single, incoming tide was 

 probably very slight, but owing to the constant renewal twice in the 

 24 hours the total effect was appreciable. 



It is conceivable, that mixing processes of a similar nature occur 

 everywhere in the mouths of fjords and wherever there is an ele- 

 vation in the sea-bottom, which stems the tidal wave. Herein 

 we possibly have an explanation of the presence of the character- 

 istic temperature minimum, which occurs in summer at a depth 

 of ca. 50 — 75 m. in all water in the Greenland Sea of so-called arc- 

 tic origin. 



If we imagine, namely, that such mixing processes are the prin- 

 cipal cause of the temperature changes in a vertical section, the origin 

 of the temperature minimum and its uniform depth everywhere in the 

 Greenland Sea can be explained in the following way. In winter the 

 uppermost layers of water are cooled down to freezing point and con- 

 vection currents then arise, producing uniform salinity in the water- 

 masses down to a depth of over 100 m. and cooling them down to 

 freezing point. Everywhere on the barriers, however, the mixing pro- 

 cesses occurring there between the ice-cold surface water and warmer, 

 more saline water from deeper layers in the sea will bring chlorides 

 and heat to the upper layer. 



Thus, the ice-cold upper layer can only obtain a thickness, which 

 is equal to the average depth on the barriers, where these mixing 

 processes occur. 



In the course of summer the uppermost layers become greatly 

 heated, in part directly by contact with the atmosphere, in part by 

 the downflow of warm water from the melting snow and ice of the 

 land, and only the lowermost part of the ice-cold layer from the winter 

 remains. Here probably there is a constant inflow of warmth from 

 below through the mixing processes on the barrier, but this is exceed- 

 ingly small in comparison with the heat added to the uppermost layers 

 and in this way a temperature minimum is then formed at the same 

 depth as the lower edge of the ice-cold layer of water (this depth, as 

 mentioned above, being equal to the average depth on the barriers) 

 and the temperature of this minimum is raised in the course of the 

 summer some hundredths of a degree above the freezing-point tem- 

 perature from the winter. 



That it really is the mixing processes, which mainly cause the 

 propagation of the temperature changes, can be seen e. g. from the 



