376 Alf Trolle. 



was due to greater salinity and heat in the lower layer and conse- 

 quently greater transport of chlorides and warmth from Ье1ол\' up- 

 wards due to mixing processes). 



Changes in temperature and salinity caused by variations of density in 

 the sea, which were independent of the local influence of the atmosphere. 



The changes in temperature and salinity in the layers below ca. 

 75 m. were not caused, according to what has been shown above, by 

 the local influence of the atmosphere, but must have arisen from 

 currents. 



To understand the conditions we may recall what has been men- 

 tioned above, that the water-masses in the sea near the coast (the 

 coast-water) consisted of a mixture of true Polar Current water and of 

 Gulf Stream water, the latter flowing in towards land through sub- 

 marine fjords in the Continental Shelf from the warm intermediate 

 layer and during the passage in towards land raised by the slope 

 of the bottom and mixed with the overlying Polar Current water. 

 Consequently, changes in density may conceivably occur, when from 

 some cause or another the proportion is changed between the amount 

 of true Polar water (i. e. a mixture of American and Siberian river- 

 water and Gulf Stream) and of Gulf Stream water. And it is con- 

 ceivable, at the same time, that changes may occur as a consequence 

 of variations in the velocity of the Polar Current, for increasing velo- 

 city will naturally increase the force of deflection and must conse- 

 quently increase the depth of the Polar Current near land, thus leading 

 to a decrease in the average density of the layer — 150 m. and con- 

 versely. 



The density changes in Øresund discussed here took place in 

 such a way, that nearly the same temperature corresponded always 

 to a definite salinity and we may conclude from this, that they were 

 mainly caused by fluctations in the velocity of the Polar Current 

 and less by changes in the composition of the water-masses. 



It may be concluded, therefore, that the velocity of the Polar 

 Current has been on the increase from September 1906 to May 1907 

 and on the decrease from May to September 1907. 



We did not succeed in making observations in the winter of 1907 

 — 08, but it seems as if the decrease of temperature and salinity in 

 the deeper layers of the water-masses in the coast-water is an an- 

 nual, periodic occurrence, as it is mentioned by Ryder (Meddelelse 

 af Grönland, Bind XVII, p. 214): "With regard to the deeper layers, 

 on the other hand, the samples taken show on an average a less salin- 

 ity in the winter and spring months than in August, a phenomenon 

 which, oAving to the somewhat problematic trustworthiness of the 

 samples, I shall not venture to try to explain ". 



