374 Alf Trolle. 



the difference as a rule occurred, it must have been due to inflow of 

 new water-masses into both layers. 



The depth of the mixed layer and of the abrupt transition in 

 density was nearly the same as that on the barrier in the mouth of 

 Øresund (ca. ôO — 75 т.). 



Changes with the seasons. 



PL XXI and XXII show at a depth of 50 — 75 m. the nearly 

 homogenous layer, in which both temperature and salinity remained 

 almost unchanged the whole year round. Thus, we may conclude that 

 the direct influence of the atmosphere reached down to this depth and 

 that here was a boundary between an upper layer from — 50 m. 

 and an under layer from 75 — 100 m., in which layers the changes 

 had a different character. 



The influence of the seasons led to density changes in the upper 

 layers, which were different near land and further out in the sea and 

 consequently led to currents. 



The changes in the course of a year consisted partly of (1) vertical 

 changes owing to direct conduction of heat, diffusion, mixing processes 

 between the layers and convection currents and (2) changes owing 

 to horizontal currents. 



As we had no simultaneous measurements in the fjords and 

 sea, it is not possible with certainty to indicate in which of these 

 ways the changes at the station have occurred, but we may assume 

 that the changes in the upper layer (0 — 50 m. ) were essentially due 

 to the varying influence of the atmosphere whilst the changes in the 

 lower layer mainly were due to the currents (the direct influence of 

 the atmosphere not reaching so far down). 



The propagation of the changes from the surface downwards 

 in a vertical section was essentially due to processes between the layers 

 or convection currents and not to direct conduction of heat or diffu- 

 sion. Thus the investigations in the spring and summer of 1907 

 showed that the warmth from the atmosphere and from the down- 

 flow of melted ice-water were only carried downwards after the ice 

 had broken up in. the fjords and wave motion and the like had 

 caused intensive mixing in the upper layers. So long as the principal 

 mass of ice remained unbroken, the warmed up water from the 

 melting ice and snow lay in the open parts off the river mouths 

 and between the ice-fields as a thin film over the upper layer, the tem- 

 perature and salinity of which remained almost unchanged what they 

 had been in the winter. 



During 9 months of the year (September — June) the atmosphere 

 was colder than the surface of the sea ( — 1.7), and during this period, 

 consequently, cooling of the uppermost layer of water took place — 

 in part in connection with the formation of ice. 



