Hydrographical Observations from the Danmark Expedition. 377 



The series of temperatures from that Expedition show, that the 

 bottom-water (100 — 400 m.) had decreasing temperature from Sep- 

 tember to March, increasing from March to June. Ryder's station 

 lay in Scoresby Sound and, Hke our station in Øresund, was in free 

 communication with the sea. At both stations the temperature and 

 sahnity decreased in the deeper layers in winter. 



We may perhaps conclude, therefore, that this decrease is a phen- 

 omenon which recurs annually and that the cause (or the main cause 

 at any rate) has been the same in both cases, namely, increasing velo- 

 city of the Polar Current in ^vinteг. 



Summary. 



PI. XX shows the variations in temperature and salinity in dif- 

 ferent depths in the mouth of Øresund in 1906 — 08. 



It is seen, that in the upper layer — 50 m. the temperature 

 was increasing in summer whilst the salinity decreased, and con- 

 versely in winter — that the temperature and salinity in the mixed 

 layer 50 — 75 m. was nearly unchanged the whole year round — and 

 that the temperature and salinity in the lower layer (75 — 150 m.) 

 decreased and increased simultaneously. 



It appears from this, that the sea did not store up any heat 

 from the atmosphere, but that the heat, which penetrated downwards 

 in the surface layer in summer, was again lost in winter. When the 

 sea below a depth of 75 m. now as a rule possessed a considerable 

 amount of heat, this must have been due to mixing with Gulf Stream 

 water and it may be remembered, that this warmer under layer on the 

 barrier in Øresund was mixed with water of the upper layer, which 

 would mean here a constant transference of heat from below upwards. 

 In other words, the atmosphere received heat from the sea here and 

 this tended to hinder the formation of ice in winter. 



Changes in the velocity of the Polar Current and variations 

 in the proportion between the amount of Polar Current water and 

 Gulf Stream water influenced the temperature and salinity below a 

 depth of 75 m. and through this affected the formation of ice in 

 Øresund. 



It proved, that in the winter of 1906 — 07, when the sea was very 

 cold, the ice in Øresund had an average thickness of ca. 1% m. and 

 only broke up in the beginning of August, whereas in the winter of 

 1907 — 08, when the sea was much warmer, the ice only had a thick- 

 ness of ca. l%m. and broke up already in July. 



It may be said quite generally, that the relatively considerable 

 amount of heat, which the sea at the coast below a depth of 75 m. 

 possessed as a rule and which resulted from an infusion of Gulf Stream 



