Hydrographical Observations from the Danmark Expedition. 371 



series for the summer from Danmarks Havn and Øresund. These 

 series show, that greatly heated and almost fresh water from the 

 melting snow and ice can persist for a long time as a definitely bounded 

 layer above the sea-water cooled down in winter, without any in- 

 crease in temperature occurring in the under layers so long as the 

 mixing processes at the surface are restricted on account of the 

 ice. But very soon after the ice had broken up and the mixing 

 processes at the surface owing to the movement of the waves became 

 stronger an equalisation of temperature took place. 



Changes from surface to bottom in the month of Øresund from September 

 1906 to June 1908. (PI. XX— XXII). 



( In the following all water with a temperature above the freezing 

 point temperature corresponding to the salinity will be called "warm" 

 water.) 



From the middle of September to May 1906 — 07 the salinity 

 in the layer — 75 m. increased, that in the layer 75 — 150 m. decreased 

 at the same time, the average salinity of the whole layer — 150 m. 

 decreased (see PI. XV). 



The increase of salinity in the upper layers was due mainly to 

 the separation of the chlorides owing to the freezing of the seawater, 

 in less degree to inflow from deeper layers by the mixing processes on 

 the barrier referred to. 



In the layer — 50 m. the average salinity increased during 

 this period from 31.44 to 32.50. A layer of ice with an average thick- 

 ness of l%m. Avas formed; this ice had a sahnity of about 9 pCt. 

 (the salinity of some sea ice, which for experiment was melted in the 

 spring of 1907). 



In the autumn, when the formation of ice was strongest, the 



salinity of the surface water was ca. 31 p. m. Thus, by the freezing 



of a layer of water 175 m. thick 0.175 x 22 gm. chlorides were 



separated out, which distributed over a layer of 50 m. in thickness 



. 1.75 X 22 

 caused an average increase in the whole layer oi = 0.77. 



The total increase however was 1.06 p. m., so that an increase of 

 ca. 0.29 p. m. was due to an inflow from the deeper layers through 

 mixing processes. 



This inflow took place especially in the first part of the winter, 

 when the water out at sea was warmer and more saline below 75 m, 

 than above this depth (see the series XI, XIII and XV). 



In the course of the winter the average salinity decreased greatly 

 in the layer 75 — 100 m. and in the whole layer — 150 m. (see PI. XX). 



24* 



