— 72 — 



minimum of 16 "/oo in June and maximum of 2I1/2 "/oo in December, at 26 m. 

 max. of 33 "/oo in July and min. of 29 "/oo in January. 



At the bottom of the Skagerak (at depths > 500 m.) the temperature 

 is on an average a Httle below 51/2° and its mean variation in the course of 

 the year < 1/2°. Even at 100 m. below the surface the annual amplitude of 

 the mean temperature is in great parts of the Skagerak less than 2° and only 

 at some few places near land over 4°. At the surface, the amplitude hes at 

 most places between 10° and 13°. The upper water layers are distinguished 

 by considerable vertical temperature gradients, and in summer especially these 

 reach a remarkable magnitude. In the middle of the Skagerak the average 

 temperature for August in thus in places at m, abt. 15°, and already at 

 20 m. only 6°. Moreover the temperature here has phases highly retarded in 

 relation to the surface, rising at 20 m., in the time from August to November 

 from 6° to something over 9°, but falhng at the surface from 15° down to 7°. 



It is to the International Investigation of the Sea that credit is 

 due for having shown that in the Kattegat and the Great Belt, in the bound- 

 ary layer between the fresh upper water and the salt bottom layer, vertical 

 tidal changes take place, which are several times greater than the correspond- 

 ing ones at the surface (thus in the Great Belt, off Korser, the 20 "/oo Isoha- 

 line at depths about 12^/2 m. makes vertical movements three times as great as 

 the surface water. The difference between high and low water at m. is on 

 an average abt. 20 cm.) and by such internal waves, the salt water of the 

 lower stratum is pumped intermittently from the Kattegat over the submarine 

 ridges into the Baltic. A series of continuous measurements in the Langeland 

 Belt in the spring of 1909 showed, for June, that the maximum for the cur- 

 rent originating from the M2 period was 19 cm/sec. at the surface, IIV2 cm/sec. 

 at 25 m., and 7^/2 cm/sec. at 35 m., and that also several other tidal periods 

 have maxima of easily measurable magnitude. The resulting current goes, for 

 the upper 15 m., out towards the Kattegat, and has, at m. it greatest speed 

 = 35 cm/sec. from 15 to 35 m. (bottom) the resultant current is however in- 

 fluent towards the Baltic; it reaches its greatest speed between 20 and 25 m., 

 where it flows 14 — 15 cm/sec. 



Continuous measurements every fourth hour at the Schultz's Grund 

 lightship have shown, for the period 1. March 1909—1. March 1911, that the 

 outflowing current towards the Kattegat reaches on an average, from the sur- 

 face down to a depth of 7 m., while the water from here down to 25 m. 

 (bottom) has a resulting movement inwards towards the Baltic. The outflowing 

 current reaches its greatest average speed at the surface (6 cm/sec. at 2^2 ni.), 



