160 PETTERSSON OCH EKMAN, SKAGERACKS OCH KATTEGATS HYDROGRAEl. 



4 — 5 cc. in the liter or 24 — 26 % oxygen. The carbonic acid did not exceed 49 — 50 cc. 

 The new -water had a considerably higher teinperature and contained a trifle more salt than 

 the former. Consequentlj^' there can be no doubt that the bottom-water of the Gullmarefjord 

 had been renewed between Februarj' and June. On the 28th of August the communica- 

 tion between the water of 34 °/|,o salt inside and outside the fjord was again interrupted 

 (see section lOC on plate VII). In February 1891 we found on inspection the state of the 

 deep layers of the fjord unaltered (see section lOD). The water of 34 7oo h^-d withdrawn 

 from the coast so far that we could not find it 7 miles off the mouth of the fjord at 

 75 Meters. 



Thus we found the hydrographic conditions in the Gullmarefjord widely different 

 in February 1891 from those of the preceding winter. Instead of foul water with only 

 12 % oxygen and a temperature at the bottom of 4°,2 we found in 1891 24 % oxygen 

 and a bottom-temperature of 7° C. The effect of this upon the -fishery was very remar- 

 kable. In 1890 and a couple of years before the fishing had been poor, but this winter 

 the capture of large codfish was extremely rich — richer than anybody could re- 

 member. 



Another fjord, the Stigfjord in Bohuslän, we found also to be liable to changes with 

 the seasons (see sections 6, A, B, C plate V), but on account of the small depth of the 

 bar the 34 water is entirely prevented from entering the fjord, and 'bank-Avater' of 32 & 



33 7oo here acts the same part as the North Sea-water of 34 7oo i^ ^^e case of the 

 Gullmarefjord. 



The layer of 34-water in the Skageracl?: has another important property. Its tem- 

 perature changes in the opposite order to that of the seasons. In summer it is the col- 

 dest, in winter the warmest water-stratum in the Skagerack. The minimum in July is 

 very conspicuous in Ekman's section on plate VIII and likewise the winter maximum in 

 section 9. The relation of these maxima and minima to the bottom-temperature 5° G. 

 of the Skagerack is mentioned on page 51, 52, 53. 



Water of 34 "/„(, is found at the surface only at the entrance to the Skagerack. 

 As an undercurrent it flows into all the deeper fjords of the Skagerack, the Christiania- 

 fjord, the Koster channel, the Gullmarefjord and also into the deep channel of the 

 Kattegat. 



C. The deepest water-stratum in the Skagerack has more than 35 "/(,„ of salt, which 

 is an infallible proof of its oceanic (Atlantic) origin. It flows into the deep Norwegian 

 channel across the N. plateau of the North Sea and arrives in an almost unaltered state 

 in the basin of the Skagerack. 



The distribution of this water at the surface of the North Sea in winter and in 

 summer is seen from the maps (plates IX and X). The limits of the 35 water are na- 

 turally changeable. Thus we found in March 1890 and in February 1891 not more than 



34 °/|,p water around the N. and W. coast of Scotland. But in March 1891 the salinity of 

 the water in the Minch and between the Orkneys and Scotland was nowhere less than 



35 "/„(,. From both sides of the Shetland islands a tongue of Atlantic water stretches in 

 a SE. direction across the North Sea toAvards the entrance of the Skageraclc. At the Avestern 

 edge of the Norwegian channel it is overlapped by lighter Avaters as is shoAvn in figs. 1 , 2, 



