182 



Salinity of the Ocean, its Variation in Oceanic Space and in Time 



8°7' 7°54' 7°20' 



Albocoral66Mbwe2 Thor9l MSars28 

 •aS-Z? 211 BllO 210 



7°0'W 7°30' 



M.S(ys22Thor92aim.LoboXX[ 

 210 SHO 223 



6°0' S'SO' 



Thor97 Almi.obaXXX2IIThor98fllmi.obi 

 3fflO 2123 --511021123 



1500 



Fig. 83. Temperature and salinity distribution through the Straits of Gibraltar at the transi- 

 tion from spring to summer (mean conditions, according to Schott). 



due to mixing, a slowly westwards decreasing salinity with the surrounding water is 

 characteristic, sinks beneath the weakly saline Atlantic water below about 300 to 

 400 m. The temperature distribution shows identical conditions. This water continues 

 to sink to about 1000-1200 m off the Spanish Bay, and from here it spreads out into 

 the Atlantic as a more or less horizontal layer of highly saline water. The di'.tribution 

 within the strait shows strong seasonal variation : at the end of the winter the contrasts 

 are reinforced, at the end of the summer they are weakened, but there is always a 

 continuous outflow of water with a high salinity from the Mediterranean into the 

 Atlantic and the submarine ridge never forms a barrier to the Mediterranean water 

 as BuEN attempted to show (1927). 



Conditions in the Straits of Bab-el-Mandeb are rather similar ("Schott, 1929). 

 The highly saline deep water of the Red Sea (S 37%o) flows over the sill at 150 m 

 depth north of the strait of Perim into the Gulf of Aden (Fig. 84). It sinks here to 

 500-1000 m and then spreads out horizontally at such a depth, in which the density 

 of the sinking water becomes equal to that of the surrounding water. 



Also the transition from the higher salinity of the North Sea (about 32%o) to the 

 lower salinity of the Baltic (about 7%o) is not at all continuous, as one might easily 

 be misled by studying mean charts only, but usually occurs rapidly, mostly in 

 two steps (Wattenberg, 1941). The first rapid change occurs near the boundary be- 

 tween Skagerrak and Kattegatt and changes its position very little in time; the second 

 much sharper change has a more variable position between the southern edge of the 

 Kattegatt through the Great and Little Belts to the rises leading to the actual Baltic 

 (Darsser and Drogen Rises). These jumps in salinity have all the properties of true 

 hydrographic fronts. They separate three water types: North Sea, Kattegatt and Baltic 

 water. Figure 85 shows the distribution of the surface salinity from the Skagerrak to the 

 Baltic in three diff'erent cases, and illustrates clearly the typical distribution at these 

 fronts. The latter are not, however, stationary in location but move around continually 



