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



165 



3. The Vertical Distribution of Salinity (in Vertical Profiles and Sections) 



(a) General Conditions 



An increase of salinity with depth is not a necessary condition for vertical stabihty 

 in the ocean, since in general the temperature decreases so rapidly that static stabihty 

 is assured. In actual fact the highest values of the sahnity in the individual oceans are 

 found at the surface or in the uppermost layers and usually a decrease of salinity down- 

 wards. Figure 69 shows the vertical distribution of salinity down to 4000 m for the same 

 station as in Fig. 52. From 40° N. to 50° S., i.e., in the troposphere, S decreases rapidly 

 below a more or less homo-hahne surface layer of varying thickness. The strong 



Fig. 69. Vertical salinity curves for a series of oceanographic stations along a meridional 

 section through the Atlantic (corresponding vertical temperature curves are shown in 



Fig. 52). 



Footnote from opposite page 



t This is demonstrated by the low salinity of the adjacent seas with a strong freshwater inflow 

 (such as the Black Sea and the Baltic a.o.) and can also be seen in coastal areas where there is a large 

 fresh-water inflow. The effect of these frequently turbid river v/aters is often found surprisingly far 

 out at sea. Charts of the mouths of the major rivers (Amazon, Congo, Tajo, La Plata) usually con- 

 tain a limited area in which the lighter water shows at the surface on top of the heavier sea-water; 

 but this is usually only the case in a thin layer and already in the wake of a ship the sea-water of much 

 more blue colour may be brought to the surface. An investigation of the mixing of the lighter river 

 water and the heavier sea-water at the mouth of a large river would be of some interest. The Suez 

 Canal shows the great effect on the salinity of solution of a salt deposit, in this case at the bottom of 

 the great Bitter Lake which is connected by the canal with the Mediterranean and with the Gulf of 

 Suez. Water of lower salinity flows in from both sides and causes a progressive dissolution of the salt 

 deposit and maintains in that way the high salinity of the water above at 50%o at the surface and 

 56%o at the bottom (about 10 m depth). Since the canal was first built (1869) when the water depth 

 was 7-56 m dissolution of the salty canal bottom has increased the depth here linearly to give a depth 

 in 1921 of 11-7 m. At the same time the salinity of 68%o in 1872 had fallen to about 52%o by 1924. 

 The available and, in parts, sparse data on the distribution of salinity in the Suez Canal and on the 

 currents caused by it have been dealt with by WiJST (1934, 1935) in two interesting papers. 



