Salinity of the Ocean, its Variation in Oceanic Space and in Time 181 



however, not in the central part of the Sargasso sea but are displaced'in the peri- 

 pheral parts towards the west, partly on the right hand (north) side of the North 

 Equatorial Current (especially at 200 m) and partly on the right-hand side of the Gulf 

 Stream (especially at 400 m, but still visible at 1000 m). This distribution is a dynamic 

 effect of the currents which cause an enormous water transport. 



Below 600 m the influence of the high salinity inflow from the European Medi- 

 terranean begins to appear and extends already at 800 m to 40° W. It remains the 

 principal phenomenon in all charts down to almost 2000 m and the remarkable 

 asymmetry between the North and the South Atlantic shows particularly clearly here. 



Below 2500 m the horizontal salinity differences already become very small though 

 there is still a noticeable salinity gradient from north to south. South of 40° S. more 

 pronounced differences in salinity reappear which indicate the increasing influence 

 of the Antarctic deep and bottom water. 



5. Salinity in Adjacent Seas and Sea Straits 



In discussing the temperature distribution in adjacent seas (see p. 1 29) it was already 

 emphasized that beneath the sill depth in all the adjacent seas theie is an almost 

 constant salinity; in the adjacent seas without winter convection it is identical with 

 the salinity of the open ocean at the sill depth off the passage ; in the adjacent seas 

 with a winter convection, on the other hand, it is identical with the surface salinity 

 at the time of the thermo-haline mixing (see Tables 56-66). 



When there are relatively large differences between the water masses of the free 

 ocean and those of the adjacent sea, the equilibration movements in the more or less 

 narrow sea straits connecting them show rather striking conditions which deserve 

 particular attention. The interchange of water between the European Mediterranean 

 and the Atlantic is a consequence of currents through the Straits of Gibraltar, which 

 carry water at the surface and in the uppermost layers into the Mediterranean to- 

 wards the east, but in the deeper layers beneath towards west. Corresponding con- 

 ditions are also found in the Straits of Bab-el-Mandeb, but in other sea straits the 

 thermo-haline structure imposes reversed flow conditions. In the Dardanelles and 

 the Bosporus, Aegean water flows into the Black Sea in the lower layers, while the 

 flow into Mediterranean occurs in the upper layers. 



Similar conditions also prevail in the connecting straits between the North Sea and 

 the Baltic, where North Sea water enters through the Oresund and the Great and 

 Little Belts along the bottom, while contrary the surface water flows out of the Baltic. 

 All these water transports are associated with considerable changes in temperature and 

 salinity. It could hardly be expected that these processes should be stationary ones. In 

 fact they are turbulent and occur in pushes and therefore cause extremely large 

 variations in both factors that they can only be investigated and understood with the 

 aid of synoptic surveys. The available summarizing descriptions of the distribution of 

 the different oceanic factors in such straits should thus be interpreted with some 

 caution. 



Figure 83 shows the distribution of temperature and sahnity according to Schott 

 (1928) through the Straits of Gibraltar for the transitional period from spring to 

 summer when average conditions prevail in the currents. The isohalines of the longi- 

 tudinal section show clearly that the highly saline Mediterranean water, for which. 



