WATER MASSES AND CURRENTS OF THE OCEANS 



179 



1.75 million mVsec. The average salinity of the inflowing water is 

 about 36.25°/oo, and that of the outflowing water is about 37.75°/oo. 

 With these values, one obtains an outflow of 1.68 million mVsec, and the 

 difference between inflow and outflow, 70,000 m Vsec, represents the excess 

 of evaporation over precipitation and run-off. A fraction of this excess 

 is made up, however, by a net inflow from the Black Sea, amounting to 

 6500 mVsec (p. 180). 



The exchange of water through the Strait of Gibraltar presents a good 

 example of how water from one region can be transformed by external 

 influences and return as a different type of water — in this case as water 

 of high salinity. The rapidity of the exchange is illustrated by stating 

 that the inflow and outflow are sufficient to provide for a complete 

 renewal of the Mediterranean Water in about seventy-five years. 



Using the figures that Schott gives for precipitation and runoff, one 

 arrives at the water budget of the Mediterranean Sea proper, which is 

 summarized in table 20. From this it appears that the total evaporation 



Table 20 

 WATER BUDGET OF THE MEDITERRANEAN SEA 



amounts to 115,400 mVsec, corresponding to an annual evaporation of 

 145 cm, which is in fair agreement with the annual evaporation in these 

 latitudes according to observations and computations (fig. 13, p. 68). 

 As one might expect, the evaporation from the Mediterranean Sea is 

 somewhat greater than that from the open ocean in the same latitude, 

 which is about 110 cm a year. 



In fig. 47 a schematic picture is given of the surface currents and the 

 flow of the Intermediate Water (according to Nielsen). Both surface 

 currents and intermediate currents have a tendency to circle the different 

 areas in a counterclockwise direction. 



The surface waters of the Black Sea flow out through the Strait of 

 Bosporus and through the Dardanefles, and Mediterranean Water flows 

 in along the bottom. Intensive mixing takes place in these narrow 

 straits, and the salinity of the inflowing water is therefore reduced 

 from more than 38.50°/oo at the entrance of the Dardanelles to between 

 35.00 and 30.00°/oo where the bottom current enters the Black Sea at 

 the northern end of the Strait of Bosporus. Similarly, the salinity of the 



