COMPOSITION OF SEA WATER 149 



Variation in the Distribution of the Salt Content of the Oceans and 

 Intracontinental Seas. 



The distribution of salts in the surface layers of the oceans 

 varies with the degrees of latitude. Thus, for the Atlantic it is 

 32.80 permille between 70° and 65° N. lat. (Schott-36: 2iy). It in- 

 creases to 37.00 permille between 30° and 20° N. lat., and decreases 

 to 35.07 permille at the equator. Then it increases again to 36.52 

 permille between 20° and 25° S. lat., after which it decreases to 

 33 permille at 70° S. lat. There are thus two maxima in the At- 

 lantic. In the Pacific we have a salinity of 31.72 permille at 60° 

 N. lat., increasing to 35.42 permille between 30° and 25° N. lat., 

 and decreasing again to 34.36 permille at 10° north of the equator. 

 Then it increases to its second maximum of 36.18 permille between 

 15° and 20° S. lat., after which it decreases again to 33.00 permille 

 at 70° S. lat. In the Indian Ocean the first maximum of 35.37 per- 

 mille lies near the equator, and the second between 25° and 30° S. 

 lat. (35.88 permille). The minimum of 34.55 permille between these 

 two lies about 10° south of the equator. Southward the decrease is 

 similar to that in the other oceans, to 33 permille at 70° S. lat. ; but 

 northward from the equator the change is oscillatory. (Kriim- 

 mel-20: j.?^.) The causes of this variation are to be sought chiefly 

 in the varying rate of evaporation from the surface of the ocean, 

 and the consequent increase in salinity. Evaporation is a func- 

 tion of the temperature, wind velocity and relative humidity. 

 (Schott-36: .? 7 (?.) Opposing factors are the amount of precipi- 

 tation, and the addition of fresh water by streams, melting ice- 

 bergs, etc. Displacement of waters of a certain salinity through 

 currents also must be considered. The following table gives the re- 

 sults of Marzelles' experiments in this direction ( Schott-36 : i'/^') : 



I. Average evaporation in 24 hours with varying temperatures 

 without considering wind velocity or humidity. 



At 1° C o . 80 mm. At 19° C 1.52 mm. 



At 11° C 0-97 mm. At 27° C 2.96 mm. 



II. Evaporation in 24 hours with the temperature of the air 

 about 20° C. and varying wind velocity. 



With velocity of 0.3 meter per second 1.21 mm. 



With velocity of 4.2 meters per second i . go mm. 



With velocity of 7.5 meters per second 2.97 mm. 



With velocity of 10.3 meters per second 4.01 mm. 



