14 



PHYSICAL PROPERTIES OF SEA WATER 



(II, 7) 



therefore, between temperatures of 0° and 30°C, the formula 



Ltf = 596 - 0.52^ 

 can be used. 



Adiabatic Temperature Changes in the Sea. Because sea water 

 is compressible, adiabatic temperature changes take place if a mass of 

 water is brought from one pressure to another without loss or gain of 

 heat. The temperature that a water sample would attain if raised 

 adiabatically to the sea surface has been called the potential temperature 

 (Helland-Hansen). Helland-Hansen has prepared convenient tables for 

 computing the potential temperature, which depends upon three vari- 



10 



10 15 



CHLORINITY. %. 



20 25 30 



SALINITY %. 



20 



35 



Fig. 2. Freezing point and temperature 

 of maximum density as functions of chlorinity 

 and salinity. 



ables: the temperature, the salinity, and the depth of the sample under 

 consideration. 



As an example of adiabatic temperature changes, it may be mentioned 

 that, if water of sahnity 34.85 °/oo and temperature 2°C is raised adiabat- 

 ically from a depth of 8000 m to the surface, the temperature drops 

 0.925°C and the potential temperature of that water is therefore 1.075°C. 



In some ocean basins the temperature in situ increases toward the 

 bottom, but only in a few isolated deeps is the potential temperature of 

 the water constant. 



Freezing-PoInt Depression and Vapor-Pressure Lowering 



Freezing-point depression and vapor-pressure lowering are unique 

 properties of solutions. If the magnitude of one of them is known for a 

 solution under a given set of conditions, the other may be readily com- 

 puted. Only the depression of the freezing point for sea water of different 

 chlorinities has been determined experimentally, and empirical equations 

 for computing the vapor-pressure lowering have been based on these 



