The relationship between the natural density and the natural specific gravity at 0° is deter- 

 mined by formula 



<^/ = <^o + D, 

 where D is the correction for temperature and salinity. 



All these values can be found from Knudsen's Hydrographic Tables, which are fundamental 

 for any kind of oceanographic work. 



The specific volume is a value the reciprocal of density, i.e. 



t 1 



while I call 



v,= (a— —0.9] 1,000 



the natural specific volume, in analogy with natural density. 



Due to the anomalous properties of water, the relationships between density and specific vol- 

 ume and salinity and temperature are expressed by very complex formulas which make it difficult 

 to find these values without using detailed tables. Therefore, for any kind of derivations and com- 

 putations usually the TS diagrams developed by Helland-Hansen for oceanographic work are used; 

 these diagrams can be constructed easily for both density and specific volume. 



The TS diagram of specific volume for salinities of 3. 0-7.5 0/00 and for temperature from 

 -2° to +10° are given in the upper part of figure 1; the lower part shows the specific volume for 

 salinities from 31-35.5 0/00 and the same temperatures. 



An examination of the TS diagrams shows that the natural density increases at all tempera- 

 ture and salinity values, while natural specific volume decreases approximately 0. 007-0. 008 with a 

 salinity increase of 0. 01 0/00. 



The density change taken as a function of temperature change is considerably more complex. 

 Thus , the heating of water only within limits higher than the temperature of maximum density for a 

 given salinity decreases the density. At high temperatures this is more pronounced than at low. 

 From the TS diagram it is evident that for sea water with salinity of 31 0/00 and higher within the 

 temperature range 0°to8°, a0.1° increase in temperature has the same effect on density and 

 specific volume as a salinity decrease of 0. 01 0/00. 



At lower temperatures and particularly at low salinities, slight changes in the water temper- 

 ature have practically no effect on its density, and, finally, with slight salinities and low tempera- 

 tures we even get a decrease in density with a drop in temperature. These phenomena are ex- 

 plained by the complexity of water structure and the irregular change in the coefficient of thermal 

 expansion resulting from it. 



Low temperatures, of the order of 2 to 3° at salinities from 34.5 to 35 0/00, are observed 

 everywhere at great ocean depths. In the Greenland Sea, the bottom temperatures vary within the 

 limits -1.0° to -1.6°, while in the Arctic Basin they vary from -0.7° to -0.9° at the same salinity. 

 Thus, we see that in the surface layers of the World Ocean, density is determined by salinity and 



11 



