The Geophysical Structure of the Sea 



Table 110, Vertical stratification of a homogeneous ocean at 0°C and 35%o 

 salinity (standard ocean) 



305 



The difference between the numerical values of the pressure in decibars and the 

 geometrical depth in metres is of the order of 1 % and remains the same also for other 

 thermo-haline vertical stratifications. It is thus permissible, as a first approximation, to 

 ignore this difference: at a depth of « geometrical metres there will be a pressure of 

 n decibars. On the other hand, the difference between dynamic and geometric depth 

 in metres is about 2%, and between dynamic metres and the pressures in decibars is 

 almost 3%. For hydrographic purposes these differences are too large to be ignored. 

 For rough calculations it is perhaps permissible and practical to approximate the 

 values of Table 110 by the following formulae: 



lO^a = 97264 - 0-44/7, 



lOV = 102823 - 0-46/7. 



The values calculated from these are accurate to some units in the fifth decimal place. 

 The pressure field can be represented by surfaces of equal pressure (isobaric surfaces). 

 If these are drawn for each decibar then the entire volume of the sea is divided into 

 layers of 1 decibar pressure difference. The pressure gradient G at any point on an 

 isobaric surface is given by the decrease in the pressure p along the normal n to this 

 surface 



G = -^ 



dn 



(IX. 10) 



