88 



DISTRIBUTION OF SALINITY, TEMPERATURE, DENSITY 



The T-S diagram has become one of the most valuable tools in physical 

 oceanography. By means of this diagram, characteristic features of the 

 temperature-salinity distribution are conveniently represented and 

 anomalies in the distribution are easily recognized. The diagram is also 

 widely used for detecting possible errors in the determination of tempera- 

 ture or salinity (p. 44). 



Water Masses and Their Formation. In accordance with Hel- 

 land-Hansen's original suggestion a water mass is defined by a T-S curve, 

 but in exceptional cases it may be defined by a single point on a T-S 

 curve — that is, by means of a single temperature and a single salinity 

 value. These exceptional cases are encountered in basins where homo- 

 geneous water is present over a wide range of depth. A water type^ 



12 •♦500-900 

 358 360 



TEMPERATURE. °C 



SALINITY. X. 



SALINITY, %o 



SALINITY, %o 



12 ^1 340 T 

 -600- 



^ •<-900- 

 6uJ 



Fig. 20. Diagrammatic representation of results of vertical mixing of water types. 

 To the left the results of mixing are shown by temperatures and salinities as functions 

 of depth, and to the right are shown in three T-S diagrams the initial water types 

 (1) and the T-S relations produced by progressive mixing (2 and 3). 



on the other hand, is defined by means of single temperature and saHnity 

 values, but a given water type is generally present along a surface 

 in the sea and has no thickness. Only in the exceptional cases that 

 were referred to are the terms ''water type" and ''water mass" inter- 

 changeable, but in oceanographic literature the terms have been used 

 loosely and without the distinction that has been introduced here. 



In many areas the T-S curves are straight lines or can be considered 

 as composed of several pieces of straight lines. Elementary considera- 

 tions show that a linear relation between temperature and salinity must 

 result if the water types, which can be defined by the end points of the 

 straight line, mix in different proportions. Similarly, a curved T-S 

 relation may result from the mixing of three different types of water. 

 Fig. 20 illustrates in two simple cases how progressive mixing alters the 

 temperature-salinity relation. These considerations are of a formalistic 

 nature, but have in many instances led to the concept that certain 



