164 Salinity of the Ocean, its Variation in Oceanic Space and in Time 



For the individual oceans the deviations from a Hnear form are larger and Wiist 

 was able to show that these were due in the first place to mixing of the surface layers 

 with the layers underneath. 



This linear dependence although unequivocal cannot be taken as a casual physical 

 relationship. This is readily seen, since if the surface salinity in an area was dependent 

 only on the difference evaporation-precipitation the constant excess of evaporation 

 (for always positive E — P) would cause it to rise continuously and a linear correla- 

 tion could not be maintained. The simple linear dependence is only a part of the gener- 

 ally applicable equation S = f{E — P, C, M) and to this equation adds the varying 

 effect of advection and mixing (Defant, 1931). This influence enters into the above 

 equation partly in the coefficient of the {E — P) term and partly in the first term which 

 represents primarily the effect of vertical mixing. If surface water of salinity S is 

 mixed with water of constant salinity 5*0 then the change of salinity due to mixing will 

 be proportional to Sq — S. The change of salinity due to processes of evaporation 

 and precipitation will be proportional to E — P. Under stationary conditions the 

 local change in surface salinity will be zero. Thus 



^4 = <S-So)-i-b(E-P) or S = So + k{E-P). 

 ot 



As shown above, this formula has been confirmed empirically and this mixing in 

 general proceeds with water masses of mean salinities of either 34'47%o or 34-92%o. 

 These values are mean values for the salinity at 400-800 m (subpolar intermediate 

 water). The fact that the value Sq is somewhat different for the individual oceans, as 

 Wiist has shown, proves the correctness of this assumption. The North Atlantic 

 north of 20° N. possesses a markedly high salinity which can be explained by the 

 absence of the weakly saline subantarctic intermediate water at a depth of 600- 

 800 m. The deep-reaching effect of the Gulf Stream and the strong inflow from the 

 Mediterranean exert by mixing a noticeable effect on the surface layer. Conditions in 

 the North Pacific are just the opposite. In contrast to the North Atlantic there is in 

 the North Pacific a well-developed subarctic intermediate current at 600-800 m, 

 which has its origin in the cold adjacent seas with a low salinity in the north-western 

 Pacific Ocean. The strong negative anomaly in the North Pacific is certainly associated 

 with this, because subtropical and adjacent seas are missing and therefore no inflow 

 of water with high sahnity can occur. The South Atlantic and the South Pacific with 

 no adjacent seas and well-developed subantarctic intermediate water show similar 

 but almost normal conditions. The difference £" — P is, however, always of decisive 

 importance, and since it is closely related to the general atmospheric circulation it 

 is clearly understood that the general outlines of the mean surface salinity must be 

 controlled by the atmospheric circulation. 



Returning to the horizontal charts, an understanding of all the salinity details in 

 these charts involves not only the vertical mixing process with the layers underneath, 

 but also all the other factors influencing the surface salinity distribution. It is, however, 

 the oceanic and the atmospheric circulation that determine the details of the hori- 

 zontal distribution of salinity. The factors "solution of salt deposits" and "inflow of 

 fresh water" play no particularly far-reaching partf although the last factor (R) of 

 Table 73 has some importance in coastal regions. 



