Chapter XXI 



The Main Features of the General 

 Oceanic Circulation and Their Physical 



Exploration 



1. The Oceanic Circulation in the Atlantic 



The results obtained by numerous expeditions in the Atlantic allow a complete and, 

 in itself, closed picture to be built up of the tropospheric and stratospheric oceanic 

 circulations. Knowledge of the circulation systems in the other oceans is not so precise, 

 but the conditions in them should not be so very different as is confirmed clearly by 

 the available observations. An attempt has been made in Fig. 331 to picture the entire 

 circulation system of the Atlantic in a somewhat schematic meridional section in 

 order to summarize its main characteristics. This representation applies mainly to 

 the western side. It can be seen that the main water movements are confined to an 

 extremely thin layer. The circular representation shows especially the enormous 

 horizontal extent of the oceanic troposphere. Its vertical thickness is, however, small 

 so that in spite of the large vertical exaggeration in scale it is difficult to picture the 

 internal circulation properly in the figure. All the main currents and singular points 

 of the current system of the sea surface are indicated at the edge of the figure. It should 

 be remembered that all extensive ocean currents are mainly surface currents and belong 

 essentially to the oceanic troposphere; they extend down to the water masses of the 

 oceanic stratosphere in only a few places and to a limited extent. This is especially so in 

 the tropics and the subtropics. 



As compared with the large horizontal extent of the oceanic troposphere the source 

 regions for the stratospheric water types appear small, nevertheless they remain the 

 regions of origin for the water movements inside the extended space of the oceanic 

 stratosphere. In these regions also the forces must be contained for a renewal of the 

 stratospheric waters and their movements. The effect of the European Mediterranean 

 which can be regarded as a lateral intrusion from the east appears of no less impor- 

 tance. The small arrows in the diagram indicate the direction of spread of the individual 

 water types; the current-like spread is thereby mostly indicated by full arrows while 

 convectional spread is shown by wavy arrows. The figure shows only the meridional 

 components of the water movement and deals only with mean conditions. The zonal 

 components surpass by far the meridional ones especially in the southern part of the 

 South Atlantic and in middle latitudes in the North Atlantic. The characteristic 

 asymmetry of the Atlantic circulation and the great importance of the Antarctic for 

 the stratification and movement of the water masses throughout the entire Atlantic 



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