CHAPTER IV 

 CENTRAL AND SOUTHERN INDIAN OCEAN 



The central and southern parts of the Indian Ocean Include the 

 regions vhich are least affected by the monsoon forces vhlch play 

 such an important role in the circulation and vater mass structure 

 in the northern part of the ocean. The vater masses in these parts 

 are only indirectly influenced by the marginal seas of the northern 

 Indian Ocean and they are analogous in formation to similar water 

 masses in the Atlantic and Pacific Oceans. 



Circulation. The absence of a sufficient number of direct current 

 measurements in the Indian Ocean has resulted In the study of cur- 

 rents by indirect methods. One of these is the dynamic method vhich 

 is very exacting in its requirements. The measurements must be 

 simultaneous and recurrent^ and should be arranged with respect to 

 any currents which may exist. This method has been used extensively 

 in the southeast part of the ocean near Australia and also in the 

 southwest off the coasts of Africa and Madagascar. 



Another indirect method Is the qualitative method, which is 

 less exacting^ and is based on the property of ocean vater to main- 

 tain its characteristics for a long period of time as it spreads in 

 the direction of flow from the region where it is formed. Tempera- 

 ture, salinity, and sometimes oxygen content, are the indices which 

 are usually selected to trace the water movements. Up to the 

 present time, the qualitative method has been useful to furnish a 

 first approximation of the general circulation of the water masses 

 In the Indian Oce_T^. 



^Muromtsev, Basic Outline of the Hydrology of the Indian Ocean , 

 p. 96. 



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