The surface circulation in the South Indian Ocean is similar to the counter clockwise circulation observed in the South Pacific and the South Atlantic Oceans. To the south of the Equator the currents are characterized by a greater degree of constancy.
In this part of the Indian Ocean, there is no seasonal reversal in the direction of the flow of the ocean currents.
However, the following are the major currents of the South Indian Ocean: (i) The South Equatorial Current, (ii) The Agulhas Current, (iii) the West Wind Drift, and (iv) the West Australian Current. These currents lead to the development of an anticlockwise circulation in the southern part of the Indian Ocean.
The South Equatorial Current, to the north of 20°S latitude flows from east to west. It attains its greatest velocity during the winter of the southern hemisphere.
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In this season the current is reinforced by the Pacific water that flows into the Indian Ocean to the north of Australia. During the southern summer, however, the flow to the north of Australia is reversed.
During the summer as well as the winter months of the southern hemisphere a branch of the South Equatorial Current deflects towards the south along the east coast of Africa, supplying water to the Agulhas Current.
The South Equatorial Current bifurcates into two branches near Madagascar (Malagasy Republic) The branch of this current which flows southward along the eastern coast of this island is called the Madagascar Current, while the other branch flowing towards the south through the Mozambique Channel is known as the Mozambique Current.
To the south of Madagascar at about 30°S latitude both these currents join together to create the Agulhas Current. The Agulhas Stream, as it is called, is a well-defined and narrow current to the south of 30°S latitude.
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From the coast its width measures less than 100 km. To the south of South Africa a major part of the Agulhas Stream deflects to the south and then towards the east.
This current sends some water into the Atlantic Ocean and some into the Indian Ocean through its branches. To the south of the continent near the Agulhas Cape, the main branch flows towards the east and converges with the West Wind Drift.
Due to change in the direction of flow of the main current to the south of Africa, a large number of eddies develop there.
Thus, a very complicated system of surface currents with seasonal variations is found there. According to Dietrich’s measurements, the transport by this current is a little more than 20 million m3/sec.