the extremely broad deep channel at depths less than 1800 meters and velocities 

 less than 1495 m/sec in the Bay of Bengal (much diluted RSIW). Figure A-5 

 shows a deep axis that shoals from 1600 to less than 1000 meters over the 

 Andaman-Nicobar Ridge and then deepens to approximately 1100 meters inside 

 the Andaman Basin, Axial velocities are less than 1495 m/sec throughout, 

 but closely approach 1495 m/sec in the passage over the Andaman-Nicobar 

 Ridge, Figure A-6 shows a relatively stable deep sound channel that extends 

 from the Somali Republic to the northern tip of Sumatra at depths of 1500 to 

 1800 meters and velocities less than 1495 m/sec (somewhat diluted RSIW). The 

 channel is considerably broader in the east (lesser concentrations of RSIW), In 

 the Mentawai Trough, axial depths are approximately 1100 meters (similar to 

 Andaman Basin). Farther south. Figure A-7 shows a relatively stable deep 

 channel over the Somali Basin at depths between 1400 and 1600 meters and 

 velocities less than 1495 m/sec (much diluted RSIW). However, east of the 

 Seychelles Islands, the deep channel fluctuates between depths and velocities 

 less than 1 100 meters and 1490 m/sec (BIW) and depths and velocities greater 

 than 1500 meters and less than 1495 m/sec (much diluted RSIW). The lack of 

 substantial concentrations of unmixed RSIW results in an extremely broad 

 channel across the area. Rapid changes in deep axial depth and velocity over 

 the Carlsberg Ridge correspond to intensive mixing of RSIW and BIW. In the 

 Mentawai Trough, axial depths are less than 1000 meters and axial velocities 

 greater than 1500 m/sec (local modification of lEW). 



In the north-south direction. Figure A-8 shows a channel that deepens 

 to the north over the Somali Basin from about 1200 meters to greater than 1600 

 meters. Deep axial velocities vary from less than 1490 m/sec in the south 

 (BIW) to less than 1495 m/sec off Mogadiscio (somewhat diluted RSIW). Higher 

 RSIW concentrations in the north result in a much narrower deep channel. 

 Farther east. Figure A-10 shows a similar deepening of the channel to the 

 north, accompanied by an increase in deep axial velocity and a northward 

 constriction in the vertical extent of the channel. Deep axial velocities 

 greater than 1495 m/sec over the Arabian Basin are associated with an east- 

 west flow of RSIW (Figure C-5). At about 6° S, latitude, sound velocity 

 perturbations above and below deep axial depth merge with the deep sound 

 channel (mixing of RSIW and BIW), Over the Mid-Indian Basin and in the 

 Bay of Bengal, Figure A-12 shows a channel that deepens to the north (from 

 less than 1000 to about 1700 meters) at velocities ranging from less than 1490 

 to less than 1495 m/sec. However, the deep sound channel is only slightly 

 wider in the south than in the north (much diluted RSIW along entire cross- 

 section) . Over the North Wharton Basin, Figure A-13 shows a relatively 

 stable deep axis at 1000 to 1200 meters (BIW) that deepens rapidly to 1500 

 meters at about 3° S. latitude (preferential RSIW flow) , shoals to 1000 meters 



17 



