east by the Equatorial Countercurrent result in the greater than 5100-meter 

 critical depths along the Equator in the Mid-Indian and North Wharton Basins. 

 Critical depths less than 5100 meters north of the Equator on either side of the 

 Maldive Islands are caused by less saline lEW carried by the North Equatorial 

 Current. Critical depths less than 5000 meters along the southern boundary of 

 the area are related to the flow of the South Equatorial Current. 



During the southwest (summer) monsoon, critical depths vary from greater 

 than 5200 meters along the Equator and west of the Laccadive Islands to less than 

 3500 meters In the strong upwelling center off the Somali Republic (Figure C-2). 

 Upwelling off the Somali Republic causes the shoalest annual critical depths 

 found in the North Indian Ocean (also see Figures A-4 and B-ll). Southwest 

 monsoon upwelling also causes critical depths less than 4700 meters off the east 

 Africa coast, less than 4400 meters off Muscat and Oman, and less than 4800 

 meters south of Java. Despite the effects of upwelling, critical depths in the 

 Arabian Sea are 100 to 300 meters deeper during the southwest monsoon due to 

 increased surface insolation. Critical depths in the Bay of Bengal are about 200 

 meters deeper during the southwest than during the northeast monsoon. The 

 clockwise circulation of the South Equatorial, Somali, and Southwest Monsoon 

 Currents causes a similar pattern in the critical depth isolines south of about 5° 

 N. latitude and west of about 70° E. longitude (4800- through 5100-meter 

 isolines) . The intense packing of isolines in the northwestern Somali Basin is a 

 result of both upwelling and an oceanic front associated with the eastern wall of 

 the Somali Current. Critical depths greater than 5100 meters between about 5° 

 N. and 5° S. latitude are related to surface insolation and the Southwest Monsoon 

 Current which carries warmer, more saline ArSW to the south. Critical depths 

 less than 5000 meters along the southern boundary of the area are related to the 

 colder, more dilute flow of the South Equatorial Current (lEW). Critical depths 

 in the Andaman Sea are similar to those for the northeast monsoon. 



South of about 10° N. latitude, critical depths are similar during both 

 monsoons in the region between the Seychelles Islands and Sumatra. This 

 indicates that critical depths are independent of monsoonal effects in this truly 

 equatorial area. However, in the Arabian Sea, Bay of Bengal, western Somali 

 Basin and in the region south of Java, critical depths vary by at least 200 meters 

 between the northeast and southwest monsoons. In the Arabian Sea and Bay of 

 Bengal, this variance is attributable to increased surface insolation during the 

 southwest monsoon (except off the coast of Muscat and Oman) . In the western 

 Somali Basin, the region south of Java, and off Muscat and Oman this variance 

 is related to upwelling caused by monsoonal reversal in surface circulation. 



26 



