Basin that terminates in the region west of Ceylon; a strong, preferential flow 

 between the Laccadive Islands and the Chagos Archipelago; a persistent flow 

 along the Equator between the Chagos-Laccadive Ridge and Sumatra; and a 

 more substantial flow into the Bay of Bengal and the Andaman Sea. All these 

 flows occur during both monsoons. Seasonal independence of RSIW flow is in 

 agreement with the findings of Duing, 1970 concerning vertical extent of 

 monsoonal effects (less than 250 meters except inthe western Somali Basin and 

 off the southwest coast of India). 



However, there is a monsoonal variation in RSIW concentrations in the 

 Gulf of Aden (Figure B-7), western Somali Basin (Figures B-11 and B-25), 

 southern Arabian Basin (Figure B-13), and Mid-Indian Basin (Figure B-35). 

 On all these seasonal T-S comparisons, higher RSIW concentrations were 

 found during the northeast monsoon. More RSIW enters the Gulf of Aden 

 during the northeast monsoon due to the lack of a northward flowing current in 

 Bab-el -Mandeb (Seriy, 1968). Therefore, relatively greater unmixed concen- 

 trations of RSIW are found during the northeast monsoon throughout the area. 

 Seasonal reversal of RSIW may occur in the western Somali Basin south of the 

 Equator as postulated by Warren, et al . , 1966 and Krause, 1968. However, 

 present data are inadequate to substantiate this reversal. 



Figure C-6 (AAIW flow) is based on inadequate data south of about 5° S. 

 latitude, particularly in the center of the area (Figure 4). Existing Nansen cast 

 data often were taken at depths that missed the well mixed AAIW core. Based 

 on all available data, the shoal bathymetry of the Chagos-Laccadive Ridge 

 precludes an AAIW flow north along 70°E. longitude. In addition, the Seychelles 

 Islands apparently cause a bifurcation in AAIW flow. When present, the AAIW 

 salinity minimum generally occurs between two RSIW salinity maxima (Figures 

 B-25, B-26, and B-33). This indicates that AAIW does not flow north between 

 the PGIW and RSIW high salinity cores as postulated by Rochford, 1966b, but 

 interfingers with RSIW below the 27.0 to 27.2 sigma-t surfaces as postulated by 

 Warren, et al . , 1966, 



Figure C-7 (BIW flow) is similar to that of Rochford, 1966a in the region 

 east of about 70° E. longitude. More extensive historical data in the southern 

 Somali and North Mascarene Basins indicates that BIW occurs persistently due 

 east and south of the Seychelles Islands (Figures B-31 and B-32) and sporadically 

 to about 5° N. latitude (Figure B-19). As noted by Rochford, 1966a, BIW occurs 

 on about the 27,4 sigma-t surface and often is separated from AAIW by a RSIW 

 salinity maximum (Figure B-35). BIW probably is as influential as RSIW in 

 blocking the northward spread of AAIW, and often mixes with AAIW to form a 

 single salinity minimum (Figure B-36). RSIW inhibits the westward flow of BIW 

 and often interfingers with BIW below the 27.4 sigma-t surface (Figure B-31). 



91 



