Indian Ocean; warm, fresh water on the eastern side of the Indian Ocean in the 

 region of the Indonesian Archipelago is responsible for larger steric anomalies 

 off the coast of Sumatra than are to be found off the coast of Africa, thus 

 causing a sea surface slope upward toward the east along the Indian Ocean 

 equator. Because of the lack of an Equatorial Undercurrent and the compara- 

 tive freshness of the near surface waters of the southern part of the Somali 

 Basin, the presence of the shallow subsurface salinity maxima at stations 1 

 and 2 between 50 m and 100 m is unexpected. It may be explained by a mass 

 influx of saline water from the south compensating for a depressed sea surface 

 on the western side of the equatorial Indian Ocean. 



Below the subsurface salinity maximum at station 1, the water freshens. 

 With the exception of weak salinity minima at 125 m and 400 m, the T-S curve 

 is quite smooth to 1500 m. The salinity minimum at 400 m is possibly the 

 result of the advection of warm, fresh Pacific Equatorial Water westward by 

 the South Equatorial Current from its formation area in the Banda Sea (Warren, 

 et al_. , 1966). The fresh water between 800 m and 1500 m (S=35.00 °/oo to 

 34.85 °/oo) consists of remnants of Antarctic Intermediate Water overlain by 

 Subtropical Subsurface Water. 



Proceeding north and west into the Somali Basin toward the Somali Coast, 

 the near surface salinity maximum disappears, and a salinity maximum appears 

 between about 800 m and 1000 m depths. This salinity maximum, which is cen- 

 tered on the 27.3 a^ surface, has been designated Red Sea Water and is preva- 

 lent throughout the Somali Basin (Fenner and Bucca, 1972). Although Red Sea 

 Water covers a large geographical area, its effects are less pronounced in the 

 Indian Ocean than those of the Mediterranean Intermediate Water in the Atlantic. 

 Fenner and Bucca (1972) report that only 200 nmi east of the Strait of Bab el 

 Mandeb, only 35% of the Red Sea Water remains unmixed. In contrast, more than 

 95% of the Mediterranean Intermediate Water was found unmixed 250 nmi west of 

 the Strait of Gibraltar. 



At stations 10 and 15 (figure 25), a shallower and much weaker salinity 

 maximum was observed at the 26.6 at surface. This is Persian Gulf Water which 

 is warmer and lighter than Red Sea Water. Much less pronounced in its effects 

 than Red Sea Water, Persian Gulf Water acquires its characteristics in the 

 small, shallow Persian Gulf, which is characterized by a large excess of 

 evaporation over precipitation and river runoff. Persian Gulf and Red Sea 

 Waters are separated by a tongue of Subtropical Subsurface Water centered 

 between the 26.7 at and 26.8 at surfaces (Warren, ejt al_. , 1966). 



Station 10 (figure 25), located slightly south of the center of the Great 

 Whirl at 5° 01.2'N, 51° 52.2'E, is an excellent illustration of the several 

 water masses present in the northwestern Indian Ocean. From the surface down 

 to 150 m this station shows nearly isohaline water of salinity between 35.0 °/oo 

 and 35.1 °/oo. This water is fresh upwelled water transported offshore from 

 the Somali Coast by southwesterly monsoon winds. The water at 200 m, showing 

 a pronounced increase of salinity from 150 m to 200 m, is of local origin, as 

 shown by its shallowness and low density. The next prominent feature at this 

 station is the salinity maximum between 300 m and 400 m. At 334 m the salinity 

 was measured at 35.41 °/oo at a at value of 26.726, which is characteristic of 

 Persian Gulf Water. At about 500 m, an intermediate salinity minimum is 

 observed. This salinity minimum, centered about the 27.0 at surface, 1s 



10 



