2i8 DISCOVERY REPORTS 



Between lo" S and the Equator sub-tropical water flows eastwards; probably as a 

 counter-current below the westward flowing tropical water of the south equatorial 

 current. North of 28° S in 30° W the sub-tropical water is covered by tropical water. 



The following table shows the depth of the 23" C. isotherm which has been assumed 

 to show the depth of the tropical water. 



Latitude 



Depth of tropical water in metres 



North of 18° S tropical water flows westwards in the south equatorial current and as 

 it approaches the Brazilian coast this current is partly deflected southwards into the 

 Brazil current. As it flows southwards, the Brazil current loses water from its left-hand 

 side in a surface drift towards the east, and in 30° W the tropical water south of 18^ S 

 is moving eastwards. The tropical water is deepest in 18° S, in the centre of the anti- 

 cyclonic movement between the south equatorial current and this movement towards 

 the east. These movements are shown on the chart of surface currents in the Atlantic 

 Ocean by Meyer (1923). 



TEMPERATURE AND SALINITY OF THE SUB-TROPICAL AND 



TROPICAL WATERS 



The surface temperature of sub-tropical water increases towards the north from 

 about 15-5° C. in winter or 18-5° C. in summer near the sub-tropical convergence; it 

 increases to 23° C. before it becomes covered with the tropical surface layer. Its surface 

 salinity increases from about 35-0 to 36-0 °/„o over the same distance. In the bottom of 

 the layer the salinity increases from 34-85 to 35-oo7„<, and the temperature remains 



about 10-5° C. 



From the surface to 50-60 m. sub-tropical water is almost uniform. Below it there 

 is a stratum of slightly higher salinity, and below this again the temperature and salinity 

 decrease gradually with depth until the discontinuity which forms the boundary of the 

 Antarctic intermediate layer is reached. 



The surface temperature of tropical water increases from 23° C. in 28° S to a maximum 

 of 28-29° C. just north of the Equator. Between the surface and the discontinuity which 

 separates the layer from the sub-tropical under-layer the temperature of tropical water 

 varies very little with depth. 



The salinity of the tropical surface layer increases from about 367„o in 28° S to a 

 maximum of 37-4 7 00 i" about 18" S. It then decreases towards the north in the south 

 equatorial current. In 9° 47' S the salinity remained uniform with depth down to 50 m., 

 and then increased to a maximum at 100 m. This is probably because the transport of 

 surface water, which under the influence of the east winds was towards the south, must 

 be compensated by a movement northwards between 80 and 100 m., similar to that which 

 has been found to move southwards in the region of westerly winds. The lowest salinity 

 found in the surface stratum was about 35-9700 just north of the Equator. The salinity 



