THE SUBTROPICAL CONVERGENCE 61 



22° 48' E. The ' Meteor' crossed the convergence in about 41 S, 22 E; it was found to 

 be particularly sharp, and visible from a long way off as a line of current disturbance 

 at the surface. The temperature rose very suddenly 5-6° C. in 1 mile and 9-1° C. in 5 or 

 6 miles (Wiist, 1926, pp. 248-9). 



In the central part of the Indian Ocean the surface temperature observations of the 

 ' Valdivia' (Schott, 1902) and the ' Gauss' (Drygalski, 1926) show that the convergence 

 lies between 40 and 41 ° S in about 76 E. The surface temperature charts of the Indian 

 Ocean by Moller (1929, figs. 17, 21) and the salinity chart by Schott (1934, pi. 1) show 

 that the region between this position and that of the convergence south-east of Africa 

 is marked by a steep temperature and salinity gradient from south to north. 



In 106-108° E (section 9, Plates XVI-XVIII) the convergence was crossed between 

 39 50' S and 38 S ; it was not well defined, and the increase of temperature and salinity 

 took place in three steps. At the first, however, in 39 50' S the temperature and salinity 

 rose from 1 1-5 to 12-5° C. and 34-6 to 34-9 °/ 00 , and, as shown by the observations 

 at St. 871 18 miles farther north, the water was largely subtropical. 



The inversion of the usual increase of salinity and temperature towards the north 

 between Sts. 869 and 870 shows that the main drift towards the east is interrupted by 

 a large eddy movement, and the high salinity of the surface water at St. 869 indicates 

 that the subtropical convergence may bend towards the south between sections 9 and 10 

 even more extensively than is shown in Fig. 4. 



South-east of Cape Leeuwin, in section 10 (Plates XIX-XXI), the temperature and 

 salinity fell suddenly towards the south in 38° 22' S from 18-5 to 14-5° C. and 35-8 to 

 35-4 °/ O0 . This sudden fall appears, however, to mark the boundary between a subtropical 

 current which flows southwards along the west coast of Australia and a current from the 

 west, rather than the southern limit of the subtropical water. At Sts. 880 and 881 in 44- 

 47 S the surface water is plainly sub-Antarctic, but at St. 879 it contains a large 

 proportion of subtropical water. There is no sharp convergence between the two waters, 

 but the surface observations, used in constructing the section, indicate that the balance 

 between the northward and southward currents lies between 39 and 40 S. 



Near Tasmania there was also no sharp convergence ; in section 1 1 (Plates XXII-XXI V), 

 west of the island, the balance between the sub-Antarctic and subtropical currents seems 

 to be reached in 44-42 S where the temperature increases from 11 to 13-5° C. and 

 the salinity from 347 to 35-0 °/ 00 . In section 12 (Plates XXV-XXVII), south-east of 

 the island, the boundary is probably in 45-47° S, with similar temperature and salinity 

 differences. There was an indication of a second current boundary in 47 33' S, where 

 the temperature and salinity fell from 10-5 to 7-5° C. and 347 to 34-2 °/ 00 ; but although 

 there is apparently a strong southward movement as far as this latitude in the subsurface 

 stratum the relatively low surface salinity at St. 899 indicates that the surface water has 

 a northward component as far as at least 47 18' S. 



The absence of a sharp convergence between the sub-Antarctic and subtropical 

 waters south of Australia is probably due to the smallness of the northward and south- 

 ward components of the two currents. It is reasonable to suppose that the shape of the 



