SUBTROPICAL WATER: MOVEMENTS 79 



December to March, the conditions are somewhat different ; the north-eastward current 

 in the Tasman Sea is turned back towards the west from Three Kings Islands, and north 

 of New Zealand the current flows west and south. As a result of these changes the iso- 

 therms make a marked advance towards the south. 



The temperature and salinity distributions east of New Zealand (Figs. 8, 11) show 

 that the water in the relatively shallow soundings between the Chatham and Antipodes 

 Islands and South Island flows principally towards the north, but they also suggest that 

 there is a strong southward movement of subtropical water in the deeper soundings 

 farther east. The surface temperature and salinity charts of Schott and Schu (1910) and 

 Schott (1934) also indicate such a southward movement, but the current chart of Merz 

 (Wiist, 1929, p. 41) for the winter months indicates that it is only weakly developed. 



Farther east the current chart suggests that the subtropical water flows principally 

 towards the west and south, having its origin in current branches which turn to the west 

 and south from the Peru current and to the south from the equatorial current. The 

 water movements in the eastern part of the ocean, between 20 and 40 S, are, however, 

 well known only in the coastal region. 



The consideration of the meteorological, current, temperature, and salinity charts of 

 the Southern Ocean shows that the subtropical currents flow farther south in summer 

 than in winter, and when sufficient observations are available it will probably be found 

 that the subtropical convergence lies farther south. 



In the Atlantic Ocean the greater southward movement of the Brazil current in 

 summer has been established by Klaehn (191 1, p. 657 et seq.), and the increase in 

 strength can be traced to the fact that the subtropical region of high pressure in the 

 South Atlantic Ocean becomes weaker and less extensive in summer and approaches 

 nearer the African coast. This leads to an increase in the frequency and strength of the 

 north winds off the west coast of Brazil, and to a greater southward movement of the 

 surface water. Farther east in the Atlantic Ocean the data are scanty but they give some 

 indication that the convergence is farther south in summer. They also show that it may 

 make a large advance towards the south which is not part of the seasonal changes 

 (see p. 59). 



In the Indian Ocean Michaelis (1923) has shown that in summer the south equatorial 

 current extends farther south and the southern branch of the current which flows round 

 the southern end of Madagascar is stronger. The southward current from the Mozam- 

 bique Channel is also strengthened in summer owing to the accumulation of water in 

 the Gulf of Zanzibar from the equatorial current and the north-east monsoon drift ; 

 and as a result the Agulhas current, which is formed by the union of the two current 

 branches off the coast of Natal, carries a larger volume of subtropical water towards the 

 south-west. The position of the convergence between the subtropical and sub-Antarctic 

 waters in the region south of Africa seems, however, to vary only within limits of 100 

 to 200 miles and there is no definite evidence of a regular seasonal change. The 

 variation appears to be greatest in the path of the current branch which forces its 

 way westwards into the Atlantic Ocean between 40 and 43 S. Merz (1925, p. 572) from 





