52 DISCOVERY REPORTS 



the general trend of the surface isotherms and isohalines indicates that the surface cur- 

 rent flows slightly north of east, but farther east, south of the Cape of Good Hope and 

 as far as 30 E, the iso-lines bend slightly southwards suggesting that the surface current 

 has a lesser northward movement and possibly a southward movement. The fact that 

 the Atlantic Ocean between 40-45 S is on the whole more free from icebergs east of 

 io° E (Admiralty Chart, No. 1241, 1910) is some confirmation of this conclusion. 



In the region south of the Cape of Good Hope the sub-Antarctic current, flowing 

 mainly towards the east, meets the Agulhas current — a strong current of subtropical 

 water flowing in the opposite direction. The two streams become largely intermixed and 

 the area is one of very irregular currents and sharp changes of temperature and salinity 

 (see pp. 60, 75). 



The main drift towards the east is also interrupted in 46-48 S by what appears to be 

 a strong cyclonic eddy movement. The existence of such an eddy is indicated by the 

 temperature, salinity, and oxygen content differences between Sts. 848 and 849 in 

 section 8 (Plates XIII-XV). The normal decrease of temperature and salinity and 

 increase of oxygen content towards the south were found to be reversed, and although 

 St. 849 was actually 150 miles south of St. 848, its water column was warmer, more 

 saline, and contained less oxygen. 



The observations made by Brennecke in the ' Planet ' (1909) also point to the existence 

 of this eddy movement. The observations tabulated among the meteorological data 

 (p. 13) show that on the voyage south-east of Cape Town the decrease to 3-4° C. in 

 47 10' S, 26 30' E, was followed by a sudden increase to 7-2° C. in 48 S, 27° 20' E, 

 and a final decrease to 3-3° C. in 49 10' S, 28 50' E. 



The observations in section 8 show that the whole of the water column from the sur- 

 face to the bottom is affected by the movement, and they suggest that the eddy is the 

 effect of the irregular configuration of the sea-bottom first on the bottom and deep 

 waters, and then on the surface water. The bottom temperatures and soundings available 

 from this region indicate that the Atlantic Indian cross-ridge is arched first towards 

 the north and then towards the south (Plate XLIV) and that Sts. 848-9 and the ob- 

 servations of the 'Planet' were made inside the second bend. The evidence as a whole 

 suggests that the eddy current at the surface is a striking example of the far-reaching 

 effect of the bottom topography. 



The isotherms for the western part of the Indian Ocean in Fig. 8 are based on the 

 charts given by Drygalski (1926, pi. v), and Schott (1902, Atlas, pi. ix), and on the 

 average temperatures for the region between 42-44 S and 40-80 E, in the month of 

 May, calculated by Krummel (191 1, II, p. 679). They bend towards the north on the 

 ridge joining Marion Island and the Crozet Islands, and on the submarine plateau north- 

 east of Kerguelen, but towards the south in the deep channel between the Crozet Islands 

 and Kerguelen. In each locality the bending of the isotherms is probably due to a 

 corresponding deviation of the surface current caused by the effect of the changing depth 

 of the sea on the main drift towards the east. The northward movement of the water over 

 the shallow ridges and the southward movement over the deep channel are in accordance 



