SUB-ANTARCTIC WATER: SURFACE CURRENT 53 



with the theoretical effect of these depth changes on the easterly drift (Ekman, 1928, 



PP- 3H-7)- 



East of ioo° E the temperature distribution suggests that the southern part of the 

 drift — the part colder than 8° C. — has a small southward tendency, whilst the warmer 

 northern half bends slightly northwards. The spreading of the isotherms is probably an 

 indication of an area of mixed water which begins in about 43 ° S, 104 E at Sts. 869 

 and 870 (section 9, Plates XVI-XVIII) and extends eastwards, south of Australia, 

 between the 8 and n° C. isotherms. 



The observations at Sts. 869 and 870 suggest that the main drift towards the east is 

 interrupted by an eddy movement similar to that found south-east of the Cape of Good 

 Hope. Throughout the whole of the water column at each station the temperatures and 

 salinities are higher at St. 869 than they are at St. 870, 160 miles farther to the north- 

 east. This eddy also appears to be caused by the effect of the bottom topography on the 

 easterly current. The topography is not well known, but the preliminary chart in 

 Plate XLIV suggests that the two stations lie where the bottom slopes steeply towards 

 the north-west from the Indian Pacific cross-ridge to the deep basin west of Australia. 

 The data are not sufficient to determine the direction of the eddy current with absolute 

 certainty, but the most reliable indication — given by the density distribution — suggests 

 that it is anticyclonic. 



The belt of mixed water which the spreading of the surface isotherms shows ts> extend 

 towards the east from Sts. 869 and 870 is probably formed as a result of numbers of such 

 eddy currents. There is evidence of an eddy between Sts. 879 and 881 in section 10 

 (Plates XIX-XXI) south-east of Cape Leeuwin, and of another between Sts. 893 and 

 895 in section 11 (Plates XXII-XXIV) south-west of Tasmania. Both eddies are 

 probably caused by the influence of the steep slope from the Indian Pacific cross-ridge 

 to the South Australian basin on the eastward current. 



The general conclusions reached with regard to the surface currents from the tem- 

 perature and salinity data are in approximate agreement with those suggested by the 

 current and ice charts. The charts of Michaelis( 1923) and Willimzik(i924) allow a north- 

 ward movement to be distinguished near Marion Island and the Crozet Islands and also 

 east of Kerguelen, and a southward movement in the deep channel between the Crozet 

 Islands and Kerguelen. 1 The charts of Michaelis also point to a divergence of the current 

 south of Australia in approximately the same latitude as the belt of mixed water de- 

 scribed above ; the southern part of the drift is shown to have a small southward move- 

 ment, whilst the northern part is deflected northwards. 



The records of drift-ice confirm several of these conclusions. The Antarctic Pilot, 1930, 

 p. 19, states that " between the Cape of Good Hope and Tasmania ice is seldom met with 

 north of 40 S. Between the 40th and 45th parallels it is mostly seen between 40 E and 

 6o° E " — north of the Marion Island-Crozet Islands ridge. " Between the 45th and 50th 

 parallels ice may be met with anywhere westward of 90 E. Eastward of that meridian " 

 — where the southern part of the drift has a southward tendency — " it is much rarer." 

 L In Michaelis' charts Kerguelen is charted incorrectly in 80° E instead of 70 E. 



