AUSTRALIAN QUATERNARY CLIMATES AND MIGRATION 



33 



Optimum, or 8,000 years ago. The probable paths now and in 

 the past are shown in Fig. 3. 



The Southern Ocean Current profoundly affects the climate 

 of a large part of Australia, particularly its south-eastern portion. 

 It bifurcates some hundreds of miles south-west of Cape Leeuwin : 

 one branch flows northwards up the west coast, the other east- 

 wards along the south coast impelled by the anti-trade winds. It 

 receives a great indraft of cold water from the Antarctic Ocean, 

 and, west of Cape Leeuwin, a surface indraft of warm water 

 from the Indian Ocean. The Challenger Expedition recorded the 

 latter as a warm sub-surface current off Cape Northumberland 

 at the south-east corner of South Australia about 400 miles wide 



FIG. 3. 



Approximate positions of paths of lows at present and in the past. I. During the six 

 cool months (after Taylor, 1920, Fig. 132) and also 8,000 years ago; II. at last glacial 

 maximum; III. 15,000 years ago when the tropical rain-forest reached Australia; IV. 

 at Postglacial Optimum, 4,000 years ago; V. before existence of Bass Strait. 



and about 250 fathoms deep flowing easterly. At Cape Leeuwin 

 it is a surface current, but at Cape Northumberland it is about 

 150 fathoms below the surface and has cooled about 16 degrees. 

 Halligan (1921) states: 



The southern branch continues as an easterly surface current across the 

 Bight, with a rate varying from 3 to 4 knot as far as Spencer Gulf. The warm 

 current from the Indian Ocean, which appears to be confined to the Bight, to 

 that point, here dips below and becomes partly merged in the main stream until 

 it strikes the Tasmanian Plateau. This obstruction, by deflecting the current to 

 the south-east, causes a further mixing of the warm and cold waters, which 

 accounts for the water in Bass Strait being generally from 2° to 4° colder than 

 the water off Cape Northumberland. 



He observes that the Tasmanian Plateau also retards the cur- 

 rent velocity in Bass Strait to the extent that the tidal currents 

 become more important and that both are largely dominated by 



