DEEP CURRENTS: PACIFIC OCEAN 99 



compensation current to balance the northward movements of Antarctic water, and the 

 eastward movement may be due to the prevailing west wind, to density differences 

 between the two oceans, and perhaps to the need for an eastward current to balance the 

 movement towards the west through the Malay Archipelago. The temperature and 

 salinity distribution gives some indication that the eastward movement is strongest in 

 the deep channel near Cape Leeuwin (Plate XLIV and section 10), where the deep water 

 has a salinity of 3478 °/ 00 . The next highest salinities were found in the central part 

 of section 11, south-west of Tasmania, and the salinity distribution suggests that the 

 current flows eastwards across the Great Bight, bending southwards as it reaches the 

 shallow water west and south of Tasmania. 



South of the deep channel the easterly movement seems to be weaker; the low 

 salinity and high temperature of the deep water, and the sinking of the isotherms and 

 isohalines between 41 and 45 S in section 10, suggest that the deep layer is diluted by 

 the sinking of water in the centre of an anticyclonic eddy in the eastward movement. 

 The reason for the existence of the eddy cannot be given with certainty, but its situation, 

 over the western end of the South Australian basin, suggests that it may be caused by 

 the influence of the sharp changes of depth on the eastward current. There is a second 

 region of low salinity in the deep current between 53 and 56 south, but in this instance 

 the salinity and temperature are both lowered by the upwelling of bottom water, pro- 

 bably in the centre of a cyclonic eddy, whose situation over the eastern end of the 

 Australian Antarctic basin shows that it too may be a consequence of the influence of 

 the bottom topography on the eastward current. 



The observations in the neighbourhood of Tasmania give little indication of the 

 existence of a southward movement of deep water in the western half of the Tasman 

 Sea ; the low oxygen content of the water north of 45 ° S in sections 1 2 and 1 3 (Plates XXV- 

 XXX) might be the result of such a movement, but it is plain that the current, if it exists, 

 has no marked effect on the temperature and salinity distributions. 



THE DEEP CURRENTS IN THE SOUTHERN PART OF 

 THE PACIFIC OCEAN 



The deep water circulation of the Pacific Ocean has been known for some time to 

 differ considerably from that of the Atlantic and Indian Oceans, but so few observations 

 have been made in the deep and bottom layers of the ocean that the conclusions reached 

 have been largely hypothetical. Wiist (1929) showed that the Arctic intermediate 

 current— the current analogous to the Antarctic intermediate current but having its 

 origin in the surface currents of the Arctic regions— is not rudimentary as it is in the 

 Atlantic Ocean, but is a strong current which flows southwards until it meets the 

 Antarctic current near the equator, and in consequence the highly saline surface waters 

 of the subtropical regions are almost entirely separated from the deep and bottom waters 

 by a poorly saline layer of intermediate water, and are not able to sink into the deep layer 

 as the surface water in the North Atlantic Ocean does. 



A careful examination of all the data available, principally observations made by the 



13-2 



