WATER MASSES AND CURRENTS OF THE OCEANS 



193 



the direction of flow becomes reversed, as is the case off the east coast of 

 Australia. No chart of the transport by the current can be prepared. 



Currents of the Equatorial Pacific 



In the Equatorial Pacific a chart of the depth to the thermocline 

 immediately gives an idea of the currents in the upper layers in the trop- 

 ical region (fig. 51). If the motion of the water below the discontinuity 



—150 — "* — »rnnAT?? RlAlI-COUNTEf ^--CURRENT- 



Fig. 51. Topography of the discontinuity surface in the equatorial region of the 

 Pacific shown by depth contours in meters, and corresponding currents. 



layer is small, the current in the upper layers must be related to the slope 

 of the discontinuity layer in such a manner that in the Northern Hemis- 

 phere the discontinuity layer sinks to the right of an observer looking 

 in the direction of the current and, in the Southern Hemisphere, sinks 

 to the left (p. 103). In the figure, arrows have been entered on the basis 

 of this rule showing the North and South Equatorial Currents flowing 

 toward the west and between them the Equatorial Countercurrent flowing 

 toward the east. The South Equatorial Current is present on both sides 

 of the Equator and extends to about 5°N, but the North Equatorial 

 Current remains in the Northern Hemisphere. Off South America the 

 flow is directed more or less parallel to the coast line, turning gradually 

 west when approaching the Equator. 



The Equatorial Countercurrent is remarkably well developed in the 

 Pacific Ocean, where, according to charts published by Puis in 1895, it is 

 present at all seasons of the year, lying always in the Northern Hemi- 

 sphere, but further away from the Equator in the northern summer. In 

 this season the velocities of the current also appear to be higher, reaching 

 values up to 100 cm/sec at the surface. The structure of the water 

 masses was first demonstrated by the Carnegie section in approximately 

 long. 140°W, which was obtained in October, 1929. Fig. 52 (top and 

 center) shows the temperature and salinity in this section between 

 the surface and 300 m. The figure brings out the great variation in the 

 depth to the thermocline in a north-south direction, the presence of 

 the surface layer of uniform temperature, and the tongue of maximum 

 salinity, which, to the south of the Equator, lies somewhat above the 

 thermocline. The bottom section shows the velocity distribution, which 



