SOUTH EQUATORIAL CURRENT 



EQUATORIAL 

 COUNTER 

 CURRENT 



NORTH 



EQUATORIAL 



CURRENT 



Figure 2. 1953 Concept of Equatorial Circulation . As 

 a result, of our studies we now have an idea why the equatorial 

 v/aters are more productive than those to the north and south. This 

 idea has been illustrated in the "slice" of the ocean shown aliove. 

 Visualize that we have sliced the ocean along longitude 150° and are 

 looking towards the west with north to our right amd south to our 

 left. The surface currents are shown by broad arrows and the ver- 

 tical temperature structure by the fine lines of equal temperature. 

 However, we wish to focus your attention on the waters at the Equa- 

 tor. Under the influence of the steady southeast tradewinds the deep 

 water comes to the surface and moves northward as shown by the 

 smaller solid black arrows. This sets up a chain of events that ends 

 with good tuna fishing. The upward nnoving water brings phosphates, 

 nitrates, and other nutrients to the lighted zone and phytoplankton 

 (one-celled plants) multiplies rapidly. The zooplankton (tiny 

 cinimals) feeds on the plants cind in turn multiplies, drifting slov/ly 

 north with the water. Larger Crustacea, squids, and small fish 

 gather to feed on the zooplankton. The tunas, the final step in the 

 oceanic production line, concentrate here where there is good feed- 

 ing much more of the time than elsewhere. 



The eastward flowing subsurface countercurrent was 

 recently discovered in our work. Its significeince to the circula- 

 tion and to the productivity of the system is not yet known. 



