DISTRIBUTION AND MIGRATION 



319 



Figure lyy. Ocean currents and limits of Antarctic pack ice {see Fig. 178). {Marr, ig^G. 



Convergence, a warm current rises up from about 1,500 to about 200 

 fathoms. This warm deep current from the Atlantic, Indian and Pacific 

 Oceans in the north comes into contact with the cold current returning 

 south, and surrenders some of its heat and a great many salts to it. In this 

 way, the current which returns to the Antarctic at a depth of 100 and 500 

 fathoms reaches a temperature of up to 34*7° F. and also gains the mineral 

 salts needed for supporting plant life. 



Since vegetable plankton which, as we have seen in Chapter 10, consists 



