3 I 8 WHALES 



krill, the Avhales' main source of food, and, in particular, we might find 

 out why krill is so plentiful near the poles and so scarce in the tropics. 



All life on earth depends on the presence of plants, since plants alone 

 can synthesize organic matter from carbonic acid and water, with the help 

 of sunlight. Now, while sunlight and water are found throughout the world, 

 carbonic acid is more soluble in cold than in warm water. Thus a bottle of 

 soda water may pop, i.e. release its carbon dioxide, if it is not kept cool 

 enough. Similarly oxygen, which all organisms need for respiration, is 

 more plentiful in cold than in warm water, while, conversely, destructive 

 bacteria prefer warmer temperatures. Consequently, organic matter 

 is more abundant in cold than in warm waters - hence the abundance of 

 vegetable plankton, and animal plankton feeding on it, near the poles. 

 Tropical seas often contain less than 5,000 micro-organisms per gallon of 

 water, while the Antarctic has been known to contain up to 500,000. On 

 the average, the Antarctic is from ten to twenty times as rich in plankton 

 as the tropics. 



This difference is not entirely due to the greater abundance of carbonic 

 acid and oxygen, since plants also require nitrates, phosphates and sulph- 

 ates and can only flourish and propagate their kind if these salts are 

 present in solution. Thus, only where oxygen and carbonic acid occur 

 together with these compounds can we expect the prolific growth of 

 plankton which is known to occur in the polar seas. Now, the distribvition 

 of marine salts is mainly governed by sea-currents, and we would therefore 

 do well to examine the nature of these currents in the Antarctic. 



The upper 100 fathoms of the Antarctic, which are at 32° F., form an 

 ocean current flowing from the continent to the north (Fig. 176). Along 

 the mainland, a fairly strong and constant easterly wind (Fig. 177) 

 deflects the current to the west, so that it flows in a north-western direction. 

 The direction of the wind farther north - between 40° and 50"" S. -becomes 

 westerly and its force much more violent, for these are the 'Roaring 

 Forties' which churn up waves high as houses and which are dreaded by 

 sailors all over the world. 



Oceanographers speak of it as the West Wind Drift, and where the cold 

 surface current from the Antarctic meets the West Wind Drift at about 

 50° to 55° S. (the so-called Antarctic Convergence), the current turns 

 downwards and splits into two (Fig. 176). One branch, the Antarctic 

 intermediate water, flows north at about 400 fathoms below the surface 

 where it can usually be followed right up to the equator, while another 

 branch returns to the Antarctic below 100 fathoms, rises to the surface 

 near the continent, surrenders its heat, and again becomes the original 

 surface current flowing N.W. The current returning to the continent (the 

 so-called deep current) has gained heat because, near the Antarctic 



