i(j8 



DISCOVERY REPORTS 



60 u SO" 40" 30" 20" IO' 



90" 80" 70" 60" SO" 40" 30" 20" IO 



IO" 20" 



Fig. 47. The distribution of the layer of minimum oxygen in the South Atlantic Ocean. From Wiss. Ergebn. dtsch. Atlant. 

 Exped. 'Meteor', Bd. ix, Beil. xxxvu. This figure shows the oxygen content at a depth of 300 m. 



Normal and abnormal conditions within the current 

 A comparison of the dissolved oxygen sections for survey I and survey II (Figs. 38-40 and 41-4) 

 shows that the oxygen depletion on the continental shelf was much more pronounced during survey I, 

 and in particular in the Walvis Bay region where even at the sea-surface inshore (WS 981) the oxygen 

 content was only 0-33 c.c. 2 /l. The consequences of such an immense depletion of dissolved oxygen 

 are discussed later (p. 199) in the consideration of its effects upon fish mortality, but for the present 

 we must consider what conditions lead up to such a catastrophic event. 



The maintenance of aerobic conditions on the continental shelf must be dependent to a great extent 

 upon the renewal of oxygen by turbulent processes. In this case one would expect, as indeed is shown 

 by the results of survey II, that in the conditions which set up a strong northerly current the introduc- 

 tion of more highly oxygenated water would be at its maximum, and the oxygen on the continental 

 shelf would probably be continually renewed. 



But if the currents were slowed down, stopped or even reversed, then the converse might be expected 

 to occur. The turbulent renewal of oxygen would be at its minimum, the effects of decomposition on 



