Shelton and Hutchings: Ocean stability and anchovy spawning in southern Benguela Current region 



329 



50 



100 



50 



X 



100 



50 



— r- 



40 



SUMMER WINTER 



DISTANCE OFFSHORE (n. miles) 

 30 20 10 50 40 30 20 



r 



50 



100 



Figure 6 



Summer (January 1978) and winter (August 1977) sections of temperature, microplankton. and chlorophyll-o values along line 44 

 just north of Cape Town, South Africa. 



1984, Largier and Swart 1987). Microplankton parti- 

 cle concentrations tend to be low in the well-mixed 

 water column but chlorophyll-a concentrations can be 

 quite high, either if nutrients accumulated in bottom 

 sediments are mixed into the euphotic zone by strong 

 storm action (Shannon et al. 1984), or if periods of calm 

 weather persist long enough for the water column to 



stabilize, albeit weakly, and phytoplankton is thereby 

 allowed to remain in the euphotic zone long enough to 

 grow. 



A section just north of Cape Town (Fig. 6) shows the 

 strong temperature front in summer between cold 

 upwelled water inshore and warm water offshore. En- 

 hanced levels of microplankton occurred in the vicinity 



