-96- 



Passage, Gerlache Straits, Bransfield Straits, and northern 

 and southwestern Weddell Sea. He also estimated the Atlantic 

 sector to be five times as rich as the Pacific sector. 

 Despite general agreement on geographical production variation, 

 conclusions should be drawn with caution. First, techniques 

 vary among investigators and are not standardized. A more 

 serious problem is the lack of systematic time-spatial 

 studies of productivity. Up to now, most studies have 

 sampled phytoplankton in limited areas at intermittent time 

 periods thus making it difficult to separate geographical 

 from seasonal or yearly variations. Ideally, representative 

 Southern Ocean areas should be studied simultaneously. 



Currents may also influence productivity. El-Sayed 

 (1968) attributed the low productivity of the Convergence 

 and other areas to surface water instability. Sverdrup 

 (1955) stated that vertical mixing maintains high productivity 

 levels while Fogg (1977) reported that "areas of high primary 

 productivity are those in which comparative stability of the 

 water column occurs." Hart (1942) concludes that the continental 

 shelf, by causing upwelling, is responsible for high productivity 

 values. Russell-Hunter (1970) agreed that the rich trophic 

 conditions of the Antarctic are due to ascending nutrient- 

 rich water. Even from this brief review, it is evident that 

 the relationship between currents and productivity is not 

 fully understood. Some consider currents and upwelling 

 important for supplying nutrients while others believe 

 stable water conditions to be conducive to high productivity. 



Seasonality has a major impact on primary productivity 

 in the Antarctic. Early studies by Hart (1934, 1942) showed 

 productivity to be limited to summer months. Moiseev (1971) 

 found that phytoplankton grows for 7-8 months at 55° S. to 

 56° S.; for 6 months at 60° S. to 65° S . ; and for less than 

 3 months south of 65° S. El-Sayed (1970) found a seasonal 

 variation in the concentration of chlorophyll-a and carbon 

 14 uptake with highest levels occurring in the summer and 

 lower levels during the winter. Foxton (1964), in examining 

 different euphotic zone levels at different times of the 

 year, found high productivity in upper levels during the 

 summer and lower productivity in lower levels. The opposite 

 occurred in winter. Further winter studies would help to 

 clarify ambiguities in this area. 



Closely related to seasonality is the amount of solar 

 radiation available for photosynthesis. El-Sayed and Mandelli 



