is established in the water after the winter mixing, caused by cooling 

 and, possibly, by the winds. In the winter, there are small, short, 

 sporadic pulses of phytoplankton, depending on the weather, since, in 

 contrast to boreal waters, the intensity of light in the winter is not 

 so low as to prevent development of algae. In the summer, thermal 

 stratification is established and phytoplankton is scarce. Its production 

 depends on the recycling of nutrients and random mixing of the water 

 during storms (Riley, 1957; Menzel , Ryther, 1960). 



Apparently, in other oceans as well around the periphery of the 

 tropical area the winter cooling is of great significance for the mixing 

 of water, enrichment of the surface layers of the water with nutrients and 

 subsequent development of plankton. For example, in the Pacific Ocean 

 in the region of 40-26°N along 155°W, the winter development of phyto- 

 plankton is explained by the deepening of the thermocline due to cooling, 

 as a result of which the nutrients reach the euphotic zone, where they 

 are immediately utilized by the phytoplankton, so that the increase in 

 their quantity is almost unnoticeable (McGowan, Williams, 1973). 



In the southern Indian Ocean, to the west of Australia (see Fig. 21), 

 in the region of 18-32°S, the decrease in the quantity of phytoplankton 

 at the end of southern hemisphere summer results from thermal stratifi- 

 cation. The increase in the quantity of phytoplankton in the winter 

 corresponds to the breakdown of this stratification. The quantity of 

 nutrients changes very little from season to season, which is also 

 apparently related to the immediate consumption of nutrient salts by the 

 algae (Tranter, 1973). 



In the lower latitude tropical regions, winter cooling does not 

 occur, thermal stratification is well developed for a long period of 

 time, and the most important factor in the seasonal development of the 

 plankton is the wind. The winds cause mixing of the water or shifting 

 of currents and the related upwelling of water. 



In the eastern Indian Ocean (see Fig. 21), between 9 and 18°S, the 

 increase in the quantity of phytoplankton and zooplankton in the winter 

 is related to the upwelling of water in the southern equatorial current 

 caused by the monsoon (Tranter, 1973). This region belongs to a distant 

 neritic community, but even within the equatorial community of the 

 Indian Ocean, the succession of monsoons has a significant influence on 

 the course of development of plankton (Kabanova, 1968). 



In the equatorial community of the Pacific Ocean in the region 

 between 120°W and 180°W from 5°S to 10°N, the maximum of seston is 

 noted in April-June in the Equatorial Countercurrent, and in October- 

 December in the South Equatorial Current, which coincides with the 

 reinforcement of the trade winds (King, Hida, 1957). The periodicity of 

 seasonal changes in the quantity of plankton in the distant neritic 

 community of the currents along the western coasts of the continents is 

 related to the upwelling of water as has been shown, e.g., for the 

 region of the California Current. The upwelling of water itself depends 

 on the wind regime (Walsh et al . , 1974). 



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