The system of equations of the model was reduced to a finite- 

 difference plan with a time step of one day, a depth step of 10 m. 



Figure 4 shows the change in biomass of elements of this system 

 with the passage of time and, consequently, increasing distance from the 

 zone of the water ascent. The biomass of phytoplankton and bacteria 

 increased most rapidly. The fine filter feeders lagged somewhat in 

 their development, coarse filter feeders developed still more slowly, 

 their biomass reaching its maximum only on day 30 of existence of the 

 system. Nevertheless, their combined effect on phytoplankton and 

 bacterial plankton, in addition to the retarded growth of the bacterial 

 plankton due to exhausting the reserves of biogens, leads to a sharp 

 decrease in the biomass of phytoplankton and bacterial plankton. The 

 inertia of the predators is still greater than that of the filter 

 feeders: the biomass of the various groups of predators reaches its 

 maximum only on day 35-50 of existence of the community. 



On day 50-60, the system reaches a state which is near steady. It 

 is characterized by low biomass of living elements and balance between 

 production and consumption of phytoplankton. This mature state of the 

 community typically shows little variability of the elements with 

 further passage of time and, consequently, little variability in space, 

 and is the state observed in oligotrophic water areas in the tropical 

 regions of the ocean, particularly the halistatic zones of the planetary 

 convergences. 



The model data agree qualitatively quite well with data obtained by 

 observation in the ocean. A comparison of the values of biomass of the 

 elements of the ecosystem obtained from the model with those observed in 

 the field is presented in Table 1. Considering the relative coarseness 

 of the model, its agreement with the original can be considered 

 acceptable. 



The model changes in vertical distribution of the elements of the 

 ecosystem with time are presented in Figure 5. During the early period 

 (t = 5 days), when the total quantity of phytoplankton was almost 

 maximal, its biomass was evenly high in the 10-50 m layer. All the 

 other living elements of the ecosystem have a more or less sharply 

 expressed maximum, related to the thermocline. However, by the 10th day 

 the reserve of nutrients in the upper layer was almost completely 

 exhausted, while at a depth of 10-20 m the maximum biomass of the 

 phytoplankton was still retained. Deeper, at the upper boundary of the 

 thermocline, nutrients passing through the thermocline began to form a 

 second, lower, maximum, which was still poorly expressed. This dual- 

 maximum structure is characteristic for the vertical distribution of 

 almost all elements of the ecosystem (Vinogradov et al., 1971). 



As the stock of nutrients in the surface layer decreased, the 

 vertical transfer of nutrients from beneath the discontinuity layer 

 continued to play an increasingly significant role in the functioning of 

 the ecosystem. The lower maximum of biomass of phytoplankton became 

 greater than the upper maximum. As the thermocline continued to descend 

 to 80-100 m and deeper, the illumination at its upper boundary became 



330 



