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and autumn and
ʴ
=
ʴ w in winter. In further results, it was taken
ʴ w = 0.5
°
,
ʴ s =1
°
(Krapivin 1996).
Seasonal and latitudinal temperature variations are known to occur in the PCE
area. The natural cycles of such variations have been incorporated in the model by
consulting the available real data and it appears interesting to consider herein the
departures of temperature from these model values. Figure 4.7 shows the biomass
of the anchovy and predatory
fluctuations. As seen from
Fig. 4.7 , if the system is functioning under normal temperature conditions, a clear-
cut division between the habitation areas of the anchovy and predatory
shes versus temperature
fl
fishes is
observed. In this case, the maximum concentration of the anchovy biomass is
observed to occur in the offshore zone about 1.5
° -
2
°
wide in longitude, whereas the
biomass of predatory
fishes attains its maximum concentration in the open ocean.
This pattern is observed throughout the area and appears to be stable 30
40 days
later for the model distributions of temperature. This pattern falls apart as soon as
the overall temperature background is subject to change. A reduction in the general
temperature level by 1 K accounts for the fact that the habitation areas of anchovy
and predatory
-
fishes increasingly intersect. Moreover, in this case their total bio-
mass rises by about 10 %. In the El Ni
ñ
of periods the effect of diffusion of the
ecosystem into the offshore and open-ocean parts disappears completely, being
Fig. 4.7 Effect of the water temperature variations on predatory fishes and anchovy biomass in
PCE at 20 ° S referred to the moment of time at = 100 days. Notation: 1 normal temperature regime;
2 the temperature is decreased by 1 K; 3 El Ni
o regime. The initial data for t = 0 were assumed to
be uniform throughout the area: B 1 = 200, B 2 = 400, B 3 = 80, B 6 = B 7 = B 9 =8,B 4 = 35, B 10 = 700,
B 13 = 3.5
ñ
10 4 , B 5 = 16, B 12 = 200, B 14 = 65 (mg/m 3 ), B 8 = 2 specimens/km 2
·
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