Geoscience Reference
In-Depth Information
Vertical transport of nutrient salts from under thermocline begins to play a
signi
cant role when biogenic level of upper layers is depleted. Hence, lower
maximum of phytoplankton biomass becomes bigger of upper maximum. Later on
under the thermocline deepening for 80
100 m and more, illumination of its upper
-
boundary is insuf
cient for intensive evolution of the phytoplankton what leads to
the separation of lower maximum from the thermocline. Such effect was observed
by Vinogradov et al. (1970) in a pelagic community of the tropical ocean. Complete
disappearance of lower maximum is observed after 50
60 days for the oligotrophy
-
and ultra-oligotrophy regions.
It is important to assess a sensitivity of upwelling ecosystem to the variations of
environmental parameters and to understand when it is stable. The system is stable
during time T if biomasses of its elements are varied in
'
physiologically acceptable
limits
. Tables
4.7
,
4.8
,
4.9
and
4.10
give some assessments of the model sensitivity
to the variations of its parameters.
As it is seen from Table
4.7
, variations on the food assimilation coef
'
cient by
±
20 % lead to the growth of mean-square deviation of the model trajectory by no
more than 4 % for Z
3
+Z
4
and by 70 % for Z
2
. Microzooplankton and
filtraters are
more sensitive to the variations of the energetic exchange coef
cient (T) and
undigested food coef
cient (H) than predators. The results of Table
4.10
show that
repetitive change of initial biomasses of predators is displayed during no more than
20
-
30 days. After that, ecosystem approaches the stable regime of its evolution.
As it follows from Fig.
4.23
the evolution of the ecosystem depends consider-
ably on the solar radiation. An increase in surface illuminance leads to the insig-
ni
cant deepening of lower maximum and to more consumption of nutrient salts
above thermocline that causes the phytoplankton depression in the surface layer.
Daily illumination equaled 2,000 kcal/m
2
is followed by maximal photosynthesis in
Table 4.7 Variability of the biomasses of upwelling ecosystem elements under the change of its
parameters
D
u
−
1
20 % u
−
1
+20%
t
z
Model
−
−
2
˃
t
z
+2
˃ʱ
+50% k
2
= 0.3
k
2
= 0.2
D
1
0.29
0.35
0.43
0.76
3.36
7.9
1.44
2.6
D
2
0.75
0.91
1.27
1.02
1.71
1.78
3.5
6.0
Notation k
2
is the turbulent coefficient,
ʱ
is the relaxation coefficient of illumination by the depth,
2
4
3
5
1
=
2
Z
200
dz
D
1
¼
1
=
200
Þ
Z
3
u; k;
ð
z
;
40
Þ þ
Z
4
u; k;
ð
z
;
40
Þ
Z
3
Z
4
;
0
2
4
3
5
1
=
2
Z
200
dz
D
2
¼
ð
1
=
200
Þ
Z
2
u; k;
ð
z
;
40
Þ
Z
2
;
0
Z
2
;
Z
3
;
and Z
4
are the observed values of Z
2
, Z
3
, and Z
4
, respectively (Vinogradov et al. 1970);
u
−
1
is the food assimilation coefficient; t
z
is the energy expenses coefficient.
Search WWH ::
Custom Search