Geoscience Reference
In-Depth Information
@
n
=@
t
þ
V
u
@
n
=@u þ
V
k
@
n
=@k þ
V
z
@
n
=@
z
2
n
=@u
2
2
n
=@k
2
2
n
=@
z
2
¼
l
d
d
d
R
p
þ
k
2
;u
@
þ
k
2
;k
@
þ
k
2
;
z
@
ð
4
:
35
Þ
@
g
=@
t
þ
V
u
@
g
=@u þ
V
k
@
g
=@k þ
V
z
@
g
=@
z ¼ T
p
þ
T
b
þ
T
r
þ
T
D
þ
T
Z
C
gb
R
b
2
g
2
2
g
2
2
g
2
2
g
z
2
þ
k
2
;u
@
=@u
þ
k
2
;u
@
=@u
þ
k
2
;k
@
=@k
þ
k
2
;
z
@
=@
ð
4
:
36
Þ
−
where H
a
=(1
h
a
)R
a
is the unassimilated food of the a-th element (a = r, D),
T
a
=t
a
a is the expenditure on energy exchange, M
a
= (
ʼ
a
+
ʼ
a,1
a)a is the mortality,
ˁ
g
is the indicator of the rate of replenishing the supplies of nutrient elements due to
decomposition of the dissolved organic matter,
ʴ
is the coef
cient of consumption
of nutrient elements in the process of photosynthesis.
As follows from Eqs. (
4.32
)and(
4.33
), a supposition that the elements of nekton
and detritus consumers do not move in space with the motion of the water masses is
made in the model. These elements are assumed to migrate independent of the
hydrophysical conditions of their environment. Let us consider two possible ver-
sions of modeling the processes of migration. The
first version is connected with an
addition to the right-hand parts of the Eqs. (
4.32
) and (
4.33
) of the terms describing
the turbulent mixing with the coef
cients k
*
> k
2
. In other words, the process of
migration is identi
ed with the process of an intensi
ed turbulent mixing, that
means it is accidental. However, the process of
fish migration manifests some
expediency in the choice of the direction of their movement. According to the
biological principle of adaptation, the migration of
fish is subject to the principle of
the complex maximization of the ef
cient food ration, with the environmental
parameters remaining within the conditions of their habitat. Hence, the motion of
fish in space with characteristic velocities ensures their location in the regions
where at this time the food and other abiotic conditions (temperature, salinity,
dissolved oxygen, chemicals concentration) are most favourable. This means that
fish migrates in the direction of a maximum gradient of the ef
cient food with the
preserved limitations of the environmental parameters.
4.6.3 The Vertical Structure of the Ocean
To qualitatively assess the role of the World Ocean ecosystems in the global carbon
cycle, it is useful to consider some aspects of the laws of formation of the vertical
distributions of organic matter. According to the Eq. (
4.25
), the number s of
maxima in its solution, p(
φ
,
ʻ
, z, t)ata
fixed time at any point (
φ
,
ʻ
) is determined
by the number l of changes of the sign of the derivative
0.5(1 + l).
It is important to know the location of the phytoplankton biomass maxima as a
function of the depth in order to understand the whole range of the biogeocenotic
processes in the ocean ecosystem. Of course, the amount and the location of the
@
p
=@
z,withs
≤
Search WWH ::
Custom Search