Geoscience Reference
In-Depth Information
where E 0 = E(
φ
,
ʻ
,0,t) is the illumination of the ocean surface,
ʱ
is the coef
cient
of light absorption by the
cients of light
attenuation due to phytoplankton (p), detritus (d), and zooplankton (Z), respec-
tively; u and
filtered sea water;
ʴ
,
ʲ
, and
ʽ
are the coef
, z, t)
closer to a real pattern of illumination changing with depth. It must be noted that the
impact of the biomass of other trophic levels on water transparency is considered to
be negligibly small.
Illumination affects the rate of photosynthesis R p . The R p parameter as a function
of E has a maximum at an optimal value of E max , which drifts from this critical
value when the illumination increases or decreases. A maximum of R p at various
latitudes
ʶ
are the parameters chosen in a concrete situation to bring E(
φ
,
ʻ
is located at depths varying as a function of season (i.e. sun elevation).
Thus, this variability with depth is most pronounced in the tropical zones. On the
average, the photosynthesis maximum is located at depths 10
φ
30 m, and in the open
water bodies it can be observed at depths below 30 m. Here E max =65
-
85 cal/cm 2 /
-
25 cal/cm 2 /day, photosynthesis
decreases in proportion to E. An apparent suppression of phytoplankton by light is
observed at E > 100 cal/cm 2 /day. These estimates are quite different in the northern
latitudes, where the photosynthesis maximum is located
day. Beginning from the depths where E =20
-
on the surface.
The rate of photosynthesis at a depth z depends on the water temperature T W , the
concentration of biogenic elements n, and the phytoplankton biomass p, as well as
on other factors, which are not considered here. To express this dependence, var-
ious equations are used, which in either form re
as a rule
fl
ect the limiting role of the elements
E, n, and p. Considering that
@ p = p @ z const with
increasing n, the following function is taken as the basic one to describe the
photosynthesis intensity at a depth z:
@ p = p @ z
0atn
0 and
R p ðu; k;
z
;
t Þ ¼k 0 T ð K T f 2 ðÞ f 3 ðÞ;
ð 4
:
19 Þ
where
K T ¼ Af 1 ðÞ;
A ¼ kA max =
E max ;
f 1 ðÞ ¼Eexp m 1 E
½
ð
=
E max
Þ
;
ð 4
:
20 Þ
½1 exp fc 2 n g h ;
f 2 ðÞ ¼ 1 exp fc 1 p g ;
f 3 ðÞ ¼
k is the proportion coef
cient; k 0 (T W ) is the function characterizing the dependence of
the rate of photosynthesis on the water temperature T W ; A max is an assimilation
number in the region of maximum photosynthesis (an increment per unit weight of
the phytoplankton organisms);
, and m are the constants the choice of which
can determine the species characteristics of the phytoplankton elements. For A max
the following estimates are valid: A max = 5.94E max in the region of the photosynthesis
minimum and 2.69E max for other regions. According to these estimates, an
assimilation number of the tropical phytoplankton in the region of the maximum
photosynthesis
ʳ 1 ,
ʳ 2 ,
ʸ
12 mgC/h. Thus, for the Peru upwelling
A max = 6.25 mgC/h. The light saturation of photosynthesis in the equatorial regions is
reached at 9 cal/cm 2 /day.
averages
11
-
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