Vertical Distribution of Chlorophyll a Along the Water Column

Platt et al. (1988a) and Platt and Sathyendranath (1988b) proposed an empirical equation to represent a vertical distribution of chlorophyll a concen tration with the Gaussian distribution. In contrast to these empirical equations, a vertical distribution of chlorophyll a concentration is proposed by the following empirical equation as a function of a vertical distribution of PAR and chlorophyll a concentration in the surface.

C(z) = [1 -(0.9 + 0.7Co) exp{-0.8PAR%(z, Co)}] exp{-0.8PAR%(z, Co)} + Co

The equation (8) reproduces a constant concentration of chlorophyll a from the surface to the just above of the chlorophyll maximum. The chlorophyll maximum and following vertical distribution of chlorophyll a are observed just on the slant line of the vertical distribution of PAR. Fig. 3 shows vertical

0.00

1.00

 0 -20 -40 (m) -60 JI & -80

1.00 EdPAR

10.00 100.00

0.01

0.10

1.00 EdPAR

10.00 100.00

Chl-a (0.5 mg m-3) 00 0.20 0.40 0.60 0.80 1.00 1.20 1.40

Chl-a (0.5 mg m-3) 00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 100.00

100.00

0.01 1 1 0.10 100.00 Figure 3: Vertical distribution of chlorophyll a concentration based on vertical distribution of photosynthetically available radiation (PAR). The PAR along the water column is given by the equation (7). Then the equation (8) estimates the vertical distribution of chlorophyll a concentration (a) for 0.2 mgm-3, (b) for 0.5 mgm-3, (c) for 1.0 mgm- , and (d) for 5.0 mgm-3 chlorophyll a concentration on the surface. Second X-axis of each figure varies to keep an overlap between vertical distribution lines of PAR and chlorophyll a concentration around the chlorophyll maximum. distributions of chlorophyll a concentration based on vertical distributions of PAR for a different full scale of chlorophyll a concentration on the second X-axis. The full scale of chlorophyll a concentration on the second X-axis is empirically adjusted to match a slant line of PAR with a slant line of chlorophyll a concentration for the depth deeper than chlorophyll maximum. Two bold lines on Fig. 3a represent vertical distributions of PAR and chlorophyll a in case of the surface chlorophyll a concentration being 0.2 mgm-3 with a full scale of chlorophyll a concentration for 1.0 mgm-3 on the second X-axis. Fig. 3a shows a deep chlorophyll maximum around 100 m and chlorophyll a concentration decreases to 150 m along a vertical distribution of PAR. Two bold lines in Fig. 3b are in case of the surface chlorophyll a concentration being 0.5 mgm-3 with a full scale of chlorophyll a concentration for 1.4mgm-3. Fig. 3b shows a deep chlorophyll maximum around 60 m. Two bold lines on Fig. 3c are in case of the surface chlorophyll a concentration being 1.0 mgm-3 with a full scale of chlorophyll a concentration for 2.5mgm-3. Fig. 3c shows a subsurface chlorophyll maximum around 40 m. Chlorophyll a concentration decreases along a vertical distribution of PAR and a valid range of chlorophyll a concentration is limited to around 60 m, where PAR percentage to the surface is about 0.1%. Two bold lines on Fig. 3d are in case of the surface chlorophyll a concentration being 5.0 mgm-3 with a full scale of chlorophyll a concentration for 9.0 mgm-3. Fig. 3d shows a surface chlorophyll maximum. A valid range of chlorophyll a concentration is limited to around 30 m where PAR percentage to the surface is about 0.1%, although chlorophyll a concentration is plotted to 80 m. The vertical distributions of chlorophyll a concentration are determined by equations (7) and (8) as a function of chlorophyll a concentration in the surface. Equation (7) determines light penetration field. Equation (8) determines vertical distribution of chlorophyll a along the light penetration field. In this hypothesis, a diffused attenuation coefficient of water is determined by chlorophyll a concentration only and there is a possibility of error to estimate vertical distribution of chlorophyll a concentration in the case of water, where suspended sediment's phytoplankton exists in addition to phytoplankton.