2.6
The Formation of the Chlorophyll Maximum
in the Indian Ocean
Y. SAI]O
I. Vertical Distribution of Chlorophyll
A typical section of chlorophyll a distribution is shown in Fig. 1. As for the surface
water, the amount of chlorophyll a was 0.1 mg m- 3 in the nothern area and below 0.05 mg
m- 3 in the southern area. A distinct chlorophyll maximum was found in the layers at
N 50
50
]
~
g.100
o
150
. I
.
/
( , //:-\ '
'- )
I
\
. , . , / ":,,, .
............ ",,, "
Fig. 1. Vertical distribution of chlorophyll a (mg m- 3 ) from samples of the TS "Kagoshima Maru",
Dec. 1963 to Jan. 1964, along 78° E longitude. (Data from ENDO and NOZAWA)
depths of 50 to 75 m in the north near the Equator (0.3-0.6 mg m- 3 ), and at 100 to 125 m
in the south (0.2-0.3 mg m- 3 ). In this area the layer of the chlorphyll maximum was
generally located in the upper part of the thermocline.
The vertical distribution of chlorophyll a and photosynthesis at a station of the same
longitude (78 0 E) is shown in Fig. 2. At this station, the Secchi disk reading was 28 m.
The chlorophyll maximum was observed at 100 m, while the maxima of phytosynthesis
determined by 14C in in situ and tank techniques were found at 75 m and 50 m depth
respectively. At the depth of chlorophyll maximum, there is still considerable in situ
photosynthesis, about one third of that of the maximum value at the 50 m layer, and a
minimum in nutrients such as silicate, phosphate and nitrate. This suggests that the
The Formation of the Chlorophyll Maximum
in the Indian Ocean
Y. SAI]O
I. Vertical Distribution of Chlorophyll
A typical section of chlorophyll a distribution is shown in Fig. 1. As for the surface
water, the amount of chlorophyll a was 0.1 mg m- 3 in the nothern area and below 0.05 mg
m- 3 in the southern area. A distinct chlorophyll maximum was found in the layers at
N 50
50
]
~
g.100
o
150
. I
.
/
( , //:-\ '
'- )
I
\
. , . , / ":,,, .
............ ",,, "
Fig. 1. Vertical distribution of chlorophyll a (mg m- 3 ) from samples of the TS "Kagoshima Maru",
Dec. 1963 to Jan. 1964, along 78° E longitude. (Data from ENDO and NOZAWA)
depths of 50 to 75 m in the north near the Equator (0.3-0.6 mg m- 3 ), and at 100 to 125 m
in the south (0.2-0.3 mg m- 3 ). In this area the layer of the chlorphyll maximum was
generally located in the upper part of the thermocline.
The vertical distribution of chlorophyll a and photosynthesis at a station of the same
longitude (78 0 E) is shown in Fig. 2. At this station, the Secchi disk reading was 28 m.
The chlorophyll maximum was observed at 100 m, while the maxima of phytosynthesis
determined by 14C in in situ and tank techniques were found at 75 m and 50 m depth
respectively. At the depth of chlorophyll maximum, there is still considerable in situ
photosynthesis, about one third of that of the maximum value at the 50 m layer, and a
minimum in nutrients such as silicate, phosphate and nitrate. This suggests that the