128
Y. ARUGA:
depth of maximum photosynthetic activity was always deeper than the depth of maximum
production in the in situ experiments.
Chlorophyll a in the eastern part of the Indian Ocean was generally low from
December to January, being about 0.1 mg m- 3 in the north and less than 0.05 mg m- 3
in the south at the surface to the west of 1000 E, and about 0.05 mg m- 3 at the surface
to the east of 100 0 E. Maximum chlorophyll concentration was often observed in the
lower part of the euphotic zone, 50 -125 meg. 50 -75 m in the equatorial region and
100-125 m in the south, corresponding to the upper limit of the thermocline. The depth
of maximum chlorophyll concentration did not coincide with the depth of maximum
photosynthetic acitivity obtained by the tank experiments. The results of the tank experiments suggested that the chlorophyll at the depth of the chlorophyll maximum had
almost lost its photosynthetic ability (SAI]O, 1965).
Daily primary production estimated by the in situ experiments from December to
january was generally 0.1-0.2 gC m- 2 d- 1 in the eastern Indian Ocean. Comparatively
high values, 0.3-0.7 gC m- 2 d-l, were obtained in the region to the south of Java,
corresponding to the region of upwelling with high photosynthetic rate of phytoplankton,
though the chlorophyll content of water was rather low. WYRTKI (1962) reported that
during the SE monsoon the region is characterized by very high concentrations of inorganic phosphate at the bottom of the euphotic layer and by a high plankton biomass;
the transparency of the water is low, indicating a high concentration of suspended matter.
RYTHER and MENZEL (1965) obtained a linear regression of the C m -2 assimilation
under natural illumination on living C m -2, both values integrated over the euphotic
zone.
The depth of the euphotic zone is, in general, inversely related to the amount of
chlorophyll and other suspended and dissolved materials in water which characteristically
absorb light (ARUGA and ICHIMURA, 1968). The light attenuation in water, together with
the weather conditions, determines the lower limit of photosynthetic activity of phytoplankton near the bottom of the euphotic zone. This consequently influences the integrated daily primary production over the euphotic zone (STEEMANN NIELSEN and AABYE
JENSEN, 1957). The depth of the euphotic zone in the Indian Ocean varies with region
as well as with season according to the variations of solar radiation on the sea surface
and the attenuation coefficient. PANIKKAR (1969) summarized the amount of chlorophyll
in the water column under unit area of sea surface in various regions of the Indian Ocean
in relation to upwelling and monsoons. In the SW part of the Indian Ocean to the Antarctic Ocean ICHIMURA and FUKUSHIMA (1963) made measurements of chlorophyll in the
surface water and found that the amount of chlorophyll increased from the Indian Ocean
to the Antarctic Ocean.
II. Seasonal Variations of Primary Production
Very few areas have been studied. Fairly intensive studies have been made in the
southeast Indian Ocean, especially along 110 0 E by Australian scientists (HUMPHREY,
1966; HUMPHREY and KERR, 1969; JITTS, 1969). Mean primary productivity (cumulative
light-saturated photosynthesis obtained by tank experiments) of the column from 0 to
150 m increased from 50 mgC m- 2 h- 1 in August to a maximum (62 mgC m- 2 h- 1 ) in
October, then decreased to a minimum (4 mgC m- 2 h- 1 ) in January, after which it in-
Y. ARUGA:
depth of maximum photosynthetic activity was always deeper than the depth of maximum
production in the in situ experiments.
Chlorophyll a in the eastern part of the Indian Ocean was generally low from
December to January, being about 0.1 mg m- 3 in the north and less than 0.05 mg m- 3
in the south at the surface to the west of 1000 E, and about 0.05 mg m- 3 at the surface
to the east of 100 0 E. Maximum chlorophyll concentration was often observed in the
lower part of the euphotic zone, 50 -125 meg. 50 -75 m in the equatorial region and
100-125 m in the south, corresponding to the upper limit of the thermocline. The depth
of maximum chlorophyll concentration did not coincide with the depth of maximum
photosynthetic acitivity obtained by the tank experiments. The results of the tank experiments suggested that the chlorophyll at the depth of the chlorophyll maximum had
almost lost its photosynthetic ability (SAI]O, 1965).
Daily primary production estimated by the in situ experiments from December to
january was generally 0.1-0.2 gC m- 2 d- 1 in the eastern Indian Ocean. Comparatively
high values, 0.3-0.7 gC m- 2 d-l, were obtained in the region to the south of Java,
corresponding to the region of upwelling with high photosynthetic rate of phytoplankton,
though the chlorophyll content of water was rather low. WYRTKI (1962) reported that
during the SE monsoon the region is characterized by very high concentrations of inorganic phosphate at the bottom of the euphotic layer and by a high plankton biomass;
the transparency of the water is low, indicating a high concentration of suspended matter.
RYTHER and MENZEL (1965) obtained a linear regression of the C m -2 assimilation
under natural illumination on living C m -2, both values integrated over the euphotic
zone.
The depth of the euphotic zone is, in general, inversely related to the amount of
chlorophyll and other suspended and dissolved materials in water which characteristically
absorb light (ARUGA and ICHIMURA, 1968). The light attenuation in water, together with
the weather conditions, determines the lower limit of photosynthetic activity of phytoplankton near the bottom of the euphotic zone. This consequently influences the integrated daily primary production over the euphotic zone (STEEMANN NIELSEN and AABYE
JENSEN, 1957). The depth of the euphotic zone in the Indian Ocean varies with region
as well as with season according to the variations of solar radiation on the sea surface
and the attenuation coefficient. PANIKKAR (1969) summarized the amount of chlorophyll
in the water column under unit area of sea surface in various regions of the Indian Ocean
in relation to upwelling and monsoons. In the SW part of the Indian Ocean to the Antarctic Ocean ICHIMURA and FUKUSHIMA (1963) made measurements of chlorophyll in the
surface water and found that the amount of chlorophyll increased from the Indian Ocean
to the Antarctic Ocean.
II. Seasonal Variations of Primary Production
Very few areas have been studied. Fairly intensive studies have been made in the
southeast Indian Ocean, especially along 110 0 E by Australian scientists (HUMPHREY,
1966; HUMPHREY and KERR, 1969; JITTS, 1969). Mean primary productivity (cumulative
light-saturated photosynthesis obtained by tank experiments) of the column from 0 to
150 m increased from 50 mgC m- 2 h- 1 in August to a maximum (62 mgC m- 2 h- 1 ) in
October, then decreased to a minimum (4 mgC m- 2 h- 1 ) in January, after which it in-