2.2
Primary Production in the Indian Ocean II
Y.ARUGA
The first measurements by the 14C technique were made during the Danish "Galathea"
Expedition (STEEMANN NIELSEN, 1952; STEEMANN NIELSEN and AABYE JENSEN, 1957).
Fairly intensive studies carried out during the International Geophysical Year and the
HOE covered a considerable part of the Indian Ocean (KABANOYA, 1968).
The 14C technique measures the photosynthetic incorporation of carbon into organic
matter and is a value between net photosynthesis and gross photosynthesis (STEEMANN
NIELSEN and HANSEN, 1959). The respiratory rate is important when we consider primary
net production and gross production, especially in evaluating results of in situ measurements of long duration and tank experiments of short duration. This difficulty should
be taken into consideration when we analyze the result of 14C uptake measurements in
relation to environmental factors.
In the present paper, the relation of primary production in the Indian Ocean to chlorophyll, light, nutrients, and other factors will be reviewed and discussed.
I. Standing Stock and Primary Production
RYTHER et al. (1966) and YENTSCH (1965) reported the primary production of the
western Indian Ocean in relation to its chemistry and hydrography. The areas of high
primary production seem to be closely related to the high level of chlorophyll. Vertical
distribution of chlorophyll and phaeophytin generally showed subsurface maximum,
which can be related to the light penetrating the water column and to vertical mixing.
The depth where maximum concentrations of total pigment, chlorophyll, and phaeophytin
occur is greater in stable waters than in less stable waters. In the upper layer of the
euphotic zone, the fraction of chlorophyll in the total pigment is usually greater, and it
decreases with depth in the lower layer. The relation of the chlorophyll-phaeophytin
ratio to light penetration in water is not linear; vertical changes in the ratio are closely
related to the depth of mixed layer or to the extent of vertical mixing of water.
In the eastern part of the Indian Ocean, Japanese scientists carried out measurements
of the photosynthetic rate of phytoplankton and the chlorophyll content of water during
the period from December to January (SAIJO, 1965). Photosynthetic rates measured by
the tank method were generally low except for the region of upwelling south of Java.
West of 100° E, the photosynthetic rate of phytoplankton in water sampled near the
surface was 0.2-0.4 mgC m- 3 h- 1 to the north of 5 0 S and 0.1 mgC m- 3 h- 1 to the south
of 5 0 S. To the east of 100 0 E, it was over 0.4 mgC m -3h -1 to the north of 10 0 Sand
0.1-0.3 mgC m- 3 h- 1 to the south of 10 0 S.
The depth of maximum photosynthetic activity obtained in tank experiments was
25 m in the north on the 78
0
E line, while it was at 50 m or 75 m in the south. The
Primary Production in the Indian Ocean II
Y.ARUGA
The first measurements by the 14C technique were made during the Danish "Galathea"
Expedition (STEEMANN NIELSEN, 1952; STEEMANN NIELSEN and AABYE JENSEN, 1957).
Fairly intensive studies carried out during the International Geophysical Year and the
HOE covered a considerable part of the Indian Ocean (KABANOYA, 1968).
The 14C technique measures the photosynthetic incorporation of carbon into organic
matter and is a value between net photosynthesis and gross photosynthesis (STEEMANN
NIELSEN and HANSEN, 1959). The respiratory rate is important when we consider primary
net production and gross production, especially in evaluating results of in situ measurements of long duration and tank experiments of short duration. This difficulty should
be taken into consideration when we analyze the result of 14C uptake measurements in
relation to environmental factors.
In the present paper, the relation of primary production in the Indian Ocean to chlorophyll, light, nutrients, and other factors will be reviewed and discussed.
I. Standing Stock and Primary Production
RYTHER et al. (1966) and YENTSCH (1965) reported the primary production of the
western Indian Ocean in relation to its chemistry and hydrography. The areas of high
primary production seem to be closely related to the high level of chlorophyll. Vertical
distribution of chlorophyll and phaeophytin generally showed subsurface maximum,
which can be related to the light penetrating the water column and to vertical mixing.
The depth where maximum concentrations of total pigment, chlorophyll, and phaeophytin
occur is greater in stable waters than in less stable waters. In the upper layer of the
euphotic zone, the fraction of chlorophyll in the total pigment is usually greater, and it
decreases with depth in the lower layer. The relation of the chlorophyll-phaeophytin
ratio to light penetration in water is not linear; vertical changes in the ratio are closely
related to the depth of mixed layer or to the extent of vertical mixing of water.
In the eastern part of the Indian Ocean, Japanese scientists carried out measurements
of the photosynthetic rate of phytoplankton and the chlorophyll content of water during
the period from December to January (SAIJO, 1965). Photosynthetic rates measured by
the tank method were generally low except for the region of upwelling south of Java.
West of 100° E, the photosynthetic rate of phytoplankton in water sampled near the
surface was 0.2-0.4 mgC m- 3 h- 1 to the north of 5 0 S and 0.1 mgC m- 3 h- 1 to the south
of 5 0 S. To the east of 100 0 E, it was over 0.4 mgC m -3h -1 to the north of 10 0 Sand
0.1-0.3 mgC m- 3 h- 1 to the south of 10 0 S.
The depth of maximum photosynthetic activity obtained in tank experiments was
25 m in the north on the 78
0
E line, while it was at 50 m or 75 m in the south. The