Primary Production in the Indian Ocean II
129
creased slowly to 25 mgC m- 2 h- 1 in April-May, then sharply to 45 mgC m- 2 h- 1 in
late May, and remained at that level until August. Mean productivity for the year was
37 mgC m- 2 h- 1 • The depth of the layer in which a significant amount of photosynthesis
(more than 0.10 mgC m- 3 h- 1 ) was measured in samples exposed to constant saturating
light varied between 130 m in October and 60 m in January. In January- February
there was low productivity (approximately 4 mgC m- 2 h- 1 ). In April-May the productivity remained uniform along the meridian but increased to 24 mgC m -2 h -1. At
other times there were 4 latitudinal intervals with distinctive seasonal variations. From
9 to 15 ° 5, waters with high productivity and sharp stratification, caused by equatorial
upwelling, were found during the period from May to October.
On the other hand, the mean daily rate of primary production estimated by the
simulated in situ method in the region along llO 0 E varied from 0.13 gC m -2d- 1 in
August to 0.08 gC m- 2 d- 1 in October to early May, rising sharply in late May to 0.18 gC
m- 2 d- 1 and again in early August to 0.27 gC m- 2 d- 1 • High values (more than 0.3 gC
m- 2 d- 1 ) were obtained in waters from 9 to 15
0
5 in June-August. The depth of the
euphotic zone varied between 76 m in October and 63 min July- August, with a mean
of 68 m. Months and latitudes with high daily rates of primary production, as mentioned
above, agree with those of high chlorophyll concentration but the depth of the chlorophyll
maximum does not necessarily coincide with that of maximum productivity.
KABANOVA (1968), summarizing the results of primary production measurements
in the Indian Ocean by the expeditions of various countries, indicated that the period
of summer 5W monsoon was more productive than the period of the winter NE monsoon.
III. Nutrients and Primary Production
5TEEMANN NIELSEN and AABYE JENSEN (1957) discussed the relation of the photosynthetic activity of phytoplankton to the concentrations of phosphate and nitrate in
the Indian Ocean. PANIKKAR (1969) illustrated the regions of high phosphate concentration in the Indian Ocean in relation to productivity. In some regions the concentration
of phosphate seems to be limiting the primary production. KABANOVA (1961) concluded
that the level of primary production was controlled by the content of biogenous elements
especially by the content of N; on the other hand, phosphate and nitrate would rapidly
be exhausted with increasing primary production (KABANOVA, 1964).
MAXIMOVA (1971) summarized the distribution of nutrients in relation to primary
productivity. The distribution of primary production in the areas north of 40° 5 followed
the same general pattern as that of nutrients. There was positive correlation between the
average values in 5° latitudinal zones of the primary production and of the nutrients in
the surface 100 m layer. In the 100 - 200 m layer the correlation of primary production
and nutrients was less distinct. In the regions where the intensity of phytoplankton
photosynthesis was not restricted by light, high levels of primary production were
observed in the areas with phosphate content in the 100 m surface layer above 60 ,ug-at
m- 2 , and primary production was characteristically low where phosphate was below
40 ,ug-at m -2.
IV. Distribution of Primary Production
RYTHER et ai. (1966) reported the distribution of the daily rate of primary production
in the western Indian Ocean. KABANOVA (1968) summarized the distribution of the mean
129
creased slowly to 25 mgC m- 2 h- 1 in April-May, then sharply to 45 mgC m- 2 h- 1 in
late May, and remained at that level until August. Mean productivity for the year was
37 mgC m- 2 h- 1 • The depth of the layer in which a significant amount of photosynthesis
(more than 0.10 mgC m- 3 h- 1 ) was measured in samples exposed to constant saturating
light varied between 130 m in October and 60 m in January. In January- February
there was low productivity (approximately 4 mgC m- 2 h- 1 ). In April-May the productivity remained uniform along the meridian but increased to 24 mgC m -2 h -1. At
other times there were 4 latitudinal intervals with distinctive seasonal variations. From
9 to 15 ° 5, waters with high productivity and sharp stratification, caused by equatorial
upwelling, were found during the period from May to October.
On the other hand, the mean daily rate of primary production estimated by the
simulated in situ method in the region along llO 0 E varied from 0.13 gC m -2d- 1 in
August to 0.08 gC m- 2 d- 1 in October to early May, rising sharply in late May to 0.18 gC
m- 2 d- 1 and again in early August to 0.27 gC m- 2 d- 1 • High values (more than 0.3 gC
m- 2 d- 1 ) were obtained in waters from 9 to 15
0
5 in June-August. The depth of the
euphotic zone varied between 76 m in October and 63 min July- August, with a mean
of 68 m. Months and latitudes with high daily rates of primary production, as mentioned
above, agree with those of high chlorophyll concentration but the depth of the chlorophyll
maximum does not necessarily coincide with that of maximum productivity.
KABANOVA (1968), summarizing the results of primary production measurements
in the Indian Ocean by the expeditions of various countries, indicated that the period
of summer 5W monsoon was more productive than the period of the winter NE monsoon.
III. Nutrients and Primary Production
5TEEMANN NIELSEN and AABYE JENSEN (1957) discussed the relation of the photosynthetic activity of phytoplankton to the concentrations of phosphate and nitrate in
the Indian Ocean. PANIKKAR (1969) illustrated the regions of high phosphate concentration in the Indian Ocean in relation to productivity. In some regions the concentration
of phosphate seems to be limiting the primary production. KABANOVA (1961) concluded
that the level of primary production was controlled by the content of biogenous elements
especially by the content of N; on the other hand, phosphate and nitrate would rapidly
be exhausted with increasing primary production (KABANOVA, 1964).
MAXIMOVA (1971) summarized the distribution of nutrients in relation to primary
productivity. The distribution of primary production in the areas north of 40° 5 followed
the same general pattern as that of nutrients. There was positive correlation between the
average values in 5° latitudinal zones of the primary production and of the nutrients in
the surface 100 m layer. In the 100 - 200 m layer the correlation of primary production
and nutrients was less distinct. In the regions where the intensity of phytoplankton
photosynthesis was not restricted by light, high levels of primary production were
observed in the areas with phosphate content in the 100 m surface layer above 60 ,ug-at
m- 2 , and primary production was characteristically low where phosphate was below
40 ,ug-at m -2.
IV. Distribution of Primary Production
RYTHER et ai. (1966) reported the distribution of the daily rate of primary production
in the western Indian Ocean. KABANOVA (1968) summarized the distribution of the mean