Light and Nutrients in the Indian Ocean
95
f3f3) Particulate and Dissolved Organic Phosphorus
When particulate and dissolved organic phosphorus values for the photic zone
(0- 200 m) are analysed, the particulate values appear to be nearly constant at 0.03 to
0.04 ,ug-at 1-1 for the whole western Indian Ocean, as seen in Table 5. This represents
about one fifth of the total organic phosphorus, while the remaining four fifth occurs as
dissolved organic phosphorus (0.15 to 0.18 ,ug-at 1-1). The values of dissolved organic
phosphorus are not widely divergent, although a decline toward lower concentrations
from 20° S to 32° S may be noted. When the total organic phosphorus levels from
0- 200 m and 200-1000 m are compared, it can be seen that the productivity near 20° S
has a consistent and pronounced effect on the data at this season for the year.
There is no pronounced accumulation of organic phosphorus at the Equator at any
depth, as was found for the Atlantic Ocean. The decline in the southerly latitudes is in
marked contrast to the increasing organic phosphorus levels as one moves southward
in the Atlantic Ocean (MCGILL, 1963). Presumably, such differences reflect the variable
influence of Antarctic water masses in the two areas.
b) Eastern Indian Ocean and Bay of Bengal
Details on the distribution of organic phosphorus in the eastern Indian Ocean are
somewhat more limited. RAO and RAO (1968) present some data on particulate and
dissolved organic phosphorus fractions for areas of the Bay of Bengal along with the
distribution of total phosphorus and inorganic phosphate. Particulate organic P values
are shown to be very low in all depth levels throughout the area, much as in the western
Indian Ocean regions. However, the high total phosphorus values found are due in part
to large quantities of dissolved organic phosphorus which makes up 80 to 90% of the
total organic phosphorus throughout the region so that the particulate organic portion
becomes almost negligible.
The data of RAO and RAO are presented in a slight rearrangement in Table 6. The
mean values given are not derived from a frequency distribution analysis as with the
western Indian Ocean areas. Spacing of the data was selected to give an indication of the
variation for depth of each phosphorus fraction. It is clear from the Table that the
Andaman Sea has lower organic phosphorus values than the area near the Burmese
coast, while the northern Bay of Bengal region shows high levels of organic phosphorus
in the surface waters. Values obtained for depths below 1000 m in the Bay of Bengal
area, however, do not show any significant concentrations of organic phosphorus in
any form.
KUMARI (1968) has examined phosphorus fractions in Porto Novo waters and has
reported on conditions in the mouth of the Vellar estuary as compared with the 10 fathom
depth offshore. His data are summarized in Table 7. In the estuary, all phosphorus
fractions at the surface are minimal in September and maximum in January. At the 10
fathom line, total phosphorus and dissolved organic phosphorus are at a maximum in
March and at a minimum in May. KUMARI suggests that his data show rapid recycling
rates for phosphorus, as well as the effects of discharge from the Vellar estuary. "The
high concentration of organic phosphorus may mostly be due to the rapid oxidation of
plankton, detritus and decomposing matter. But as the waters are nearshore, and mixed
with the discharge of the estuarine waters of the Vellar river, it may be expected to contribute to the high concentration of organic phosphorus ... The high phosphorus content
95
f3f3) Particulate and Dissolved Organic Phosphorus
When particulate and dissolved organic phosphorus values for the photic zone
(0- 200 m) are analysed, the particulate values appear to be nearly constant at 0.03 to
0.04 ,ug-at 1-1 for the whole western Indian Ocean, as seen in Table 5. This represents
about one fifth of the total organic phosphorus, while the remaining four fifth occurs as
dissolved organic phosphorus (0.15 to 0.18 ,ug-at 1-1). The values of dissolved organic
phosphorus are not widely divergent, although a decline toward lower concentrations
from 20° S to 32° S may be noted. When the total organic phosphorus levels from
0- 200 m and 200-1000 m are compared, it can be seen that the productivity near 20° S
has a consistent and pronounced effect on the data at this season for the year.
There is no pronounced accumulation of organic phosphorus at the Equator at any
depth, as was found for the Atlantic Ocean. The decline in the southerly latitudes is in
marked contrast to the increasing organic phosphorus levels as one moves southward
in the Atlantic Ocean (MCGILL, 1963). Presumably, such differences reflect the variable
influence of Antarctic water masses in the two areas.
b) Eastern Indian Ocean and Bay of Bengal
Details on the distribution of organic phosphorus in the eastern Indian Ocean are
somewhat more limited. RAO and RAO (1968) present some data on particulate and
dissolved organic phosphorus fractions for areas of the Bay of Bengal along with the
distribution of total phosphorus and inorganic phosphate. Particulate organic P values
are shown to be very low in all depth levels throughout the area, much as in the western
Indian Ocean regions. However, the high total phosphorus values found are due in part
to large quantities of dissolved organic phosphorus which makes up 80 to 90% of the
total organic phosphorus throughout the region so that the particulate organic portion
becomes almost negligible.
The data of RAO and RAO are presented in a slight rearrangement in Table 6. The
mean values given are not derived from a frequency distribution analysis as with the
western Indian Ocean areas. Spacing of the data was selected to give an indication of the
variation for depth of each phosphorus fraction. It is clear from the Table that the
Andaman Sea has lower organic phosphorus values than the area near the Burmese
coast, while the northern Bay of Bengal region shows high levels of organic phosphorus
in the surface waters. Values obtained for depths below 1000 m in the Bay of Bengal
area, however, do not show any significant concentrations of organic phosphorus in
any form.
KUMARI (1968) has examined phosphorus fractions in Porto Novo waters and has
reported on conditions in the mouth of the Vellar estuary as compared with the 10 fathom
depth offshore. His data are summarized in Table 7. In the estuary, all phosphorus
fractions at the surface are minimal in September and maximum in January. At the 10
fathom line, total phosphorus and dissolved organic phosphorus are at a maximum in
March and at a minimum in May. KUMARI suggests that his data show rapid recycling
rates for phosphorus, as well as the effects of discharge from the Vellar estuary. "The
high concentration of organic phosphorus may mostly be due to the rapid oxidation of
plankton, detritus and decomposing matter. But as the waters are nearshore, and mixed
with the discharge of the estuarine waters of the Vellar river, it may be expected to contribute to the high concentration of organic phosphorus ... The high phosphorus content