86
D. A. MCGILL:
between r Nand 18
0
N latitudes, from August to early October. SHARMA (1968) finds
the upwelling extending progressively from south to north throughout the period from
February to July/August. This agrees with REDDY and SANKARANARAYANAN (1968,
a and b), for data on the distribution of phosphates and silicates in the upper 200 m.
The regional differences in the concentration of nutrients along the coast in the closing
phase of the SW monsoon are attributed to the varying intensities of this upwelling.
The post monsoon is characterized by more vertical stability of the waters and by uniform
distribution of the nutrient properties.
S. V. S. RAo (1957) reported high values of total phosphorus for the inshore waters
of the Malabar coast off Calicut for January to March and July to October. These high
values of total P coincide with high inorganic phosphate in the SW monsoon period; but
as noted above the relationship on the east coast is inverse. JA YARAMAN and SESHAPPA
(1957) reported higher values of total phosphorus on the west coast of India when
compared with the east coast for both SW and NE monsoon periods. The total phosphorus
in the sediments also reflects the prevalence of upwelling conditions (MURTY, REDDY
and VARADACHARI, 1968; SIDDlQUE and CHAUDHURY, 1968; CHATERJI, KARUNAKARAN
and SIDDIQUE, 1968).
An offshore region of upwelling is reported by RAO and JAYARAMAN (1966) in the
Minicoy area of the Arabian Sea. However, this seems to be more related to postmonsoon
conditions. It is suggested that such enrichment may have a considerable impact on the
peak tuna catches in this region. Likewise, PANIKKAR and JAYARAMAN (1966) correlate
the upwelling on the SW coast with the main region of the sardine-mackerel fishery.
A full understanding of the factors responsible for the enrichment conditions is not yet
available since it falls into no single cause-and-effect category but is a result of complex
interactions. As BANSE (1966) states, the continuing scarcity of studies during the biologically most important season in a region which produces much of India's marine fish
makes interpretation tenuous.
2. Evaluation of Organic Phosphorus Concentrations
Measurements of the concentrations for various components of the complete cycle
for phosphorus were also made during IIOE. Determinations for total phosphorus, when
carried out along with evaluations of the inorganic phosphate concentration, provide
an estimate of the total organic phosphorus by difference. In addition, when separate
determinations of organic phosphorus in the particulate. matter from a filtered water
sample are made, the distinction of the particulate and dissolved organic fractions is
possible by difference. Such data provide for the evaluation of the relationships in the
phosphorus cycle.
a) Western Indian Ocean and Arabian Sea
Determinations of the various organic components of the phosphorus cycle were
carried out by the author on the" Atlantis II" expeditions. Equivalent areas were sampled
at periods almost exactly at 6 months opposite to each other in the yearly cycle, and each
cruise covered the Arabian Sea at the peak of monsoon conditions. Nutrient observations
from the 1963 SW monsoon have already been presented in this paper and elsewhere
(MCGILL, 1966). The available data on the organic phosphorus concentrations have been
D. A. MCGILL:
between r Nand 18
0
N latitudes, from August to early October. SHARMA (1968) finds
the upwelling extending progressively from south to north throughout the period from
February to July/August. This agrees with REDDY and SANKARANARAYANAN (1968,
a and b), for data on the distribution of phosphates and silicates in the upper 200 m.
The regional differences in the concentration of nutrients along the coast in the closing
phase of the SW monsoon are attributed to the varying intensities of this upwelling.
The post monsoon is characterized by more vertical stability of the waters and by uniform
distribution of the nutrient properties.
S. V. S. RAo (1957) reported high values of total phosphorus for the inshore waters
of the Malabar coast off Calicut for January to March and July to October. These high
values of total P coincide with high inorganic phosphate in the SW monsoon period; but
as noted above the relationship on the east coast is inverse. JA YARAMAN and SESHAPPA
(1957) reported higher values of total phosphorus on the west coast of India when
compared with the east coast for both SW and NE monsoon periods. The total phosphorus
in the sediments also reflects the prevalence of upwelling conditions (MURTY, REDDY
and VARADACHARI, 1968; SIDDlQUE and CHAUDHURY, 1968; CHATERJI, KARUNAKARAN
and SIDDIQUE, 1968).
An offshore region of upwelling is reported by RAO and JAYARAMAN (1966) in the
Minicoy area of the Arabian Sea. However, this seems to be more related to postmonsoon
conditions. It is suggested that such enrichment may have a considerable impact on the
peak tuna catches in this region. Likewise, PANIKKAR and JAYARAMAN (1966) correlate
the upwelling on the SW coast with the main region of the sardine-mackerel fishery.
A full understanding of the factors responsible for the enrichment conditions is not yet
available since it falls into no single cause-and-effect category but is a result of complex
interactions. As BANSE (1966) states, the continuing scarcity of studies during the biologically most important season in a region which produces much of India's marine fish
makes interpretation tenuous.
2. Evaluation of Organic Phosphorus Concentrations
Measurements of the concentrations for various components of the complete cycle
for phosphorus were also made during IIOE. Determinations for total phosphorus, when
carried out along with evaluations of the inorganic phosphate concentration, provide
an estimate of the total organic phosphorus by difference. In addition, when separate
determinations of organic phosphorus in the particulate. matter from a filtered water
sample are made, the distinction of the particulate and dissolved organic fractions is
possible by difference. Such data provide for the evaluation of the relationships in the
phosphorus cycle.
a) Western Indian Ocean and Arabian Sea
Determinations of the various organic components of the phosphorus cycle were
carried out by the author on the" Atlantis II" expeditions. Equivalent areas were sampled
at periods almost exactly at 6 months opposite to each other in the yearly cycle, and each
cruise covered the Arabian Sea at the peak of monsoon conditions. Nutrient observations
from the 1963 SW monsoon have already been presented in this paper and elsewhere
(MCGILL, 1966). The available data on the organic phosphorus concentrations have been