84
D. A. MCGILL:
(3) Concentrations of Nutrients in the SE Indian Ocean
The numerous papers of ROCHFORD should be consulted for the details of nutrient
conditions in the waters of the SE Indian Ocean and around Australia. Two areas of
upwelling were identified by ROCHFORD (1962): 1. Along the shelf and slope region of
NW Australia, south of Timor, as distinguished by high surface phosphate levels of
0.2 to 0.3 Ilg-at 1-\ with the maximum upwelling occurring before September, and
2. along the shelf and slope region of the eastern Arafura Sea, from the Aroe Islands to
the Gulf of Carpentaria, where the highest surface phosphate values in the oceanic
waters of Autralia were found (0.66 Ilg-at 1-1) and the maximum upwelling probably
occurred before August, "During the period of the SE trade winds, enough uplift of deeper
water occurs along the NW coast of Australia to increase the surface phosphate content
of these coastal waters to about three times that of the surrounding areas. During the
same period, the phosphate values of the surface waters in the eastern Arafura Sea
increased to about 6 times that of the surrounding area." (ROCHFORD, 1962, p. 250).
In contrast, phosphate values in the Great Australian Bight were only about one-quarter
to one-half those in subtropical waters elsewhere. This has been attributed by ROCHFORD
to the continual isolation from the waters of higher phosphate content to the south,
since he finds a residence time, based upon salinity, of at least 1- 2 years.
WYRTKI (1962), on the other hand, locates the main upwelling of the SE monsoon
season along the coast of Java and Sumbawa in a region characterized by very high concentrations of inorganic phosphate (over 0.7 Ilg-at 1-1) at the bottom of the euphotic
zone. It was believed that the NW monsoon season would not show similar enrichment
by upwelling, however. BRUJEWICZ et al. (1966) have reported seasonal changes of the
concentration of nutrients in the low latitudes, especially in the eastern part of the
equatorial and southern tropical zone of the Indian Ocean. A marked change of dynamic
conditions due to monsoon changes affects the layers from the surface down to 1500 m
in this region.
y) Inshore Areas of the Bay of Bengal and South Indian Peninsula
The development of upwelling areas during the monsoon has special significance
for the coastal areas near the large population centers of Asia, since the nutrient enrichment may have important relations to the fisheries. A number of authorities have examined various locations around the Bay of Bengal for upwelling conditions, but the seasonal
and yearly variation in the conditions of this circulation introduce much confusion. Many
authors cite the particular significance of the estuarine character of Bay of Bengal waters
(T. S. S. RAo, 1957). Thus, SANKARANARAYANAN and REDDY (1968) believe that the
highly estuarine nature of the Bay narrows the biological influence of the nutrients and
emphasizes the contribution of suspended organic and inorganic particulate matter.
They conclude that the conditions in the Bay necessitate the use of extensive small regional
and temporal observations to obtain an integrated picture of the property distributions.
aa) Andaman Sea and Burmese Coast
REDDY, MURTY and SANKARANARAYANAN (1968) report very high PO/--p concentrations (> 12 flg-at I-I) in the waters around the Andaman Islands and suggest an
association between the occurrence of coral banks and the abnormal phosphate levels.
It is noteworthy that the Andaman Sea is a region of the highest productivity by phyto-
D. A. MCGILL:
(3) Concentrations of Nutrients in the SE Indian Ocean
The numerous papers of ROCHFORD should be consulted for the details of nutrient
conditions in the waters of the SE Indian Ocean and around Australia. Two areas of
upwelling were identified by ROCHFORD (1962): 1. Along the shelf and slope region of
NW Australia, south of Timor, as distinguished by high surface phosphate levels of
0.2 to 0.3 Ilg-at 1-\ with the maximum upwelling occurring before September, and
2. along the shelf and slope region of the eastern Arafura Sea, from the Aroe Islands to
the Gulf of Carpentaria, where the highest surface phosphate values in the oceanic
waters of Autralia were found (0.66 Ilg-at 1-1) and the maximum upwelling probably
occurred before August, "During the period of the SE trade winds, enough uplift of deeper
water occurs along the NW coast of Australia to increase the surface phosphate content
of these coastal waters to about three times that of the surrounding areas. During the
same period, the phosphate values of the surface waters in the eastern Arafura Sea
increased to about 6 times that of the surrounding area." (ROCHFORD, 1962, p. 250).
In contrast, phosphate values in the Great Australian Bight were only about one-quarter
to one-half those in subtropical waters elsewhere. This has been attributed by ROCHFORD
to the continual isolation from the waters of higher phosphate content to the south,
since he finds a residence time, based upon salinity, of at least 1- 2 years.
WYRTKI (1962), on the other hand, locates the main upwelling of the SE monsoon
season along the coast of Java and Sumbawa in a region characterized by very high concentrations of inorganic phosphate (over 0.7 Ilg-at 1-1) at the bottom of the euphotic
zone. It was believed that the NW monsoon season would not show similar enrichment
by upwelling, however. BRUJEWICZ et al. (1966) have reported seasonal changes of the
concentration of nutrients in the low latitudes, especially in the eastern part of the
equatorial and southern tropical zone of the Indian Ocean. A marked change of dynamic
conditions due to monsoon changes affects the layers from the surface down to 1500 m
in this region.
y) Inshore Areas of the Bay of Bengal and South Indian Peninsula
The development of upwelling areas during the monsoon has special significance
for the coastal areas near the large population centers of Asia, since the nutrient enrichment may have important relations to the fisheries. A number of authorities have examined various locations around the Bay of Bengal for upwelling conditions, but the seasonal
and yearly variation in the conditions of this circulation introduce much confusion. Many
authors cite the particular significance of the estuarine character of Bay of Bengal waters
(T. S. S. RAo, 1957). Thus, SANKARANARAYANAN and REDDY (1968) believe that the
highly estuarine nature of the Bay narrows the biological influence of the nutrients and
emphasizes the contribution of suspended organic and inorganic particulate matter.
They conclude that the conditions in the Bay necessitate the use of extensive small regional
and temporal observations to obtain an integrated picture of the property distributions.
aa) Andaman Sea and Burmese Coast
REDDY, MURTY and SANKARANARAYANAN (1968) report very high PO/--p concentrations (> 12 flg-at I-I) in the waters around the Andaman Islands and suggest an
association between the occurrence of coral banks and the abnormal phosphate levels.
It is noteworthy that the Andaman Sea is a region of the highest productivity by phyto-