Pacific Trade Winds Biome
381
monsoon, to satisfy balance between the archipelagic flow-through and the SEC of the
Indian Ocean. As noted earlier, the Banda Sea is a major pass for flow from the Pacific
Ocean to the Indian Ocean past Halmahera and Ceram in the north, and by the Flores
Sea and Timor to the south. Currents are weak and variable in intermonsoon periods.
Anticyclonic gyral flow persists in the Celebes Sea during all seasons, though it extends
farther west during the Northeast Monsoon; strong flow passes south of Mindanao, returning
to the Pacific (to enter the SECC) together with flow leaving the Molucca Sea around the
Halmahera gyre. During boreal summer, when the gyre is displaced to the east, surface drift
is received from the Sulu Sea; in winter, this drift through the Sulu archipelago is reversed.
The SEC of the Pacific Ocean flows westward into, and through, the Coral Sea diverging
when it meets the Australian continent at 18–19
S during the dry season; during the
Northeast Monsoon season of austral summer, the divergence migrates equatorward to
at least 14
S. At this divergence, to the east of the 200-m topography of the Queensland
Plateau, there is a feed into the East Australian Current to the south and—to the north—a
cyclonic circuit around the Gulf of Papua and the Solomon Sea (Andrews and Clegg,
1989) which transports 10–15×10
6 m
−3 sec
−1 into the Indonesian archipelago. In the area
of the divergence itself, currents are weak and include a persistent cyclonic eddy in which
water is transported onto and over the Great Barrier Reef. The Coral Sea is a uniformly
oligotrophic region, in which water-column stability is very strong and where the surface
layers are strongly nitrate-deficient; at the end of the austral summer (wet) monsoon there
is a strong difference between Solomon Sea (low) and Coral Sea (high) surface salinities.
Seasonal variability of mixed-layer depth is slight (Wyrtki, 1961) in the Sulu, Celebes,
and Flores Seas, but elsewhere it responds as expected to changes in monsoon wind
stress: in the central and northern parts of the South China Sea, mixed-layer depths are
shallow (30–40 m) in the southeast monsoon, deepening (to 70–90 m) during the winter
monsoon. By the end of boreal winter, the mixed layer has deepened here to 100 m.
In the Banda Sea and also in the shelf areas of the Arafura Sea, the changes are even
greater, upwelling under the influence of the southeast monsoon (May–August) forcing
a 2
C temperature drop at the surface and reducing the mixed layer to < 20 m deep.
Other monsoon-driven, persistent upwelling regions within the province were predicted
by Wyrtki (1961) to be (i) off the Macassar peninsula; (ii) along the coast of Vietnam,
where temperature drops of >1
C occur during the southerly monsoon; (iii) on the coast
of Sarawak; and (iv) south of Hong Kong in the South China Sea. Satellite observations
permit other locations of coastal upwelling to be located: given the geography of the region
and the complexity of seasonal flows, it will be very surprising indeed if multiple locations
are not identified when careful exploration is undertaken of the relevant high-precision
AVHRR-derived SST images. Hendiarti et al. (2004) discuss such a situation on the
southern coast of Java, and simple examination of SST and chlorophyll images confirms
that the upwelling region off Vietnam that was predicted by Wyrtki does indeed exist.
The consequences of the unique meteorology (heavy rainfall and intense cloud cover)
over the Indo-Pacific Archipelago are significant for biological oceanographic processes:
the rivers of the archipelago discharge 30 × 10
9 tons of sediment annually into coastal
water, or about twice the sediment discharge of the Amazon. The coastal rivers of
Southeast Asia discharge another 41 × 10
9 tons. Together, this is more than twice the
sediment discharged from all other rivers (Milliman and Meade, 1983).
Regional Response of the Pelagic Ecosystem
Throughout this province, the complex topography both of the land and of the seabed
is likely to produce many nonpersistent hydrographic instabilities, themselves likely to
be associated with nutrient transport to the photic zone and biological enhancement.
Such features are difficult to predict or map comprehensively, even with satellite imagery,
because of the extensive and pervasive cloud cover of the region.
381
monsoon, to satisfy balance between the archipelagic flow-through and the SEC of the
Indian Ocean. As noted earlier, the Banda Sea is a major pass for flow from the Pacific
Ocean to the Indian Ocean past Halmahera and Ceram in the north, and by the Flores
Sea and Timor to the south. Currents are weak and variable in intermonsoon periods.
Anticyclonic gyral flow persists in the Celebes Sea during all seasons, though it extends
farther west during the Northeast Monsoon; strong flow passes south of Mindanao, returning
to the Pacific (to enter the SECC) together with flow leaving the Molucca Sea around the
Halmahera gyre. During boreal summer, when the gyre is displaced to the east, surface drift
is received from the Sulu Sea; in winter, this drift through the Sulu archipelago is reversed.
The SEC of the Pacific Ocean flows westward into, and through, the Coral Sea diverging
when it meets the Australian continent at 18–19
S during the dry season; during the
Northeast Monsoon season of austral summer, the divergence migrates equatorward to
at least 14
S. At this divergence, to the east of the 200-m topography of the Queensland
Plateau, there is a feed into the East Australian Current to the south and—to the north—a
cyclonic circuit around the Gulf of Papua and the Solomon Sea (Andrews and Clegg,
1989) which transports 10–15×10
6 m
−3 sec
−1 into the Indonesian archipelago. In the area
of the divergence itself, currents are weak and include a persistent cyclonic eddy in which
water is transported onto and over the Great Barrier Reef. The Coral Sea is a uniformly
oligotrophic region, in which water-column stability is very strong and where the surface
layers are strongly nitrate-deficient; at the end of the austral summer (wet) monsoon there
is a strong difference between Solomon Sea (low) and Coral Sea (high) surface salinities.
Seasonal variability of mixed-layer depth is slight (Wyrtki, 1961) in the Sulu, Celebes,
and Flores Seas, but elsewhere it responds as expected to changes in monsoon wind
stress: in the central and northern parts of the South China Sea, mixed-layer depths are
shallow (30–40 m) in the southeast monsoon, deepening (to 70–90 m) during the winter
monsoon. By the end of boreal winter, the mixed layer has deepened here to 100 m.
In the Banda Sea and also in the shelf areas of the Arafura Sea, the changes are even
greater, upwelling under the influence of the southeast monsoon (May–August) forcing
a 2
C temperature drop at the surface and reducing the mixed layer to < 20 m deep.
Other monsoon-driven, persistent upwelling regions within the province were predicted
by Wyrtki (1961) to be (i) off the Macassar peninsula; (ii) along the coast of Vietnam,
where temperature drops of >1
C occur during the southerly monsoon; (iii) on the coast
of Sarawak; and (iv) south of Hong Kong in the South China Sea. Satellite observations
permit other locations of coastal upwelling to be located: given the geography of the region
and the complexity of seasonal flows, it will be very surprising indeed if multiple locations
are not identified when careful exploration is undertaken of the relevant high-precision
AVHRR-derived SST images. Hendiarti et al. (2004) discuss such a situation on the
southern coast of Java, and simple examination of SST and chlorophyll images confirms
that the upwelling region off Vietnam that was predicted by Wyrtki does indeed exist.
The consequences of the unique meteorology (heavy rainfall and intense cloud cover)
over the Indo-Pacific Archipelago are significant for biological oceanographic processes:
the rivers of the archipelago discharge 30 × 10
9 tons of sediment annually into coastal
water, or about twice the sediment discharge of the Amazon. The coastal rivers of
Southeast Asia discharge another 41 × 10
9 tons. Together, this is more than twice the
sediment discharged from all other rivers (Milliman and Meade, 1983).
Regional Response of the Pelagic Ecosystem
Throughout this province, the complex topography both of the land and of the seabed
is likely to produce many nonpersistent hydrographic instabilities, themselves likely to
be associated with nutrient transport to the photic zone and biological enhancement.
Such features are difficult to predict or map comprehensively, even with satellite imagery,
because of the extensive and pervasive cloud cover of the region.