Pacific Trade Winds Biome
383
(Dupouy et al., 1988). Such occurrences have major significance for basin-scale budgets of
inorganic nitrogen and are typical of the nitrate-limited oligotrophic ocean, a limitation
that is only seasonally relieved in the southern Coral Sea by the deepening of the mixed
layer, during the peak of the Southeast Monsoon of austral winter. Otherwise, the phytoplankton of the Coral Sea is recorded as being dominated by the pico fraction (<2 m),
although quite high productivity (1–3 g C m
−2 d
−1 ) has been measured adjacent to the
continental margins, as along the Papua Barrier Reef and in the Louisiade Archipelago
(Furnas and Mitchell, 1996b); here, nutricline and associated DCM were deep (100 m and
60–125 m, respectively) and annual productivity was computed to be 100–200 g C m
−2 .
In the Indonesian region, observations at sea confirm the general inferences made
from satellite data; chlorophyll biomass at the surface is enhanced during the southeast
monsoon from 0.25 to 25 mg m
−3 above levels occurring during the northeast monsoon.
This seasonal buildup of biomass, associated with an increase in the rate of primary
production, is greatest in the eastern seas (Banda, Flores, and Seram) and decreases
westward through the archipelago, becoming a very slight effect in the Sulawesi Sea
and the Makassar Strait (Kinkade et al., 1997). The predicted downwelling-upwelling
seasonal cycle in the Banda Sea has been observed, with predictable consequences for
photic zone nitrate (Wetsteyn et al., 1990) and seasonal primary production (Zevenboom
and Wetsteyn, 1990; Gieskes et al., 1990). In general, the degree of seasonal chlorophyll
enhancement throughout the archipelago seems to be correlated with sea surface temperature and hence the relative strength of the seasonal upwelling effect; in the Banda Sea,
chlorophyll integrated over 0–25 m is five times higher in austral winter, during the southeast monsoon (Gieskes et al., 1988). In August, during the southeast monsoon (upwelling
and low irradiance), the surface layer is homogenous down to 60 m and primary production rate is highest at the surface, whereas during February, under the influence of the
(downwelling and high-irradiance) northerly monsoon, stratification is established and a
DCM forms at 40–80 m. At these depths, phycoerythrin-containing Synechococcus occur
at very high concentrations of 10
4 –10
5 cells cm
−3 . Primary production rate is higher during the southerly than the northerly monsoon (1.85 and 09 g C m
−2 d
−1 , respectively).
Patches having even higher production rates (<7 g C m
−2 d
−1 ) occur to the south of New
Guinea, where upwelling occurs over the outer slope of the Papuan Barrier Reef (Furnas
and Mitchell, 1996a).
The mesozooplankton biomass of the Banda Sea is almost doubled at the onset of the
upwelling process, when chlorophyll accumulation reaches 3–4 mg m
−3 , by the rise from
depth of large populations of Calanoides philippinensis together with Rhincalanus nasutus,
which reach an abundance 4000 m
−2 , grazing on phytoplankton and microzooplankton.
Again as expected, vertical excursions during diel migration are reduced in the turbid
water associated with the southerly monsoon. A consequence of this change in behavior
is a stronger diel difference in gut chlorophyll in copepods between the two seasons; it
should also be noted that, once again, tropical mesozooplankton herbivores account for
only a small part of primary production (5–25% daily) or of standing stock (2–6% daily).
The biomass of micronekton responds similarly but with smaller magnitude; there is a
difference of only about 50% between the two monsoon seasons (Schalke et al. 1990).
The South China Sea is less oligotrophic than the adjacent waters of the western Pacific
with which exchange occurs through the Straits of Luzon; the nutricline is shallower, and
surface chlorophyll almost twice that of the adjacent Pacific. The physical processes, forced
by the reversing monsoon winds, which control phytoplankton production in the South
China Sea were recently modeled by Liu et al. (2002b). This reproduces quite closely the
observed nutrient and biomass profiles, and suggests three areas where upwelling appears
to induce exceptionally large seasonal blooms: off the east coast of Vietnam, to the east of
Luzon, and along the northern edge of the Sunda Shelf. The SeaWiFS and AVHRR images
confirm that coastal upwelling occurs on the east coast of Vietnam, especially during the
383
(Dupouy et al., 1988). Such occurrences have major significance for basin-scale budgets of
inorganic nitrogen and are typical of the nitrate-limited oligotrophic ocean, a limitation
that is only seasonally relieved in the southern Coral Sea by the deepening of the mixed
layer, during the peak of the Southeast Monsoon of austral winter. Otherwise, the phytoplankton of the Coral Sea is recorded as being dominated by the pico fraction (<2 m),
although quite high productivity (1–3 g C m
−2 d
−1 ) has been measured adjacent to the
continental margins, as along the Papua Barrier Reef and in the Louisiade Archipelago
(Furnas and Mitchell, 1996b); here, nutricline and associated DCM were deep (100 m and
60–125 m, respectively) and annual productivity was computed to be 100–200 g C m
−2 .
In the Indonesian region, observations at sea confirm the general inferences made
from satellite data; chlorophyll biomass at the surface is enhanced during the southeast
monsoon from 0.25 to 25 mg m
−3 above levels occurring during the northeast monsoon.
This seasonal buildup of biomass, associated with an increase in the rate of primary
production, is greatest in the eastern seas (Banda, Flores, and Seram) and decreases
westward through the archipelago, becoming a very slight effect in the Sulawesi Sea
and the Makassar Strait (Kinkade et al., 1997). The predicted downwelling-upwelling
seasonal cycle in the Banda Sea has been observed, with predictable consequences for
photic zone nitrate (Wetsteyn et al., 1990) and seasonal primary production (Zevenboom
and Wetsteyn, 1990; Gieskes et al., 1990). In general, the degree of seasonal chlorophyll
enhancement throughout the archipelago seems to be correlated with sea surface temperature and hence the relative strength of the seasonal upwelling effect; in the Banda Sea,
chlorophyll integrated over 0–25 m is five times higher in austral winter, during the southeast monsoon (Gieskes et al., 1988). In August, during the southeast monsoon (upwelling
and low irradiance), the surface layer is homogenous down to 60 m and primary production rate is highest at the surface, whereas during February, under the influence of the
(downwelling and high-irradiance) northerly monsoon, stratification is established and a
DCM forms at 40–80 m. At these depths, phycoerythrin-containing Synechococcus occur
at very high concentrations of 10
4 –10
5 cells cm
−3 . Primary production rate is higher during the southerly than the northerly monsoon (1.85 and 09 g C m
−2 d
−1 , respectively).
Patches having even higher production rates (<7 g C m
−2 d
−1 ) occur to the south of New
Guinea, where upwelling occurs over the outer slope of the Papuan Barrier Reef (Furnas
and Mitchell, 1996a).
The mesozooplankton biomass of the Banda Sea is almost doubled at the onset of the
upwelling process, when chlorophyll accumulation reaches 3–4 mg m
−3 , by the rise from
depth of large populations of Calanoides philippinensis together with Rhincalanus nasutus,
which reach an abundance 4000 m
−2 , grazing on phytoplankton and microzooplankton.
Again as expected, vertical excursions during diel migration are reduced in the turbid
water associated with the southerly monsoon. A consequence of this change in behavior
is a stronger diel difference in gut chlorophyll in copepods between the two seasons; it
should also be noted that, once again, tropical mesozooplankton herbivores account for
only a small part of primary production (5–25% daily) or of standing stock (2–6% daily).
The biomass of micronekton responds similarly but with smaller magnitude; there is a
difference of only about 50% between the two monsoon seasons (Schalke et al. 1990).
The South China Sea is less oligotrophic than the adjacent waters of the western Pacific
with which exchange occurs through the Straits of Luzon; the nutricline is shallower, and
surface chlorophyll almost twice that of the adjacent Pacific. The physical processes, forced
by the reversing monsoon winds, which control phytoplankton production in the South
China Sea were recently modeled by Liu et al. (2002b). This reproduces quite closely the
observed nutrient and biomass profiles, and suggests three areas where upwelling appears
to induce exceptionally large seasonal blooms: off the east coast of Vietnam, to the east of
Luzon, and along the northern edge of the Sunda Shelf. The SeaWiFS and AVHRR images
confirm that coastal upwelling occurs on the east coast of Vietnam, especially during the