Pacific Coastal Biome
425
seasonal flow, seasonal wind stress, and coastal alignment combine to force intermittent
or seasonal upwelling. Even with the precautions already discussed concerning the aliasing
of the SeaWiFS data by CDOM, these images still provide the most efficient way of
identifying these manifold locations. Some of these will be discussed later: the most
obvious candidates for upwelling sites are the westward-facing gulf on the south coast of
Papua–New Guinea, the edge of the Sunda shelf, and also along the east coast of Vietnam.
This region undergoes major change during ENSO events like that of 1982–83 (Chao
et al., 1996) that were initiated by increased evaporative cooling in late 1982, followed
by weak NE and SW monsoons in succession. Increased heat content of surface water
during this period is better explained by weakened circulation than by changes in
latent heat flux. This resulted in seriously reduced upwelling on the Vietnam coast.
Subsequently, the record NE monsoon that followed produced major downwelling at
the coast around the marginal seas. This sequence was repeated during the 1986–87
event and are probably typical.
Regional Response of the Pelagic Ecosystem
Although I know of no comprehensive surveys of regional primary productivity, it is
evident that it is relatively high in the marginal gulfs compared with the open shelf, and
this was already evident from the very first voyages deploying the
14 C production method
in the 1950s. Platt and Subbha Rao (1975) list average figures for the Gulf of Thailand
and the Vietnam coast: recall that the latter is an upwelling regime during the southerly
monsoon (Liu et al., 2002b) of 12–13 g C m
−2 day
−1 compared to 03–06 g C m
−2 day
−1
for the remainder of the SUND province, though it is not easy to separate data from the
deep basins and the continental shelves in their presentation. A glance at any SeaWiFS
image of the entire region will convince you that, overall and at all seasons, chlorophyll
values are higher over the shelf regions than over the intervening deep basins. A quick
review of serial 7- or 30-day images also shows that the seasonal sequence differs in
the eastern and western shelf regions: the western region responds to the Northeast
Monsoon of boreal winter with a seasonal chlorophyll maximum, while the eastern region
is greener during austral winter under the influence of the Southeast Monsoon. The
coastal upwelling off Vietnam responds to the alongshore Southwest Monsoon winds
of boreal summer; that in the coastal Aru Gulf is most active also at the same season,
forced by the Southwest Monsoon winds of the southern hemisphere. We may assume
that this is a general response to seasonal deepening of the mixed layer and consequent
nutrient entrainment. The surface chlorophyll biomass in the SUND province is essentially
invariant seasonally in the archived climatology.
The images also confirm what could be predicted from regional geography and circulation: that a coastal zone of high pigment concentration water occurs commonly:
off Papua–New Guinea and in the adjacent Gulf of Carpentaria,; along the south coast
of Borneo; in the Gulf of Tonkin and on the east coast of Vietnam; in the Straits of
Malacca; and finally off the Mekong delta. To what extent this signal can be referred to
biological activity, or is due to CDOM, is uncertain. However, one aspect of the ecology
of this province can be observed, though with some technical reservations at these low
latitudes, with satellite images: this is the occurrence in some tidally mixed shelf areas of
coccolithophore blooms, presumably of Emiliania huxleyi (Brown, 1995b). The MODIS
calcite images for 2001 suggest that such blooms are widespread in coastal regions to the
east of the deep basins during the SE monsoon, and on the Sunda Shelf and Java Sea
during the NW monsoon.
The locations of coastal upwelling features, forced by interaction between seabed and
terrestrial topography and the local wind strength and direction, have been generalized
in the discussion of the deep basins of the archipelago (see Archipelagic Deep Basins
425
seasonal flow, seasonal wind stress, and coastal alignment combine to force intermittent
or seasonal upwelling. Even with the precautions already discussed concerning the aliasing
of the SeaWiFS data by CDOM, these images still provide the most efficient way of
identifying these manifold locations. Some of these will be discussed later: the most
obvious candidates for upwelling sites are the westward-facing gulf on the south coast of
Papua–New Guinea, the edge of the Sunda shelf, and also along the east coast of Vietnam.
This region undergoes major change during ENSO events like that of 1982–83 (Chao
et al., 1996) that were initiated by increased evaporative cooling in late 1982, followed
by weak NE and SW monsoons in succession. Increased heat content of surface water
during this period is better explained by weakened circulation than by changes in
latent heat flux. This resulted in seriously reduced upwelling on the Vietnam coast.
Subsequently, the record NE monsoon that followed produced major downwelling at
the coast around the marginal seas. This sequence was repeated during the 1986–87
event and are probably typical.
Regional Response of the Pelagic Ecosystem
Although I know of no comprehensive surveys of regional primary productivity, it is
evident that it is relatively high in the marginal gulfs compared with the open shelf, and
this was already evident from the very first voyages deploying the
14 C production method
in the 1950s. Platt and Subbha Rao (1975) list average figures for the Gulf of Thailand
and the Vietnam coast: recall that the latter is an upwelling regime during the southerly
monsoon (Liu et al., 2002b) of 12–13 g C m
−2 day
−1 compared to 03–06 g C m
−2 day
−1
for the remainder of the SUND province, though it is not easy to separate data from the
deep basins and the continental shelves in their presentation. A glance at any SeaWiFS
image of the entire region will convince you that, overall and at all seasons, chlorophyll
values are higher over the shelf regions than over the intervening deep basins. A quick
review of serial 7- or 30-day images also shows that the seasonal sequence differs in
the eastern and western shelf regions: the western region responds to the Northeast
Monsoon of boreal winter with a seasonal chlorophyll maximum, while the eastern region
is greener during austral winter under the influence of the Southeast Monsoon. The
coastal upwelling off Vietnam responds to the alongshore Southwest Monsoon winds
of boreal summer; that in the coastal Aru Gulf is most active also at the same season,
forced by the Southwest Monsoon winds of the southern hemisphere. We may assume
that this is a general response to seasonal deepening of the mixed layer and consequent
nutrient entrainment. The surface chlorophyll biomass in the SUND province is essentially
invariant seasonally in the archived climatology.
The images also confirm what could be predicted from regional geography and circulation: that a coastal zone of high pigment concentration water occurs commonly:
off Papua–New Guinea and in the adjacent Gulf of Carpentaria,; along the south coast
of Borneo; in the Gulf of Tonkin and on the east coast of Vietnam; in the Straits of
Malacca; and finally off the Mekong delta. To what extent this signal can be referred to
biological activity, or is due to CDOM, is uncertain. However, one aspect of the ecology
of this province can be observed, though with some technical reservations at these low
latitudes, with satellite images: this is the occurrence in some tidally mixed shelf areas of
coccolithophore blooms, presumably of Emiliania huxleyi (Brown, 1995b). The MODIS
calcite images for 2001 suggest that such blooms are widespread in coastal regions to the
east of the deep basins during the SE monsoon, and on the Sunda Shelf and Java Sea
during the NW monsoon.
The locations of coastal upwelling features, forced by interaction between seabed and
terrestrial topography and the local wind strength and direction, have been generalized
in the discussion of the deep basins of the archipelago (see Archipelagic Deep Basins