Pacific Coastal Biome
419
from Hainan to Taiwan under the influence of the Southwest monsoon; at the Taiwan
Straits this northward flow is reinforced by the northward flow of some Kuroshio water
(see earlier discussion).
Beyond the eastern boundary of this province lies the warm flow of the Kuroshio, the
velocity maximum of which is topographically locked to the continental slope (steepto around Taiwan), which then continues northward through the Bashi Strait between
Taiwan and the Ryuku chain and along the western slope of the Okinawa trough that
here forms the edge of the continental shelf of the East China Sea. During its passage
northward outside the shelf break, some Kuroshio surface water leaves the main axis and
passes onto the continental shelf around Taiwan as the Taiwan Warm Current into the
East China Sea, though mainly during winter (Fan, 1982), and into the Yellow Sea as the
Yellow Sea Warm Current (Su et al., 1990).
On the western side of the Sea of Japan, the flow of cold subarctic coastal water from the
Sea of Okhotsk encounters Kuroshio water on the eastern side of the Korean peninsula,
where a prominent thermal front is formed. Meanders of the Kuroshio propagate to the
north along the edge of the shelf (Shibata, 1983) with a wavelength of about 300 km.
A distinct shelf-edge front develops on the landward side of such meanders and of the
cyclonic eddies that they shed (Chen et al., 1992). Shelf-edge eddies appear in satellite
images as warm Kuroshio water outlining cyclonic cores of cold shelf or slope water.
Upwelling from 400–500 m occurs within the cold cores (Zheng et al., 1992). Apart from
the vorticity in shelf-edge meanders and cyclonic eddies, upwelling occurs along the
Zhenjiang coast at about 26–30
N (Guan, 1984), on the northwest coast of Taiwan, and
in the quasipermanent cyclonic eddy south of Cheju Island.
As the Kuroshio rounds Taiwan, it encounters the sharply curved and steep topography
of the continental shelf of the East China Sea; a westward loop current across the shelf
resembles the loop current of the Gulf of Mexico, but unlike that feature, it does not
detach from the meandering jet (Hsueh et al., 1992). The consequence of these processes
is a regional upwelling in the vicinity of the Penghu Islands where a cold thermal anomaly
is frequently observed at the shelf break; upwelling here is episodically enhanced by the
onset of the northerly monsoon winds in boreal autumn. Nitrate-replete water reaches
the surface from thermocline depths during these episodes (Fan, 1982).
During boreal summer, the wind stress of the Southwest Monsoon and the northward flow of the China Coastal Current causes upwelling at the coast in a water mass
that is much modified by river water. Such water has unusual nutrient characteristics,
being highly enriched in nitrogen, including nitrate, but relatively deficient in phosphate.
Upwelled water has a phosphate concentration (< 07 M) that is an order of magnitude greater than in the overlying, river-modified surface water of the shelf so that after
upwelling the resultant water mass is near the Redfield ratio (Chen et al., 2001, 2004). A
similar process may occur during winter mixing over the shelves of the East China Sea;
in spring, the available phosphate in the euphotic zone may be rapidly depleted relative
to nitrate, in excess because of the influence of river water in the shelf water mass.
This region is much subject to the passage of tropical cyclones, here called typhoons,
during boreal summer (Shiah, 2000); when these pass over the normally oligotrophic
conditions of the shelf of the East China Sea they induce deep mixing in the water column,
together with resuspension of sediments and a brief but massive discharge of freshwater
from flooded rivers. Nitrate and POM values at 40 m increase by about 175% and 75%,
respectively, and a burst of productivity is thereby induced: autotrophic and bacterial
production rates were each found to double after the passage of a typhoon in 1996.
Regional Response of the Pelagic Ecosystem
This is one of the regions where we have to be very circumspect in our inferences
concerning surface chlorophyll from satellite data. It was well understood that the CZCS
419
from Hainan to Taiwan under the influence of the Southwest monsoon; at the Taiwan
Straits this northward flow is reinforced by the northward flow of some Kuroshio water
(see earlier discussion).
Beyond the eastern boundary of this province lies the warm flow of the Kuroshio, the
velocity maximum of which is topographically locked to the continental slope (steepto around Taiwan), which then continues northward through the Bashi Strait between
Taiwan and the Ryuku chain and along the western slope of the Okinawa trough that
here forms the edge of the continental shelf of the East China Sea. During its passage
northward outside the shelf break, some Kuroshio surface water leaves the main axis and
passes onto the continental shelf around Taiwan as the Taiwan Warm Current into the
East China Sea, though mainly during winter (Fan, 1982), and into the Yellow Sea as the
Yellow Sea Warm Current (Su et al., 1990).
On the western side of the Sea of Japan, the flow of cold subarctic coastal water from the
Sea of Okhotsk encounters Kuroshio water on the eastern side of the Korean peninsula,
where a prominent thermal front is formed. Meanders of the Kuroshio propagate to the
north along the edge of the shelf (Shibata, 1983) with a wavelength of about 300 km.
A distinct shelf-edge front develops on the landward side of such meanders and of the
cyclonic eddies that they shed (Chen et al., 1992). Shelf-edge eddies appear in satellite
images as warm Kuroshio water outlining cyclonic cores of cold shelf or slope water.
Upwelling from 400–500 m occurs within the cold cores (Zheng et al., 1992). Apart from
the vorticity in shelf-edge meanders and cyclonic eddies, upwelling occurs along the
Zhenjiang coast at about 26–30
N (Guan, 1984), on the northwest coast of Taiwan, and
in the quasipermanent cyclonic eddy south of Cheju Island.
As the Kuroshio rounds Taiwan, it encounters the sharply curved and steep topography
of the continental shelf of the East China Sea; a westward loop current across the shelf
resembles the loop current of the Gulf of Mexico, but unlike that feature, it does not
detach from the meandering jet (Hsueh et al., 1992). The consequence of these processes
is a regional upwelling in the vicinity of the Penghu Islands where a cold thermal anomaly
is frequently observed at the shelf break; upwelling here is episodically enhanced by the
onset of the northerly monsoon winds in boreal autumn. Nitrate-replete water reaches
the surface from thermocline depths during these episodes (Fan, 1982).
During boreal summer, the wind stress of the Southwest Monsoon and the northward flow of the China Coastal Current causes upwelling at the coast in a water mass
that is much modified by river water. Such water has unusual nutrient characteristics,
being highly enriched in nitrogen, including nitrate, but relatively deficient in phosphate.
Upwelled water has a phosphate concentration (< 07 M) that is an order of magnitude greater than in the overlying, river-modified surface water of the shelf so that after
upwelling the resultant water mass is near the Redfield ratio (Chen et al., 2001, 2004). A
similar process may occur during winter mixing over the shelves of the East China Sea;
in spring, the available phosphate in the euphotic zone may be rapidly depleted relative
to nitrate, in excess because of the influence of river water in the shelf water mass.
This region is much subject to the passage of tropical cyclones, here called typhoons,
during boreal summer (Shiah, 2000); when these pass over the normally oligotrophic
conditions of the shelf of the East China Sea they induce deep mixing in the water column,
together with resuspension of sediments and a brief but massive discharge of freshwater
from flooded rivers. Nitrate and POM values at 40 m increase by about 175% and 75%,
respectively, and a burst of productivity is thereby induced: autotrophic and bacterial
production rates were each found to double after the passage of a typhoon in 1996.
Regional Response of the Pelagic Ecosystem
This is one of the regions where we have to be very circumspect in our inferences
concerning surface chlorophyll from satellite data. It was well understood that the CZCS