420
Chapter 11: The Pacific Ocean
algorithms were not able properly to distinguish CDOM from chlorophyll, although
this instrument was intended originally for coastal analysis, and the user community
progressively restricted its use to oceanic conditions once the limitations were understood.
One of the first indications that the problem remained was the finding by Gong et al.
(1998) that SeaWiFS data overestimated sea-truthed chlorophyll data on the Chinese shelf
by a factor of 5. The recent demonstration that much of the signal from the Amazon plume
derives from CDOM supports that finding (Hu et al., 2004). Examination of the currently
available images show a relatively invariant enhancement of “chlorophyll” the length of
the coast of China from Hainan northward with a permanent penetration offshore that
corresponds very well with the effluent from the Yangtse River. Only the eastern coast
of the Sea of Japan lacks this coastwise signal. We assume that the climatology obtained
from SeaWiFS data for the shelf of this province is dominated by nonliving Colored
organic material (CDOM) from river water and await a resolution of this problem with
impatience.
With the caution just expressed, examination of monthly and seasonal images shows
that the Yellow and Bohai Seas and the coastal regions of the East China Sea are dominated
by their sediment load almost year-round, whereas the Sea of Japan—having no major
river effluents except the far-field effects of the Amur River late in the year—shows
evidence of a spring bloom from February to May, after which oligotrophy appears to
become established. A 50-km coastal band of high pigment, either CDOM or chlorophyll,
occurs the length of the coast from the Yellow Sea to Hainan year-round, whereas off the
Yangtse River a major high-pigment feature stretches far seaward toward the east before
turning south along the coast.
Even if we cannot visualize them here as elsewhere, three principal processes must
regulate primary production in this province: (i) the province-wide winter cooling and
mixing of the water column alternating with summer stratification will generate a spring
bloom whose timing will depend both on the seasonal irradiance cycle and on seasonal
differences in water clarity; (ii) the coastal zone, especially in front of the major river
mouths, will have a turbidity front, beyond which there will be a zone of enhanced
primary production at the appropriate season; and (iii) there will be enhanced production
in response to the various local eddying and upwelling processes.
From surface observations, a general boreal spring increase in chlorophyll of surface
waters is noted in the East China Sea (Li and Fei, 1992), and enhancement of phytoplankton growth has also been observed in association with persistent eddies and upwelling.
The river mouths, especially that of the Yangtse, and the cyclonic eddy south of Sheju
Island were noted by Guo (1992) as supporting enhanced growth of neritic diatoms
(Coscinodiscus, Skeletonema, Melosira, and Chaetoceros). The intrusions of Kuroshio water
onto the shelf as shelf-edge eddies transport significant amounts of nitrate; one such
eddy was computed to carry more nutrients than the combined annual river discharges
(Chen et al., 1992). Where the intrusion of these eddies over the shelf break results in
locally strong vertical stratification, blooms and the development of strong subsurface
chlorophyll maxima may occur at any season.
Fortunately, we now have access to the results of a systematic grid survey (four
seasons, seven cross-shelf lines of stations) of the northern shelf of the East China
Sea organized by the Ocean University of Taiwan (Gong et al., 2003, and associated
papers), and this is a useful model for the entire province south of the Yellow Sea.
The northwest corner of the survey grid was well within the discharge plume from the
Yangtse River, and this was reflected in nutrient enrichment there year-round; nevertheless, primary production in winter was light-constrained to < 10% of the peak rates of
summer. Further seaward, away from the influence of the Yangtse plume, productivity
was seasonally nutrient-limited but—somewhat curiously—seasonal changes in the production rate were rather small, so that the annual productivity of the two zones differed
Chapter 11: The Pacific Ocean
algorithms were not able properly to distinguish CDOM from chlorophyll, although
this instrument was intended originally for coastal analysis, and the user community
progressively restricted its use to oceanic conditions once the limitations were understood.
One of the first indications that the problem remained was the finding by Gong et al.
(1998) that SeaWiFS data overestimated sea-truthed chlorophyll data on the Chinese shelf
by a factor of 5. The recent demonstration that much of the signal from the Amazon plume
derives from CDOM supports that finding (Hu et al., 2004). Examination of the currently
available images show a relatively invariant enhancement of “chlorophyll” the length of
the coast of China from Hainan northward with a permanent penetration offshore that
corresponds very well with the effluent from the Yangtse River. Only the eastern coast
of the Sea of Japan lacks this coastwise signal. We assume that the climatology obtained
from SeaWiFS data for the shelf of this province is dominated by nonliving Colored
organic material (CDOM) from river water and await a resolution of this problem with
impatience.
With the caution just expressed, examination of monthly and seasonal images shows
that the Yellow and Bohai Seas and the coastal regions of the East China Sea are dominated
by their sediment load almost year-round, whereas the Sea of Japan—having no major
river effluents except the far-field effects of the Amur River late in the year—shows
evidence of a spring bloom from February to May, after which oligotrophy appears to
become established. A 50-km coastal band of high pigment, either CDOM or chlorophyll,
occurs the length of the coast from the Yellow Sea to Hainan year-round, whereas off the
Yangtse River a major high-pigment feature stretches far seaward toward the east before
turning south along the coast.
Even if we cannot visualize them here as elsewhere, three principal processes must
regulate primary production in this province: (i) the province-wide winter cooling and
mixing of the water column alternating with summer stratification will generate a spring
bloom whose timing will depend both on the seasonal irradiance cycle and on seasonal
differences in water clarity; (ii) the coastal zone, especially in front of the major river
mouths, will have a turbidity front, beyond which there will be a zone of enhanced
primary production at the appropriate season; and (iii) there will be enhanced production
in response to the various local eddying and upwelling processes.
From surface observations, a general boreal spring increase in chlorophyll of surface
waters is noted in the East China Sea (Li and Fei, 1992), and enhancement of phytoplankton growth has also been observed in association with persistent eddies and upwelling.
The river mouths, especially that of the Yangtse, and the cyclonic eddy south of Sheju
Island were noted by Guo (1992) as supporting enhanced growth of neritic diatoms
(Coscinodiscus, Skeletonema, Melosira, and Chaetoceros). The intrusions of Kuroshio water
onto the shelf as shelf-edge eddies transport significant amounts of nitrate; one such
eddy was computed to carry more nutrients than the combined annual river discharges
(Chen et al., 1992). Where the intrusion of these eddies over the shelf break results in
locally strong vertical stratification, blooms and the development of strong subsurface
chlorophyll maxima may occur at any season.
Fortunately, we now have access to the results of a systematic grid survey (four
seasons, seven cross-shelf lines of stations) of the northern shelf of the East China
Sea organized by the Ocean University of Taiwan (Gong et al., 2003, and associated
papers), and this is a useful model for the entire province south of the Yellow Sea.
The northwest corner of the survey grid was well within the discharge plume from the
Yangtse River, and this was reflected in nutrient enrichment there year-round; nevertheless, primary production in winter was light-constrained to < 10% of the peak rates of
summer. Further seaward, away from the influence of the Yangtse plume, productivity
was seasonally nutrient-limited but—somewhat curiously—seasonal changes in the production rate were rather small, so that the annual productivity of the two zones differed