Effects of cold eddy on phytoplankton production and assemblages in Luzon strait bordering the South China Sea |
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| Authors: | Yuh-Ling Lee Chen Houng-Yung Chen I -I Lin Ming-An Lee Jeng Chang |
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| Institution: | (1) Department of Marine Biotechnology and Resources, National Sun Yat-sen University, Kaohsiung, Taiwan;(2) Institute of Marine Biology, National Sun Yat-sen University, Kaohsiung, Taiwan;(3) Department of Atmospheric Sciences, National Taiwan University, Taipei, Taiwan;(4) Department of Environmental Biology and Fishery Science, National Taiwan Ocean University, Keelung, Taiwan;(5) Institute of Marine Biology, National Taiwan Ocean University, Keelung, Taiwan |
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| Abstract: | The biochemical effects of a cold-core eddy that was shed from the Kuroshio Current at the Luzon Strait bordering the South
China Sea (SCS) were studied in late spring, a relatively unproductive season in the SCS. The extent of the eddy was determined
by time-series images of SeaWiFS ocean color, AVHRR sea surface temperature, and TOPEX/Jason-1 sea surface height anomaly.
Nutrient budgets, nitrate-based new production, primary production, and phytoplankton assemblages were compared between the
eddy and its surrounding Kuroshio and SCS waters. The enhanced productivity in the eddy was comparable to wintertime productivity
in the SCS basin, which is supported by upwelled subsurface nitrate under the prevailing Northeastern Monsoon. There were
more Synechococcus, pico-eucaryotes, and diatoms, but less Trichodesmium in the surface water inside the eddy than outside. Prochlorococcus and Richelia intracellularis showed no spatial differences. Water column-integrated primary production (IPP) inside the eddy was 2–3 times that outside
the eddy in the SCS (1.09 vs. 0.59 g C m−2d−1), as was nitrate-based new production (INP) (0.67 vs. 0.25 g C m−2d−1). INP in the eddy was 6 times that in the Kuroshio (0.12 g C m−2d−1). IPP and INP in the eddy were higher than the maximum production values ever measured in the SCS basin. Surface chlorophyll
a concentration (0.40 mg m−3) in the eddy equaled the maximum concentration registered for the SCS basin and was higher than the wintertime average (0.29
± 0.04 mg m−3). INP was 3.5 times as great and IPP was doubled in the eddy compared to the wintertime SCS basin. As cold core eddies form
intermittently all year round as the Kuroshio invades the SCS, their effects on phytoplankton productivity and assemblages
are likely to have important influences on the biogeochemical cycle of the region. |
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| Keywords: | Phytoplankton assemblage primary production new production eddy Luzon Strait Kuroshio South China Sea |
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