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Modeling long‐term change of planktonic ecosystems in the northern S outh C hina S ea and the upstream K uroshio C urrent
Author(s) -
Li Qian P.,
Wang Yanjun,
Dong Yuan,
Gan Jianping
Publication year - 2015
Publication title -
journal of geophysical research: oceans
Language(s) - English
Resource type - Journals
eISSN - 2169-9291
pISSN - 2169-9275
DOI - 10.1002/2014jc010609
Subject(s) - plankton , biogeochemical cycle , ecosystem , diazotroph , environmental science , trichodesmium , mesocosm , nutrient , pelagic zone , water column , oceanography , marine ecosystem , biology , nitrogen , nitrogen fixation , ecology , chemistry , geology , organic chemistry
Field studies suggested that the biogeochemical settings and community structures are substantial different between the central Northern South China Sea (NSCS) and the upstream Kuroshio Current (KC). In particular, the water column of KC is characterized by substantially lower nutrients and productivity but higher Trichodesmium abundance and nitrogen fixation compared to the NSCS. The mechanism driving the difference of the two marine ecosystems, however, remains inadequately understood. Here, a one‐dimensional biogeochemical model was developed to simulate the long‐term variability of lower‐trophic planktonic ecosystem for two pelagic stations in the NSCS and the KC near the Luzon Strait. The physical model included the vertical mixing driven by air‐sea interaction and the Ekman pumping induced by wind stress curl. The biological model was constructed by modifying a nitrogen‐based NPZD model with the incorporation of phosphorus cycle and diazotroph nitrogen fixation. After validation by several field data sets, the model was used to study the impact of long‐term physical forcing on ecosystem variability in the two distinct stations. Our results suggested that nutrient transport above nitracline during summer was largely controlled by vertical turbulent mixing, while Ekman pumping was important for nutrient transport below the nitracline. Our results also indicated that diazotroph community structure and N 2 fixation in the NSCS and the KC could be strongly influenced by physical processes through the impacts on vertical nutrient fluxes. The disadvantage of diazotroph in the NSCS in compared to the KC during the summer could be attributed to its high nitrate fluxes from subsurface leading to outcompete of diazotrophs by faster growing nondiazotroph phytoplankton.