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General Session 1: Physical oceanic processes: Dynamics and physical-biological-biogeochemical interactions |
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Seasonal variability of sea surface chlorophyll distribution for mesoscale eddies in the South China Sea
GS1-42
Mingxian Guo* , South China Sea Institute of Oceanology, Chinese Academy of Sciences
Peng Xiu, South China Sea Institute of Oceanology, Chinese Academy of Sciences
shiyu Li, School of Environmental Science and Engineering, Sun Yat-sen University
Fei Chai, State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, State Oceanic Administration
Huijie Xue, School of Marine Sciences, University of Maine
Presenter Email: guomingxian@scsio.ac.cn
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| Mesoscale eddies can influence sea surface chlorophyll distribution through complicated horizontal and vertical motions. Although vertical displacement of isopycnal during eddy formation, which is called eddy pumping, has been involved as the main mechanism influencing the biogeochemical cycles inside mesoscale eddies, our study shows the response of satellite-observed chlorophyll (CHL) to eddy motions in the South China Sea (SCS) varies seasonally. A total of 174 cyclonic eddies with 1274 identifications and 172 anticyclonic eddies with 1292 identifications were tracked from 10 years of satellite measured Sea Level anomaly (SLA) fields in the SCS. The corresponding spatial pattern of CHL anomaly composite is dipole in summer and monopole in winter, indicating that sea surface CHL are regulated by horizontal rotational velocity of eddies (referred to as eddy advection) in summer and eddy pumping in winter. Further investigations based on a coupled physical-biogeochemical model show that CHL distribution responds to eddy pumping in subsurface and eddy advection in bottom of euphotic zones in both summer and winter. The reason leading to the seasonal variation of eddy motions are found to be the seasonal variation of mixed layer depth. In summer, because the mixed layer depth is shallow, the nutrient change induced by eddy pumping only retain in subsurface so that the sea surface CHL distribution can only be affected by eddy advection. In winter, the deepening of mixed layer depth homogenize the nutrients of sea surface with subsurface, where eddy pumping notably changes the nutrients, allowing the eddy pumping to be observed from sea surface CHL changes. |
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