Phytoplankton size classes changed oppositely over shelf and basin areas of the South China Sea during 2003-2018

Abstract Phytoplankton size classes (PSC) is closely related to the export of surface carbon to the deep ocean, by affecting the phytoplankton photosynthetic efficiency, particle sinking rate, and the structure of the marine food chain .etc. As the largest marginal sea of the western North Pacific, there have been some researches of satellite-retrieved PSC algorithms and PSC-relative POC export in the South China Sea (SCS), however, long-term changes of PSC and its effect on POC export in the SCS are still poorly understood. In this study, we constructed a reliable long-time series PSC dataset in the SCS by evaluating the performances of published empirical PSC models. Our results revealed opposite changes of PSC on shelf and basin areas of the SCS in the past 16 yrs (2003-2018). Over the shelf regions, the proportion of phytoplankton in micro-size class (20-200 µm) raised significantly (0.28 unit·year-1, p