Summer Phytoplankton Blooms Induced by Upwelling in the Western South China Sea

Abstract

During summer, phytoplankton blooms occur frequently off the southeast Vietnam coast in the western South China Sea (WSCS). Using multi-source remote sensing data, such as sea surface temperature (SST), sea surface wind (SSW), aerosol optical thickness (AOT), sea level anomalies (SLA), and chlorophyll-a (Chl-a) data from 1998 to 2020 and in situ observations of analyzed data, we report the patterns of spatial variation of summer phytoplankton blooms in this region. The partial correlation and multiple stepwise linear regression analyses reveal that Ekman transport (ET) and Ekman pumping velocity (EPV) exert a greater impact on the summer phytoplankton blooms than the other environmental factors, suggesting that the phytoplankton blooms in the region may be mainly triggered by the enhanced nutrients by wind-induced upwelling and vertical mixing. AOT only weakly correlates with Chl-a concentration in the region, probably these prominent abundant nutrients in the region come from upwelling and convective-overturn. A northeastward jet causes the distribution of high Chl-a in the WSCS to be plume-shaped. A new finding in this study is that the northward current in this area may cause the northward deviation of phytoplankton blooms from the areas of upwelling.