Contributions of physical and biogeochemical processes to phytoplankton biomass enhancement in the surface and subsurface layers during the passage of Typhoon Damrey

Abstract

AbstractIn this study, a one‐dimensional physical‐biogeochemical coupled model was established to investigate the responses of the upper ocean to Typhoon Damrey in the basin area of the South China Sea. The surface chlorophyll a concentration (Chl a) increased rapidly from 0.07 to 0.17 mg m−3 when the typhoon arrived and then gradually reached a peak of 0.61 mg m−3 after the typhoon's passage. The subsurface Chl a decreased from 0.34 to 0.17 mg m−3 as the typhoon arrived and then increased gradually to 0.71 mg m−3. Analyses of model results indicated that the initial rapid increase in the surface Chl a and the decrease in the subsurface Chl a were caused mainly by physical process (vertical mixing), whereas the subsequent gradual increases in the Chl a in both the surface and subsurface layers were due mainly to biogeochemical processes (net growth of phytoplankton). The gradual increase in the Chl a lasted for longer in the subsurface layer than in the surface layer. Typhoon Damrey yielded an integrated primary production (IPP) of 6.5 × 103 mg C m−2 (~14% of the annual IPP in this region).