Variations of chlorophyll-a and particulate organic carbon in the Yellow-Bohai Sea: in response to the Typhoon Lekima event

Typhoon events have large impacts on marginal seas’ environmental conditions with implications for biological processes and carbon cycling. However, little is known about the responses of phytoplankton and particulate organic carbon (POC) to typhoon events in the Yellow-Bohai Sea (YBS). In this study, we utilized satellite-derived datasets of chlorophyll-a (Chl-a) and POC, together with key physical parameters, to analyze their responses to the Typhoon Lekima event induced heavy rainfall and strong winds. Overall, there were enhanced upwelling, strengthened currents, and increased terrestrial runoff during weakened Typhoon Lekima in the YBS. The basin-scale response of Chl-a showed large differences post the Typhoon Lekima event, with a decrease in the Bohai Sea (BS, 0.34 ± 3.0 mg m−3) but an increase in Yellow Sea (YS, 0.23 ± 1.7 mg m−3 in the south YS and 0.54 ± 0.8 mg m−3 in the north YS). The increase of Chl-a in the YS was attributed to increased nutrients, whereas the reduction of Chl-a in the BS was caused by dilution and water exchange with the North Yellow Sea. However, there was an overall increase in POC post-Typhoon Lekima in both BS and YS. The increase of POC in the majority of BS resulted largely from enhanced sediment resuspension and terrigenous input. The increase of POC in the nearshore waters of YS was attributable to enhanced biological production, sediment resuspension, and terrigenous input of POC, whereas the increase of POC in the central YS was partly due to transportation of high-POC waters from nearshore to offshore via strengthened current. Our study highlights the complex impacts of typhoon events on the carbon cycle in marginal seas.