Impact of Tropical Cyclone on Coastal Phytoplankton Blooms and Underlying Mechanisms

Northern Beibu Gulf, China This study examines the impact of tropical cyclone (TC) "Wipha" (2019) on phytoplankton chlorophyll- a (Chl- a ) dynamics, using observations from two buoy stations (S1 and S2). Results indicate that persistently high turbidity at the inner bay (station S1) restricted underwater light availability, resulting in an insignificant change in mean daily Chl- a concentrations, despite sufficient nutrients. Conversely, at the outer bay (station S2), Chl- a significantly increased after the storm, exhibiting notable delayed correlations with elevated turbidity ( r = 0.87, p < 0.01) and aerosol deposition ( r = 0.90, p < 0.01). The differential phenomenon at two locations highlights that distinct environmental control the responses of phytoplankton dynamics to the tropical cyclone, primarily related to light availability and nutrient sources. In contrast to prior studies, the nutrient source leading to increased Chl- a at the outer bay may result from wet deposition of aerosols and re-suspension of suspended matter, rather than direct terrestrial nutrient inputs. Additionally, the prolonged turbidity recovery period (up to 5 days) at the inner bay substantially limited phytoplankton growth, highlighting TC-induced turbidity as a critical factor constraining phytoplankton blooms in eutrophic coastal environments. • Turbidity recovery time critically impacts phytoplankton growth after tropical cyclones. • Sediment resuspension and aerosol deposition drive Chl- a increases during TC events. • Light availability, not nutrients, limits phytoplankton growth at high turbidity levels. • Lagged correlations reveal strong links between Chl- a and turbidity, aerosols, and rainfall.