Impact of Tropical Cyclone on Coastal Phytoplankton Blooms and Underlying Mechanisms

Abstract

Study Region

Northern Beibu Gulf, China

Study Focus

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.

New Hydrological Insights for the Region

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.