Biological response to typhoon in northern South China Sea: A case study of “Koppu”

●Phytoplankton biomass and primary production increased obviously during Koppu′s intrusion.●Pearl River discharge after rainfall increased the nutrients concentration.●Algal bloom was observed around the southern coastal waters of Hong Kong.●Primary production in the offshore was enhanced by extra vertical nutrient transport induced by Koppu.

Obviously increased phytoplankton biomass and primary production was observed via both in situ investigation and remote sensing analysis in the northern South China Sea during typhoon Koppu′s intrusion in September 2009. Sea surface temperature declined in both coastal and offshore area when Koppu arrived. In the offshore waters, stratification was weakened due to vertical mixing and sea surface temperature distribution pattern changed after the Koppu′s arrival. The in situ data showed that extreme high primary production (PP) value (35 mgC m−3 h−1) appeared near the Dan′gan Island indicating a potential algal bloom around the southern coastal waters of Hong Kong. Obviously increased nutrient loadings were also observed in the near-shore surface waters shortly after the typhoon′s arrival. According to both in situ observation and remote sensing results, it is suggested that PP in the offshore water was stimulated by extra vertical nutrient transport induced by Koppu; while the enhanced phytoplankton biomass and potential bloom along the coastal was mostly contributed by the increased Pearl River discharge after rainfall, which was also regulated by the typhoon event.