The water in the South China Sea (SCS) belongs to tropical oligotrophic type with low primary productivity. This SCS is frequently affected by tropical cyclones. Strong tropical cyclones can trigger violent disturbances in the upper ocean, bringing nutrients into the surface layer, which increases phytoplankton primary production. Due to limited influence of fast-moving, weak cyclones on offshore deep waters and related marine ecosystems, previous studies focused generally on contribution of strong or slow-moving typhoons on marine ecosystems in the SCS. The present study analyzes increase in chlorophyll after a fast-moving, weak tropical storm in the continental shelf, investigating possible influence of a short-lived tropical storm using wind, currents, and other oceanographic data on phytoplankton over continental shelf. The results indicate the generally low chlorophyll-a (<0.1 mg·m-3) in the continental region of the western SCS east of Hainan province before the storm, and more than 30% increase of chlorophyll-a (>0.14 mg·m-3) after the storm. The prominent increase of chlorophyll-a may be associated with the tropical storm. Analyses of vertical CTD (conductivity-temperature-depth recorder) temperature profiles and ADCP (acoustic Doppler current profilers) current profiles imply that the storm can induce strong inertial oscillation and precipitation as well as mixing/entrainment, together with tide influences, trigger uptake of nutrients and support increase of chlorophyll-a. In addition, comparing with deep seas, the relative shallow nitracline in continental shelf regions is also favorable to upwelling of nutrients.
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