Remote-sensing observations of Typhoon Soulik (2013) forced upwelling and sediment transport enhancement in the northern Taiwan Strait

The Taiwan Strait plays an important role in water and sediment exchange between the East China Sea and the South China Sea. On 13 July 2013, Typhoon Soulik crossed the Taiwan Strait, causing a significant impact on the strait’s marine system. In this article, we document the use of remote-sensing data to study this impact by comparing sea surface temperature (SST), spatial distributions and concentrations of chlorophyll (Chl-a), and total suspended matter (TSM) in the strait over different time periods. During and after the typhoon, the TSM of the waters near the Minjiang estuary dramatically increased, while Chl-a and SST significantly decreased. To the southeast of Pingtan Island, the SST decreased and Chl-a significantly increased, causing strong upwelling that lasted eight to ten days. To the northwest of Taiwan Island, Chl-a and the TSM of the coastal waters dramatically increased. The strong cyclonic wind-stress of the typhoon enhanced heat exchange between the water and the atmosphere, and a large amount of rainfall and run-off significantly decreased the SST. During the typhoon, the increased sediment discharged into the strait by rivers, and the re-suspension of seafloor sediment, increased the concentration of TSM in the coastal waters. Seawater with relatively high sediment concentration was transported to the middle of the strait after being carried by wind-induced flows. In the waters near the typhoon’s path, especially in the upwelling area, nutrient-rich bottom water stirred by the typhoon promoted an outbreak of aquatic organisms and significantly increased the probability of a red tide occurrence.