Upwelling in the Taiwan Strait during the summer monsoon detected by satellite and shipboard measurements

Abstract

The Taiwan Strait is located at the confluence of the East China Sea and the South China Sea in the west Pacific Ocean. Several upwelling zones in the Taiwan Strait are noted for their high fisheries production; these upwelling zones have been studied in the past decade, but we have no overall picture on the size and temporal changes of these upwelling zones due to only limited in situ observation over short periods of time. The present paper investigates upwelling in the Taiwan Strait with satellite remote sensing data of NOAA-derived Sea Surface Temperature (SST) and SeaWiFS-derived Chlorophyll- a (Chl- a) and shipboard measurements during summer 1998. Results reveal five upwelling zones: (1) coastal upwelling near Pingtan Island (PTU), (2) coastal upwelling between Meizhou and Xiaman (MXU), (3) big coastal upwelling near Dongshan Island (DSU), sometimes extending to offshore, (4) small occasional upwelling near the Penghu Island (PHU) and (5) an intensive upwelling in the Taiwan Bank (TBU). TBU was extensively studied over summer 1998. Results showed that the TBU looks like a banana in shape in the southern edge of the Taiwan Bank; it intensifies in its southeastern edge. The size of TBU was about 2500–3000 km 2, with a mean value of 2796 km 2. The temperature difference between the upwelling and non-upwelling areas was about 2.5–3.5 °C for early August with a mean value of 2.3 °C on July to October. Series of images indicated a short-term variation of TBU and showed that high Chl- a concentrations (up to 0.8–2 mg m −3) zones coincided with low SST (25–26 °C) zones in terms of location, time, and shape. These upwelling zones change with size and intensity center from time to time. Field measurements of water temperature, salinity, and Chl- a in 1998 are consistent with satellite measurements.