Varying intensity of Kuroshio intrusion into Southeast Taiwan Strait during ENSO events

• The effects of El Niño events in the Taiwan Strait are seven months behind the monthly Niño 3.4 index.
• The seasonal amount of Kuroshio water in the Taiwan Strait is proportionally highest in spring.
• In a El Niño event with seven-month lag, the Kuroshion intrusion is stronger than other events.
• The biological activities clearly affect nutrients concentrations especially in spring.

The Taiwan Strait is the only direct passage between the South China Sea (SCS) and the East China Sea. Variations in the intensity of Kuroshio Branch and surface currents in the SCS result in seasonal and inter-annual variability in the hydrography of the SE Taiwan Strait, where the northwardly pointing funnel-like Penghu Channel is located. These currents vary with the intensity and direction of monsoons. The teleconnection between air-sea interaction of the east Pacific and west Pacific reportedly has time differences. The data in this study reveal that the salinity of the seawater in the Penghu Channel is highest during El Niño events with a seven-month lag to the monthly Niño 3.4 index, and lowest during La Niña periods, also with a lag of seven months to the monthly Niño 3.4 index. The chemical parameters also vary with these events. The concentrations of apparent oxygen utilization, nutrients, and hydrogen ions vary with the mixing ratio of SCS water and Kuroshio Branch water. The maximum concentrations of nutrients are significantly higher during the summer, seven months after a La Niña event (La Niña-7), than in other seasons. However, biological activities also affected these chemical parameters. In spring, active photosynthesis consumes more nutrients and hydrogen ion concentrations in La Niña-7 periods than in normal-7 periods.