Nutrient flux and transport by the Kuroshio east of Taiwan

The Kuroshio is the western boundary of the North Pacific Ocean. To estimate the nutrient flux and transport in the upper 250 m, measurements were conducted along a transect across the Kuroshio at 23.75° N, east of Taiwan. The results showed that the Kuroshio flowed northward at a maximum velocity varying between 0.7 and 1.4 m s^− 1 at a depth of 100 m. The flow volume transport in the upper 250 m ranged from 13.43 to 17.51 Sv, accounting for 51–67% of the transport above 1000 m. The shoreward sloping isopycnals were revealed to be favorable for carrying nutrients onto the East China Sea shelf. The “nutrient stream” was located primarily at depths from 300 to 600 m, and the maximum flux ranged from 4.2 to 7.9 mmol m^− 2 s^− 1 for nitrates and from 0.4 to 0.7 mmol m^− 2 s^− 1 for phosphates. Nutrient transport in the upper 250 m varied within the range of 16.8–31.1 kmol s^− 1 for nitrates and 0.8–3.9 kmol s^− 1 for phosphates. This study suggests that 1) nitrate transport in the upper 250 m increases and 2) phosphate transport above 1000 m decreases during downstream transport, implying that the Kuroshio interacts with nearby ecosystems during its downstream journey.