Kuroshio subsurface water feeds the wintertime Taiwan Warm Current on the inner East China Sea shelf

The Taiwan Warm Current (TWC) has an overwhelming influence on the heat, salt, and nutrients balance on one of the broadest shelf in the world, the East China Sea shelf. In winter, the TWC flows in an unusual upwind direction and reaches the Changjiang (Yangtze River) Estuary, but its origin and pathway are intensely debated. Here combined evidences from current measurement, hydrographic, and stable isotopic data all suggest that the wintertime TWC intrusion off the Changjiang Estuary mainly originates from the Kuroshio subsurface water northeast of Taiwan, rather than from the Taiwan Strait warm water. The Kuroshio-branched water northeast of Taiwan can intrude into the inner shelf near the Zhe-Min Coast via bottom layer, manifesting by a pronounced boundary at 50 m isobath around 28°N, and thereby feeds the TWC intrusion into the Changjiang Estuary. The intrusion complicates the hydrological process in the estuary and shelf sea, and its impact on marine environment deserves more research attentions.