[1] Tide effects on the structure of the near-field Changjiang River plume and on the extension of the far-field plume have often been neglected in analysis and numerical simulations, which is the focus of this study. Numerical experiments highlighted the crucial role of the tidal forcing in modulating the Changjiang River plume. Without the tidal forcing, the plume results in an unrealistic upstream extension along the Jiangsu coast. With the tidal forcing, the vertical mixing increases, resulting in a strong horizontal salinity gradient at the northern side of the Changjiang River mouth along the Jiangsu coast, which acts as a dynamic barrier and restricts the northward migration of the plume. Furthermore, the tidal forcing produces a bidirectional plume structure in the near field, and the plume separation is located at the head of the submarine canyon. A significant bulge occurs around the head of the submarine canyon and rotates anticyclonically, which carries a large portion of the diluted water toward the northeast and merges into the far-field plume. A portion of the diluted water moves toward the southeast, which is mainly caused by tidal rectification. This bidirectional plume structure is more evident under certain wind conditions. During the neap tide with the reduced tidal energy, the near-field plume extends farther offshore, and the bulge becomes less evident. These dynamic behaviors are maintained and are fundamentally important in the region around the river mouth even under the summer monsoon and the shelf currents, although in the far field the wind forcing and shelf currents eventually dominate the plume extension.

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Measuring the transport of the Changjiang (also known as the Yangtze) River-derived buoyant coastal current, that is, the Min-Zhe Coastal Current, is of great importance for understanding the fate of terrestrial materials from this large river into the open ocean, but it is usually difficult to achieve because of the energetic tidal currents along the Chinese coast. In February 2012, a detiding cruise survey was carried out using the phase-averaging method. For the first time, this coastal current has been quantified with in situ data and has been shown to have a volume transport of 0.215 Sv (1 Sv [ 10 6 m 3 s 21 ) and a maximum surface velocity of ;50 cm s 21 . The ratio between the volume transport of the buoyant coastal current and that of the Changjiang is O(10). Freshwater transport by the buoyant coastal current accounts for over 90% of the Changjiang River's discharge. Buoyancy and winds are both important in driving this current.

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Conventional wisdoms on river plume dynamics suggest that a down‐shelf buoyant coastal current will ultimately be trapped at a specific depth, that is, the trapping depth, as constrained by riverine outflow and offshore bottom Ekman transport. Theoretically, a prerequisite down‐shelf current is necessary to form a stable bottom‐trapped river plume. In this study an alternative is described by carrying out a modeling study on the Zhe‐Min Coastal Current (ZMCC). Buoyant water from the Changjiang River is a major factor driving the ZMCC, as is common in bottom‐trapped river plumes; however, the trapping depth is more determined by tidal mixing. When the plume water comes to the sloping topography, strong tidal mixing induces a mixing front, shoreward of which the bottom Ekman layer occupies the entire water column. Such a tidal‐induced front maintains a down‐shelf frontal current, which is intensified both at the surface due to the thermal wind balance and on the top of bottom boundary layer due to the tidal rectification. Direct wind‐induced transport only covers a small fraction of the ZMCC; however, it redistributes the plume water and, thus, affects the coastal current. The tide‐induced frontal trapping depth varies much less between seasons than that predicted by previous plume theories. Instead, it fluctuates strongly in the spring‐neap cycle. Even in summer when upwelling‐favorable winds prevail, the mixing front still sustains a down‐shelf coastal current. Intense tidal mixing exists in many coastal waters, which might be an alternative mechanism in forming bottom‐trapped river plumes and their associated buoyant coastal current.