The Changjiang River delivers a huge amount of freshwater, nutrients and sediments to the East China Sea. The eco-dynamics in the Changjiang estuary and adjacent shelf region is significantly modulated by physical processes related to the freshwater plume and the intrusion of oceanic water masses.

A multidisciplinary research cruise was conducted from the Changjiang River mouth to the outer plume area in the summer of 2021. A towed, undulating vehicle equipped with coupled physical-biogeochemical sensors were employed to obtain high-resolution observations along a across-shelf transect. Freshwater flowing from the estuary with high velocity can cause strong mixing, sediment suspension and the turbidity maxima zone (TMZ) in the near-field region, which results in light limitation and low chlorophyll concentrations. As the velocity shear between the upper freshwater and lower seawater decreased, instability was weakened and stratification was developed, which initialized phytoplankton biomass, and phytoplankton blooms occurred at the outcrop location of the main front. In the outer plume area where the Taiwan Warm Current water was present, chlorophyll concentrations were greatest in the subsurface layer rather than the surface layer. A couple of parameters were calculated to quantify physical processes in the river plume and to identify their role in phytoplankton distributions.