Transport and cycling of dissolved organic carbon (DOC) are active in estuaries. However, a comprehensive understanding of the sources, sinks, and transformation processes of DOC throughout the river-estuary-ocean continuum is yet to be derived. Additionally, the adsorption of terrestrial dissolved organic carbon (tDOC) onto surfaces of suspended sediment that modulates carbon transport, transformation, and long-term carbon storage, influencing regional and global carbon budgets is frequently neglected in related coastal and estuarine studies due to the complex interplay of physical and biogeochemical processes. Taking the high-turbidity Changjiang Estuary and adjacent shelf sea as a case study area, this study applies a physics-biogeochemistry coupled model to investigate DOC cycling in the river-estuary-ocean continuum. DOC is classified into two types depending on the origin, namely terrigenous DOC (tDOC) and marine DOC (mDOC). A tDOC-adsorption-floc-population model that integrates floc behavior with tDOC adsorption processes was also developed. Simulation results were compared with observation and showed a satisfactory model performance. Our study indicates that in summer, the distribution of DOC in the Changjiang Estuary is driven by both hydrodynamics and biogeochemical processes, while in winter, it is primarily driven by hydrodynamics. The spatial transition from terrigenous-dominated DOC to marine-dominated DOC occurs mainly across the contour line of a salinity of 20 PSU. Additionally, the source-sink patterns in summer and winter are significantly different, and the gradient changes in chlorophyll-a indicate the transition between sources and sinks of DOC. Results also indicate that approximately 12.8 % of DOC is removed via adsorption when passing through the turbidity maximum zone (TMZ). The dominant mechanism of tDOC adsorption is governed by floc size, with Brownian motion and differential sedimentation alternating as the primary mechanism, whereas fluid shear exerts a relatively minor influence. These findings highlight the need for incorporating suspended sediment dynamics into regional and global carbon cycle models to enhance predictions of carbon transport and transformation in estuarine and coastal systems.

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