Anthropogenic river management drives decadal shifts in organic carbon sequestration in the Yellow River Estuary.

Estuaries serve as critical global hotspots for organic carbon (OC) burial. This study investigates multi-decadal deltaic OC dynamics in relation to historical river diversion and water-sediment regulation (WSR) in the Yellow River Estuary, using sediment cores BH-0 and NS-29 analyzed via organic geochemical proxies and elemental chemostratigraphy. The sedimentary records reveal a transition from a natural, terrigenous-dominated setting to a managed system regulated by altered sediment delivery and marine productivity. Prior to the 1976 channel diversion, the BH-0 site received massive fluvial loads, sustaining high sedimentation and accumulation rates but low OC concentrations. The 1976 diversion redirected the sediment plume southward to the Qingshuigou channel; the post-diversion sediment deficit at BH-0 coincided with a lower long-term OC burial flux and carbon‑nitrogen decoupling. Conversely, this hydrographic rearrangement directed sediment and OC transport toward the NS-29 site, establishing an efficient sink sustained by synchronized carbon and nitrogen burial. After 2002, both cores recorded increased TOC and TN concentrations despite the continued decline in basin-scale sediment supply, while their local burial patterns remained contrasting. Changes in TOC-TN relationships and sedimentary geochemical indicators further suggest shifts in organic matter inputs, accumulation, and preservation between the two depositional settings. By revealing a spatial reorganization, rather than a uniform change, in coastal OC burial, our study provides a new perspective on how anthropogenic river management influences blue carbon cycling and carbon budgets in heavily regulated river-dominated deltas worldwide.