Dual fronts control partitioned parameterization of light attenuation off a highly-turbidity estuary: A partitioned...

Light attenuation in water, driven by optically active constituents (OACs), critically shapes marine ecosystems off highly turbid estuaries like the Changjiang Estuary (CJE). Combining satellite products and simulated parameters with in-situ observeation data, this study reveals that sediment and plume fronts partition the CJE into three subregions (depth≤20 meters, 20-50 meters, ≥50 meters), each exhibiting distinct OACs distributions and light attenuation mechanisms. A set of subregion-specific parameterization scheme for the diffuse attenuation coefficient (K_d) was developed using multi-linear regression, based on the observed parameters of field survey cruise including suspended sediment concentration (SSC), chlorophyll (Chl) and salinity. Validation results showed superior performance (Zone 1: R²=0.84; Zone 2: R²=0.83) over traditional unpartitioned models (R²=0.46), highlighting SSC dominance in estuaries and salinity influence in transitional regions. Dual fronts regulate a "low-high-low" primary productivity pattern from the estuary to the shelf sea off the CJE, linking high productivity and hypoxia-prone zones (DO<2mg/L) to nutrient-rich intermediate zones. This spatially explicit framework highlights the role of frontal dynamics in structuring biogeochemical gradients, offering a critical tool to improve the predicting capability of coastal ecosystem in responses to sediment flux variability, eutrophication, and climate-driven hydrographic shifts. The methodology, adaptable to other high-turbidity estuaries, advances management strategies for mitigating hypoxia and sustaining fisheries under escalating anthropogenic pressures.