Control of atmospheric deposition and hydrodynamic conditions on black carbon distribution in coastal sediments

Black carbon (BC) can be introduced into marginal seas through fluvial systems or atmospheric deposition. It has raised significant concerns regarding marine ecological security, climate change, and the global carbon cycle. However, the factors controlling the spatial distribution of BC content in coastal sediments are still debated. The Shandong Peninsula coast in the North Yellow Sea is adjacent to regions with high BC emissions and lacks direct river inflow. Here, we examined the spatial distributions of BC content and its stable carbon isotopes in surface sediments of the region, aiming to elucidate their sources and drivers in coastal areas. The results reveal that the content of BC decreases in both the southward and seaward directions. The reduction in sedimentary organic carbon (SOC) content is observed only along the path of the southward coastal current. Pearson's correlation analysis between BC content and both SOC content and grain size parameters, combined with source apportionment based on δ¹³C values, reveals distinct sources and drivers. However, the strong correlation between BC content and finer particles is largely obscured by nearshore samples that have high BC contents. Overall, the southward decline in BC and SOC contents is predominantly influenced by regional hydrodynamic conditions, whereas the enrichment of BC in nearshore zones is attributed to atmospheric deposition from human-induced coal combustion in the adjacent regions during winter months. The significant heterogeneity in the spatial distributions of BC and SOC contents indicates that BC and OC in coastal sediments have distinct sources and fates. This finding emphasizes the importance of considering BC and OC as separate categories in both marine carbon cycling research and the assessment of the global carbon budget.