Sedimentary record of black carbon in Daya Bay: Temporal evolution and source apportionment over the past 140 years

Black carbon (BC) is a critical component of carbon burial in coastal marine sediments, particularly in anthropogenically impacted systems. Despite its clear anthropogenic origins, the deposition history, source apportionment, and the long-term responses of BC to fuel source transitions remain poorly constrained in sedimentary records from the southeastern coastal region of China. To address this gap, we analyzed BC, total organic carbon (TOC), and δ¹³C in a well-dated sediment core (spanning the last 140 years) from Daya Bay (DYB) in the northern South China Sea (NSCS). The 140-year chronological framework was validated using artificial radionuclides (^239+240Pu, ¹³⁷Cs) and by aligning TOC and total nitrogen (TN) profiles with those from an existing nearby core. Our results demonstrate the dominance of fossil fuel-derived BC (BC_Ff) in the sedimentary pool, accounting for 63.8 ± 23.2% of total BC and indicative of incomplete combustion processes. The reconstructed record reveals two distinct depositional phases: (1) From the 1890s to the 1960s, BC content exhibited a moderate decline, likely due to constrained coal availability and socioeconomic disruptions during early modern conflicts in China. (2) From the 1960s to the 2020s, BC concentrations increased markedly, driven by rapid industrialization and urbanization. After China's Reform and Opening-Up policy initiated in 1978, the sustained increase in BC concentrations has paralleled the growth in both population and gross domestic product. Our findings provide a quantitative constraint on the long-term coupling between human activities and coastal BC dynamics, offering a robust framework to differentiate short-term anthropogenic perturbations from the cumulative effects on marine carbon sequestration.