ABSTRACT

Black carbon (BC) in marine sediments provides aunique archive of combustion history and a reservoir for long-termcarbon storage. However, the distinct roles of char BC (CBC) andsoot BC (SBC) in combustion-source tracing and carbon-cycleassessment remain poorly resolved in marginal seas. Here, weanalyze four sediment cores from the Beibu Gulf, South China Sea,using benzene poly(carboxylic acid) (BPCA) and chemothermaloxidation at 375 °C (CTO-375) methods to resolve subtypespecificBC records. CBC accounted for 52−57% of the estimatedtotal BC burial across all settings, consistent with sustainedbiomass-burning contributions. SBC exhibited higher spatiotemporalvariability and sensitivity to fossil fuel expansion, particularlynear industrial zones. Estimated BC burial fluxes varied spatially,largely reflecting differences in representative sedimentation rates rather than BC content. Notably, nearshore sites exhibited higherburial despite lower BC content. Centennial-scale profiles revealed that SBC effectively traced regional transitions from biomass tofossil fuel combustion, while CBC preserved the long-term fire legacy. These findings highlight the complementary roles of CBC andSBC in reconstructing combustion histories and assessing BC burial in marginal seas. Burial of biomass-derived BC can contribute tonet atmospheric CO2 sequestration, whereas fossil-derived BC burial represents the transfer of fossil carbon into long-termsedimentary storage.