Sedimentary records of char and soot during 1950s-2020s in a high-deposition-rate estuary of the South China

Black carbon (BC) in marine sediments serves as an important archive of anthropogenic activity. This study investigates the deposition profiles of BC in a sediment core from the Pearl River Estuary (PRE) over the past seven decades (1949-2021), combining thermal/optical reflectance (TOR) analysis with Bayesian mixing modeling. Results show that BC burial fluxes (11.0-29.2 g m^-2 a^-1) in the PRE are significantly higher than those in other Chinese marginal seas, reflecting intense anthropogenic influence and high sediment accumulation (4.6 cm a^-1). Char, constituting 72%-96% of BC, captures a clear signature of energy transition through its changing ratio with soot. The record progresses from a char-dominated stable phase (1949-1977) through industrial divergence (1980s-1990s) to a soot-favoring shift (1990-2010), a trend primarily driven by energy structure evolution. The post-2010 decline in both components highlights the effective implementation of stringent air pollution control policies. Source apportionment based on δ¹³C_BC and Char/Soot ratios revealed that biomass burning contributed 57%-65% of BC, significantly higher than in northern Chinese marginal seas, while coal combustion and vehicle emissions accounted for 34%-42% and 0.5%-1.7%, respectively. This high-resolution reconstruction of BC deposition quantitatively reveals that biomass burning dominated the BC source-to-sink in the PRE, offering novel insights into the region's anthropogenic carbon footprint.