Atmospheric deposition of dissolved black carbon contributes to the refractory dissolved organic carbon pool in coastal waters.

This study selected Jiaozhou Bay (JZB), a typical semi-enclosed urbanized bay in northern China, to collect carbonaceous aerosol samples. Using the benzene polycarboxylic acid (BPCA) method to quantify aerosol dissolved black carbon (DBC), we analyzed the seasonal variations in its abundance and deposition fluxes, as well as their driving factors. By integrating multiple input sources, we evaluated the critical role of atmospheric deposition in the allochthonous DBC input to the JZB and its contribution to the marine refractory dissolved organic carbon (RDOC) pool. Results indicate that aerosol DBC mainly originated from anthropogenic emissions in the Bohai Rim region and Yellow Sea coastal provinces, with fossil fuel combustion being the dominant source across all seasons. The DBC dry deposition flux peaked in winter, driven primarily by variations in concentration. Significant positive correlations were observed among DBC, water-soluble organic carbon (WSOC) and black carbon (BC). Based on these relationships, linear regression models were established to estimate the dry (6.08 t yr-1) and wet (21.96 t yr-1) DBC deposition fluxes in the JZB. Atmospheric deposition accounted for 25.11%-40.78% of the total allochthonous DBC input to the bay. Consequently, the global atmospheric DBC deposition flux to the ocean was estimated to reach 2.125 ± 0.128 Tg yr-1 (WSOC-based). These findings provide essential data for further refining global carbon cycle models and highlights the potential role of atmospheric DBC deposition in marine carbon sequestration.