Black carbon (BC), operationally defined as carbonaceous compounds with organic carbon content exceeding 60%, forms through incomplete combustion of biomass and fossil fuels. Its persistence in environments over centuries to millennia stems from polycyclic aromatic hydrocarbon structures. While riverine transport and atmospheric deposition dominate BC delivery to oceans, with deep-sea sediments serving as terminal reservoirs, critical knowledge gaps persist regarding terrestrial BC flux dynamics, spatiotemporal transport heterogeneity, and isotopic anomalies in marine dissolved BC—particularly its radiocarbon aging, δ¹³C deviations, and mass balance discrepancies.
The long-term carbon sequestration capacity of BC constitutes a climate-regulating factor. Although anaerobic methanotrophic archaea (ANME) have demonstrated BC-producing potential in culture experiments, their role in marine BC cycling remains underexplored. Through geochemical analysis of BC in cold seep carbonates from the South China Sea and Gulf of Mexico, we report the first discovery of exceptionally low δ¹³C_BC values (−45.2‰), providing direct field evidence for ANME-derived BC. Bayesian mixing modeling reveals 2–33% microbial contributions to BC in seep carbonates, suggesting cold seep systems may represent a previously unrecognized source of ¹⁴C-depleted dissolved BC in deep oceans.

Cold seep,Anaerobic oxidation of methane,Black carbon