Terrestrial Biomolecular Burial Efficiencies on Continental Margins

The fate of terrestrial organic carbon (OCterr) exported from large rivers in marginal seas is an integral component of land‐ocean‐atmosphere carbon dynamics and influences on atmospheric CO2 concentrations on millennial and longer timescales. In this study, we employ a novel approach to constrain burial efficiencies for source‐specific terrestrial biomolecules (long‐chain n‐alkanes and n‐fatty acids) in two river‐marginal sea systems. We find for the Pearl River‐South China Sea system that 34 ± 19% and 11 ± 4% of n‐alkanes and n‐fatty acids, respectively, are preserved across the transport pathway from the river mouth to inner shelf. In contrast, terrestrial biomolecular burial efficiencies were markedly higher (64 ± 17% and 84 ± 30% of n‐alkanes and n‐fatty acids, respectively) in the Yellow River‐Bohai Sea/Yellow Sea system. These findings reveal markedly different fates of OCterr in these two fluvial‐marine systems, as well as sharp contrasts in OCterr reactivity within each system. Plain Language Summary Burial efficiencies of source‐specific biomarker compounds in coastal sediments can provide new insights into the fate of terrestrial organic carbon in marine environments. In this study, we determine mineral surface area‐normalized loadings of higher plant‐derived long‐chain n‐alkanes and n‐fatty acids in two Chinese fluvial/marginal sea systems in order to examine terrestrial organic carbon burial efficiencies. We find marked contrasts in terrestrial organic carbon burial efficiency between both fluvial systems and terrestrial biomolecules. These differences imply sharply contrasting fates of different components of terrestrial organic matter during transport and sedimentation, which in turn shed new light on underlying mechanisms and carry implications for interpretation of past and present‐day variations in terrestrial organic carbon sequestered in continental margin sediments. Key Points We employ a novel approach to constrain burial efficiencies for source‐specific terrestrial biomolecules in two fluvial/marine systems Terrestrial biomolecular burial efficiencies decrease along transport pathway, reflecting degradation during dispersal and sedimentation Terrestrial biomolecular burial efficiencies are much higher in Yellow River‐Bohai Sea/Yellow Sea than those in Pearl River‐South China Sea