Search

Lateral particle transport in shelf/slope settings of marginal sea systems may potentially supply allochthonous particulate organic carbon (POC) to the ocean interior. The magnitude and prevalence of such processes has implications for our understanding of the functioning and efficiency of modern biological carbon pump processes, as well as for interpretation of deep ocean sediment records. Yet, ages and relative contribution of POC from different sources to deep ocean basins are much less understood. Here, based on radiocarbon (Fm, fraction modern), stable carbon (δ13Corg), and other geochemical analysis of particles intercepted by time‐series sediment traps deployed at three different depths (1,000, 2,150, and 3,200 m), we constrain the source of the sinking POC in the deep basin of northern South China Sea (SCS). The results show that the modern POC derived from surface ocean productivity, acting as the vertical vector, accounts for 87% ± 4% of sinking POC on average, while the lateral vector (aged POC hosted on resuspended sediment) comprises the remainder (13%). The contribution of laterally supplied POC increases with depth and is composed of aged POC derived from several sources. The majority stems from sediment resuspension of the northeastern SCS slope, that entrains aged marine POC (dominant), fossil OC, and soil OC (least significant). The diminished proportion of fossil OC in deep basin sinking POC relative to Taiwan‐proximal areas is likely due to its dispersion via resuspension–deposition loops and dilution by POC stemming from modern surface ocean productivity during the delivery. Plain Language Summary: Quantification of fresh and aged sinking particulate organic carbon (POC) and their vertical and lateral transfer in the marginal sea systems is crucial to budget the global carbon cycle. The South China Sea (SCS) is one of the largest marginal seas in the world, the ages, and relative contribution of POC from different sources to deep basins are poorly constrained. In this study, we provide a first assessment on the age and source of sinking POC in the deep northern SCS basin based on radiocarbon (Fm), stable carbon (δ13Corg), and other geochemical parameters. The results show that 87% ± 4% of sinking POC in the deep basin (1,000–3200 m) derives from modern surface ocean productivity via vertical export. The aged POC supplied via lateral transport has minimal impact on the fluxes and temporal dynamics of the sinking POC. However, the contribution of laterally supplied POC increases with depth and is composed of aged POC derived from several sources: aged marine POC, fossil OC, and soil OC. The importance of laterally supplied POC and complexity of aged POC sources increase with depth, underlining the importance of considering sedimentary OC resuspension and dispersion in bathypelagic and sedimentary records of these dynamic marginal sea systems. Key Points: Multigeochemical data are used to constrain the age and source of sinking particulate organic carbon (POC) in the northern South China SeaThe sinking POC is dominated by vertically settled fresh marine POC, while the aged POC from lateral transport makes a minor contributionThe aged POC is composed of aged marine POC, fossil OC, and soil OC, its contribution and complexity increase with depth [ABSTRACT FROM AUTHOR]