Carbon Isotopic Constraints on Basin‐Scale Vertical and Lateral Particulate Organic Carbon Dynamics in the Northern South China Sea

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 (F-m, fraction modern), stable carbon (delta C-13(org)), 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.
Journal of Geophysical Research: Oceans, 127 (8)
ISSN:0148-0227
ISSN:2169-9275