Spatial variability in the abundance, composition, and age of organic matter in surficial sediments of the East China Sea

Understanding the sources and fate of organic matter (OM) sequestered in continental margin sediments is of importance because the mode and efficiency of OM burial impact the carbon cycle and the regulation of atmospheric CO ₂ over long time scales. We carried out molecular (lignin-derived phenols from CuO oxidation), elemental, isotopic (δ¹³C, Δ¹⁴C), and sedimentological (grain size and mineral surface area) analyses in order to examine spatial variability in the abundance, source, age of surface sediments of the East China Sea. Higher terrigenous organic matter values were found in the main accumulating areas of fluvial sediments, including the Changjiang (Yangtze) Estuary and Zhejiang-Fujian coastal zone. Isotopic and biomarker data suggest that the sedimentary OM in the inner shelf region was dominated by aged (Δ¹⁴C = -423 ± 42‰) but relatively lignin-rich OM (Λ = 0.94 ± 0.57 mg/100 mg OC) associated with fine-grained sediments, suggesting important contributions from soils. In contrast, samples from the outer shelf, while of similar age (Δ¹⁴ C = -450 ± 99‰), are lignin poor (Λ = 0.25 ± 0.14 mg/100 mg OC) and associated with coarse-grained material. Regional variation of lignin phenols and OM ages indicates that OM content is fundamentally controlled by hydrodynamic sorting (especially, sediment redistribution and winnowing) and in situ primary production. Selective sorption of acid to aldehyde in clay fraction also modified the ratios of lignin phenols. The burial of lignin in East China Sea is estimated to be relatively efficient, possibly as a consequence of terrigenous OM recalcitrance and/or relatively high sedimentation rates in the Changjiang Estuary and the adjacent Zhejing-Fujian mud belt. Key Points Spatial variability in the abundance, source, age in surface sediment of the ECS Contrasting behavior of OM from inner to outer shelf Burial of lignin in ECS is relatively efficient, especially in inner shelf