The dispersal of sedimentary terrestrial organic matter in the East China Sea (ECS) as revealed by biomarkers and hydro-chemical characteristics

Abstract

Terrestrial organic matter (TOM) in surface sediments from the lower Yangtze River and adjacent East China Sea (ECS) shelf was characterized using elemental, stable carbon isotope and molecular analysis. The results show that it is heterogeneous and derives from various sources in the lower river transect (RC transect) and inner shelf transect (ZJ transect), but is more homogeneous and presumably derives from a single source in the cross-shelf transect (PN transect). The trends in sedimentary TOM abundance indicated by high molecular weight n-alkane abundances and distributions, lignin-derived products, δ 13C values of total organic carbon ( δ 13C TOC) and ratio of TOC to total nitrogen (C/N) suggest a southward (off-estuary) transport mode of TOM along the inner shelf transect while, counter intuitively, the opposite or no trend in TOM off-estuary transport occur along the cross-shelf transect. We therefore suggest that Yangtze-discharged OM is transported southwards along the Zhejiang-Fujian coast (ZJ transect) and enters the Southern Okinawa Trough via near bottom currents, from where it is ultimately delivered back upslope to the middle shelf by the Kuroshio invading water, consistent with the hydro-chemical characteristics of the ECS.