Origins of terrestrial organic matter in surface sediments of the East China Sea shelf

Terrestrial organic matter (TOM) is an important component of marine sedimentary OM, and revealing the origins and transport mechanisms of TOM to the East China Sea (ECS) is important for understanding regional carbon cycle. A novel approach combining molecular proxies and compound-specific carbon isotopes is used to quantitatively constrain the origins and transport mechanisms of TOM in surface sediments from the ECS shelf. The content of terrestrial biomarkers of (C-27+C-29+C-31) n-alkanes (52 to 580 ng g(-1)) revealed a seaward decreasing trend, the delta C-13(TOC) values (-20.6aEuro degrees to -22.7aEuro degrees) were more negative near the coast, and the TMBR (terrestrial and marine biomarker ratio) values (0.06 to 0.40) also revealed a seaward decreasing trend. These proxies all indicated more TOM (up to 48%) deposition in the coastal areas. The Alkane Index, the ratio of C-29/(C-29+C-31) n-alkanes indicated a higher proportion of grass vegetation in the coastal area; While the delta C-13 values of C-29 n-alkane (-29.3aEuro degrees to -33.8aEuro degrees) indicated that terrestrial plant in the sediments of the ECS shelf were mainly derived from C-3 plants. Cluster analysis afforded detailed estimates of different-sourced TOM contributions and transport mechanisms. TOM in the Zhejiang-Fujian coastal area was mostly delivered by the Changjiang River, and characterized by higher %TOM (up to 48%), higher %C-3 plant OM (68%-85%) and higher grass plant OM (56%-61%); TOM in the mid-shelf area was mostly transported by aerosols, and characterized by low %TOM (less than 17%), slightly lower C-3 plant OM (56%-72%) and lower grass plant OM (49%-55%).