Distribution, source and burial of sedimentary organic carbon in the east China seas

        The ocean is the largest active carbon reservoir on Earth. Transport and burial of the sedimentary carbon affect marine biogeochemical processes and marine carbon cycle on different time scales, and even have an important impact on the global climate change. Distribution, transport and burial of sedimentary carbon in marginal seas are an important part of the global carbon cycle. The east China seas includes the Bohai Sea, Yellow Sea and East China Sea and are characterized by broad shelves. They receive enormous amount of fluvial sediment from the Huanghe and Changjiang rivers and bury abundant sedimentary organic carbon.

         Based on the investigated data of China over the past 30 years and collected information, including 5796 stations of organic carbon and other relevant geochemical and sedimentological parameters, we preliminarily compiled a 1:3000000 distribution map of sedimentary organic carbon of the east China seas, elaborated the distribution characteristics, sources and buried flux of sedimentary organic carbon, and discussed the influence of hydrodynamic forces, sediment composition and human activities on it. The results show: (1) TOC contents in the sediments ranges from 0.01 to 2.12% in the east China seas. And there are high values in the mud areas such as the central Bohai Sea, eastern coast of the Shandong Peninsula, central South Yellow Sea, southwest of Jeju Island, old Huanghe River estuary, southeast of the Yellow Sea, and Zhejiang-Fujian coast. (2) δ¹³C values are from -25.80~-20.00‰ and ~70% of sedimentary organic carbon is marine source. (3) range of Δ¹⁴C in the sedimentary organic carbon is -871 ~ -137‰. The age of sedimentary organic carbon is older in the areas of the old Huanghe River estuary, Jiangsu sand ridges, outer shelf of the East China Sea and northeast Taiwan. (4) The burial rates of organic carbon in the mud areas are higher in the east China seas, which reaches maximum value of 68.8 g/m²/yr in the Bohai Sea mud area and is generally low near the old Huanghe River estuary (15.2 g/m²/yr). The burial amount of sedimentary organic carbon is about 8.2 Mt/yr. The distribution and burial of terrigenous organic carbon in the BYES are mainly influenced by the large river inputs and complex marine hydrodynamic environment, while human activities such as dam construction have significantly altered the burial of organic carbon in coastal mud areas.