Oceanographic and human impacts on the compositions of sedimentary organic matter along the southern coast of Zhoushan

Three sediment cores were collected from the southern coastal area of Zhoushan Island, and their lignin-derived phenol, bulk elemental composition, stable carbon isotope, particle size and ²¹⁰Pb activities were determined. The objective of this study was to determine the compositional changes of the sedimentary organic matter along this coastal area in the past 80 years as a result of anthropogenic and oceanographic-related processes. The results of this study showed that the sources and distribution of sedimentary organic matter along this coastal area were affected by the accelerated development on these islands and mainland China. Moreover, the increased contribution of terrestrial organic matter from the rivers in the mainland from the 1930s to the 1980s was likely the result of human activities. The drastic increase in the vanillic acid to vanillin ratio, (Ad/Al)v, in the 1970s and 1980s coincided with the start of rapid development in Zhoushan, resulting in the increased erosion of more degraded terrestrial organic matter along the coast. Trends of increasing marine organic matter toward the present could be due to a combination of reduced river input and sea level rise. Overall, our results showed that the sedimentary organic matter along the southern coastal zone of Zhoushan main island was affected by riverine input from the mainland, and showed a tendency toward decreasing terrestrial organic matter and particle size. Thus, local input and increased phytoplankton production will play a more important role in the carbon dynamics in this coastal area in the future. (245 words).