EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Biogeochemical processes in continental slope sediments of the Dongsha Area, South China Sea

Tiantian Sun1,2,3, Daidai Wu1, and Ying Ye2
Tiantian Sun et al.
  • 1Key Laboratory of Gas Hydrate, Guangzhou Institute of Energy Conversion, Chinese Academy of sciences, Guangzhou 510640, China.
  • 2Ocean College, Zhejiang University, Zhoushan 316021, China.
  • 3Leibniz Institute for Baltic Sea Research, Geochemistry and Isotope Biogeochemistry Group, Warnemunde, Germany (

Serving as an indicator or fluid seepage from seabed sediments, cold seeps are ubiquitous along continental margins worldwide. In this study, a 14 m long sediment core (# 973-4) from the Dongsha Area on the northern continental slope of the South China Sea, was investigated to trace the cold seep activity and sedimentary paleo-environmental changes and its consequence for sediment mineralogy, contents of major and trace elements, total organic and inorganic carbon and total TRIS (total reducible inorganic sulfur) and δ34S of sulfide minerals. In addition, planktonic foraminifera were selected for accelerator mass spectrometer carbon 14 (AMS14C) dating [1]. Furthermore, we identified the strength and effects of cold seep activity and its impact on the underlying seawater redox condition, and finally elucidated the derived force and paleoenvironment constraints of cold seep activity. C-S-Fe geochemistry, δ34S of sulfide minerals and major and trace elements suggest that anaerobic oxidation of methane (AOM) occurred at 619-900 cmbsf (centimeters below seafloor). The 34S enrichments (up to 23.6 ‰), abundant TRIS contents, high S/C ratios close to the seawater, together with high enrichments of Mo indicate temporal sulfidic methane seep events. Lithological distribution and AMS14C dating of planktonic foraminifera show that a turbidite (~35ka) is related to a foram-rich interval (440-619 cm) and increased carbonate productivity during the Last Glacial Maximum (LGM). An enrichment of Mo and U was observed accompanied by low contents of other trace and major (Al, Ti, V, Ni, Fe, Mn and Cu) in this interval. The foram-rich interval of cold seep sediments was probably linked to the phenomenon of inconsecutive sedimentary sequence due to the turbidites, which resulted in the lack of Fe, Mn and Ba. Based on the new results, it can be speculated that this area has experienced several episodes of methane seep activity and aerobic oxidation occurring alternatively in the last glacial period which may have been caused by fluctuating non-steady conditions. Further exploration of AOM should focus on the impact of rapid deposition, especially the impact of turbidites on sedimentary biogeochemical processes.

[1] Zhang Bidong, Pan Mengdi, Wu Daidai etc. Distribution and isotopic composition of foraminifera at cold-seep Site 973-4 in the Dongsha area, northeastern South China Sea. J. Asian Earth Sciences.


The research supported by the Institution of South China Sea Ecology and Environmental Engineering, Chinese Academy of Sciences (no. ISEE2018YB03) and the special project for marine economy development of Guangdong Province (no. GDME-2018D002).

How to cite: Sun, T., Wu, D., and Ye, Y.: Biogeochemical processes in continental slope sediments of the Dongsha Area, South China Sea , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4602,, 2020