Sulfur isotope geochemistry of the central Japan Sea sediments (IODP Exp. 346) 20-150 kyr ago; implications for the evolution of Asian Monsoon climate system

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Author(s): Oshio, Shu; Yamaguchi, Kosei E.; Takahashi, Satoshi; Naraoka, Hiroshi; Ikehara, Minoru
Author Affiliation(s): Primary:
Toho University, Chiba, Japan
University of Tokyo, Japan
Kyushu University, Japan
University of Kochi, Japan
Volume Title: AGU 2016 fall meeting
Source: American Geophysical Union Fall Meeting, Vol.2016; American Geophysical Union 2016 fall meeting, San Francisco, CA, Dec. 12-16, 2016. Publisher: American Geophysical Union, Washington, DC, United States
Note: In English
Summary: Asian monsoon climate system has started about 50 Ma, after the collision of the Indian and Eurasian continents followed by uplift of the Himalaya and Tibetan Plateau. It has influenced sediments in the Japan Sea, where cm-scale alternation of Corg-rich dark layers and Corg-poor light layers occurs. This is most likely due to temporal changes in the nutrient status and/or oceanic redox conditions, which are likely caused by the fluctuations in the intensity of continental weathering and ocean currents, both of which were ultimately caused by the variable monsoon system. In order to obtain insights into the evolving oceanic redox state and the monsoon system, we conducted sulfur speciation and isotope study for the marine sediment core samples recovered in the central Japan Sea by IODP Exp. 346. The light layers have lower Spy (0.03-0.25 wt.%) contents when compared to the dark layers (0.26-1.49 wt.%). The Corg contents have similar distribution (0.34-1.10 wt.% for light layers and 1.16-3.38 wt.% for dark layers). However, the SSO4 contents (0.02-0.64 wt.%) and the δ34S values (-34 to -38 ppm) did not show such light-dark distinction. Elevated Spy/Corg ratios (0.03-1.00) in the dark layers are interpreted to represent sulfide formation in the anoxic water column by bacterial sulfate reduction. During deposition of light layers, oxidation of sulfide minerals could have resulted in formation of sulfate minerals without significant isotope fractionation, as observed in this study. Regardless of the type of the sediments (dark vs. light), sulfate was not limiting during bacterial sulfate reduction, as reflected in the sulfur isotope compositions. We speculate that, during deposition of dark layers, enhanced summer monsoon activity caused heavy rainfall and increased source-rock weathering, runoff of the Yangtze River, and nutrient input into the East China Sea and the Tsushima Warm Current. Inflow of nutrient-rich and less salty water into the Japan Sea triggered enhanced biological activity, water-column density stratification, transport of organic matter into deeper ocean and consumption of dissolved oxygen, and ultimately the creation of anoxic water body to allow bacterial sulfate reduction. (syngenetic sulfide formation)
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 24 Surficial Geology, Quaternary Geology; Cenozoic; Expedition 346; Integrated Ocean Drilling Program; Isotope ratios; Isotopes; North Pacific; Northwest Pacific; Pacific Ocean; Quaternary; S-34/S-32; Stable isotopes; Sulfur; West Pacific
Coordinates: N313700 N434600 E1390500 E1285930
Record ID: 2017051565
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