Abstract: Stable tungsten isotopes (δ¹⁸⁶/¹⁸⁴W) are a promising new geochemical proxy for tracing surface material cycles and reconstructing ancient ocean environments. A clear understanding of the source-sink system of stable W isotopes in the ocean is essential for expanding the application. Research indicates that riverine input constitutes the primary source of W in modern oceans, while non-euxinic sediments serve as the main sink. However, the fluxes and isotopic characteristics of different types of non-euxinic sediment sinks remain unclear. Hydrothermal sediments, enriched in hydrothermal sourced iron-manganese oxides, can adsorb significant amounts of W from seawater during sedimentation, resulting in authigenic W enrichment and making them a potentially significant sink. This study analyzed hydrothermal sediment samples from ODP Site 834A in the Lau Basin, South Pacific, to estimate the contribution of hydrothermal sediments to the global oceanic W budget. The high W/ Th in the samples suggests minimal detrital input, while the W/Mo ratio, rare earth element distributions, and δ186/184W values indicate that W in the sediments was primarily adsorbed from seawater by iron-manganese oxides, with manganese oxides playing
a dominant role. The lower-than-expected isotopic fractionation between sediments and seawater may reflect porewater effects driven by rapid sedimentation and high depositional flux. Based on the W/Mn ratios and global hydrothermal Mn fluxes, the hydrothermal sediments W sink flux is estimated to constitute less than 5% of the total riverine input, implying the presence of other unrecognized major W sinks. 

Key words: stable tungsten isotope, hydrothermal sediments, oceanic tungsten cycle