Distribution characteristics and influencing factors of Mo in surface sediments of Qinghai Lake

Key words: 
• Mo element /
• Redox proxies /
• Organic matter /
• Trace elements /
• Lacustrine mudstone

Abstract: V/(V+Ni), V/Cr, U/Th, Uauto and Ce are the traditional redox proxies of Marine strata, but there are multiple solutions to the redox identification of lacustrine strata. Molybdenum(Mo) is a new redox proxies, but the fixation mechanisms of Mo under various redox conditions in lake environment are not well understood, which limits the application potential of Mo in the reconstruction of lake paleoenvironment. This article systematically tested surface sediment samples from Qinghai Lake, analyzed the planar enrichment characteristics of Mo, and explored the corresponding relationships between Mo content and continental input, grain size, element content, organic matter content of sediment and water environment. The preliminary results show that Qinghai Lake is an alkaline, suboxic and brackish water lake, and Mo element is slightly enriched in the sediments in deep water area. Continental input and grain size of sediment do not affect Mo enrichment. Mo can not be settled and enriched by adsorption of clay minerals and Fe oxyhydroxides in weakly alkaline-alkaline lake basin. Although Mn oxyhydroxides may adsorb Mo and settle, Mo will be re-released from the sediment into the water body as the sediment transforms into a reducing environment. There is a good correlation between organic matter abundance and Mo content, indicating that, at the deep part of lake, the hypolimnion becomes dysoxic. Organic matter adsorption and preservation are the main controlling factors of Mo enrichment in sediments.