Abstract The concentration and isotopic composition of sedimentary molybdenum (Mo) has been used to distinguish different redox environments in modern marine settings and in the geological record. We report Mo concentrations and δ98Mo from porewaters and sediments in three anoxic East Anglian salt marsh pond environments: (1) ‘iron-rich’ sediments containing high concentrations of dissolved ferrous iron (up to 2 mM), (2) ‘sulfide-rich’ sediments containing very high concentrations of aqueous sulfide (up to 10 mM) and, (3) sediments that we consider to be intermediate between ‘iron-rich’ and ‘sulfide-rich’ conditions. In iron-rich sediments, we suggest that iron speciation and mineralogy controls the concentration and isotopic composition of Mo. Despite similar aqueous sulfide profiles, the intermediate and sulfide-rich pond sediment have different porewater Mo concentrations and δ98Mo. In the sulfide-rich pond sediment, we suggest that the concentration and isotopic composition of Mo is controlled by solubility equilibrium with an Fe-Mo-S mineral species (e.g. FeMoS4) due to similarities in sediment and porewater δ98Mo throughout the sediment column. In the intermediate pond sediment, we conclude that active breakdown of iron oxides redistributes porewater Mo, observable as a peak of dissolved Mo (>100 ppb), which diffuses within the sedimentary porewaters. The sedimentary δ98Mo is higher in sulfide-rich and intermediate pond sediment (mean = 1.66‰, range = 0.98–1.92‰) than in iron-rich pond sediment (mean = 1.10‰, range = 0.28–1.65‰) with all ponds having sedimentary δ98Mo that is lower than seawater. The maximum sedimentary δ98Mo observed in these anoxic sediments, which is 0.5–0.7‰ lower than seawater, appears to be set by Fe-Mo-S equilibration with ambient thiomolybdate species. We suggest diagenetic overprinting can cause more efficient capture of pond water Mo and causes sediment δ98Mo of originally iron-rich pond sediment to evolve to higher values at progressively higher aqueous sulfide concentrations.

中文翻译：

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盐沼池塘沉积物中的钼地球化学

摘要 沉积钼 (Mo) 的浓度和同位素组成已被用于区分现代海洋环境和地质记录中的不同氧化还原环境。我们报告了三个缺氧东盎格利亚盐沼池塘环境中孔隙水和沉积物中的 Mo 浓度和 δ98Mo：（1）“富含铁”的沉积物，其中含有高浓度的溶解亚铁（高达 2 mM），（2）“富含硫化物” ' 沉积物含有非常高浓度的硫化物水溶液（高达 10 mM），以及 (3) 我们认为介于“富含铁”和“富含硫化物”条件之间的沉积物。在富含铁的沉积物中，我们认为铁的形态和矿物学控制着 Mo 的浓度和同位素组成。中等和富硫化物池塘沉积物具有不同的孔隙水Mo浓度和δ98Mo。在富含硫化物的池塘沉积物中，由于整个沉积柱中沉积物和孔隙水 δ98Mo 的相似性，我们建议 Mo 的浓度和同位素组成受与 Fe-Mo-S 矿物种类（例如 FeMoS4）的溶解度平衡控制。在中间池塘沉积物中，我们得出结论，铁氧化物的主动分解重新分布了孔隙水 Mo，可观察到溶解的 Mo (>100 ppb) 的峰值，其在沉积孔隙水中扩散。沉积 δ98Mo 在富硫化物和中间池塘沉积物中（平均值 = 1.66‰，范围 = 0.98-1.92‰）高于富含铁的池塘沉积物（平均值 = 1.10‰，范围 = 0.28-1.65‰），所有池塘都具有低于海水的沉积δ98Mo。在这些缺氧沉积物中观察到的最大沉积 δ98Mo，比海水低 0.5-0.7‰，似乎是由 Fe-Mo-S 与周围硫钼酸盐物种的平衡设定的。我们建议成岩叠印可以更有效地捕获池塘水 Mo 并导致最初富含铁的池塘沉积物的沉积物 δ98Mo 在逐渐升高的含水硫化物浓度下演变为更高的值。