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<p>The use of molybdenum isotopes (δ<sup>98</sup>Mo) as a paleo-redox proxy requires quantifications of fluxes and isotopic fractionations in each molybdenum sink. However, no systematic tests on δ<sup>98</sup>Mo variations in different oxic sediments have been made due to limitations of analytical precision and sample number in pioneering studies. Here, we present the δ<sup>98</sup>Mo data of ferromanganese nodules sampled at various global basins, which exhibit large variations from −0.95‰ to −0.51‰ with appreciable negative correlations between δ<sup>98</sup>Mo and manganese–iron ratios. Diagenetic nodules, experiencing dissolution and re-precipitation of manganese oxides in marine sediments, have lower δ<sup>98</sup>Mo by ~0.3‰ and higher molybdenum contents relative to hydrogenetic nodules. We suggest that changes in relative proportions of manganese and iron oxides and early diagenesis of marine sediments likely influence overall molybdenum isotope fractionations in oxic sinks. Hence, evolution of ancient marine manganese and iron cycles can influence sedimentary δ<sup>98</sup>Mo signatures, especially in low-oxygen Precambrian oceans.</p>

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Molybdenum isotope fractionations between ferromanganese oxides and seawater influenced ancient sedimentary isotopic signatures

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年7月18日

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  • Mengchun Cao,
  • Guang-Yi Wei,
  • Feifei Zhang,
  • Xiangwen Ren,
  • Xuefa Shi,
  • Yi-Bo Lin,
  • Tao Li,
  • Sihui Chen,
  • Hong-Fei Ling,
  • Jian Cao

摘要

The use of molybdenum isotopes (δ98Mo) as a paleo-redox proxy requires quantifications of fluxes and isotopic fractionations in each molybdenum sink. However, no systematic tests on δ98Mo variations in different oxic sediments have been made due to limitations of analytical precision and sample number in pioneering studies. Here, we present the δ98Mo data of ferromanganese nodules sampled at various global basins, which exhibit large variations from −0.95‰ to −0.51‰ with appreciable negative correlations between δ98Mo and manganese–iron ratios. Diagenetic nodules, experiencing dissolution and re-precipitation of manganese oxides in marine sediments, have lower δ98Mo by ~0.3‰ and higher molybdenum contents relative to hydrogenetic nodules. We suggest that changes in relative proportions of manganese and iron oxides and early diagenesis of marine sediments likely influence overall molybdenum isotope fractionations in oxic sinks. Hence, evolution of ancient marine manganese and iron cycles can influence sedimentary δ98Mo signatures, especially in low-oxygen Precambrian oceans.