Molybdenum (Mo) elemental and isotopic systematics represent one of the most widely applied trace element-isotope proxies in paleoenvironmental research, offering unique advantages in reconstructing global and local redox conditions, especially in tracing sulfidic conditions (Kendall, 2021). Firstly, we review the development, merits and limitations of Mo elemental and isotopic mass balance models. Considering the substantial differences in the Mo elemental-isotopic cycle between modern oceans and ancient anoxic oceans, we systematically review the selection principles of the isotope fractionation values and burial rates under different Mo removal pathways, on the basis of the geochemical characteristics (Qin et al., 2022; Xu et al., 2023).
Furthermore, we assess the reliability of various sedimentary archives—including sulfidic organic-rich shales, sedimentary Fe-Mn deposits, and carbonates—and discuss the uncertainties associated with their ability to reflect coeval seawater Mo isotope compositions. Notably, recent advances in Mo isotope geochemistry in carbonate systems underscore the significant influence of syn-depositional redox conditions, which call for a more integrated understanding of water column and pore water chemistry.

References
Kendall, B. (2021). Recent advances in geochemical paleo-oxybarometers. Annual Review of Earth and Planetary Sciences, 49(1), 399-433.
Qin, Z., Xu, D., Kendall, B., Zhang, X., Ou, Q., Wang, X., Li, Jie, Liu, J., 2022. Molybdenum isotope-based redox deviation driven by continental margin euxinia during the early Cambrian. Geochimica et Cosmochimica Acta, 325, 152-169.
Xu, D., Qin, Z., Wang, X., Li, J., Shi, X., Tang, D., & Liu, J. 2023. Extensive sea-floor oxygenation during the early Mesoproterozoic. Geochimica et Cosmochimica Acta, 354, 186-196.
 

Molybdenum isotopes,Mass balance model,Redox reconstruction,Diagenesis