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<p>Laboratory studies detected non-mass-dependent Fe-isotope fractionation during magnetotactic-bacteria-controlled iron (III) reduction, suggesting its potential as a biomineralization proxy. In nature, the preservation of the non-mass-dependent Fe-isotope signature may be difficult due to the abundance of other Fe-rich materials. Here we report a set of distinctly large non-mass-dependent Fe-isotope composition in the top 6.5 cm of the oxic-anoxic transition zone from a sediment core of Lake Aha, southwestern China. Negative ∆'<sup>57</sup>Fe<sub>d</sub>-δ'<sup>56</sup>Fe<sub>d</sub> and positive ∆'<sup>57</sup>Fe<sub>d</sub>-[Mn] correlations support that an abundance of manganese (IV) and ongoing sulfate reduction created a zone of Fe-limited porewaters in the top 6.5 cm of the sediment where magnetotactic bacteria thrived. Non-mass-dependent Fe-isotope signatures were not detected in a sediment core taken at a nearby site in the same lake where in the oxic-anoxic transition zone porewater Fe concentrations were orders-of-magnitude higher. The discovery of non-mass-dependent Fe-isotope signatures in natural sediment offers clues to detecting similar biosignatures.</p>

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Large non-mass-dependent iron isotope fractionation in an oxic-anoxic transition zone of lake sediments

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年11月26日

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  • Liuting Song,
  • Alfonso Mucci,
  • Franck Poitrasson,
  • Peter Dillon,
  • Shuhai Xiao,
  • Xiaodi Zheng,
  • Yilong Song,
  • Zhongliang Wang,
  • Congqiang Liu,
  • Huiming Bao

摘要

Laboratory studies detected non-mass-dependent Fe-isotope fractionation during magnetotactic-bacteria-controlled iron (III) reduction, suggesting its potential as a biomineralization proxy. In nature, the preservation of the non-mass-dependent Fe-isotope signature may be difficult due to the abundance of other Fe-rich materials. Here we report a set of distinctly large non-mass-dependent Fe-isotope composition in the top 6.5 cm of the oxic-anoxic transition zone from a sediment core of Lake Aha, southwestern China. Negative ∆'57Fed-δ'56Fed and positive ∆'57Fed-[Mn] correlations support that an abundance of manganese (IV) and ongoing sulfate reduction created a zone of Fe-limited porewaters in the top 6.5 cm of the sediment where magnetotactic bacteria thrived. Non-mass-dependent Fe-isotope signatures were not detected in a sediment core taken at a nearby site in the same lake where in the oxic-anoxic transition zone porewater Fe concentrations were orders-of-magnitude higher. The discovery of non-mass-dependent Fe-isotope signatures in natural sediment offers clues to detecting similar biosignatures.