Chemical forms of cerium in ferromanganese crusts from the Global Ocean: Implications for the fractionation of cerium isotopes
Abstract
The oxidative enrichment and isotopic fractionation of cerium (Ce) in contact with vernadite (δ-MnO2) serve as paleoredox indicators in both terrestrial and marine environments. However, the molecular processes that govern the scavenging of Ce from the dissolved 3+ to the insoluble 4+ states remain obscure. Adsorption experiments on synthetic δ-MnO2 suggest that aqueous Ce(III) precipitates as ceric hydroxide (Ce(OH)4), an unidentified mineral. Here, the atomic-scale structure of Ce in natural vernadite from ferromanganese crusts collected across the Pacific, Atlantic, and Indian Oceans was examined using advanced high-energy-resolution extended X-ray absorption fine structure spectroscopy. The findings provide the first direct evidence for the uptake of Ce as mononuclear Ce(IV) complexes on the layer edges (DES complex) and on Mn(IV) vacancy sites (Half-INC complex) of vernadite. Density functional theory-based Gibbs free-energy calculations show that hydrolysis of the surface complexes promotes the oxidation of Ce(III) to Ce(IV). Quantum mechanical calculations predict that the equilibrium ¹³⁶Ce/¹⁴⁰Ce isotope fractionation factor between Ce(III) dissolved in seawater and the Ce(IV) complexes can reach 10³lnα = 1.4-1.5 at 25 °C, indicating that the ¹³⁶Ce/¹⁴⁰Ce ratio has high potential as a new paleoredox proxy
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BibTeX
@article{manceau2026chemical,
title = {{Chemical forms of cerium in ferromanganese crusts from the Global Ocean: Implications for the fractionation of cerium isotopes}},
author = {Alain Manceau and Jianlin Liao and Yan Li and Andrea Giacomelli and Marius Retegan and Andrea Koschinsky and Stephan N. Steinmann and Olivier Mathon},
journal = {Communications Earth \& Environment},
year = {2026},
month = sep,
doi = {10.1038/s43247-026-03196-6},
url = {https://hal.science/hal-05762853v1},
note = {CC BY-NC 4.0},
}
RIS
TY - JOUR
TI - Chemical forms of cerium in ferromanganese crusts from the Global Ocean: Implications for the fractionation of cerium isotopes
AU - Alain Manceau
AU - Jianlin Liao
AU - Yan Li
AU - Andrea Giacomelli
AU - Marius Retegan
AU - Andrea Koschinsky
AU - Stephan N. Steinmann
AU - Olivier Mathon
PY - 2026
DA - 2026/09/24
JO - Communications Earth & Environment
DO - 10.1038/s43247-026-03196-6
UR - https://hal.science/hal-05762853v1
AB - The oxidative enrichment and isotopic fractionation of cerium (Ce) in contact with vernadite (δ-MnO2) serve as paleoredox indicators in both terrestrial and marine environments. However, the molecular processes that govern the scavenging of Ce from the dissolved 3+ to the insoluble 4+ states remain obscure. Adsorption experiments on synthetic δ-MnO2 suggest that aqueous Ce(III) precipitates as ceric hydroxide (Ce(OH)4), an unidentified mineral. Here, the atomic-scale structure of Ce in natural vernadite from ferromanganese crusts collected across the Pacific, Atlantic, and Indian Oceans was examined using advanced high-energy-resolution extended X-ray absorption fine structure spectroscopy. The findings provide the first direct evidence for the uptake of Ce as mononuclear Ce(IV) complexes on the layer edges (DES complex) and on Mn(IV) vacancy sites (Half-INC complex) of vernadite. Density functional theory-based Gibbs free-energy calculations show that hydrolysis of the surface complexes promotes the oxidation of Ce(III) to Ce(IV). Quantum mechanical calculations predict that the equilibrium ¹³⁶Ce/¹⁴⁰Ce isotope fractionation factor between Ce(III) dissolved in seawater and the Ce(IV) complexes can reach 10³lnα = 1.4-1.5 at 25 °C, indicating that the ¹³⁶Ce/¹⁴⁰Ce ratio has high potential as a new paleoredox proxy
SN - 2662-4435
ER -