Redox overprinting and anthropogenic source shifts recorded by mercury isotope systematics in Eastern Mediterranean deep-sea sediments
Abstract
Deep-sea sediments constitute long-term archives of mercury (Hg) burial, yet the chronological record can be biased by post-depositional diagenetic processes, particularly in areas with high organic matter export and redox variations. We present Hg stable isotope data from Holocene deep-sea sediment cores of the Ionian Sea (Eastern Mediterranean) to quantify how depositional redox conditions, early diagenesis, and anthropogenic forcing shape sedimentary Hg systematics. The distinct organic-rich sapropel S1 developed during the early Holocene provides a natural redox perturbation experiment. During sapropel formation, Hg concentrations and accumulation rates increased markedly in concert with organic carbon burial, reflecting efficient scavenging of dissolved seawater Hg under enhanced productivity and stratified water-column conditions with reduced deep-water ventilation. Hg isotope signatures remained invariant and indistinguishable from background sediments, implying minimal isotopic fractionation during primary deposition and preservation of contemporaneous seawater isotope signatures. In contrast, post-depositional oxidation (“burn-down”) of the sapropel induced substantial Hg remobilization and redistribution across redox fronts, generating pronounced negative excursions in δ202Hg (up to ∼1.6‰, relative to background) coincident with manganese and molybdenum enrichments. These shifts suggest that early diagenesis imposed strong mass-dependent fractionation (MDF), most likely during oxidative mobilization and subsequent re-immobilization of Hg into authigenic phases. Throughout sapropel deposition and oxidation, mass-independent fractionation (MIF, Δ199Hg and Δ200Hg) remained largely unaffected, indicating that Hg MIF signatures appear insensitive to these post-depositional processes and may preserve surface-derived signatures. The upper oxic sediments in the late Holocene show little impact of redox-driven diagenesis on Hg and record two isotopically distinct anthropogenic phases. A modest Hg enrichment during the late Iron Age–Roman period is characterized by elevated δ202Hg and near-zero Δ199Hg values, consistent with lateral transport of local metallurgical residues. In contrast, Industrial Era sediments display sharply increased Hg enrichment accompanied by lower δ202Hg and slightly positive Δ199Hg values, suggesting dominant inputs from industrial Hg emissions at a broader scale. Together, these results suggest that sedimentary Hg isotopes preserve both depositional and diagenetic information. When interpreted within a stratigraphically constrained redox framework, paired MDF–MIF systematics provide a robust approach for disentangling redox overprinting from source variability, thereby strengthening the reliability of marine sediments as archives of past Hg cycling and environmental change.
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BibTeX
@article{chen2026redox,
title = {{Redox overprinting and anthropogenic source shifts recorded by mercury isotope systematics in Eastern Mediterranean deep-sea sediments}},
author = {Xiaowei Chen and Daniel Cossa and Jiawang Wu and Lars-Eric Heimbürger-Boavida and Songjing Li and Zhao Wang and Stéphane Guédron and Wang Zheng and Yi Liu and Jiubin Chen and Ruoyu Sun},
journal = {Geochimica et Cosmochimica Acta},
year = {2026},
month = sep,
doi = {10.1016/j.gca.2026.08.033},
url = {https://hal.science/hal-05785853v1},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - JOUR
TI - Redox overprinting and anthropogenic source shifts recorded by mercury isotope systematics in Eastern Mediterranean deep-sea sediments
AU - Xiaowei Chen
AU - Daniel Cossa
AU - Jiawang Wu
AU - Lars-Eric Heimbürger-Boavida
AU - Songjing Li
AU - Zhao Wang
AU - Stéphane Guédron
AU - Wang Zheng
AU - Yi Liu
AU - Jiubin Chen
AU - Ruoyu Sun
PY - 2026
DA - 2026/09/01
JO - Geochimica et Cosmochimica Acta
DO - 10.1016/j.gca.2026.08.033
UR - https://hal.science/hal-05785853v1
AB - Deep-sea sediments constitute long-term archives of mercury (Hg) burial, yet the chronological record can be biased by post-depositional diagenetic processes, particularly in areas with high organic matter export and redox variations. We present Hg stable isotope data from Holocene deep-sea sediment cores of the Ionian Sea (Eastern Mediterranean) to quantify how depositional redox conditions, early diagenesis, and anthropogenic forcing shape sedimentary Hg systematics. The distinct organic-rich sapropel S1 developed during the early Holocene provides a natural redox perturbation experiment. During sapropel formation, Hg concentrations and accumulation rates increased markedly in concert with organic carbon burial, reflecting efficient scavenging of dissolved seawater Hg under enhanced productivity and stratified water-column conditions with reduced deep-water ventilation. Hg isotope signatures remained invariant and indistinguishable from background sediments, implying minimal isotopic fractionation during primary deposition and preservation of contemporaneous seawater isotope signatures. In contrast, post-depositional oxidation (“burn-down”) of the sapropel induced substantial Hg remobilization and redistribution across redox fronts, generating pronounced negative excursions in δ202Hg (up to ∼1.6‰, relative to background) coincident with manganese and molybdenum enrichments. These shifts suggest that early diagenesis imposed strong mass-dependent fractionation (MDF), most likely during oxidative mobilization and subsequent re-immobilization of Hg into authigenic phases. Throughout sapropel deposition and oxidation, mass-independent fractionation (MIF, Δ199Hg and Δ200Hg) remained largely unaffected, indicating that Hg MIF signatures appear insensitive to these post-depositional processes and may preserve surface-derived signatures. The upper oxic sediments in the late Holocene show little impact of redox-driven diagenesis on Hg and record two isotopically distinct anthropogenic phases. A modest Hg enrichment during the late Iron Age–Roman period is characterized by elevated δ202Hg and near-zero Δ199Hg values, consistent with lateral transport of local metallurgical residues. In contrast, Industrial Era sediments display sharply increased Hg enrichment accompanied by lower δ202Hg and slightly positive Δ199Hg values, suggesting dominant inputs from industrial Hg emissions at a broader scale. Together, these results suggest that sedimentary Hg isotopes preserve both depositional and diagenetic information. When interpreted within a stratigraphically constrained redox framework, paired MDF–MIF systematics provide a robust approach for disentangling redox overprinting from source variability, thereby strengthening the reliability of marine sediments as archives of past Hg cycling and environmental change.
SN - 0016-7037
SN - 1872-9533
ER -