Experimental investigation of a deep organic carbon cycling promoted by carbonate reduction in subduction zones
Abstract
Recent studies show that subduction zones host both biogenic and abiotic organic carbon. The latter can form under high-pressure and high-temperature conditions, yet the mechanisms and redox controls remain poorly constrained. We present piston-cylinder experiments at 700°C and 3 GPa simulating carbonate reduction in the presence of antigorite over a wide oxygen fugacity range, from about ΔFMQ -4 to -1 relative to fayalite-magnetite-quartz (FMQ) buffer. Graphitic carbon forms under all investigated redox conditions, and is systematically associated with chlorite derived from antigorite breakdown. Raman spectroscopy, TOF-and Orbi-SIMS analyses indicate that under the most reducing conditions investigated i.e., approaching those imposed by wüstite-magnetite buffer (ΔFMQ ≈ -4), abundant graphitic carbon forms and is highly ordered, hydrogen-poor and dominated by aromatic structures. In contrast, less reducing conditions (buffered at nickel-nickel oxide, ΔFMQ ≈ -1), yield smaller amounts of highly disordered, partially hydrogenated and oxygenated graphitic carbon. These differences, observed under identical pressure and temperature, primarily reflects the influence of oxygen fugacity, indicating a redox-driven formation pathway distinct from the thermal maturation and graphitization of biogenic organic matter. Such redox-driven precipitation of graphitic carbon may promote transient carbon storage, facilitate volatile transport into the deep mantle and contribute to the diversity of metastable carbon species involved in the deep carbon cycling.
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BibTeX
@article{besognet2026experimental,
title = {{Experimental investigation of a deep organic carbon cycling promoted by carbonate reduction in subduction zones}},
author = {Laurie Besognet and Baptiste Debret and Marcus Rohnke and Imène Esteve and Alexandre Corgne and Julien Siebert and Bénédicte Ménez},
journal = {Earth and Planetary Science Letters},
year = {2026},
month = oct,
doi = {10.1016/j.epsl.2026.120365},
url = {https://hal.science/hal-05785316v1},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Experimental investigation of a deep organic carbon cycling promoted by carbonate reduction in subduction zones
AU - Laurie Besognet
AU - Baptiste Debret
AU - Marcus Rohnke
AU - Imène Esteve
AU - Alexandre Corgne
AU - Julien Siebert
AU - Bénédicte Ménez
PY - 2026
DA - 2026/10/08
JO - Earth and Planetary Science Letters
DO - 10.1016/j.epsl.2026.120365
UR - https://hal.science/hal-05785316v1
AB - Recent studies show that subduction zones host both biogenic and abiotic organic carbon. The latter can form under high-pressure and high-temperature conditions, yet the mechanisms and redox controls remain poorly constrained. We present piston-cylinder experiments at 700°C and 3 GPa simulating carbonate reduction in the presence of antigorite over a wide oxygen fugacity range, from about ΔFMQ -4 to -1 relative to fayalite-magnetite-quartz (FMQ) buffer. Graphitic carbon forms under all investigated redox conditions, and is systematically associated with chlorite derived from antigorite breakdown. Raman spectroscopy, TOF-and Orbi-SIMS analyses indicate that under the most reducing conditions investigated i.e., approaching those imposed by wüstite-magnetite buffer (ΔFMQ ≈ -4), abundant graphitic carbon forms and is highly ordered, hydrogen-poor and dominated by aromatic structures. In contrast, less reducing conditions (buffered at nickel-nickel oxide, ΔFMQ ≈ -1), yield smaller amounts of highly disordered, partially hydrogenated and oxygenated graphitic carbon. These differences, observed under identical pressure and temperature, primarily reflects the influence of oxygen fugacity, indicating a redox-driven formation pathway distinct from the thermal maturation and graphitization of biogenic organic matter. Such redox-driven precipitation of graphitic carbon may promote transient carbon storage, facilitate volatile transport into the deep mantle and contribute to the diversity of metastable carbon species involved in the deep carbon cycling.
SN - 0012-821X
ER -