Experimental evidence for abiotic organic aqueous species at high-pressure conditions
Carla Tiraboschi  1, 2@  , Carmen Sanchez-Valle  2@  
1 : Dipartimento di Fisica e Geologia, Università degli Studi di Perugia, 06123 Perugia (Italy)
2 : Institut für Mineralogie, University of Münster, 48149 Münster (Germany)

The deep carbon cycle plays a fundamental role in Earth's dynamics, influencing a wide range of processes, from volcanic activity to the genesis of deep diamonds. Its relevance extends across multiple domains, including the origin and evolution of life on Earth to climate and sustainability.

At high-pressure subsolidus conditions, carbon mobilization primarily occurs through the dissolution of carbon-bearing phases by aqueous fluids. While carbonate solubility has been extensively investigated, the contribution of reduced carbon forms has only recently gained attention [1], and their role in the deep carbon cycle remains poorly constrained. Several open questions persist, particularly regarding the speciation and composition of the resulting COH fluid. Recent studies have suggested that organic aqueous species may serve as a previously unrecognized mechanism for carbon mobilization at depth. Thermodynamic models [2] predict the stability of aqueous organic solutes under specific conditions, a hypothesis supported by evidence from natural samples [3]. However, the extent of their contribution to deep carbon transport remains uncertain, as their in-situ formation conditions and stability at high pressures are still debated [4].

Here we present results from Hydrothermal Diamond Anvil Cell experiments aimed at characterizing the composition of COH fluids in equilibrium with quartz and either graphite or glass-like carbon, at pressures up to 2 GPa and temperatures up to 800 °C. Our findings provide experimental evidence for the formation of aqueous organic species from the dissolution of reduced carbon in aqueous fluids at oxidizing conditions. These results suggest that high-pressure organic compounds may play a crucial role in carbon transport and cycling at depth, with significant implications for carbon fluxes in subduction zones.

[1] Tiraboschi et al (2022) Eur.J.Mineral. 34, 59-75 [2] Sverjensky et al. (2014) Nat.Geosci. 2, 909-913 [3] Bouilhol et al. (2022) Nat.Commun. 13, 1-10 [4] Szlachta et al. (2022) Geochem.Perspect.Lett. 21, 28-31


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