The fate of carbon dioxide in water-rich fluids under extreme conditions

Journal Article · Sat Oct 01 00:00:00 EDT 2016 · Science Advances

DOI:https://doi.org/10.1126/sciadv.1601278· OSTI ID:1489269

Pan, Ding; Galli, Giulia

Investigating the fate of dissolved carbon dioxide under extreme conditions is critical to understanding the deep carbon cycle in Earth, a process that ultimately influences global climate change. We used first-principles molecular dynamics simulations to study carbonates and carbon dioxide dissolved in water at pressures (P) and temperatures (T) approximating the conditions of Earth’s upper mantle. Contrary to popular geochemical models assuming that molecular CO₂(aq) is the major carbon species present in water under deep Earth conditions, we found that at 11 GPa and 1000 K, carbon exists almost entirely in the forms of solvated carbonate ( ${\text{CO}}_3^{2-}$ ) and bicarbonate ( ${\text{HCO}}_3^{-}$ ) ions and that even carbonic acid [H₂CO₃(aq)] is more abundant than CO₂(aq). Furthermore, our simulations revealed that ion pairing between Na⁺and ${\text{CO}}_3^{2-}$ / ${\text{HCO}}_3^{-}$ is greatly affected byP-Tconditions, decreasing with increasing pressure at 800 to 1000 K. Our results suggest that in Earth’s upper mantle, water-rich geofluids transport a majority of carbon in the form of rapidly interconverting ${\text{CO}}_3^{2-}$ and ${\text{HCO}}_3^{-}$ ions, not solvated CO₂(aq) molecules.

• Research Organization: Argonne National Laboratory (ANL)
• Sponsoring Organization: Alfred P. Sloan Foundation; USDOE Office of Science - Office of Basic Energy Sciences - Materials Sciences and Engineering Division
• DOE Contract Number: AC02-06CH11357
• OSTI ID: 1489269
• Journal Information: Science Advances, Journal Name: Science Advances Journal Issue: 10 Vol. 2; ISSN 2375-2548
• Publisher: AAAS
• Country of Publication: United States
• Language: English