Abiogenic Hydrocarbon Production at Lost City Hydrothermal Field

TLDR

Low‑molecular‑weight hydrocarbons in natural hydrothermal fluids have been attributed to abiogenic Fischer‑Tropsch type reactions, yet clear evidence for such a process has remained elusive. The study aims to present concentration, stable‑isotope, and radiocarbon‑isotope data from hydrocarbons dissolved in hydrogen‑rich fluids venting at the ultramafic‑hosted Lost City Hydrothermal Field. The authors obtained these data by measuring hydrocarbon concentrations and isotopic compositions in the vent fluids. An inverse trend in the stable carbon and hydrogen isotopic composition of C1–C4 hydrocarbons, together with radiocarbon evidence excluding seawater bicarbonate, indicates mantle‑derived inorganic carbon leached from host rocks and demonstrates that abiotic hydrocarbon synthesis can occur in the presence of ultramafic rocks, water, and moderate heat.

Abstract

Low-molecular-weight hydrocarbons in natural hydrothermal fluids have been attributed to abiogenic production by Fischer-Tropsch type (FTT) reactions, although clear evidence for such a process has been elusive. Here, we present concentration, and stable and radiocarbon isotope, data from hydrocarbons dissolved in hydrogen-rich fluids venting at the ultramafic-hosted Lost City Hydrothermal Field. A distinct “inverse” trend in the stable carbon and hydrogen isotopic composition of C 1 to C 4 hydrocarbons is compatible with FTT genesis. Radiocarbon evidence rules out seawater bicarbonate as the carbon source for FTT reactions, suggesting that a mantle-derived inorganic carbon source is leached from the host rocks. Our findings illustrate that the abiotic synthesis of hydrocarbons in nature may occur in the presence of ultramafic rocks, water, and moderate amounts of heat.