Ice Converts Phenols into Persistent Mineral-Bound Polymers.

Freezing fundamentally alters how minerals transform dissolved phenols in cold environments. As water freezes, solutes are excluded from the crystal lattice and concentrated into microscopic pockets of unfrozen liquid, creating reaction conditions far more extreme than those of bulk solution. Here, we compare catechol oxidation on a key soil manganese oxide under freeze-thaw versus room-temperature conditions. Freezing redirects products from soluble humic-like substances to thermally stable, mineral-bound polymers. Freeze-thaw conditions removed over 50% of dissolved organic carbon within 24 h compared to less than 10% at room temperature, with solid-phase carbon increasing over 50-fold. The attenuation of the effect with increasing salinity is consistent with freeze-concentration as a key driver and indicates that the pathway should be strongest in freshwater and low-salinity frozen environments. Freeze-thaw conditions also converted preformed soluble products into mineral-bound forms, demonstrating that the process operates on a range of substrates. These findings reveal an unrecognized abiotic carbon stabilization pathway that could operate when microbial decomposition is suppressed by freezing with direct implications for carbon dynamics in permafrost and seasonally frozen environments.