Overview

• Experiments at −10°C released more iron from goethite than liquid water at +4°C, overturning the assumption that freezing slows chemical reactions.
• Advanced microscopy revealed concentrated, highly acidic micro-pockets between ice crystals that enable mineral dissolution even near −30°C.
• Repeated freeze–thaw cycles enhanced iron release by freeing trapped organics that fuel further reactions.
• Salinity controlled the effect, with fresh and brackish conditions increasing dissolution and seawater suppressing it.
• Researchers link the mechanism to the recent orange tint in some Arctic rivers and note the PNAS results chiefly apply to acidic frozen settings as broader tests proceed.