Ice can dissolve iron minerals more effectively than liquid water, according to a new study from Umeå University. The discovery could help explain why many Arctic rivers are now turning rusty orange as permafrost thaws in a warming climate.

The study, published in PNAS, shows that ice at minus 10 degrees Celsius releases more iron from common minerals than liquid water at 4 degrees Celsius. This challenges the long-held belief that frozen environments slow down chemical reactions.